| S.No | Question | Option A | Option B | Option C | Option D | Answer | Solution | Comments | Status | Action |
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| 1 | An air preheater | increases evaporative capacity of a boiler. | increases the efficiency of boiler. | enables low grade fuel to be burnt. | all of the above. | d | Air preheaters (APH) is the shell and tube heat exchangers used for preheating the air which is fed to the boiler or furnaces/kilns for combustion of fuels. Air pre – heaters primary objective is to extract the waste heat from the flue gases leaving the boiler. | Comments | Active | |
| 2 | Which of the following is a fire tube boiler? | Locomotive boiler | Babcock and Wilcox boiler | Stirling boiler | None of the above | a | The examples of the fix tube boiler are the simple vertical Cochran, Lancashire, Cornish, locomotive, scotch marine and velcon boiler. The examples of water tube boilers are la – mont boiler, Benson, sterling Babcock and Wilcox, yarrow and Loffler boiler. | Comments | Active | |
| 3 | What is the effect of bleeding? | It decreases the power developed by the turbine. | The boiler is supplied with hot water. | It increases thermodynamic efficiency of turbine. | All Of above. | d | Bleeding refers to extraction, from the turbine of steam bleed or extraction is from intermediate stages of the turbine. For an extraction cum condensing steam turbine, steam is extracted from various stages and used as per downstream requirement. This is typically for a co – generation (combined heat and power) unit where besides the power generation, the steam turbine extraction steam is used for utility purposes. Extracted steam is supply to feed water which increases the mean temperature of heat addition which increases the efficiency by reducing the total heat supplied. |
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| 4 | Corrosion In boilers is minimised by maintaining boiler water as | Acidic | Alkaline | At high pressure | None of the above | b | By using high pH of water corrosion in the boiler proper generally occurs. When the boiler water alkalinity is low or when the metal is exposed to oxygen bearing water either during operation or idle periods. High temperatures and stresses in the boiler metal tend to accelerate the corrosive mechanisms. | Comments | Active | |
| 5 | Compression ratio of petrol engines is in the range of | 2 to 3 | 8 to 12 | 16 to 20 | None of the above | b | In petrol (gasoline) engines used in passenger cars for the past 20 years, compression rations have typically been between 8:1 and 12:1. | Comments | Active | |
| 6 | Source of electrical energy in SI engine is | battery | magneto | generator | any of the above | d | All are source of electricity | Comments | Active | |
| 7 | Piston rings are generally made of following material: | Cast iron | Aluminium | Copper | Carbon steel | a | Cast iron | Comments | Active | |
| 8 | Detonation in spark ignition engines is due to early autoignition of the charge | near the spark plug | near the exhaust valve | near the suction valve | near the combustion cylinder walls | d | When flame front from auto ignition and spark ignition, collides detonation occurs. | Comments | Active | |
| 9 | For a four-stroke diesel engine exhaust gas temperature | Increases with load | Decreases with load | Is constant throughout the variation of load | No prediction is possible | a | As the load increases, we have to give more fuel to the engine, which will lead to more heat release and increases in exhaust temperature. | Comments | Active | |
| 10 | Which process is not associated with diesel cycle? | Constant pressure | Constant volume | Adiabatic | Isothermal | d | Comments | Active | ||
| 11 | The ratio of isentropic heat drop to the heat supplied is called | Rankine efficiency | Stage efficiency | Reheat factor | Internal efficiency | a | Work done on pump, per kg of water, \(W_{P}=h_{2}-h_{1}\) Energy added in steam generator \(q_{1}=h_{3}-h_{2}\) Work delivered by turbine \(W_{T}=h_{3}-h_{4}\) Energy rejected in the condenser \(q_{2}=h_{4}-h_{1}\) The thermal efficiency of the Rankine cycle is given by \(η=\frac{q_{1}-q_{2}}{q_{1}}=\frac{(h_{3}-h_{2})-(h_{4}-h_{1})}{h_{3}-h_{2}}\) \(=\frac{(h_{3}-h_{4})-(h_{2}-h_{1})}{h_{3}-h_{2}}\) |
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| 12 | Steam turbines are governed by which of following methods? | Throttle governing | Nozzle control governing | Bypass governing | All of above | d | Throttle governing, by pass governing and nozzle governing are all different methods of steam turbine governing. The mentioned three methods are used to keep the turbine speed constant at varying load condition. The function of a governor is to control the fluctuation of speed of a prime mover within the prescribed limits with the variation of loads on it. In case of steam turbines when it is connected to drive an alternator for converting its mechanical energy into electrical energy device is used to vary the turbine output according to the load on the alternator with very small fluctuations in speed called governor. In throttle governor the steam is throttled down to lower pressure according to the load on the turbine before it is supplied to the turbine. It reduces the enthalpy drop. In nozzle governor the first stage nozzles are split – up groups which are controlled by individual throttle valves. Various arrangements of valves and group of nozzles are employed In by – pass governor: the load regulation is achieved by throttle governing upto the stage of economical loads. However the maximum loads the additional amount of steam required cannot be passed through the first – stages since the required additional number of nozzles is not available. This difficulty of steam regulation is overcome by employing by – pass governing. |
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| 13 | A Jerk pump used for fuel injection system is | Vane type | Rotary type | Reciprocating type | None of the above | c | A fuel – infection pump in an oil engine which supplied impulsively an accurately measured charge to the nozzle at the time of the opening of the inlet valve. This type infection pump consists of a reciprocating plunger inside a barrel. The plunger of a jerk type pump is driven by camshaft. | Comments | Active | |
| 14 | For a single stage impulse turbine, having nozzle angle a, maximum blade efficiency' under ideal conditions is given by | \(\frac{cosα}{2}\) | \(\frac{cos^{2}α}{2}\) | \(\frac{cos2a}{2}\) | cos2 α | d | \( V_{ω_{1}}+V_{ω_{2}}=AC+AF=FC=FB+BC\) \(=Vr_{2}cosβ_{2}+Vr_{1}cosβ_{1}\) \(=V_{r_{1}cos}β_{1}(1+\frac{Vr_{2}cosβ_{2}}{Vr_{1}cosβ_{1}})\) \(=Vr_{1}cosβ_{1}[1+K_{B}\)] \(Vω_{1}-u[1+K_{B}\)] \(=V_{1}cosα_{1}-u\)[1+K_{β}]] Now blade efficiency \(η_{b}=\frac{2(Vω_{1}+Vω_{2})u}{V12}\) Speed ratio \(Ï=\frac{u}{v}\) \(η_{β}=\frac{(V_{1}cosα_{1}-u)(1+K_{β})u}{V12}\) \(=2[cosα_{1}-Ï\)(1+K_{β})Ï] \(=2[Ïcosα_{1}-Ï^{2}\)[1+K_{β}]] Now blade efficiency \(η_{b}=\frac{2(Vω_{1}+Vω_{2})u}{V12}\) Speed ratio \(Ï=\frac{u}{V_{1}}\) \(η_{β}=\frac{(V_{1}cosα_{1}-u)[1+K_{β}\)u}{V12}] \(=2[cosα_{1}-Ï\)(1+K_{β})Ï] \(=2[Ïcosα_{1}-Ï^{2}\)[1+K_{β}]] For maximum efficiency \(\frac{dη_{β}}{dÏ}=0⇒2[cosα_{1}-2Ï\)(1+K_{β})] \(∴Ï= \frac{cosα_{1}}{2}\) And \(η_{bmax}=2(\frac{cosα_{1}}{2}.cosα_{1}-\frac{cosα12}{4})(1+K_{β})\) \(=\frac{2cos^{2}α_{1}}{4}.(1+1)\) \(=cos^{2}α_{1}\) Take \(K_{β}=1\) (blade friction factor) |
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| 15 | In steam turbine the reheat factor | increases with increase in number of stages | decreases with increase in number of stages | remains same | does not depend on number of stages | a | Reheat factor = \(\frac{Cumulative enthalpy drop isentropic (S=C)}{isentropic overall enthalpy drop}\) \(RF-1.03 to 1.04\) Overall efficiency \(η_{o}=RF×stage efficiency\) \(RF depends on\) * No of stages * Stage efficiency * Initial and final pressure * Steam condition \(RFâˆNo of stages\) |
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| 16 | The latent heat of steam with increase in pressure | does not change | increases | decreases | remains unpredictable | c | Here \(P_{1}| Comments |
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| 17 | Why intercooling in multistage compressors is done? | To minimise the work of compression | To cool the air delivery | To cool the air during compression | None of these | a | An increase in pressure ratio in a single stage reciprocating compressor causes an increase in temperature a decrease in volumetric efficiency and an increase in work input. So for the same higher pressure ratio, multi – stage compression is efficient. Intercooling * In multi – stage compression with intercooling, where the gas is compressed in stages and cooled between each stage by passing it through a heat exchanger called an intercooler. * P – V and T – S diagram of the compression with intercooling is shown in the figure below P – V and T – S diagrams for a two stage steady flow compression process. * It can be seen that interceding is done at constant pressure and is represented by a horizontal line on the P – V diagram. * This reduction in temperature means a reduction in internal energy at the delivered air and since this energy must have come from the input energy required to drive the machine, this results in a decrease in input work requirement for a given mass of delivered air. * The low pressure ratio in a cylinder improves volumetric efficiency. |
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| 18 | In the impulse turbine the steam expands in | blade | nozzle | partly in nozzle and partly in blade | none of the above | b | In an impulse turbine, the steam enters at a higher pressure and undergoes expansion. The pressure of the steam reduces in the nozzle and remains constant while passing through the moving blades. The velocity or kinetic energy of the steam increase in the nozzle and reduces while passing through the moving blades. K.E. of steam increases in nozzle while remains same. While passing on moving blade. Pressure energy in nozzle decrease while K.E. increases. |
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| 19 | A Pelton wheel is ideally suited for | High head and low discharge | High head and high discharge | Low head and low discharge | medium head and medium discharge | a | Head Specific speed Turbine > 300 m 0 – 60 Pelton 30 to 300 m 60 – 300 Francis < 30 m 300 – 600 Propeller 600 - 1000 Kaplan |
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| 20 | Compared to reciprocating steam engines, steam turbines | have higher efficiency | have low steam consumption | have less frictional losses due to sliding parts | all of above | d | Comments | Active | ||
| 21 | Combustion in CI engine is | Homogeneous | Heterogeneous | Could be either (a) or (b) | None of the above | b | In CI engines or diesel engine, only air is compressed and then the fuel is injected at the last stage. So no proper mixing before combustion takes place so the CI engiens are heterogeneous combustion engines. Homogeneous charge compression Ignition (HCCI) is a form of internal combustion in which well – mixed fuel and oxidizer (typically air) are compressed to the point of auto – ignition. | Comments | Active | |
| 22 | Tetra ethyl lead in fuel is used to | Increase the lubrications | Decrease octane number | Increase octane number | None of the above | c | Tetraethyl lead was used in early model cars to help reduce engine knocking, boost octane, ratings and help with wear and tear on valve seats within the motor. But due to its bad effects on nature now it is prohibited to use. |
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| 23 | Why compounding of steam turbine is done? | To improve efficiency | To reduce exit losses | To reduce rotor speed | All of the above | c | Compounding of steam turbine is used to reduce the rotor speed by extracting the energy from the steam in a number of stage. It is the process by which rotor speed come to its desired value. A multiple system of rotors are connected in series keyed to a common shaft and the steam pressure or velocity is absorbed in stages as it flows over the blades compounding is achieved by using more than one set of nozzles blades, rotors, in a series, keyed to a common shaft. So that either the steam pressure or the jet velocity is absorbed by the turbine is stages. It also avoid over speeding of turbine to avoid damage. | Comments | Active | |
| 24 | Delay period of CI engine fuel is affected by | Properties of fuel | Atomization of fuel | Compression ratio of engine | All the above | d | The primary factors investigated are those pertaining to the fuel spray, such as injection timing. Quantity and pressure (affecting drop size velocity and injection rate) hole diameter (affecting drop size and injection rate) and spray from (nozzle type), and those pertaining to the engine, such as temperature, pressure and air velocity. Engine operating variables such as speed and load affect the ignition delay because they change the primary factors such as injection pressure, compression temperature pressure and air velocity. It has been found that under normal running conditions, compression temperature and pressure are the major factors. All other factors have only secondary effects. Under starting conditions when ignition is marginal, mixture formation becomes as important as compression temperature and pressure such factors as air velocity and spray from which affect the mixing pattern can have a very pronounced effect on ignition delay. |
