HEAT AND MASS TRANSFER MCQ
Q21. A furnace is made of a brick wall of thickness 0.5 m and conductivity 0.75 W/m K. For the same heat loss and temperature drop, what should be the thickness of diatomite earth of thermal conductivity 0.15 W/m K?
(a) 0.05 m
(b) 0.1 m
(c) 0.2 m
(d) 0.5 m.
Q22. Two walls of same thickness and cross-sectional area have thermal conductivities in the ratio 1 : 2. If same temperature difference is maintained across the wall faces, the ratio of heat flow Q1/Q2 will be
Q23. An ideal gas at 27°C is heated at constant pressure till the volume becomes three times. The temperature of the gas will then be
Q24. A pipe carrying steam at 215°C traverses as room and heat is lost to the surrounding air at 27°C. The major fraction of heat loss to the surroundings will be essentially due to
(d) conduction and radiation put together.
Q25. A hot metal piece kept in air cools from 80 to 70°C in t1 seconds, from 70 to 60°C in t2 seconds and from 60 to 50°C in t3 seconds. Then
(a) t1 = t2 = t3
(b) t1 < t2 < t3
(c) t1 > t2 > t3
(d) none of the above.
Q26. A humidification process means
(a) decrease in relative humidity
(b) an increase in specific humidity
(c) a decrease in temperature
(d) an increase in temperature.
Q27. Which of the following components in a vapour absorption plant is a substitute for the compressor of the vapour compression system?
(b) Heat exchanger and generator
(c) Aqua pump and generator
(d) Absorber, equa pump and generator.
Q28. The thermal conductivity is expressed as
(a) W/m K
(b) W/m2 K
(c) W/hm K
(d) W/h2 m2 K.
Q29. Heat transfer from higher temperature to low temperature takes place according to
(a) Fourier law
(b) First law of thermodynamics
(c) Second law of thermodynamics
(d) Zeroth law of thermodynamics.
Q30. Consider the following properties of air-water vapour mixture:
(a). dry bulb temperature.
(b). wet bulb temperature.
(c). specific humidity.
(d). all of the above.
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