The evaporator is kind of heat transfer apparatuses where the heat transfer is done by forced convection or natural convection. And it’s an important component of refrigeration system and air conditioning system.
Evaporation process is rejection of water (or other liquids) by concentrating the solution. The required time for this process can by shortened by increasing the surface area, the solution is exposed to it, or by exposing the solution to heating to a higher temperature.
How does evaporator work ?
For a basic refrigerant cycle shown in figure 1, which is used in many forms in all common air conditioning, refrigeration, heat pump applications. It uses a proper refrigerant that has the capability to change phase from liquid to gas and from gas to liquid.
For a home air conditioning example, the refrigerant enters the compressor is a low pressure cool gas, where it compressed to a high pressure hot gas, then passes to the condenser. In the condenser coil, the refrigerant phase changes from hot gas at high pressure to hot liquid at high pressure. This condensation causes a large heat rejection to surrounding.
The liquid refrigerant is then passed through a fixed nozzle or expansion device to exit as a cold liquid at a low pressure. Finally refrigerant enters the evaporator at about 70% to 80% liquid and 20% to 30% vapor.
In the evaporator a very large amount of heat is absorbed from surrounding (the indoor air) causing the liquid refrigerant to boil and turn into a gas phase, which is passed to compressor to repeat the cycle again untile the indoor air be comfortable and sufficiently cool.
The evaporator works at a constant temperature as long as the pressure remains constant.