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| 25 | In a petrol engine the spark plug gap is of the order | 0.10 mm | 0.60 mm | 0.01 mm | 0.15 mm | b | Carnot spark plug gap is 0.6 to 1.7 mm. | Comments | Active | |
| 26 | Thermal efficiency of a gas turbine plant as compared to diesel engine plant is | Higher | Lower | Same | May be higher or lower | b | In gas turbine, 70% of the output of gas turbine is consumed by compressor. I.C engine have much lower auxiliary consumption. Further combustion temperature of IC engines is much higher compared to gas turbine. 1. For a given volume, the gas/air has less energy content compared to fuel. 2. In a gas turbine the gas has to be highly compressed by compressor and for this it consumes some amount of energy out from turbine. 3. The internal irreversibities like friction are more in a gas turbine. |
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| 27 | The injection pressure in diesel engines is of the order of | 30 — 40 bar | 100- 150 bar | 170 —220 bar | 400-600 bar | b | \( η_{th} diesel=30-40%\) \(η_{th} gas turbine=20-2 5%\) |
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| 28 | In a four-cylinder petrol engine, the standard firing order is | 1-2-3-4 | 1-4-3-2 | 1- 3- 2- 4 | 1-3-4-2 | d | 1- 3 – 4 – 2 | Comments | Active | |
| 29 | By advancing the spark timing in S.I. engine, the tendency of knocking | increases | decreases | remains unaffected | may increase or decrease | a | Knocking: * It is due to the auto ignition of the end portion of the unbalanced charge in the combustion chamber factors affecting knocking in SI engine. * Advancing the spark the tendency to knock will increase. * The high inlet temperature of the air – fuel mixture will increase knocking. * A higher compression ratio, the tendency to knock will increase. * By increasing coolant water temperature, the knocking will increase. * The flame speed is affected by the fuel air ratio. Also, the flame temperature and reaction time are different for different air – fuel ratio. * If the fuel air ratio is high it will decrease the knocking tendency in the spark – ignition engine. * Increasing the speed will cause less knocking. |
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| 30 | The ratio of brake power to indicated power of an I.C Engine is called | Mechanical efficiency | Thermal efficiency | Relative efficiency | a | \( η_{mech}=\frac{BP}{IP}=\frac{BP}{BP+FP}\) \(IP=\frac{P_{m}.LANn}{60}\) \(BP=\frac{2πNT}{60}\) \(η_{indicated}=\frac{IP}{m_{f}×C_{V}}\) \(η_{break}=\frac{BP}{m_{f}×C_{V}}\) \(η_{mech}=\frac{η_{break}}{η_{indicated}}\) |
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| 31 | Which one of the following turbines is used in underwater power stations? | Pelton turbine | Deriaz turbine | Tubular turbine | Turgo-impulse turbine | c | The tubular turbine is a reliable machine that can operate continuously for long periods of time, making it ideal for use in underwater power stations. | Comments | Active | |
| 32 | Thermal efficiency of a closed cycle gas turbine plant increases by | Reheating | Intercooling | Regenerator | All the above | d | concept of closed cycle gas turbine: It works on the Brayton’s cycle /Joule’s cycle. Joule cycle Process 1 – 2: Isentropic compression Process 2 – 3: heating of gas at constant pressure Process 3 – 4: The expansion of gas is entropically Process 4 – 1: Cooling of gas at constant pressure. Regeneration * It is a process during which heat is transferred to a thermal energy storage device (called a regenerator) during one part of the cycle and is transferred back to the working fluid during another part of cycle. * In a gas turbine regeneration is done between the exit gas from the turbine and the air coming out of the compressor. * In the regeneration process there is reduction in heat supplied to the gas but there is no effect on the turbine and the compress work. * Therefore, the regeneration will not increase the work ratio in the turbine but the efficiency of the turbine increases in the regeneration process. Reheating * Reheating is the method of increasing the mean temperature of heat rejection. * In this, the gas is again heated after it has expanded in the gas turbine. Effect of Reheating * This increases the work output of the turbine by keeping the compressor work constant. * The mean temperature of heat rejection is may increases or decreases depending upon the reheat pressure conditions, so efficiency can increase or decrease. * For a given power output, the fuel consumption rate decreases. * Work ratio decreases. Intercooling * Intercooling between the stages in the compressor leads to decrease in the compressor work input therefore it will also help to increase the work ratio of the gas turbine plant resulting in decrease in the thermal efficiency, but the scope of regeneration will increase. P – V and T – S diagram for a two stage steady – flow compression process. |
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| 33 | The specific gravity of commonly used diesel is | 1 | 0.7 | 0.85 | 0.5 | c | Specific gravity of diesel = 0.82 to 0.95 | Comments | Active | |
| 34 | The performance of reciprocating compressor is compared on the basis of which efficiency? | Volumetric | Mechanical | Overall | Isothermal | d | \( η_{isothermal }=\frac{Wisothermal }{Indicated work}\) For isothermal process WD in compression will be minimum \(WD_{isothermal} Comments |
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| 35 | For the same compression ratio and heat input, the efficiency of an Otto cycle engine as compared to diesel engine is | more | less | equal | none of these | a | \(η=1-\) Compression ratio (is same for all) \(=\frac{V_{2}}{V_{1}}\) Least heat rejection will give highest efficiency because is same heat rejection is least for 4†– 1. \(Q_{supp}\) \(∴η_{otto}>η_{dual}>η_{diesel}\) \(\frac{Q_{rej}}{Q_{supp}}\) |
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| 36 | The amount of air which is supplied for complete combustion is called | primary air | secondary air | tertiary air | none of these | b | The minimum amount of air which supplied the required amount of oxygen for complete combustion of a fuel is called the stoichiometric or theoretical air. The amount of air in excess of the stoichiometric air is known as percent excess air. Amount of air less than stoichiometric is called deficiency of air. |
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| 37 | Flash point for diesel fuel should be | minimum 49oc | maximum 49oC | minimum 99oC | maximum 99oC | a | The flashpoint of diesel fuel is between 125- and 180-degrees Fahrenheit (52 to 82áµ’C). The flashpoint of any liquid can. Change as the pressure in the air around it changes. | Comments | Active | |
| 38 | The compressor performance at high altitude as compared to sea level will be | same | higher | lower | may be higher or lower depending on other factors | c | At higher altitudes, air density decreases and air compressor performance is degraded and it can take a lot longer to complete tasks than at lower altitudes. As altitude increases the atmospheric pressure decreases. Atmospheric pressure is caused by the weight of all the air molecules above you pressing down and compressing the air around you. At higher altitudes, there is less air above you, which results less weight. Which results in a lower atmospheric pressure. At elevated altitudes, lower atmospheric pressure means that the air molecules are less tightly packed together and have lower density. When an air compression draws in air as part of its intake process it draws a fixed volume of air. It the air density is lower, fewer air molecules are drawn in with this air into the compressor. This results in a smaller volume of compressed air and less air is delivered to the receiver tank and tools during each compression cycle. | Comments | Active | |
| 39 | Sulphur content in diesel fuel should not be more than | 10% | 5% | 1% | 0.01% | c | The ash content in diesel oil should not be more than 0.01% while sulphur content in diesel engine oil should not be more than 1% petroleum derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffin’s including n – iso and cycloparaffins) and 25% (aromatic hydrocarbons (including naphthalenes and alkylbenzenes). The average chemical formula for common diesel fuel is , ranging approximately from to . \(C_{12}H_{23}\) \(C_{10}H_{20}\) \(C_{15}H_{28}\) | Comments | Active | |
| 40 | Solid injection in C.I. engine refers to injection of | Liquid fuel only | Liquid fuel and air | Solid fuel | Solid fuel and air | c | The infection of atomized fuel oil into the combustion chamber of a diesel engine under the pressure of the liquid fuel itself. | Comments | Active | |
| 41 | Rankine cycle efficiency of a good steam power plant may be in the range of | 15 to 20% | 35 to 45% | 70 to 80% | 90 to 95% | b | 30 – 45% | Comments | Active | |
| 42 | The net work done per kg of gas in a polytropic process is equal to | \(P_{1}v_{1}log_{e}\frac{v_{2}}{v_{1}}\) | P1 (v1 – v2) | \(P_{2}(v_{2}-\frac{v_{1}}{v_{2}})\) | \(\frac{P_{1}v_{1}-P_{2}v_{2}}{n-1}\) | d | \(\) \(∵W=12ÏdV and polytropio process PV^{n}=C\) \(=12\frac{C}{V^{2}} dV=\frac{CV^{1-n}}{1-n}\)12] \(=\frac{c}{1-n}(V21-n-V11-n)\) \(=\frac{[CV11-n-CV21-n\)}{n-1}] \(=\frac{[P_{1}V1n.V11-n-P_{2}V_{2}V21-n}{n-1}\) \(W_{1-2}=\frac{P_{1}V_{1}-P_{2}V_{2}}{n-1}\) |
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| 43 | In an irreversible process there is | loss of heat | no loss of work | gain of heat | none of the above | a | Irreversibility is mainly due to friction which produces heat in action. So supplied energy is dissipated or wasted in form of heat. | Comments | Active | |
| 44 | Which of the following is not a property of system? | Temperature | Pressure | Specific volume | Heat | d | Heat is not property, it is a path function | Comments | Active | |
| 45 | Diesel cycle efficiency is maximum when cut off is | minimum | maximum | zero | none of the above | c | \( η=1-\frac{1}{r^{K-1}}(\frac{rcK-1}{K(r_{c}-1)})\) \(r_{c}=cut off ratio\) \(Lower the r_{c}, η increases\) \(η_{max}=1-\frac{1}{r^{K-1}}.\frac{1}{K}\) \(K=ν=\frac{C_{P}}{C_{V}}\) \(r=compression ratio\) |
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| 46 | Which cycle has maximum efficiency for the same temperature limits? | Brayton | Carnot | Rankine | Stirling | b | Between two same temperature limits a number of engines are connected than that engine will have the maximum efficiency which is reversible or carnot. This is known as carnot theorem. | Comments | Active | |
| 47 | The polytropic index of expansion n in the equation P Vn = C for constant volume process is | 1 | 1.4 | \(∞\) | 0 | c | In polytropic process \(PV^{n}=C\) If then V = C \(n=∞\) |
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| 48 | Kelvin's—Planck law deals with conversion of | Work | Heat | Work into Heat | Heat into work | d | Kelvin’s plank law deals with conversion of heat into work. ⇒ It states that it is impossible to devise a cyclically operating heat engine, the effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work. This implies – it is impossible to build a heat engine that has 100% thermal efficiency. The efficiency of a heat engine is “The amount of useful work obtained (output) for a given amount of input†|
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| 49 | The work done in constant volume process is | maximum | minimum | zero | unpredictable | c | Work done = Pressure × change in volume Change in volume for constant volume process = 0 So WD = 0 |
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| 50 | Internal energy change of an ideal gas is a function of the following: | Pressure | Temperature | Volume | Humidity | b | An energy from inherent in every system is the internal energy, which arises from the molecular state of motion of matter. Internal energy increases with rising temperature and with changes of state or phase from solid to liquid and liquid to gas. Internal energy for ideal gas U = f (T) |
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| 51 | The unit of entropy is | kg / J K | J / kg. m | J / kg K | J / S | c | Specific entropy \(S=\frac{S}{m}\) \(Entropy (∆S)=\frac{Q}{T} (J/kgK)\) |
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| 52 | In a reversible adiabatic process heat added equal to | zero | positive value | \(c_{v}(\frac{λ-1}{1-n})(T_{2}-T_{1})\) | \(P_{1}v_{1}log_{e}\frac{v_{1}}{v_{2}}\) | a | In adiabatic process no heat interaction occur. | Comments | Active | |
| 53 | Heat and work are | point functions | path functions | system properties | none of the above | b | Heat and work are area under the T – S and P – V curve respectively, So these depend on path taken by the process not on end condition. The parameters which depends on end conditions are known as properties of system. | Comments | Active | |
