Heat Transfer, Refrigeration and Air Conditioning – Section 1

11. According to Dalton’s law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

A. Pb = pa – pv
B. Pb = pa + pv
C. Pb = pa x pv
D. Pb = pa/pv

Correct Answer: B. Pb = pa + pv

12. The heat transfer by conduction through a thick sphere is given by

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Correct Answer: Option B

13. The relative humidity is defined as

A. the mass of water vapor present in 1 m3 of dry air
B. the mass of water vapor present in 1 kg of dry air
C. the ratio of the actual mass of water vapor in a unit mass of dry air to the mass of water vapor in the same mass of dry air when it is saturated at the same temperature and pressure.
D. the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air at the same temperature and pressure

Correct Answer: D. the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air at the same temperature and pressure

14. Fourier’s law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

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Correct Answer: Option A

15. The heat transfer by conduction through a thick sphere is same as through a thick cylinder.

A. True
B. False

Correct Answer: B. False

16. In aqua-ammonia and Lithium-bromide water absorption refrigeration systems, the refrigerants are respectively

A. water and water
B. water and lithium bromide
C. ammonia and lithium bromide
D. ammonia and water

Correct Answer: D. ammonia and water

17. As relative humidity decreases, the dew point temperature will be __________ wet bulb temperature.

A. same as
B. lower than
C. higher than

Correct Answer: B. lower than

18. The process of heat transfer from a hot body to a cold body, in a straight line, without affecting the intervening medium, is called radiation.

A. True
B. False

Correct Answer: A. True

19. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ρ = Density of fluid, cp = Specific heat at constant pressure, and μ = Coefficient of absolute viscosity)

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Correct Answer: Option C

20. The optimum effective temperature for human comfort is

A. higher in winter than in summer
B. lower in winter than in summer
C. same in winter and summer
D. not dependent on season

Correct Answer: B. lower in winter than in summer

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