It is cooling coil in a refrigeration system. The liquid refrigerant enters into the evaporator and is converted into vapor by taking latent from the items to be cooled. The items to be cooled surround the evaporator. The evaporator inlet is connected to the outlet of the expansion valve. The evaporator outlet is connected to the inlet of the compressor.
Types of Evaporators
(a) Air cooling coil (direct system)
(b) Liquid cooling coil (indirect system)
Air Cooling Coil Evaporator (Direct System)
In these, air is cooled by the cooling coil. This cooled air cools the products placed in contact with air as in case of a fridge or window air conditioner.
Liquid Cooling Coil Evaporator (Indirect System)
In these, liquid (brine) is cooled by the cooling coil. This cooled liquid cools the products to be cooled as in case of ice plants and central air conditioning plants.
Types of Air Cooling Coils
(i) Dry evaporators
(ii) Flooded evaporators
These are used in small (≤ 3 tons) and medium refrigeration plants (≥ 3 and ≤ 50 tons). These are used with hermetic sealed compressors and commercial refrigeration units. In these refrigerant becomes dry saturated vapor just before the outlet of the evaporator and super heated vapors enters the compressor. The cooling effect is contributed both latent and sensible heat effect.
These are used in fridges, window air conditioners, water coolers, cinema houses, hospitals etc. This type of evaporator uses expansion valve capillary tube in domestic units and thermostatic expansion valve in commercial units.
These are used with large cooling capacity industrial refrigeration units(≥50 tons). In these, refrigerant remains in liquid and vapor state at the just outlet of the evaporator. This liquid vapor mixture enter into a cylindrical unit called the accumulator which sends only the vapors to the compressor and liquid is sent back at the inlet of the evaporator. In this type, entire evaporator is used more effectively for causing cooling effect by the latent heat only.
These are used in big industries and refineries having large cooling requirements. This type of evaporator uses low side and high side float valves as expansion devices.