| 54 | Clausius inequality statement indicates that | \(∳\frac{δϕ}{T}=0\) | \(∳\frac{δϕ}{T}≥0\) | \(∳\frac{δϕ}{T}<0\) | \(∳\frac{δϕ}{T}≤0\) | d | \( \frac{δ}{T}≤0\) The equal sign in the clausius inequality above applies only to the ideal or carnot cycle. Since the integral represents the net change in entropy in one complete cycle, it attributes a zero entropy change to the most efficient engine cycle, and makes it clear that entropy does not decrease even in the ideal engine cycle. The clausius inequality applied to any real engine cycle and implies a negative change in entropy on the cycle. That is, the entropy given to the environment during the cycle is larger than the entropy transferred to the engine by heat from the hot reservoir. \(\frac{δ∅}{T}<0 irrersible process\) \(\frac{δ∅}{T}=0 reversible process\) \(\frac{δ∅}{T}>0 Impossible process\) |
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| 55 | Area under T — S diagram represents | heat transfer for reversible process | heat transfer for irreversible process | heat transfer for all processes | heat transfer for adiabatic process | a | Area under T – S diagram gives heat transfer. \(Q=TdS=T∆S or dQ=Tds\) Area under p – V diagram gives \(W=PdV=P∆V\) |
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| 56 | During throttling process | Internal energy does not change | Pressure does not charge | Entropy does not change | Enthalpy does not change | d | The process in which high pressure fluid is converted into lower one is called throttling. Here enthalpy h = constt Workdone W = 0 Ideally this process is isothermal |
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| 57 | The entropy of the universe is | Increasing | Decreasing | Constant | Unpredictable | a | A thermodynamic quantity representing the unavailability of a system’s thermal energy for conversion into mechanical work, after interpreted as the degree of disorder or randomness in the system is called entropy. According to the second law of thermodynamics, entropy will always increase in the universe. \(dS_{univ}=dS_{sys}+dS_{surr}\) \(dS_{sys}+dS_{surr}>0 due to irreversibility \) So, \(dS_{univ}>0, 2nd law of thermodynamics\) If it is less than zero it means impossible process. |
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| 58 | Work done in free expansion process is | zero | minimum | maximum | positive/negative | a | Work done in case of free expansion. The work done is zero in case of a free expansion process. Reason: There is no restraining opposing force or pressure as expansion occurs against vacuum so, \(dw=0 (in case of free expansion)\) |
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| 59 | A streamlined body is defined as a body about which | Drag is zero | Flow is laminar | Flow is along streamlines | Flow separation is suppressed | d | A streamlined body is a shape of that lowers the friction drag between fluid, like air and water, and an object moving through that fluid. Drag is a force that slows down motion, friction drag is special kind of drag. A stream lined body is defined as the body whose surface coincides with the stream lines, when the body is placed in a flow. In that case the separation of flow will take place only at trailing edge (or rearmost part of the body). Behind a stream lined body, wake formation zone will be very small and consequently the pressure drag will be very small. Thus the total drag on the stream lined body will be due to friction (shear) only. | Comments | Active | |
| 60 | The specific speed of a turbine is expressed as | \(\frac{Np}{H}\) | \(\frac{Np}{H^{2}}\) | \(\frac{Np}{H^{3/4}}\) | \(\frac{Np}{H^{5∕4}}\) | d | \( N_{S}=\frac{NP}{H^{5/4}}\) | Comments | Active | |
| 61 | A convergent duct produces | deceleration in supersonic and acceleration in subsonic flow | acceleration in both supersonic and subsonic flow | deceleration in both supersonic and subsonic flow | acceleration in supersonic and deceleration in subsonic flow | a | \( M<1(subsonic)→M=1(Sonic)→accelerated\) | Comments | Active | |
| 62 | The concept of stream function which is based on the principle of continuity is applicable to | Three-dimensional flow | Two-dimensional flow | Uniform flow cases only | Irrotational flow only | b | It is defined as the scalar function of space and time, such that its partial derivative with respect to any direction gives the velocity component at right to that direction. It is denoted by and defined only for two – dimensional flow. \(Ψ\) Properties of stream function Ψ: * If stream function exists, it is possible case of fluid flow which may be rotational or irrotational. * If the stream function satisfies the Laplace equation \(\frac{∂Ψ}{∂x}=-v\) \(\frac{∂Ψ}{∂y}=u\) |
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| 63 | The displacement thickness for a boundary layer | may be greater than the boundary layer thickness | must be less than momentum thickness | represents momentum deficit in a flow | represents mass deficit in a flow | d | Reduction of mass per second = mass deficit Displacement thickness (mass deficit) \(δ=0δ(1-\frac{μ}{U})dy\) Momentum thickness (Momentum deficit) \(δθ=0δ\frac{μ}{U} (1-\frac{μ}{U})dy\) Energy thickness (Energy deficit) \(δ_{E}=0δ\frac{μ}{U}(1-\frac{μ^{2}}{U^{2}})dy\) \(δ>δ_{E}>δ_{θ}\) |
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| 64 | The specific speed of a hydraulic pump is the speed of geometrically similar pump working against a unit head and | delivering unit quantity of water | consuming unit power | having unit velocity of flow | having unit radial velocity | b | Specific speed \(N_{S}=NP/H^{5/4}\) If unit and P = 1 unit then \(H=1\) \(N_{S}=N\) |
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| 65 | For low head and high discharge, the most suitable water turbine is | Pelton | Francis | Kaplan | None of the above | c | Head Specific speed Turbine > 300 m 0 – 60 Pelton 30 to 300 m 60 – 300 Francis < 30 m 300 – 600 Propeller 600 - 1000 Kaplan |
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| 66 | The two stagnation points for ideal flow over a circular cylinder coincide when | the free stream is uniform. | the circulation about the cylinder is very small. | the circulation about the cylinder exceeds a critical value. |
the circulation about the cylinder is a critical value. | d | Stagnation point is a point in a flow field where the local velocity of the fluid is zero. Flow behind cylinder where the circulation about the cylinder a critical value, will be zero. (= gamma) | Comments | Active | |
| 67 | Run-away speed of a Pelton wheel means | Full load speed | No load speed | No load speed without a governor mechanism | None of the above | c | The maximum unsafe speeds of the runner due to sudden decrease in load on turbine is called run – away speed. The runaway speed is about twice the nominal speed of the Pelton – wheel. The runaway speed of a water turbine is its speed at full flow and no shaft load with wicket gates wide open. It is equivalent to governor fail or no governor. | Comments | Active | |
| 68 | Water hammer is developed in | Pen stock | Draft tube | Turbine | Surge tank | a | Water hammer is developed in a penstock. It is developed due to the reduction in load on the generator. This reduction causes the governor to close the turbine gates and thus creating an increased pressure in the penstack. A penstack is a slice or gate or intake structure that controls water flow or an enclosed pipe that delivers water to hydro – turbines and sewage system. The consequence of the pressure rise in the spiral case and penstack is the water hammer phenomenon, whose effects can be devastating in some cases, upto breaking pipes and calamities produced in the are(a) Draft tube: IT is a diverging tube fitted at the exit of runner of turbine and used to utilize the kinetic energy available with water at the exit of runner. This draft tube at the end of the turbine increases the pressure of the exiting fluid at the expense of its velocity. Surge tank: A surge tank is a water storage device used as a pressure neutralizer in hydro power water conveyor systems in order to damper excess pressure variance. |
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| 69 | Which of the following equations is known as momentum principle? | \(F=\frac{ⅆ(m^{2}v)}{ⅆt}\) | \(F=\frac{ⅆv}{ⅆt}\) | \(F=\frac{ⅆ(mv)}{ⅆt}\) | \(F=\frac{ⅆ(m^{2}v)}{ⅆt^{2}}\) | c | In physics, the principle of conservation of momentum states that when you have an isolated system with no external forces the initial total momentum of objects before a collision equals the final total momentum of the objects after the collision. It is used to formulate the newton’s 2nd law of motion. Change in momentum per unit time is given as force. F = ma = mdv/at = d(mv)/dt |
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| 70 | A shock wave which occurs in a supersonic flow represents a region in which | a zone of silence exists. | there is no change in pressure, temperature and density, | there is sudden change in pressure, temperature and density. | velocity is zero. | c | Shack waves are highly localized irreversible in the flow. * Within the distance of a mean free path, the flow passes from a supersonic to a subsonic state, the velocity decreases suddenly and the pressure rises sharply. * A shock is said have occurred of there is an abrupt reduction of velocity in the downstream in course of supersonic flow in a passage or around a body. * Shock waves are characterized by a sudden increase in pressure temperature and density of the gas through which it propagates |
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| 71 | An equipotential line | has no velocity component normal to it | has no velocity component tangential to it | is a line of constant velocity | is a line of zero normal acceleration | a | For equi – potential line \(ϕ=C or dϕ=0 ∴u=v=0\) \(-u=\frac{∂ϕ}{∂x}, -v=\frac{∂ϕ}{∂y} \) Equipotential line is a imaginary line in a field of flow such that the total head is the same for all points on the line, and therefore the direction of flows is perpendicular to line at all points. Long this potential function remains constant. |
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| 72 | In laminar flow through a circular tube, the Darcy — Weisbach friction factor depends only on the Reynold's number and the two are related by | \(f=\frac{1}{R_{e}}\) | \(f=\frac{16}{R_{e}}\) | \(f=\frac{0.314}{Re1/4}\) | \(f=\frac{64}{R_{e}}\) | d | The Darcy – Weisbach equation contains a dimensionless friction factor known as the Darcy – friction factor. This is also variously called the Darcy weisback friction factor, friction factor, resistance coefficient, or flow coefficient. | Comments | Active | |
| 73 | An ideal fluid is one which | is incompressible | has negligible surface tension | is compressible | is non viscous and incompressible | d | An ideal fluid is one which is incompressible and nonviscous i.e. density of fluid should be constant and fluid should not have internal resistance between layers. | Comments | Active | |
| 74 | Which of the following is the primary fuel in nuclear power? | U233 | U238 | U235 | U239 | c | Nuclear fuel is the fuel that is used in a nuclear reactor to sustain a nuclear chain reaction. These fuels are fissile and the most common nuclear fuels are the radioactive metals uranium – 235 and plutonium – 239. | Comments | Active | |
| 75 | The flow is said to be subsonic when Mach number is | Equal to unity | Less than unity | Greater than unity | None of above | b | Mach No (M) \(=\frac{inertia force}{Elasic force}\) \(=\frac{ÏAV^{2}}{KA}\) \(=\frac{V}{\frac{K}{Ï}}=\frac{V}{C} \) \(if M<0.8-Subsonic flow\) \(0.8 \(3 |
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| 76 | Along a stream line | Velocity is constant | φ is zero | Ψ is zero | Ψ is constant | d | The liners along which velocity function is constant are known as equipotential lines. The lines along which stream function is constant are known as stream lines. \(∅\) \(Ψ\) | Comments | Active | |
| 77 | Prandtl’s universal equation is given as where U = centre line velocity y = distance of pipe from wall R = radius of pipe Uf = shear friction velocity = \(\frac{Ï„_{0}}{Ï}\) |
U =Umax+2.5 Uf loge \((\frac{y}{R})\) | U =Umax+3.5 Uf loge \((\frac{y}{R})\) | U =Umax+4.5 Uf loge \((\frac{y}{R})\) | U =Umax+5.5 Uf loge \((\frac{y}{R})\) | a | \( U=U_{max}+2.5 Uf*log_{e}(\frac{y}{R})\) | Comments | Active | |
| 78 | One stoke is equal to | 1 cm2 /s | 1 m2 /s | 1 ft2 /s | 1 m.m2 /s | a | \( 1 stoke=1 cm^{2}/sec =10^{-4} m^{2}/s\) | Comments | Active | |
| 79 | In centrifugal pumps cavitation is reduced by | Increasing the flow velocity | Reducing discharge | Throttling the discharge | Reducing suction head | d | Cavitation is the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapor pressure of the fluid and sudden collapsing of these bubbles in the region of higher pressure. * In centrifugal pumps the cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced. * Hence if the pressure at the suction side of the vapor pressure of the liquid then the cavitation may occur. * In order to determine whether cavitation will occur in any portion of the suction side of the pump. The critical value of Thomas cavitation factor is calculate(d) \((σ)\) \(σ=\frac{H_{atm}-H_{V}-H_{S}-h_{LS}}{H}\) * H = head developed by the pump \(* H_{S}=suction pressure head in m of water.\) \(*H_{V}=Vapour pressure head in m of water.\) \(*h_{LS}=Heat test due to friction in suction pipe.\) If the value of is greater than (critical cavitation factor) the cavitation will not occur in that pump. So, the cavitation can be reduced by reducing the suction head. \(σ\) \(σ_{c}\) |
