Refrigeration & Equipment Engineering

Unit 3 - Parts of refrigeration systems

3.2.Evaporator
The process of heat removal from the substance to be cooled or refrigerated is done in the device known as Evaporator. Evaporator is also known as Boiler, Freezing unit, Low side, cooling coil, chilling unit.It is the natural tendency of the heat that it is always from warm body to cold body. If two substances are at the same temperature, no heat transfer between them. If there is a temperature difference between them, heat flows from the warm substance to the colder one. Thus it is said that heat is transferred from high temperature to low temperature. The heat that must be transferred enters a refrigerated space in three ways.

• The heat leaks through the wall surrounding.
• As the door open, outside heat rushes into the refrigerated space.
• The heat of the food stuff material is introduced into the refrigerated space.

All this heat flows towards the evaporator and touches to the cooling coil of the evaporator. Liquid refrigerant at the cooling coil picks up this heat and absorb it so the liquid refrigerant transferred into vapour.The cooling coil, consists at good conductor at heat, permits to rapid heat transfer. The conductor which has no effect on the refrigerant is determined to use. Metal is a good conductor which is always used in evaporator. Iron or steel is used for all refrigerants generally. Brass and Copper can be used with all refrigerant except ammonia because copper is soluble in pure ammonia. The effect of heat transfer depends upon,

• The rate of heat transfer
• Controlling quantity of heat
• Air circulation
• Air velocity
• Air distribution
• Material
• Temperature difference
• Velocity of Refrigerants
• Thickness of the evaporator coil
• Contact surface area