Heat Transfer, Refrigeration and Air Conditioning Questions

• The heat rejection factor (HRF) is given by
• An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m2). The critical thickness of insulation will be
• The amount of heat flow through a body by conduction is
• In order to collect liquid refrigerant and to prevent it from going to a __________ , a device known as accumulator is used at the suction of compressor.
• The dry bulb temperature during sensible heating of air
• A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be
• In a vapour compression system, the condition of refrigerant is dry saturated vapour
• The vertical and uniformly spaced lines on a psychrometric chart indicates
• A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness
• The coefficient of performance of a domestic refrigerator is __________ as compared to a domestic air-conditioner.
• The rate of heat flow through a body is . The term is known as temperature gradient.
• The dehumidification process, on the psychrometric chart, is shown by
• The transfer of heat by molecular collision is known as
• A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h1, h2 and h3 respectively. The average heat transfer coefficient for the cube is
• During sensible cooling of air, the relative humidity increases.
• Wein's law states that the wave length corresponding to __________ is proportional to the absolute temperature.
• The coefficient of performance of vapour compression refrigeration system is quite __________ as compared to air refrigeration system.
• In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = By-pass factor)
• The wet bulb temperature at 100% relative humidity is __________ dry bulb temperature.
• Sensible heat factor is given by (where S.H. = Sensible heat, and L.H. = Latent heat)