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| 80 | Momentum thickness is given by which of following equations? | \(0δ=(1-\frac{u}{U})ⅆy\) | \(0δ\frac{u}{U}(1-\frac{u}{U})ⅆy\) | \(0δ\frac{u}{U}(1-\frac{u^{2}}{U^{2}})ⅆy\) | None of above | c | Displacement thickness \(δ^{*}=0δ(1-\frac{μ}{U})dy \) Momentum thickness \(Q=0δ\frac{μ}{U}(1-\frac{μ}{U})dy\) Energy thickness \(δ^{**}=0δ\frac{μ}{U}(1-\frac{μ^{2}}{U^{2}})dy \) |
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| 81 | Which of the following turbines is suitable for specific speed ranging from 300 to 1000 and heads below 30 m? | Francis | Kaplan | Propeller | Pelton | b | Head Specific speed Turbine > 300 m 0 – 60 Pelton 30 to 300 m 60 – 300 Francis < 30 m 300 – 600 Propeller 600 - 1000 Kaplan |
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| 82 | At what distance r from the centre of a pipe of radius R will the average velocity occur? | r = 0.593 R | r=O.45 R | r = 0.707 R | r = 0.36 R | c | velocity profile \(u=-\frac{1}{4μ}\frac{∂P}{∂x}(R^{2}-r^{2})\) \(u=U_{max}(1-(\frac{r}{R})^{2})\) \(∵U_{max}=-\frac{1}{4μ}\frac{∂P}{∂x} R^{2}\) \(u=U=U_{max}×(1-(\frac{r}{R})^{2})\) \(∴1-(\frac{r}{R})^{2}=\frac{1}{2}\) \([∵\frac{U}{U_{max}}=\frac{1}{2}\) \((\frac{r}{R})^{2}=\frac{1}{2}\) \(∴r=\frac{R}{2}=0.707R\) |
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| 83 | The most probable value of speed ratio of Kaplan turbine is | 0.45 | 0.75 | 1.15 | 2.0 | d | Speed ratio \(K_{u}=\frac{u}{2gh}\) \(=\frac{tangential velocity}{spout velocity}\) |
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| 84 | A shock wave is produced when | a sonic flow changes to supersonic flow | a subsonic flow changes to sonic flow | a supersonic flow changes to subsonic flow | none of the above | c | Shock waves are highly localized irreversibities in the flow. * Within the distance of a mean free path, the flow passes from a supersonic to a subsonic state, the velocity decreases suddenly and the pressure rises sharply, A shack is said to have occurred if there is an abrupt reduction of velocity in the downstream in course of a supersonic flow in a passage or around a body. * Normal shocks are substantially perpendicular to the flow and oblique shocks are inclined at any angle. * Shock formation is possible for confined flows as for external flows. * Normal shock and oblique shock may mutually interact to make another shock pattern. * So the change of flow from supersonic to subsonic at high pressure in an extremely thin region, is known as shack wave. During normal shock waves 1. Velocity of flow decreases 2. Pressure increases 3. Specific volume decreases 4. Temperature increases 5. Entropy increases 6. Stagnation pressure increases. [Stagnation pressure at a stagnation point in a fluid flow. At a stagnation point the fluid velocity is zero. In an incompressible flow, stagnation pressure is equal to the sum of the free – stream static pressure and the free – stream dynamic pressure. Stagnation pressure is sometimes referred to as pitot pressure because it is measured using a pitot tube] 7. Density increases. |
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| 85 | Which is the most commonly used following equation for velocity of distribution for laminar flow through pipes? | \(U=U_{m_{ax}}(1-\frac{r}{R})\) | \(U=U_{max}(1-(\frac{r}{R})^{2})\) | \(U=U_{max}(1-(\frac{r}{R})^{3})\) | \(U=U^{2}_{max}(1-(\frac{r}{R})^{2})\) Where Umax = centre line velocity R = Radius of pipe |
b | The formula for the laminar velocity profile has to be mentioned first. The derivation of it is possible to find in every book dedicated to the fluid mechanics. The Laminar velocity profile of the fluid flow governed by the pressure gradient is parabolic. \(V=V(max)(1-(\frac{r}{R})^{3})\) Where R is the tube radius V(max) is the maximal velocity or the centerline velocity of the velocity profile. It is assumed that there is only one velocity component in the tube axis direction. This velocity profile expression can be also rewritten as a function of average velocity. \(V_{avg}=V_{max}/2\) \(\frac{V}{V_{max}}=1-(\frac{r}{R})^{2} \) This is a quadratic equation so profile will be parabolic. |
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| 86 | The sonic velocity in a fluid medium is directly proportional to | Mach number | Density | Pressure | square root of temperature | d | Sonic velocity \(V=γRT ∴VâˆT\) |
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| 87 | A two-dimensional flow field is described by the velocity components u = 2x and v = -2y. The corresponding velocity potential function will be | \(ϕ=y^{2}-x^{2}\) | \(ϕ=2(x+y)\) | \(ϕ=x^{2}-y^{2}\) | \(ϕ=x^{2}+y^{2}\) | a | As we know that If \(∅=velocity function\) Then \(\frac{ ∂∅}{∂x}=-u, \frac{∂∅}{∂y}=-v\) So here \(u=2x, and v=-2y\) For option \(a, ∅=y^{2}=x^{2}\) \(\frac{∂∅}{∂x}=-2x \frac{∂∅}{∂y}=2y=-v\) \(=-u\) \(∴u=2x, v=-2y\) |
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| 88 | Viscosity has the following dimensions: | MLT-2 | ML-1 T-2 | ML-2 T-2 | ML-1 T—1 | d | \( \frac{N-S}{m^{2}}=\frac{MLT^{-2}.T}{L^{2}}=ML^{-1}T^{-1}\) Shear stress \(τ=μ.\frac{du}{dx}\) \(du=velocity\) \(dx=distance\) \(μ=Viscosity\) \(Pa(\frac{N}{m^{2}})=μ \frac{m/s}{m}\) \(\frac{MLT^{-2}}{L^{2}}=μ\frac{LT^{-1}}{L}\) \(μ=(ML^{-1}T^{-1})\) |
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| 89 | The most essential feature of turbulent flow is | large discharge | High velocity | Velocity and pressure at a point exhibit irregular fluctuations of high frequency | Velocity at a point remains constant with time | c | Fluctuation of velocity and pressure. | Comments | Active | |
| 90 | Across a normal shock | the pressure and temperature rise | the velocity and pressure increase | the velocity and pressure decrease | the velocity and density decrease | a | Shock waves are highly localized irreversibities in the flow. * Within the distance of a mean free path, the flow passes from a supersonic to a subsonic state, the velocity decreases suddenly and the pressure rises sharply, A shack is said to have occurred if there is an abrupt reduction of velocity in the downstream in course of a supersonic flow in a passage or around a body. * Normal shocks are substantially perpendicular to the flow and oblique shocks are inclined at any angle. * Shock formation is possible for confined flows as for external flows. * Normal shock and oblique shock may mutually interact to make another shock pattern. * So the change of flow from supersonic to subsonic at high pressure in an extremely thin region, is known as shack wave. During normal shock waves 1. Velocity of flow decreases 2. Pressure increases 3. Specific volume decreases 4. Temperature increases 5. Entropy increases 6. Stagnation pressure increases. [Stagnation pressure at a stagnation point in a fluid flow. At a stagnation point the fluid velocity is zero. In an incompressible flow, stagnation pressure is equal to the sum of the free – stream static pressure and the free – stream dynamic pressure. Stagnation pressure is sometimes referred to as pitot pressure because it is measured using a pitot tube] 7. Density increases. |
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| 91 | Which of the following is not a dimensionless number? | the coefficient of lift | the pipe friction factor | the Manning's coefficient | the coefficient of discharge | c | Lift force, \(F_{L}=C_{L}×\frac{Ïu^{2}L^{2}}{2}\) Heat loss, \(h_{f}=\frac{∆P}{Ïg}=\frac{fLV^{2}}{2gD}\) Manning formula \(C=\frac{1}{N} m^{1/6}\) (m = hydraulic mean depth, N = Manning coefficient, C = Chezy’s constant (no unit) \(Velocity , V=Cd×2gH\) \(C_{d}=Coefficient discharge\) \(C_{L}=Coefficient of lift\) \(h_{f}=Friction factor\) |
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| 92 | In turbulent flow which of the following gives exact velocity distribution? | Logarithmic distribution | Blasius equation | Power law with index varying | Prandtl one seventh power | d | Logarithmic distribution at any distance (y) \(u_{max}-u=2.5u^{*}log (\frac{R}{y})\) \(u_{max}-u=Velocity defect\) \(u=Shear velocity=\frac{Ï„}{Ï}\) Prandlt’s universal equation - Blausius equation \(f=\frac{0.079}{(Re)^{1/4}}\) - Power law \(\frac{u}{u_{max}}=(\frac{y}{R})^{1/n}\) - Prandtl 1/nth power law \(when Re=1.1×10^{5}, n=7\) Then \(\frac{u}{u_{max}}=(\frac{y}{R})^{1/7}[most accurate\)] |
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| 93 | Compressibility effects can be treated as negligible when the Mach number is | 1 | upto 0.2 | upto 0.5 | less than I | b | Mach no = \(\frac{Inertia force}{elastic force}\) If M < 0.3 incompressible force i.e., negligible compressibility If 0.3 < M < 1 subsonic flow. If M = 1 sonic flow. If 1 < M < 5 supersonic flow If M > 5 hyper sonic flow |
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| 94 | In the Navier Stokes equation the forces considered are | Pressure, viscous and turbulence | Gravity, pressure and viscous | Gravity, pressure and turbulence | Pressure, gravity, turbulence and viscous | b | This equation describes motion of viscous fluid (Laminar flow) By using Newton’s 2nd law. \(Ï(\frac{∂V}{∂t}+u\frac{∂v}{∂x}+v\frac{∂v}{∂y}+w\frac{∂v}{∂z})\) \(=-∇P+Ïg+μ∇^{2}V\) \(a_{L}=Local acceleration\) \(a_{c}=Convective acceleration\) \(P_{f}=Pressure force\) \(F_{b}=Body force(gravity)\) \(F_{v}=Viscous force\) |
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| 95 | The viscosity of water with respect to air is about | 50 times | 55 times | 60 times | 65 times | a | Viscosity of air at 27ᵒC \(=18.6×10^{-6} Pa.S\) Viscosity of water at 27ᵒC \(=900×10^{-6} Pa.S\) \(\frac{μ_{air}}{μ_{water}}=\frac{900×10^{-6}×100}{18.6×10^{-10}}\) \(=\frac{9000}{186}=48.39\) \(=49 approx\) |
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| 96 | The velocity distribution at any section of pipe for steady laminar flow is | Laminar | Exponential | Parabolic | Hyperbolic | c | The formula for the laminar velocity profile has to be mentioned first. The derivation of it is possible to find in every book dedicated to the fluid mechanics. The Laminar velocity profile of the fluid flow governed by the pressure gradient is parabolic. \(V=V(max)(1-(\frac{r}{R})^{3})\) Where R is the tube radius V(max) is the maximal velocity or the centerline velocity of the velocity profile. It is assumed that there is only one velocity component in the tube axis direction. This velocity profile expression can be also rewritten as a function of average velocity. \(V_{avg}=V_{max}/2\) \(\frac{V}{V_{max}}=1-(\frac{r}{R})^{2} \) This is a quadratic equation so profile will be parabolic. Velocity distribution curves for laminar and turbulent. |
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| 97 | Bernoulli's equation is applicable to | Compressible fluids | Incompressible fluids | Newtonian fluids | non-Newtonian fluids | b | For Bernoulli’s equation to be applied, the following assumption must be met: * The flow must be steady (velocity, pressure and density cannot change at any point). * The flow must be incompressible – even when the pressure varies, the density must remain constant. * Friction by viscous force must be minimal. |
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| 98 | Velocity head is given by | \(\frac{v}{g}\) | \(\frac{v^{2}}{2g}\) | \(\frac{v^{3}}{2g}\) | \(\frac{v^{2}}{2g^{2}}\) | b | Bernoulli’s equation formula is a relation between pressure, kinetic energy, and gravitational potential energy of a fluid in a container. The total mechanical energy of the moving fluid comprising the gravitational potential energy of elevation, the energy associated with the fluid pressure and the K.E of the fluid motion, remains constant. The formula for Bernoulli’s principle is given as: \(P+\frac{1}{2}ÏV^{2}+Ïgh=constant \) \(\frac{P}{Ïg}+\frac{V^{2}}{2g}+h=constant \) Where \(\frac{P}{Ïg}=pressure head\) \(\frac{V^{2}}{2g}=Velocity head\) \(h=Potential head\) |
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| 99 | Eulers dimensionless number relates | Inertia and Gravity force | Viscous and Inertia force | Pressure and Inertia force | Buoyant and viscous force | c | The Euler number is a dimensionless value used for analyzing fluid flow dynamics problems where the pressure difference between two points is important. The Euler number can be interpreted as a measure of the ratio of the pressure forces to the inertial forces. It determines in closed pipe flow the cavitation phenomena. The Euler number can be expressed as |
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| 100 | In a laminar flow Reynold number is | less than 2000 | more than 2000 | more than 2000 but less than 4000 | none of above | * | Reynold’s no decides nature of flow for different condition like pipe if \(Re<2000-Laminar\) \(Re>4000-Turbulent\) \(2000 \(Re<5×10^{5}-Laminar flow\) \(Re>10^{7}-Turbulent flow\) \(5×10^{5} Comments |
