- 1. Thermal Engineering MCQs Correct Answer Q1. What happens to the saturation pressure of water, if the saturation temperature is increased? a) Increases b) Decreases c) RemainsUnchanged d) Can’tbe defined Q2. Whichof the followingis a correct statement? a) CarnotHeat Enginewill have 100% efficiency b) Carnotefficiency isindependentoftemperaturelimits c) Actual efficiency <Carnotefficiency <100% d) Carnotcycleis a practical cycle Q3. Isentropic process is always; a) Reversibleadiabaticprocess b) Constantentropyprocess c) Both(a) & (b) d) NOTA Q4. What will be the COP of a heat pump consuming 2 kW of power while rejecting 10 kJ of heat per second working between temperature limits of 323 K and 273 K.? a) 6 b) 6.46 c) 7.46 d) 5 Q5. Clausius inequality can be applied to the system working between; a) Two thermal reservoirs b) N no. ofthermal reservoirs c) Threethermal reservoirs d) Fourthermal reservoirs e) All ofthe above Q6. Piston cylinder arrangement without valves is an example of which kind of thermodynamic system; a) Open system b) Closedsystem c) Isolatedsystem d) NOTA Q7. Carnot cycleis represented on T-s plot as; a) Rectangle b) Square c) Circle d) Rhombus e) NOTA
- 2. Q8. Gases behaves as an ideal gas at; a) LowpressureandHightemperature b) Lowtemperature andHighpressure c) Highpressure andHightemperature d) NOTA Q9. Ideal gas equation can be written as; a) Pv = mRT b) Pv = nRuT c) Pv = nMRT d) All ofthe above Q10. How is absolute pressure measured? a) Gaugepressure+Atmosphericpressure b) Gaugepressure – Atmosphericpressure c) Gaugepressure/ Atmosphericpressure d) Noneof the above Q11. According to Joule's law,the internal energy of a perfect gas is the functionof absolute a) Density b) Pressure c) Temperature d) Volume Q12. Boundary layer thickness is the distance fromthe boundary to the point where velocity of the fluid is a) Equal to 10% of freestream velocity b) Equal to 50% of freestream velocity c) Equal to 90% of freestream velocity d) Equal to 99% of freestream velocity Q13. Unit of thermal conductivity inS.I. units is a) J/m² sec b) J/m °Ksec c) W/m °K d) Option(b) and (c) above. Q14. In free convectionheat transfer transition from laminar to turbulent flow is governed by the critical value of the a) Reynold'snumber b) Grashoff'snumber c) Reynold'snumber,Grashoff'snumber d) Prandtl number, Grashoff'snumber Q15. Sensible heat is the heat required to a) Changevapourinto liquid b) Changeliquidinto vapour c) Increasethe temperatureof a liquid orvapour d) Convertwaterinto steam andsuperheatit
- 3. Q16. Log mean temperature differencein case of counter flow compared to parallel flow willbe a) Same b) More c) Less d) Dependsonotherfactors Q17. The rate of heat flow through a body is Q = [kA (T₁ - T₂)]/x. The term x/kA is knownas a) Thermal coefficient b) Thermal resistance c) Thermal conductivity d) Noneof these Q18. In free convectionheat transfer, Nusselt number is function of a) GrashoffnumberandReynoldnumber b) GrashoffnumberandPrandtl number c) Prandtl number andReynoldnumber d) Grashoffnumber,Prandtl numberand Reynoldnumber Q19. Which of the followingis a dimensionless equation? a) Reynold'sequation b) Euler'sequation c) Weber'sequation d) All ofthe above Q20. The fluid will rise in capillary when the capillary is placed in fluid, if a) the adhesionforcebetweenmoleculesoffluidandtubeislessthan the cohesion betweenliquidmolecules b) the adhesionforcebetweenmoleculesoffluidandtubeismorethan the cohesion betweenliquidmolecules c) the adhesionforcebetweenmoleculesoffluidandtubeisequal to the cohesion betweenliquidmolecules d) NOTA Q21. Vapour compression refrigeration is somewhat like a) Carnotcycle b) Rankinecycle c) ReversedCarnotcycle d) ReversedRankinecycle e) NOTA Q22. Clapeyron equation is a relation between a) Temperature,pressureandenthalpy b) Specificvolumeandenthalpy c) Temperatureandenthalpy d) Temperature,pressure,andspecificvolume e) Temperature,pressure,specificvolumeandenthalpy
- 4. Q23. In a diesel engine, the fuel is ignited by a) Spark b) Injectedfuel c) Ignitor d) Heat resultingfromcompressionairthatis suppliedfromcombustion Q24. The break power of an engine is always.............theindicated power a) Equal to b) Less than c) Greaterthan d) Noneof the above Q25. Octane number is determined by comparing the performance of the petrol with the followinghydrocarbons a) Iso-octane b) Alphamethyl naphthalene c) Mixtureofnormal heptaneand iso-octane d) Mixtureofparaffin’sandaromatics Q26. A heat exchanger with heat transfer surface area A and overallheat transfer coefficientU handles two fluids of heat capacities C1 AND C2 such that C1> C2. The NTU of the exchanger is given by a) AU/C2 b) e-AU/C2 c) e-AU/C1 d) AU/ C1 Q27. A counter flow heat exchanger is used to heat water from 20 degrees Celsius to 80 degrees Celsius by using hot exhaust gas entering at 140 degrees Celsius and leaving at 80 degrees Celsius. The LMTDof the heat exchanger is a) 80 degreesCelsius b) 60 degreesCelsius c) 110degreesCelsius d) not determinableas0/0isinvolved Q28. In a double pipe counter flow heat exchanger if heat capacity rates are equal, the temperature profiles of twofluids along its length is a) parabolic b) cubic c) parallel straightline d) exponential Q29. What is the purpose of using bafflesin shell-and-tube heat exchangers? a) to maintainuniformspacingbetweentubes b) to enhanceheat transfer c) botha. and b. d) noneofthe above
