Heat Transfer Refrigeration and Air Conditioning MCQ with Answers

Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure. It is therefore measured by wrapping a wet wick around the bulb of a thermometer and the measured temperature corresponds to the wet bulb temperature.

The wet bulb temperature during sensible heating of air increases.

Thermal conductivity of solid metals with rise in temperature normally decreases. The thermal conductivity of the metal is directly proportional to the absolute temperature and mean free path of the molecules. The mean free path decreases with the increase in temperature so that the thermal conductivity decreases with the temperature.

Normally the thermal conductivity of solid metals decreases with rise in temperature.

The Prandtl number (Pr) or Prandtl group is a dimensionless number, named after the German physicist Ludwig Prandtl, defined as the ratio of momentum diffusivity to thermal diffusivity.

The Grashof number (Gr) is a dimensionless number in fluid dynamics and heat transfer which approximates the ratio of the buoyancy to viscous force acting on a fluid. It frequently arises in the study of situations involving natural convection and is analogous to the Reynolds number.

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the Prandtl number and Grashoff's number.

In a refrigerating machine, heat rejected is greater than heat absorbed.

Humidity ratio by mass can be expressed as the ratio between the actual mass of water vapor present in moist air - to the mass of the dry air.

Humidity ratio is normally expressed in kilograms (or pounds) of water vapor per kilogram (or pound) of dry air.