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| 101 | For conduction through thick-walled tube, the value of mean radius, rm used in heat conduction (with r1 inner radius and r2 outer radius) is given by | \(\frac{(r_{2}-r_{1})}{2}\) | \(\frac{(r_{2}+r_{1})}{2}\) | \(\frac{(r_{2}-r_{1})}{In\frac{r_{2}}{r_{1}}}\) | \(\frac{(r_{2}+r_{1})}{In\frac{r_{2}}{r_{1}}}\) | c | \( r_{m}=\frac{r_{2}-r_{1}}{ln (\frac{r_{2}}{r_{1}})}\) | Comments | Active | |
| 102 | What does a high value of Prandtl number indicate? | rapid heat transfer by forced convection to natural convection | rapid diffusion of momentum by viscous action compared to diffusion energy | relative heat transfer by conduction to convection | all the above | b | A high Pr number (>5) means that heat transfer is more favorable to occur by fluid momentum than by thermal diffusion, In other words, high Pr number means that heat transfer is favored to occur by fluid momentum rather than by fluid conduction. | Comments | Active | |
| 103 | The heat transfer equation is known as \(\frac{∂^{2}t}{∂x^{2}}+\frac{∂^{2}t}{∂y^{2}}+\frac{∂^{2}t}{∂z^{2}}=0\) | Steady state Steady state refers to a stable condition that does not change over time. Time variation of temperature is zero. Hence, \(\frac{∂}{∂x}(K\frac{∂T}{∂x})+\frac{∂}{∂y}(K\frac{∂T}{∂y})+\frac{∂}{∂z}(K\frac{∂T}{∂Z})+e^{'}gen=0\) If material is homogeneous and isotropic the thermal conductivity of the material would be constant. \(\frac{∂^{2}T}{∂x^{2}}+\frac{∂^{2}T}{∂y^{2}}+\frac{∂^{2}T}{∂z^{2}}+\frac{e^{'}gen}{K}=0\) \(∆^{2}T=\frac{- e^{'}gen}{K}\) The above equation is also known as Poisson’s equation. When there is no heat generation inside the element, the differential heat conduction equation will become. \(\frac{∂^{2}T}{∂x^{2}}+\frac{∂^{2}T}{∂y^{2}}+\frac{∂^{2}T}{∂z^{2}}=0\) Or \(∆^{2}T=0\) The above equation is also known as laplace equation Fourier equation \(Q=-KAdT/dx\) |
Poisson's equation | Fourier’s equation | Laplace's equation | d | \( \frac{∂}{∂x}(K\frac{dT}{dx})+\frac{∂}{∂y}(K\frac{∂T}{∂y})+\frac{∂}{∂z}\) \((K\frac{∂T}{∂Z})+(Ïgen'=Ïc\frac{∂T}{∂t}\) This is the general heat conduction equation in Cartesian co – ordinates special cases. |
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| 104 | Thermal conductivity of water | First increases with temperature then decreases with temperature | Increases steadily with temperature | Decreases with temperature | Does not depend on temperature | a | Water, aqueous solutions and multi – hydroxyl molecules the thermal conductivity of most liquids decreases but this happens only upto 130ᵒC. Beyond 130ᵒC, K values decreases with temperature. The reason behind has something to do with hydrogen boding breaking of water as the temperature goes up. | Comments | Active | |
| 105 | Stefan Boltzmann law is expressed as | Eb = σT4 | Eb = σ(ΔT)4 | Eb = σ(ΔT)1.4 | Eb = σT1.4 | a | Stefan – Botzmann law, statement that a total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature. If ϵ is the radiant energy emitted from a unit area in one second (that is the power from a unit area) and T is the absolute temperature (in Kelvins), then , the greek letter sigma (σ) representing the constant of proportionality, called the Stefan Boltzmann constant. This constant has the value . The law applies only to black bodies, theoretical surfaces, that absorb all incident heat radiation. \(ϵ=σT^{4}\) \(5.67×10^{-8} watt/m^{2}/K^{4}\) | Comments | Active | |
| 106 | A grey body is one whose absorptivity | vanes with temperature. | varies with wavelength of incident ray. | varies with temperature and wavelength of incident ray. | does not vary with temperature and wavelength of incident ray. | d | Grey body – Imperfect black body - It partially absorbs \(ϵ-emissivity= \frac{Thermal radiation of grey body}{Thermal radiation of black body}\) \(0<ϵ_{gray}<1\) Absorptivity of grey body does not depends on temperature and wavelength. It emits radiation at each wavelength in a constant ratio less than 1. |
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| 107 | With usual notation, the term is called \(\frac{Ïvl}{µ} \) | Reynold's number | Prandtl number | Froude number | Nusselt number | a | \( Re=\frac{ÏVL}{μ}\) | Comments | Active | |
| 108 | Prandtl number for water varies from | 0.5 – 1.0 | 1.0 – 5.0 | 5.0 – 10.0 | 10.0 - 102 | c | Approx value of Pr for water = 7 | Comments | Active | |
| 109 | With usual notation, the term is called \(\frac{C_{p}μ}{k} \) | Reynold's number | Prandtl number | Froude number | Nusselt number | b | Prandlt no = Pr = \(\frac{Momentum diffusivity}{Thermal diffusivity}=\frac{ν}{α}\) \(=\frac{μ/Ï}{(K/C_{P}.Ï)}\) \(=\frac{C_{P}μ}{K}\) \(μ=dynamic viscosity\) \(Ï=density\) \(K=thermal conductivity\) \(C_{P}=Specific heat\) \(Reynold^{'}s no=Re= \frac{Inertia force}{Viscous force}\) \(Ï=density\) \(v=velocity\) \(D=diameter of passage\) \(μ=viscosity\) |
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| 110 | With usual notations, for black body | α = 0, Ï„ = 0, Ï = 1 | α = 1, Ï„ = 0, Ï = 0 | α = 1, Ï„ = 1, Ï = 0 | None of the above | b | For black body Absorptivity \(α=1\) Reflectivity, \(Ï=0\) Transmissivity \(Ï„=0\) |
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| 111 | A composite wall consists of three different materials having conductivities as K, 2K and 4K respect very. The temperature drops across different materials will be in ratio of | 1: 1:1 | 1: 2: 4 | 4: 2: 1 | 2: 4: 1 | c | Fourier’s law \(Q=-KA\frac{dT}{dx}\) \(dTâˆ\frac{1}{K}\) So, temperature will just reciprocal to thermal conductivity is ratio higher the K, lower the dT. \(∴K_{1}:K_{2}:K_{2}=K:2K:4K\) \(∆T_{1}:∆T_{2}:∆T_{3}=4 :2 :1\) |
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| 112 | For spheres the critical thickness of insulation is given by | \(\frac{h}{2k}\) | \(\frac{2k}{h}\) | \(\frac{h}{k}\) | \(\frac{h}{2Ï€k}\) | b | \( t_{cr}=2k/h Sphere\) \(t_{cr}=K/h Cylinder \) |
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| 113 | The thermal conductivity is expressed as | W/mK | W/m2K | W/hmK | W/h2m2K | a | \(\) \(Q=-KAdT/dx\) \(W=K×m^{2}×K/m\) \(K^{'}s unit=W/m-k\) |
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| 114 | With usual notation the term hL/K is called | Reynold number | Prandtl number | Froude number | Nusselt number | d | Nusselt number (Nu) is the ratio of convective to conductive heat transfer at a boundary in a fluid. Convection includes both advection (fluid motion) and diffusion (conduction). The conductive component is measured under the same conditions as the convective but for a hypothetically motionless fluid. It is a dimensionless number, closely related to the fluids Rayleigh number. Nu = Convective heat transfer/conductive heat transfer \(=h/(K/L)=hL/K\) |
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| 115 | A body cools from 85o C to 70o C in 7 minutes. The time taken by the body for further cooling to 55o C will be | 7 minutes | more than 7 minutes | less than 7 minutes | 0.7 minutes | a | \( ∵Q= -KA\frac{dT}{dx}\) \(∵dT and (K, A)\) Are same in both cases so Q will be same and hence time will also same |
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| 116 | In the non-dimensional Biot. number, the characteristic length is the ratio of | Volume of solid to its surface area | Surface area to volume of solid | Perimeter to surface area of solid | Surface area to perimeter of solid | a | Volume/Surface area = Characteristic length | Comments | Active | |
| 117 | Which of the following is expected to have highest thermal conductivity? | Water | Melting ice | Solid ice | Steam | c | Thermal conductivity \(K_{solid}>K_{liquid}>K_{gas}\) Ice is solid hence its thermal conductivity will higher than melting ice, water and steam. |
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| 118 | For gases Prandtl number is | near unity | between 5 to 50 | between 60 to 100 | between 150 to 300 | a | For gases momentum diffusivity and thermal diffusivity will be approximately equal so, Pr nearly equals to 1. | Comments | Active | |
| 119 | Which mode of heat transfer play’s insignificant role in a coaling tower? | Radiation | Evaporative cooling | Convection cooling | All the above | b | A cooling tower is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water’s temperature. As this occurs, a small volume of water is evaporated, reducing the temperature of the water being circulated through the tower. When the water and air meet, a small amount of water is evaporated, creating a cooling action. No radiation takes place there HVAC also do same type of cooling. |
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| 120 | In the heat flow equation Q = kA (t1 — t2)/x, the term (t1 — t2)/x is known as | thermal conductivity | thermal coefficient | thermal resistance | temperature gradient | d | Temperature gradient \(=\frac{dT}{dx}\) | Comments | Active | |
| 121 | Dropwise condensation occurs on the following surface: | Oily | Smooth | Glazed | Coated | a | Dropwise condensation * In dropwise condensation, the vapor condenses on the surfaces in the form of drops. * It occurs on a non – wettable cooling surface where the liquid condensate drops do not spread. * It is desirable because of its higher heat transfer rates. * When the surface is coated with a promoter like Teflon, grease, oil, mercaptan, aleic acid etc. |
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| 122 | A correction of L.M.T.D is necessary in case of | cross flow heat exchanger | parallel flow heat exchanger | counter flow heat exchanger | all of the above | c | Corrected LMTD counter flow heat exchanger = Correction factor × LMTD counter flow |
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| 123 | At thermal equilibrium, the absorptivity and emissivity are | unity | zero | different | equal | d | In most case absorptivity of a body in equal to its emissivity under thermal equilibrium conditions. Kirchoff’s law states that for an arbitrary body emitting and absorbing thermal radiation in thermodynamic equilibrium, the emissivity is equal to the absorptivity. In general, both the emissivity ϵ, and the absorptivity α of a surface depends on the temperature and the wavelength of the radiation. | Comments | Active | |
| 124 | In case of heat exchanger, the value of logarithmic mean temperature difference should be | as small as possible | as large as possible | constant | none of the above | a | The value of corrected LMTD should be less than the theoretical LMTD considering counter current flow. Thus, the LMTD correction factor is less than 1 also, for steady state operation of the heat exchanger, its value should be more than 0.75. | Comments | Active | |
| 125 | L.M.T.D in case of counter flow heat exchanger as compared to parallel flow heat exchanger is | higher | lower | same | cannot be predicted | a | Counter flow heat exchangers are inherently more efficient than parallel flow heat exchangers because they create a more uniform temperature difference between the fluids over the entire length of the fluid path. In parallel flow the temperature difference is not uniform throughout the length while in case of counter flow temperature difference is approximately same at any point throughout the length of heat exchanger as shown in fig.   |
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| 126 | The thickness of thermal boundary layer is equal to hydrodynamic boundary layer when Prandtl number is equal to | 0 | 0.1 | 0.5 | 1.0 | d | \( Prandtl no= \frac{momentum difference }{Thermal differnce }\) \(=\frac{μC_{P}}{K}\) \(=Pr^{V3}=\frac{hydrodynamic boundary thickness}{thermal boundary thickness}\) \(\frac{δ}{δt}=Pr^{V3} \) \(if Pr=1⇒δ=δt\) \(if Pr>1⇒δ>δt\) \(if Pr<1⇒δ<δt\) |
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| 127 | In case of black body | Transmissivity is one | Absorptivity is zero | Reflectivity is one | None of the above | d | A black body is a idealize physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name black – body is given because at absorbs all colors of light. A black body also emits , black body radiation. For perfect black body absorptivity = 1, Reflectivity = 0, Transmissivity = 0. |
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| 128 | With rise in temperature, thermal conductivity of solid material | Decreases | Increases | Remains constant | Cannot be predicted | a | For metals, since atoms are closely bounded hence as the temperature increases. Thermal agitation increases within them and mean free path of the atoms increases, leading to resistance to thermally active electrons which causes resistance to conductivity. Thermal conductivity of any material is dependent on two things: 1. The motion of free electrons 2. Lattice vibrations The thermal conductivity of gases increases with temperature. Thermal conductivity of liquids decreases with increasing temperature as the liquid expands and the molecules have apart. In the case of solids, because of lattice distortions, higher temperatures make it difficult for electrons to flow, hence the thermal conductivity of metals decreases. NOTE: * Thermal conductivity depends on the chemical composition of the substance. * Thermal conductivity of the liquids is more than the gasses and the metals have the highest. * Thermal conductivity of the gases and liquid increases with the increase in temperature. * Thermal conductivity of the metal decreases with the increase in temperature. * Metal crystalline in a structure, have greater thermal conductivity than non – metal. * Thermal conductivity is affected by the phase change. |
