Heat Transfer, Refrigeration and Air Conditioning Questions

• The rato of energy transferred by convection to that by conduction is called
• Upto the critical radius of insulation,
• The critical thickness of insulation is the ratio of thermal conductivity of the insulating material (k) to the heat transfer coefficient at the outer surface of the insulation (h0).
• Pressure of water vapour is given by
• In counter-current flow heat exchanger, the logarithmic temperature difference between the fluids is __________ as compared to parallel flow heat exchanger.
• For a given dry bulb temperature, as the relative humidity __________ the wet bulb temperature will increase.
• The drier in a refrigeration system removes moisture in the system.
• Wet bulb temperature indicates the moisture content in air.
• A vapour absorption refrigeration system
• The relative humidity lines on a psychrometric chart are
• A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is
• The value of the wave length for maximum emissive power is given by
• The __________ point of ammonia is -77.7°C.
• Environmental protection agencies advice against the use of chloro-fluoro-carbon refrigerants since
• The heat is transferred by conduction, convection and radiation in
• The by-pass factor of a cooling coil decreases with
• The expansion valve in a refrigerator controls the flow of refrigerant.
• Emissivity of a body will be equal to its absorptivity at all temperatures.
• The by-pass factor, in case of sensible cooling of air, is given by (where td1 = Dry bulb temperature of air entering the cooling coil, td2 = Dry bulb temperature of air leaving the cooling coil, and td3 = Dry bulb temperature of the cooling coil)
• A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called