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- Question
Thermal conductivity of a material may be defined as the
Options- A. quantity of heat flowing in one second through a slab of the material of area 1 cm2 and thickness 1 cm when its faces differ in temperature by 1° C
- B. quantity of heat flowing in one second through one cm of material when opposite faces are maintained at a temperature difference of 1° C
- C. heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces
- D. all of the above
- Correct Answer
- all of the above
- 1. If a gas is to be liquified, its temperature must be
Options- A. increased to a value above its critical temperature
- B. reduced to a value below its critical temperature
- C. equal to critical temperature
- D. none of the above Discuss
- 2. The index which corelates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as
Options- A. mean radiant temperature
- B. effective temperature
- C. dew point temperature
- D. none of these Discuss
- 3. The ratio of emissive power of a body to the emissive power of a perfectly black body is called emissivity.
Options- A. Agree
- B. Disagree Discuss
- 4. According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
Options- A. directly proportional to the surface area
- B. directly proportional to the difference of temperatures between the two bodies
- C. either (a) or (b)
- D. both (a) and (b) Discuss
- 5. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
Options- A. one
- B. two
- C. three
- D. four Discuss
- 6. When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by
Options- A. operating the machine at higher speeds
- B. operating the machine at lower speeds
- C. raising the higher temperature
- D. lowering the higher temperature Discuss
- 7. A one tonne refrigerating machine means that
Options- A. one tonne is the total mass of machine
- B. one tonne refrigerant is used
- C. one tonne of water can be converted into ice
- D. one tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min Discuss
- 8. The cooling of air, without any change in its specific humidity, is known as sensible cooling.
Options- A. Correct
- B. Incorrect Discuss
- 9. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called
Options- A. humidity ratio
- B. relative humidity
- C. absolute humidity
- D. degree of saturation Discuss
- 10. The air cooling system mostly used in transport type aircrafts is
Options- A. simple air cooling system
- B. simple evaporative air cooling system
- C. boot-strap air cooling system
- D. all of these Discuss
Heat Transfer, Refrigeration and Air Conditioning problems
Search Results
Correct Answer: equal to critical temperature
Correct Answer: effective temperature
Correct Answer: Agree
Correct Answer: both (a) and (b)
Correct Answer: three
Correct Answer: lowering the higher temperature
Correct Answer: one tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min
Correct Answer: Correct
Correct Answer: degree of saturation
Correct Answer: boot-strap air cooling system
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