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| 129 | A radiation shield is used around thermocouples in order to measure more accurately the temperature of | Solid | Gases | Freezing liquid | Boiling liquid | b | Gases have no definite volume so to measure the temperature by thermocouple one need shiel(d) The gas is free to pass through the shield and thermocouple are heated. The thermocouple junction radiates to the shield which is much hotter than the surrounding walls. Thus the radiative loss and hence temperature error is significantly reduced. The shield itself radiates to the walls. | Comments | Active | |
| 130 | The fouling factor | Increases the overall heat transfer coefficient. | Decreases the overall heat transfer coefficient. | Is equal to the overall heat transfer coefficient. | None of the above. | b | Fouling increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers. It also decrease fluid flow, accelerates corrosion and increases pressure drop across heat exchangers. Different types of fouling mechanisms have been identified. The fouling factor represents the theoretical resistance to heat flow due to a build up of a layer of dirt or other fouling substance on the tube surfaces of the heat exchanger. Over all heat transfer coefficient \(\frac{1}{UA}=\frac{1}{h_{0}A_{0}}+\frac{f_{0}}{A_{0}}+\frac{l_{n}(Do/Di)}{2Ï€KL}+\frac{1}{hiAi}+\frac{fi}{Ai}\) factor. It decreases the overall heat transfer coefficient and is used as a factor of safety in heat exchanger designing. \(f=fauling \) |
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| 131 | On which of the following factors does the amount of radiation depend? | Temperature of body | Type of surface of body | Nature of body | All of the above | d | The nature of the thermal radiation depends on the nature of the surface, surface area, color of the surface and temperature of body. \(Q=σAf_{1-2}(T14-T24)\) A = Surface area f = Shape factor T = Absolute temperature |
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| 132 | The dimensionless number relevant in transient heat conduction is | Fourier number | Grashoff number | Weber number | Archmedes number | a | unsteady state or transient heat conduction Temperature = f (time) \(-T=f(Ï„)\) \(-T≠f(space)\) Here \(\frac{T-T_{∞}}{T_{0}-T_{∞}}=Ï^{-(hA/ÏCV)t}\) Time constant \(Ï„=\frac{ÏVC}{hA}\) T = Temperature of body after time t Initial temperature of body \(T_{0}=\) = Surrounding temperature \(T_{∞}\) h = Convective heat transfer coefficient A = Surface area V = Volume of body = Density of body \(Ï\) C = Specific heat of body . T \(\frac{hA}{ÏCV} t=\frac{h}{ÏC}.\frac{A}{V}. t=\frac{h}{ÏC}\frac{1}{L_{c}}\) LC = Characteristic length \(=\frac{h}{Ï_{C}}.\frac{1}{L_{C}}.\frac{L_{C}}{L_{C}}.\frac{K}{K}.t\) \((K=thermal conductivity)\) \(=\frac{hL_{C}}{K}.(\frac{K}{Ï_{C}}).\frac{t}{LC2}\) \(\frac{hL_{C}}{K}=Biot no\) \((\frac{K}{Ï_{C}})=Thermal diffusivity\) \(=Bi.\frac{α.t}{LC2}\) \(∴\frac{T-T_{∞}}{T_{i}-T_{∞}}=Ï^{-BixFo}\) |
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| 133 | In which of the following cases, transmission of heat is smallest? | Solids | Alloys | Gases. | Liquids | c | In gases atoms arranged loosely, there is less molecular transmission of heat as compared to solids liquids and alloys. Thermal conductivity \(K_{Solid}>K_{Liquid}>K_{gas}\) |
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| 134 | A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For less heat transfer | the better insulating material must be put outside, | any of the two insulations may be placed inside or outside. | the temperature of the steam must be taken into account while deciding as to which insulation is put where. | the better insulation must be put inside. | b | \( K_{1} \(R_{th}âˆ\frac{1}{K}⇒R_{th})_{1}>R_{th})_{2}\) should be placed on pipe first and then . If is placed on pipe 1st , higher heat loss will occur from pipe to interface of superior and inferior material and thickness of should be greater than and combinely should be less than critical thickness. \(R_{th})_{1}\) \(R_{th})_{2}\) \(R_{th})_{1}\) \(R_{th})_{1}\) \(R_{th})_{2}\) |
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| 135 | Which instrument is used to measure the temperature inside furnace? | Gas thermometer | Optical pyrometer | Alcohol thermometer | Mercury thermometer | b | Optical pyrometer | Comments | Active | |
| 136 | When the thickness of insulation on a pipe exceeds the critical value. | The heat flow rate decreases. | The heat flow rate increases. | The heat flow rate remains constant. | None of the above. | a | The insulation radius at which resistance to heat flow is minimum and consequently heat flow rate is maximum. Note the critical radius of insulation depends on the thermal conductive of the insulation (K) and the external convection heat transfer coefficient h. \(r_{cr}âˆk, h\) \(if r>r_{cr} or\) \(r Comments |
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| 137 | The radial heat transfer rate through hollow cylinder increases as the ratio of outer radius to inner radius | increases | decrease | remains constant | none of the above | b | \(H.T. (Q)=∆T/R_{TH}\) \(R_{TH}=\frac{ln(r_{2}/r_{1})}{2Ï€KL}\) \(∴Qâˆln (\frac{r_{2}}{r_{1}})\) As \(r_{2}/r_{1}↓\) \(Q will↑\) |
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| 138 | Which of the following property is poor for gases? | Transmissivity | Absorptivity | Reflectivity | All of the above | c | Gases can easily transmit and absorb the radiation but cannot reflect effectively. | Comments | Active | |
| 139 | The temperature of sun can be measured by using | Radiation pyrometer | Standard thermometer | Mercury thermometer | None of above | a | Pyrometer are used to measure very high temperature upto 3000áµ’C of furnace or of sun. | Comments | Active | |
| 140 | automobile radiator is which type of heat exchanger? | Cross flow | Regenerator | Counterflow | Recuperator | a | Most commonly made out of aluminium, automobile radiators utilize a cross – flow heat exchanges design. The two working fluids are generally air and coolant (50 – 50 mix of water and ethylene glycol). As the air flows through the radiator. The heat transferred from the coolant to the air. The purpose of the air is to remove heat from the coolant, which causes the coolant to exit the radiator at a lower temperature than it entered. | Comments | Active | |
| 141 | Thermal diffusivity of a substance is inversely proportional to | specific heat | density of substance | both (a) and (b) | none of the above | c | Thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI derived unit of m2/s. Thermal diffusivity \((α)=\frac{heat conducted}{heat stored}=K/ÏC_{P}\) \(α is the thermal diffusivity\) \(K is the thermal conductivity (W/mK)\) \(Ï is the density (kg/m^{3})\) \(C_{P} is the specific heat capacity (J/KgK)\) |
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| 142 | Which one of the following modes of heat transfer would take place predominantly from boiler furnace to water wall? | Convection | Conduction | Radiation | Conduction & convection | c | All modes of heat transfer would be seen here, but most dominant would be radiation because in radiation the transfer of heat between two surfaces is proportional to and in case of conduction and convection HT is directly proportional to only to DT hence this difference would be huge as compared to conduction and convection. Hence, radiation would be dominant. \(T^{4}\) | Comments | Active | |
| 143 | Planck's law holds good for | Polished bodies | Black bodies | All coloured bodies | None of above | b | It explains the spectral energy distribution of radiation emitted by a black body (a hypothetical body that completely absorbs all radiant energy falling upon it) reaches some equilibrium temperature and then remits that energy as quickly as it absorbs it. | Comments | Active | |
| 144 | According to Wien's law the wavelength corresponding to maximum energy is proportional to | T | T2 | T3 | T4 | a | According to planck’s law, the wavelength corresponding to the maximum energy is inversely proportional to temperature. It is obtained from wein displacement law. The wein’s displacement law can be obtained be determining the maxima of planck’s law. Wien’s displacement law states that the black – body radiation curve for different temperatures will peak at different wave lengths that are inversely proportional to the temperature. Wein’s displacement law states that the spectral radiance of black body radiation per unit wavelength, peaks at the wavelength given by \(λ\) \(λ=bT\) \(b=Wein^{'}s constant=3×10^{-3} mK\) |
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| 145 | Which number has significant role in forced convection? | Mach number | Reynold's number | Prandtl number | Peclet number | b | It is indicative of the relative importance of inertial and viscous effects in a fluid motion. \(Re=ÏVd/μ\) \(Ï=density\) \(V=velocity\) \(d=diameter of passage\) \(μ=Dynamic viscosity\) At large Re numbers, the inertia forces, which are proportional to the density and the velocity of the fluid, are large relative of the fluid, are large relative to the viscous forces, thus the viscous forces cannot prevent the random and rapid fluctuations of the fluid (turbulent region). The Reynolds number at which the flow becomes turbulent is called the critical Reynolds number for feat plate the critical Re is experimentally determined to be approximately Re critical = \(5×10^{5}\) Except these there are two more number s of dimensionless number which are really important in forced convection, Nusselt no. and Prandtl no. |
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| 146 | Least value of Prandtl number can be expected in the following: | Water | Salt solution | Sugar solution | Liquid metals | d | Liquid Metal Prandlt number is given as \(Pr=\frac{Momentum diffusivity}{Thermal diffusivity}\) \(Pr=\frac{(μ/Ï)}{(K/μC_{p})}\) Where S.I. units Momentum diffusivity \(m^{2}/s\) Thermal diffusivity \(m^{2}/s\) Dynamic viscosity (ð›) Pa – s = NS/m2 Thermal conductivity (K) W/m.K Specific heat ( \(C_{P})\) J/Kg.K Density (ð›’) Kg/m3 Pr = around 7.56 for water (at 18áµ’C) Pr = 13.4 at 0áµ’C for salt solution Pr = 1000 for sugar Pr = 0.06 for molten lithium |
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| 147 | The following has least value of conductivity: | Rubber | Air | Water | Plastic | b | Thermal conductivity \(K_{solid}>K_{liquid}>K_{gas}\) Alr is approximately insulator for heat conduction. |
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| 148 | Radiation heat transfer occurs at a speed of | Sound | Light | 60,000 km/hr | 350 m/s | b | Energy transfer by radiation occurs at the speed of light and suffers no attenuation in vacuum. Radiation can occur b/w two bodies separated by a medium colder than both bodies. According to Maxwell theory, energy transfer takes place via electromagnetic waves in radiation. Electromagnetic waves transport energy like other waves and travel at the speed of light. Electromagnetic waves are characterized by their frequency and wavelength where: where C is the speed of light in that medium in a vaccum C = m/s. \(ν(H_{z})\) \(λ(μm)\) \(λ=C/ν\) \(2.99×10^{8}\) Note that the frequency and wavelength are inversely proportional. |
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| 149 | Thermal Radiation occurs in the wavelength range of | 10-1 to 10-2 micron | 0.1 to 102 micron | 10-2 to 10-4 micron | None of the above | b | Thermal radiation is electromagnetic radiation emitted from all matter that is at a non – zero temperature in the wavelength range from 0.1 to 100μm. It includes part of the ultraviolet (UV), and all of the visible and infrared (IR). \(μm\) | Comments | Active | |
| 150 | The lowest value of Nusselt Number will be | Less than one | Always greater than one | May be less than one or greater than one | One | d | The Nusselt number is the ration of convective to conductive heat transfer across a boundary. The convection and conduction heat flows are parallel to each other and normal to the boundary surface. \(N_{u}=\frac{hL}{K}=\frac{Convective H.T.}{Conductive H.T.}\) Where h is the convective heat transfer coefficient of the flow, L is the characteristics length, K is the thermal conductivity of the fluid. When Nu = 1 then HT taking place purely by conduction. There is always the heat transfer by conduction across two different temperatures of a fluid. As the convection start to begin in fluids the Nusselt number start to increase, because convection will further increase heat transfer and very soon will dominate over conduction hence at least i.e. \(Nu=1\) \(HT_{conv}=HT_{cond}\) |
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| 151 | Chemical formula of Freon-12 is | CCl2.F2 | CCl2.F3 | CCl3.F2 | CCl3.F3 | a | Di – chloro, di – flouro methane \(CCl_{2}F_{2}\) | Comments | Active | |
