Heat Transfer, Refrigeration and Air Conditioning Questions

• A boot-strap air cooling system has
• The logarithmic mean temperature difference (tm) is given by (where Δt1 and Δt2 are temperature differences between the hot and cold fluids at entrance and exit)
• Reynolds number is the ratio of
• The thermostatic expansion valve is used in __________ type of evaporators.
• 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
• According to Newton's law of cooling, the heat transfer from a hot body to a cold body is
• The ratio of emissive power of a body to the emissive power of a perfectly black body is called emissivity.
• The index which corelates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as
• If a gas is to be liquified, its temperature must be
• Thermal conductivity of a material may be defined as the
• When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by
• A one tonne refrigerating machine means that
• The cooling of air, without any change in its specific humidity, is known as sensible cooling.
• The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called
• The air cooling system mostly used in transport type aircrafts is
• The evaporator used in house-hold refrigerators is
• The capacity of the cooling tower and spray ponds __________ as the wet bulb temperature of air decreases.
• Dehydration is the process of removing water vapour from the surrounding air.
• If the evaporator temperature is kept constant, the coefficient of performance of a refrigeration cycle __________ with the increase in condenser temperature.
• The heat transfer by conduction through a thick cylinder(Q) is given by (where T1 = Higher temperature, T2 = Lower temperature, r1 = Inside radius, r2 = Outside radius, l = Length of cylinder, and k = Thermal conductivity)