Heat Transfer(Engineering > Chemical Engineering ) Questions and Answers

Question 1. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
  1.    (COP)R = (COP)HP = 0.6
  2.    (COP)R = 2.5; (COP)HP = 1.5
  3.    (COP)R = 1.5; (COP)HP = 2.5
  4.    (COP)R = (COP)HP = 2.5
Explanation:-
Answer: Option C. -> (COP)R = 1.5; (COP)HP = 2.5
Question 2. In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is
  1.    Infinity
  2.    Zero
  3.    Same as average heat transfer co-efficient for tube side
  4.    None of these
Explanation:-
Answer: Option A. -> Infinity
Question 3. Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the
  1.    Maximum resistance in the series
  2.    Sum of all resistances
  3.    Average of all resistances
  4.    Minimum resistance presents in the series
Explanation:-
Answer: Option B. -> Sum of all resistances
Question 4. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical?
  1.    1
  2.    < 1
  3.    > 1
  4.    None of these
Explanation:-
Answer: Option A. -> 1
Question 5. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place
  1.    Between two bodies in physical contact with each other
  2.    Between two bodies not in physical contact with each other
  3.    From one part of a body to the another part of the same body
  4.    Both B & C
Explanation:-
Answer: Option B. -> Between two bodies not in physical contact with each other
Question 6. Pick out the wrong statement.
  1.    The controlling resistance in case of heating of air by condensing steam is in the air film
  2.    The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant tem
  3.    In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs
  4.    Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature
Explanation:-
Answer: Option C. -> In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs
Question 7. A body is called grey if the monochromatic emissivity of the body is
  1.    Zero
  2.    Unity
  3.    Same for all wavelengths
  4.    Different for all wavelengths
Explanation:-
Answer: Option C. -> Same for all wavelengths
Question 8. Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law.
  1.    Stefan's
  2.    Dalton's
  3.    Wien's
  4.    Kirchoffs
Explanation:-
Answer: Option C. -> Wien's
Question 9. Rate of crystallisation does not depend upon the
  1.    Extent of supersaturation
  2.    Turbulence within the solution
  3.    Number and active surface area of the crystals
  4.    None of these
Explanation:-
Answer: Option D. -> None of these
Question 10. Stefan-Boltzman law applies to __________ body.
  1.    Black
  2.    White
  3.    Grey
  4.    Any colour
Explanation:-
Answer: Option A. -> Black
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