| 152 | In a vapour compression system the condition of refrigerant before entering the compressor | Saturated liquid | Wet vapour | Dry saturated liquid | Superheated vapour | b | 1 – 2 – isentropic compression 2 – 3 – Isobaric heat rejection 3 – 4 – Isenthalpic expansion 4 – 1 – Isobaric heat rejection 1- entry point of compressor point 1 should be at saturated vapour curve but practically it appears in wet vapour region (1’) |
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| 153 | The capillary tube, as an expansion device, is used in | Domestic refrigerators | Water coolers | Room air-conditioner | All of these | d | The function of expansion device: It reduces the pressure from the condenser to evaporator and it supplied the flow of refrigerant to the evaporator as per the desired capacity. Capillary tube: It is a narrow tube of constant cross – section area. The pressure drop in the capillary tube is achieved due to frictional resistance and due to the acceleration of the fluid in the tube. The pressure drop is directly proportional to the length of the capillary tube and inversely proportional to the diameter of the capillary tube it is used in the domestic refrigerators water coolers and window air conditioners. |
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| 154 | In a vapour compression system, a throttle valve is used in place of an expansion valve | it improves the (C)O.P. | it leads to significant cost reduction | the positive work in isentropic expansion of liquid is very small | none of the above | c | Since a specific volume of liquid is very small hence work obtained will not justify the cost of the expander. Secondly, the frictional and thermodynamics losses in expanding the liquid will make the gain in work negative. So isentropic process of expansion is replaced by an isenthalpic process through throttling. 3 – 4 Isenthalpic processes 3 – 4’ Isentropic process |
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| 155 | The expression is used to determine \(\frac{0⋅622Pv}{P-Pv}\) | relative humidity | specific humidity | degree of saturation | partial pressure | b | Humidity ratio/Specific humidity (ω) is water vapour (MV) contained in air vapour mixture per kg of dry air Ma \(ω=\frac{Mv}{Ma}=0.622 \frac{P_{v}}{P-Pa}\) \(P=partial pressure \) |
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| 156 | Where does the lowest temperature occur in a vapour compression cycle? | Condenser | Compressor | Evaporator | Expansion valve | c | 1 – 2 = Compression of vapor 2 – 3 = Vapor superheat removed in condenser 3 – 4 = Vapor converted to liquid in condenser 4 – 5 = Liquid flashes into liquid + vapor across expansion valve 5 – 1 = Liquid + vapor converted to all vapor in evaporator. [A fictitious T – S diagram for a typical refrigeration) You can easily notice that the region of the lowest temperature in the cycle lies within the evaporator (5 – 1), typically at its entrance. Before it starts with drawing heat from the enclosed container or room it is in. Before that point, the saturated liquid – refrigerant undergoes flash evaporation within the valve (constant - enthalpy process) , where pressure reduction occurs, which has a direct effect on lowering the temperature of the liquid and vapor refrigerant mixture. |
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| 157 | Which has minimum freezing point? | Freon-22 | Freon-12 | Cardon dioxide | Ammonia | a | Refrigerant Freezing point Freon – 11 (Tri – chloro flouro methane) -168ᵒF Freon – 12 (Dichloro flouro methoane -252ᵒF Freon – 22 (Di – flouro – mono chloro methane) -256ᵒF R – 717 (Ammonia) -107.9ᵒF |
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| 158 | which refrigerant is used vapour absorption refrigerator? | Freon | Sulphur dioxide | Water | Acqua-Ammonia | d | * Vapor absorption refrigeration system Water – refrigerant Lithium bromide – absorbent * Ammonia – Water (NH3 – H2O) system Ammonia – Refrigerant Water – Absorbent |
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| 159 | Which of the refrigerant is least used these days? | Freon-12 | sulphur dioxide | carbon dioxide | ammonia | c | Feron – 12, dichlor Fluoro carbon (CFC), completely prohibited dangerous for Ozone layer. \( C, Co_{2} (least used)\) | Comments | Active | |
| 160 | Dry ice is produced by expanding | Liquid ammonia | Liquid Freon-22 | Carbon dioxide | Liquid Freon-12 | c | First gases with a high concentration of carbon dioxide are produced. Such gases can be a by – product of another process such as producing ammonia from nitrogen and natural gas, oil refinery activities or large – scale fermentation. Second the carbon dioxide rich gas is pressurized and refrigerated until it liquefies. Next, the pressure is reduced. When this occurs some liquid vaporises, causing a rapid lowering of temperature of the remaining liqui(d) As a result the extreme cold cause the liquid to solidify a snow like consistency. Finally the snow like solid carbon dioxide is compressed into small pellets or larger blocks of dry ice, fine particles called dry ice show was produced by expanding liquid carbon dioxide. \(Co_{2}\) | Comments | Active | |
| 161 | Relative humidity during sensible cooling process | increases | decreases | remains same | cannot be predicted | a | Process A – B is sensible cooling | Comments | Active | |
| 162 | The curved lines on psychrometric chart indicate | specific humidity | Relative humidity | Dew point temperature | Dry bulb temperature | b | Psychrometric chart lines structure | Comments | Active | |
| 163 | A heat pump working on reversed Carnot cycle has COP of 5. If it works as a refrigerator taking 1 KW of work input the refrigerating effect will be | 1 KW | 2KW | 3 KW | 4 KW | d | \( COP)_{HP}=5\) \(and COP)_{HP}=COP_{)rej}+1\) \(=COP)_{rej}=5-1=4\) \(Now COP)_{rej}=\frac{Refrigeration effect}{Work consumed}\) \(4=\frac{RE}{1}\) \(RE=4KW\) |
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| 164 | The following refrigerant is most miscible with oil. | R-717 | R-11 | R-22 | R-12 | a | Ammonia – R 717 | Comments | Active | |
| 165 | Among the refrigerants namely R-11, R-12 and R- 717, the ratio of specific heat is highest for | R-12 | R-22 | R-11 | R-717 | d | Specific heat ratio R – 11 – 1.14 R – 12 – 1.14 R – 22 – 1.18 R – 717 – 1.32 |
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| 166 | A refrigerant used for absorption refrigerators working on heat received from solar collectors is a mixture of water and | Carbon dioxide | Lithium bromide | Freon-12 | Sulphur dioxide | b | * Vapor absorption refrigeration system Water – refrigerant Lithium bromide – absorbent * Ammonia – Water (NH3 – H2O) system Ammonia – Refrigerant Water – Absorbent |
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| 167 | If the specific humidity of the moist air remains same but its dry bulb temperature increases | its dew point temperature increases | its dew point temperature decreases | its dew point temperature remains constant | none of the above | c | During process A – B - Specific humidity is constant - Sensible heating occurs - Extend the process till saturation curve point c is obtained, which will represent dew point – temperature which is constant. |
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| 168 | If Pv partial pressure of water vapour in air and Ps is the saturation pressure of water vapour at the same temperature, the relative humidity is equal to | 1- \(\frac{P_{V}}{P_{s}}\) | 1- \(\frac{P_{s}}{P_{v}}\) | Ps-Pv | Pv/Ps | d | The ratio of the mass of water vapour actually present in certain volume of air (m) to the mass of water vapour (M) required to saturate the same volume of air at the same temperature is called relative humidity (RH) or relative humidity as the ratio of vapor partial pressure in the air to the saturation vapor partial pressure if the air at the actual dry bulb temperature. Relative humidity is related to the partial pressure of water vapor in the air. AT 100% humidity, the partial pressure is equal to the vapor pressure and no more water can be enter the vapor phase. If the partial pressure is less the vapor pressure, then evaporation will take place, as humidity is less than 100%. \(∅=\frac{P_{V}}{P_{S}}\) |
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| 169 | Air refrigeration works on which cycle? | Rankine | Bell-Coleman cycle | Both (b) & (c) | Reversed Carnot cycle | b | Bell colleman cycle [P – V Diagram][T – S Diagram] |
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| 170 | In vapour compression cycle, heat rejected is 65 KW and work done in compression is 10 KW, the COP of refrigerator will be | 6.5 | 5.5 | 5.0 | none of the above | b | \( Q_{i}+W_{C}=Q_{R}\) \(Q_{i}=65-10=55\) = Refrigeration effect = Heat absorbed \(COP=\frac{RE}{WD}=\frac{55}{10}=5.5\) |
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| 171 | Ammonia refrigerant is | Non-toxic | non-inflammable | Toxic and non-inflammable | Highly toxic and inflammable | d | There are 2 key disadvantage to using ammonia as a refrigerant. - It is not compatible with copper, so it cannot be used in any system with copper pipes. - Ammonia is poisonous in high concentration. Two factors however mitigate this risk. * Ammonia’s distinctive smell is detectable at concentrations, well below – those considered to be dangerous, and ammonia is lighter than air, so if any gas does leak, it will rise and dissipate in the atmosphere. - Highly toxic - Highly inflammable under compression |
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| 172 | In MHD power generation system, the electrical conductivity of air increased by | Heating it to very high temperatures | Seeding | Both (a) and (b) | None of these measures | c | In an open cycle MHD (magnetic hydro dynamic) system, atmospheric air at very high temperature and pressure is passed through the strong magnetic field. Load is first processed and burnet in the combustor at a high temperature of about 2700áµ’C and pressure about 12 ATP with preheated air from the plasma. Then a seeding material such as potassium carbonate is injected to the plasma to increase the electrical conductivity of air. | Comments | Active | |
| 173 | Air conditioning is concerned with maintaining the following: | Temperature | Humidity | Cleanliness | All the above | d | AC function: Cooling, dehumidification and purification of air. | Comments | Active | |
| 174 | A device is used to remove moisture from a refrigerant is called | Dehumidifier | Solenoid | Expansion valve | Drier | d | Drier: It is used to remove the moisture from the refrigent. Sometimes it is also called as a dehydrator. Dehumidifier: Used to maintain low level of moisture in air. Expansion valve: To control the amount of the refrigerant released into the evaporator and to regulate the pressure of the refrigerant. |
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| 175 | If wet bulb depression is zero, then relative humidity is equal to | 0% | 50% | 100% | None of the above | c | Wet bulb depression is the difference between the dry bulb and wet bulb temperature. WBD = DBT – WBT Hence, when DBT = WBT, implies that relative humidity = 100%. Therefore when the wet bulb depression is zero the relative humidity is 100%. |
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| 176 | In a Psychrometric process the sensible heat added is 30 kJ/ sec and latent heat added is 20 KJ/ se(c) The sensible heat factor for the process will be | 0.3 | 0.6 | 0.67 | 1.5 | b | Sensible heat factor \(SHF=\frac{Sensible heat}{Sensible heat+Latent heat}\) \(\frac{SH}{SH+LH}=\frac{30}{30+20}=0.6\) |
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| 177 | The condition for maximum efficiency of reaction turbine is given by | Vb = V1 cos α | Vb = V12 cos α | Vb = (V1 cos α)/2 | Vb = V12 cos α/2 | a | Diagram efficiency of reaction turbine \(η_{d}=\frac{2Ï(2 cos α_{1}-Ï)}{1-Ï^{2}+2Ï cos α_{1}}\) \(Ï=velocity ration=\frac{blade velocity}{absolute velocity}\) \(=\frac{V_{b}}{V_{1}}\) \(∴α_{1}=nozzle angle for maximum efficiency\) \(\frac{dη_{d}}{dÏ}=0\) \(=2cosα_{1}-2Ï=0\) \(=Ï=cosα_{1}⇒\frac{V_{b}}{V_{1}}=cosα\) \(η_{d})_{max}=\frac{2cos^{2}α_{1}}{1+cos^{2}α_{1}}\) [V1 being the absolute speed of the steam entering the blades and α being nozzle angle] |
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| 178 | The COP of a domestic refrigerator is | less than 1 | more than 1 | equal to 1 | varies from -1 to+1 | b | For effective refrigeration COP should be always greater than 1. \(COP)_{ref}>1\) |
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| 179 | In an ideal refrigeration system based on reversed Carnot cycle, the condenser and evaporator temperatures are 27 °C and -13 °C respectively. The C.O.P of the cycle would be | 6.5 | 7.5 | 0.15 | 10.5 | a | \( COP)_{ref}(based on reversible carnot cycle)=\frac{T_{L}}{T_{H}-T_{L}}\) \(T_{L}=evaporator temperature \) \(=-13℃=260K\) \(T_{H}=condenser temperature \) \(=27℃=300K\) \(COP)_{ref}=\frac{260}{300-260}=\frac{260}{40}=6.5\) |
