Construction characteristics of the evaporator are selected to maximize the rate of heat transfer, oil return and efficiency of the cycle, while minimizing cost and risk of damage during freezing and maintenance requirements. Three main structures in the evaporator construction of bare pipes, plate-finned surface and tube. Bare-tube evaporators, called the primary surface, evaporators, because all their heat transfer surface in physical contact with the evaporation of the coolant. Plate-finned surface and tube evaporators are called secondary surfaces of evaporators, because their fins are not in direct contact with the refrigerant. In this design, the plate or fins with attached to the pipes that heat flows from the edges to the primary surface to achieve the refrigerant.
Bare-tube evaporator coils are available in different sizes, shapes and designs. They, as a rule, in order to meet the requirements of the application. The General form for bare the coils are placed flat zigzag, oval trombone and spirals. Bare-tube evaporators built using steel, copper or aluminium pipes or tubes. Steel pipe is used for large industrial and commercial storage evaporators and those used in the ammonia refrigerant system. Copper and aluminum tubes are used in the production of small evaporators are designed for use in residential and commercial units using other refrigerants than ammonia...