- 5. Q30. According to Archimedes’ principle, if a body is immersed partially or fully in a fluid then the buoyancy forceis _______theweight of fluid displaced by the body. a) equal to b) lessthan c) morethan d) unpredictable Q31. The fin efficiency is defined as the ratio of actual heat transfer fromthe fin to a) Heat transferfromthe same fin withadiabatictip b) Heat Transferfromanequivalentfinwhichisinfinitelylong c) Heat Transferfromthesame fin ifthe temperature alongthelengthof finis same as basetemperature d) Heat Transferthroughthebasearea ofthe same fin e) Noneof the above Q32. A 1 cm diameter, 30 cm long fin made of aluminum having k= 237 W/m. K is attached to a surface at 80 0 C. Surface is exposed to ambient air at 220 C with h= 11W/ m2 K. If the fin can be assumed to be very long, its efficiency is a) 0.60 b) 0.67 c) 0.72 d) 0.77 e) 0.88 Q33. What happens when the thickness of insulation on a pipe exceeds the criticalvalue? a) Heat transferrate increases b) Heat transferrate decreases c) Heat transferrate remainconstant d) noneofthese Q34. In heat exchangers, the value of logarithmic mean temperature differenceshould be a) maximumpossible b) minimumpossible c) zero d) constant Q35. The cylindrical portion of short length, whichconnects converging and diverging section of venturimeter, is called as a) diffuser b) connector c) throat d) manometertube Q36. Fourier law of heat conduction is based on the assumption that a) Heat flowthroughasolid isonedimensional b) Heat flowisin steadystate c) Both(a) and (b) d) Noneof the options
- 6. Q37. The ratio of energy transferred by convectionto that by conductionis called a) Stantonnumber b) Nusseltnumber c) Biotnumber d) Precletnumber Q38. When heat is transferred by molecular collision, it is referred to as heat transfer by a) Conduction b) Convection c) Radiation d) Scattering Q39. NTU method is used to calculate: a) Rate ofheat transfer b) Rate ofliquidflow c) Rate ofconductionheat d) Rate ofradiation Q40. Which one is true for an opaque body? a) Transmissivityiszero b) Reflectivityiszero c) Absorptivityiszero d) Reflectivityisunity Q41. To have high effectivenessof fins a) finmust bethick and closelyspaced b) finmust bethin and closelyspaced c) finmust bethick and widelyspaced d) finmust bethin and widelyspaced Q42. What is the relation between the rate of convectionheat transfer and the rate of mixing in turbulent fluid flow? a) the rate of convectionheattransferdecreaseswithincreaseinthe rate of mixing in turbulentfluidflow b) the rate of convectionheattransferincreaseswithincreaseinthe rate ofmixing in turbulentfluidflow c) the rate of convectionheattransferdoesnotaffect by the changeinthe rate of mixinginturbulent fluidflow d) noneofthe above Q43. Assume fluid flowingin a tube forcefully.Thevelocity boundary layer develops along the tube. Thickness of this boundary layer increases in the flow direction until the boundary layer reaches the tube centre. This region from the tube inlet to the point at whichthe boundary layers merge at the centerline is called as a) laminarentry region b) hydraulicentryregion c) hydrostaticentryregion d) hydrodynamicentry region e) noneofthe above
- 7. Q44. What is hydrodynamically developed region in fluid flowinginside a pipe? a) a regionwherevelocityprofileofthefluidispartiallydeveloped b) a regionwherevelocityprofileofthefluidisfullydeveloped c) a regionwherevelocityprofileofthefluidchangesaccordingto thedistance d) noneofthe above Q45. For laminar flow over a flat plate, the average value of a Nusselt number is prescribed by the relation; Nu = 0.664 (Re) 0.5 (Pr) 0.33 Whichof the following is then a false statement? a) Densityhasto be increasedfourtimes b) Plate lengthhasto be decreasedfourtimes c) Specificheathas to beincreasedfourtimes d) Dynamicviscosityhasto be decreasedsixteentimes Q46. For the same heat transfer Q and same overall heat transfer coefficientUo,surface area required for cross flow operation is always a) lessthan LMTD forparallel flow b) morethan LMTD forparallel flow c) same asLMTD forparallel flow d) unpredictable Q47. If there are no externally induced flow velocities,then the Nusselt number (Nu) does not depend upon a) Prandtl number (Pr) b) Reynoldsnumber(Re) c) Grashofnumber(Gr) d) noneofthe above Q48. The Grashof number in natural convectionplays same role as a) Prandtl number (Pr)in forcedconvection b) Reynoldsnumber(Re)inforcedconvection c) Nusseltnumber(Nu) in forced convection d) noneofthe above Q49. The emissive power of a body depends upon a) temperatureof the the body b) characteristicsofthe surfaceofthe body c) botha and b d) noneofthe above Q50. What is the relation between emissive power of a real body (E) and emissive power of black body (Eb)when both are at same temperature? a) Eb/ E = 1 b) Eb/ E = α c) E / Eb = 1 d) E / Eb = α