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| 180 | Stage efficiency of steam turbine is equal to | blade efficiency / nozzle efficiency | nozzle efficiency / blade | nozzle efficiency x blade efficiency | 1- blade efficiency | c | A stage is defined as the combination of a ring of nozzles (fixed blades) and a ring of moving blades. The energy supplied corresponds to the isentropic heat drop, ΔH in the nozzle. The stage efficiency, is given by \(η_{S}\) work done/Energy supplied per stage \(η_{S}=\) \(=(Vω_{1}+vω_{2})u/∆H\) The stage, efficiency becomes equal to the blade efficiency if there are no friction losses in the nozzles. Thus, \(η_{S}=Nozzle efficiency×blade efficiency\) \(=(Vω_{1}+Vω_{2})u/∆H\) \(={(Vω_{1}+Vω_{2})u/(V12/2)}×{(V12/2)/∆H}\) \(=η_{n}×η_{b}\) Notation have usual meaning |
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| 181 | Bleeding in turbine means | leakage of steam | steam doing no useful work | extracting steam for pre-heating feed water | removal of condensed steam | c | Bleed is amount of steam output from turbine through pipe and exit from final state of turbine. This bleed enter to feed water heater (low and high) and dearotor to increase unit efficiency. Or rather bleed is the amount of steam drained out of the steam turbine during the expansion of steam and this rejected heat energy is used to heat the feed water supplied to the boiler. |
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| 182 | In the absorption refrigeration cycle, the compressor of vapour compression refrigeration cycle is replaced by | Liquid pump | Generator | Absorber and Generator | Absorber, Liquid pump and Generator | d | In vapor compression refrigeration system (VCRS), the components used as evaporator, compressor, condenser and expander. In the vapour absorption system, the compressor is replaced with the absorber, pump and generator is replaced with the absorber, pump and generator. |
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| 183 | Most widely used material of solar cell is | Arsenic | Cadmium | silicon | Steel | c | Silicon is, by far, the most common semi – conductor material used in solar cells, representing approximately 95% of the modules sold today. It is also the second most abundant material on earth (after oxygen) and the most common semi – conductor used in computer chips. | Comments | Active | |
| 184 | Biogas consists of | only methane | methane and co2 with some impurities | A special organic gas | None of the above | b | Biogas consists mainly of methane and carbon dioxide. It can also include small amounts of hydrogen sulphide, siloxanes and some moisture. The relative quantities of these vary depending on the type of waste involved in the production of the resulting biogas. It occurs naturally in compost heaps, as swamp gas, and as a result of enteric fermentation in cattle and other ruminants. Biogas can also be produced in anaerobic digesters from plant or animal waste or collected from landfills. It is burned to generate engines to produce electricity. | Comments | Active | |
| 185 | Foggy condition in atmosphere results when | Hot and humid air mixes with cold dry air. | cold and dry air mixes with hot and dry air. | Hot and humid air mixes with hot and dry air. | None of the above. | a | Fog shows up when water vapor, or water in its gaseous form in not and humid air, condenser by cool dry air. During condensation, molecules of water vapour combine to make it tiny liquid water droplets that hand in the air. You can see fog because of these tiny water droplets. Water vapour a gas, is invisible. Fog happens when it is very humid. There has to be lot of water vapour in the air for fog to form. In order for fog to form, dust or some kind of air pollution needs to be in the air. Water vapour condenses around these microscopic solid particles. Sea fog, which shows up near bodies of salty water is formed as water vapor condenses around bits of salt. |
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| 186 | With an increase in suction pressure the volumetric efficiency of a reciprocating refrigeration compressor | increases | decreases | remains constant | may increase or decrease depending upon the type of refrigerant | a | of reciprocating refrigeration compressor \( η_{vol}\) \(η_{vol}=1+C-C(\frac{P_{2}}{P_{1}})^{1/n}\) \(C=Clearance compressor\) \(C=\frac{Clearance volume}{swept volume}\) \(\frac{P_{2}}{P_{1}}=Pressure ratio\) as \(C↑ then η_{vol}↓\) as \(\frac{P_{2}}{P_{1}} ↑then η_{vol}↓\) depends on ambient pressure and temperature, suction pressure and temperature, as suction pressure P, increases, pressure ratio decreases and increases. \(η_{vol}\) \(η_{vol}\) delivery pressure \(P_{2}=\) |
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| 187 | The colour of halide torch flame, in case of leakage of freon refrigerant will change to | Bright green | Yellow | Red | Orange | a | Leakage of refrigerant from a refrigeration system affects the performance of a sealed system (systems with hermetic compressors) adversely. Due to refrigerant leakage, the running time of the system increases continuously. Both suctions as well as discharge pressures reduce due to loss of refrigerant. There will be less liquid and more flash gas, which has negative effect on several components of the system. The halide leak detector works on the principle of change of colour of a flame in the presence of the refrigerants when a fluorocarbon based refrigerant such as R12 or R22 is sucked through a sampling tube and passed over a surface whose surface temperature is high (around 500), then the refrigerant vapour breaks down and forms a foul smelling gas known as phosgene (CoCl2) when this gas is passed over a glowing copper (heated by the flame of the torch itself). If forms copper chloride which changes the colour of the flame from pale blue to bright green. \(℃\) Electronic leak detector is based on the principle that when halogen vapour is heated, positive ion concentration is increased and this increase is suitably magnified to an audible or visual signal. |
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| 188 | The difference between dry bulb temperature and wet bulb temperature is called | Dry bulb depression | Wet bulb depression | Dew point temperature | Degree of saturation | b | DBT – WBT = Wet bulb depression DBT – DPT = dew point depression |
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| 189 | A closed cycle gas turbine works on | Carnot cycle | Rankine cycle | Ericsson cycle | joule cycle | d | Joule cycle is thermodynamic cycle using constant pressure heat addition and rejection. Fuel and compressor are used to heat and increase the pressure of the gas, the gas expands and spins the blade of the turbine which produces electricity. Joule cycle is a thermodynamic cycle which represents the operation of constant pressure heat engine. It is also known as Brayton cycle. 1- 2 isentropic component. 2 – 3 Constant pressure heat addition 3 – 4 Isentropic experiment 4 – 1 Constant pressure heat rejection |
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| 190 | During sensible cooling of air the specific humidity | increases | decreases | remains constant | first increases then decreases | c | during sensible cooling * Specific humidity remains same * DBT decreases * Enthalpy & WBT will decrease * Relative humidity will increase |
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| 191 | In a centrifugal compressor the pressure developed depends on | Impeller tip velocity | Inlet temperature | Compression index | All of the above | d | Centrifugal compressors differ from reciprocating compressors because the pressure developed is a function of the density of air or gas, the speed of the impeller, and of the restriction of the flow. Inlet air temperature will decide density of inlet air. According to compression will occur and it will depend on compression index n and compression ratio. \(PV^{n}=C\) | Comments | Active | |
| 192 | The thermal efficiency of an ideal gas turbine plant is given by | rλ-1 | 1- rλ-1 | 1- \((\frac{1}{r})^{\frac{λ}{λ-1}}\) | 1- \( (\frac{1}{r})^{\frac{υ-1}{υ}}\) | d | \( Q_{in}=mC_{p}(T_{3}-T_{3})\) \(Q_{out}=-mC_{p}(T_{1}-T_{4})\) \(=mCp(T_{4}-T_{1})\) Efficiency \(η=1-\frac{Q_{out}}{Q_{in}}\) \(=1-\frac{T_{4}-T_{1}}{T_{3}-T_{2}}\) \(=1-\frac{T_{1}(\frac{T_{4}}{T_{1}}-1)}{T_{2}(\frac{T_{3}}{T_{2}}-1) }\) For isentropic processes 1 – 2 and 3 – 4 \(\frac{T_{2}}{T_{1}}=(\frac{P_{2}}{P_{1}})^{\frac{γ-1}{γ}}\) [This equation must be remembered as it is very important] \(\frac{T_{3}}{T_{4}}=(\frac{P_{3}}{P_{4}})^{\frac{γ-1}{γ}}\) We get \(\frac{T_{2}}{T_{1}}=\frac{T_{3}}{T_{4}}⇒\frac{T_{4}}{T_{1}}=\frac{T_{3}}{T_{2}}\) \(∴η=1-\frac{T_{1}}{T_{2}}\) \(η=1-(\frac{P_{1}}{P_{2}})^{\frac{γ-1}{γ}}\) \(\frac{1}{Pr. ratio}=\frac{1}{r}\) \(η=1-(\frac{1}{r})^{\frac{γ-1}{γ}} or η=1-\frac{1}{r^{\frac{υ-1}{υ}}}\) Take for given option \(γ=υ\) |
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| 193 | A series of normal flat vanes are mounted on the periphery of a wheel, the vane speed being V. For maximum efficiency the speed of the liquid jet striking the vanes should be | \(\frac{V}{3}\) | \(\frac{V}{2}\) | V | 2V | d | Efficiency of jet \(η=\frac{Runner power}{Water power}=\frac{Wd/sec}{KE/sec}\) \(=\frac{Ï. AV(v-u)u}{\frac{1}{2}(Ïav)v12}\) For maximum power \(\frac{d_{η}}{d_{u}}=\frac{2}{V12}\frac{d}{du}(vu-u^{2})=0\) \(=\frac{2}{v12}(v-2u)=0\) \(=v-2u=0\) \(=u=\frac{v}{2} or V_{jet}=2 vane velocity\) \(η_{max}≤50%\) |
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| 194 | If the number of jets in a Pelton wheel installation are n, its specific speed is proportional to | n | n1/2 | n3/4 | n5/4 | b | Specific speed of turbine with n jets. \(N_{s}=\frac{Nn.P}{H^{5/4}}\) ∴ – no of jets in turbine \(N_sâˆn\) |
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| 195 | The air temperature at which water vapour in the air starts condensing is known as | Dew point | dry bulb | wet bulb | saturation temperature | a | Humidity ratio/Specific humidity (ω) is water vapour (MV) contained in air vapour mixture per kg of dry air Ma \(ω=\frac{Mv}{Ma}=0.622 \frac{P_{v}}{P-Pa}\) \(P=partial pressure \) |
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| 196 | The specific humidity is the mass if water Vapour present in (per) | Kg of dry air | m3 of dry air | m3 of wet air | kg of wet air | a | Humidity ratio/Specific humidity (ω) is water vapour (MV) contained in air vapour mixture per kg of dry air Ma \(ω=\frac{Mv}{Ma}=0.622 \frac{P_{v}}{P-Pa}\) \(P=partial pressure \) |
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| 197 | The dry bulb temperature during heating and dehumidification | decreases | increases | H. – Cooling and humidifying H – Humidifying H.H. Heating and humidifying S.H. Sensible heating H.D – heating and dehumidifying D – Dehumidifying C.D – Cooling and dehumidifying S.C – Sensible cooling During the heating and dehumidifying process dry bulb temperature of the air increases while its dew point and wet bulb temperature reduces. Also relative humidity and humidity or specific humidity also decreases. |
unpredictable | b |  |
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| 198 | The wet bulb temperature is a measure of which humidity? | Relative | Absolute | Specific | None of above | a | Thermometer has a wet cloth around bulb * As Water evaporates, the bulb is cooled. * Like when you get cold when you get out of a swimming pool. * The difference between dry and wet bulb temperatures is related to relative humidity. - No water will evaporate at 100% RH, so bul(b) \(T_{dry}=T_{wet}\) |
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| 199 | In a refrigeration cycle the heat is rejected by refrigerant at | Condenser | Evaporator | Expansion valve | Compressor | a | In a compressor, the compression of the suction vapour from the evaporator to the condenser pressure takes place. In a typical refrigerant condenser. Refrigerant enters the condenser in a super-heated state. It is first de – superheated and then condensed by rejecting heat to an external medium. The refrigerant may leave the condenser as a saturated or a sub – cooled liquid, depending upon the temperature of the external medium and design of the condenser.  The evaporator is the component of a refrigerator system in which heat is removed from the air, water or any other body required to be cooled by the evaporating refrigerant. An expansion device in a refrigeration system normally serves two purposes. One is the thermodynamic function of expanding the liquid refrigerant from the condenser pressure to the evaporator pressure. The other is the control function which may involve the supply of the liquid to the evaporator at the rate at which it is evaporated. |
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| 200 | Concentrating type solar collectors are used to generate temperatures in the range of | up to 100°C | 100-500 °C | less than 80 °C | none of these | b | A concentrating solar collector is a solar collector that uses reflective surfaces to concentrate sunlight into a small area. Where it is absorbed and converted to heat or, in the case of solar photovoltaic (PV) devices, into electricity. Concentrators can increase the power flux of sunlight hundreds of times. This class of collector is used for high temperature applications such as steam productions such as steam production for the generation of electricity and thermal detoxification. | Comments | Active |
