Heat Transfer, Refrigeration and Air Conditioning problems
- 1. A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is
Options- A. 20°C
- B. 40°C
- C. 60°C
- D. 66.7°C Discuss
Correct Answer: 20°C
- 2. The value of the wave length for maximum emissive power is given by
Options- A. Kirchhoff's law
- B. Stefan's law
- C. Wein's law
- D. Planck's law Discuss
Correct Answer: Wein's law
- 3. The __________ point of ammonia is -77.7°C.
Options- A. freezing
- B. boiling Discuss
Correct Answer: freezing
- 4. Environmental protection agencies advice against the use of chloro-fluoro-carbon refrigerants since
Options- A. these react with water vapour and cause acid rain
- B. these react with plants and cause green-house effect
- C. these react with oxygen and cause its depletion
- D. these react with ozone layer Discuss
Correct Answer: these react with ozone layer
- 5. The heat is transferred by conduction, convection and radiation in
Options- A. melting of ice
- B. boiler furnaces
- C. condensation of steam in condenser
- D. none of these Discuss
Correct Answer: boiler furnaces
- 6. The by-pass factor of a cooling coil decreases with
Options- A. decrease in fin spacing and increase in number of rows
- B. increase in fin spacing and increase in number of rows
- C. increase in fin spacing and decrease in number of rows
- D. decrease in fin spacing and decrease in number of rows Discuss
Correct Answer: decrease in fin spacing and increase in number of rows
- 7. The expansion valve in a refrigerator controls the flow of refrigerant.
Options- A. Correct
- B. Incorrect Discuss
Correct Answer: Correct
- 8. Emissivity of a body will be equal to its absorptivity at all temperatures.
Options- A. Yes
- B. No Discuss
Correct Answer: No
- 9. The by-pass factor, in case of sensible cooling of air, is given by (where td1 = Dry bulb temperature of air entering the cooling coil, td2 = Dry bulb temperature of air leaving the cooling coil, and td3 = Dry bulb temperature of the cooling coil)
Options- A.
- B.
- C.
- D.
Discuss
Correct Answer:
- 10. A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
Options- A. dry air
- B. moist air
- C. saturated air
- D. specific humidity Discuss
Correct Answer: saturated air
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