Discussion
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- Question
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)
- Correct Answer
- both (a) and (b)
- 1. 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
- 2. The thermostatic expansion valve is used in __________ type of evaporators.
Options- A. flooded
- B. DX coil
- C. dry Discuss
- 3. Reynolds number is the ratio of
Options- A. energy transferred by convection to that by conduction
- B. kinematic viscosity to thermal diffusivity
- C. inertia force to viscous force
- D. none of the above Discuss
- 4. The logarithmic mean temperature difference (tm) is given by (where ?t1 and ?t2 are temperature differences between the hot and cold fluids at entrance and exit)
Options- A.
- B.
- C. tm = (?t1 - ?t1) loge(?t1/?t1)
- D.
Discuss
- 5. A boot-strap air cooling system has
Options- A. one heat exchanger
- B. two heat exchangers
- C. three heat exchangers
- D. four heat exchangers Discuss
- 6. 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
- 7. 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
- 8. 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
- 9. 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 Discuss
- 10. 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
Heat Transfer, Refrigeration and Air Conditioning problems
Search Results
Correct Answer: three
Correct Answer: dry
Correct Answer: inertia force to viscous force
Correct Answer:
Correct Answer: two heat exchangers
Correct Answer: Agree
Correct Answer: effective temperature
Correct Answer: equal to critical temperature
Correct Answer: all of the above
Correct Answer: lowering the higher temperature
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