Dry Expansion Evaporator:

In the dry-expansion evaporator, generally the liquid refrigerant is fed up by an expansion valve. The expansion valve controls the flow  of rate of refrigerant to the evaporator in such a manner that all of the liquid is vaporized and the vapour is also superheated to a restricted extent by the time it attain the outlet end. On the inlet of the evaporator, the

  Direct Expansion Evaporator

refrigerant is chiefly in the liquid form having a small amount of vapour formed like a result of flashing at the expansion valve. Since the refrigerant passes through the evaporator, more & more liquid is vaporized through the load. The refrigerant, by the time it attain the end of the evaporator, is purely in the vapour state & that too superheated. Therefore the evaporator in its length is filled up with a varying proportion of liquid & vapour. In the evaporator the amount of liquid will vary along the load on the evaporator. The inside of the evaporator is away from 'dry' but wetted along liquid. All the same, this kind is called the 'dry-expansion' system to differentiate it from the 'flooded' system & also probably because by the time the refrigerant attain the evaporator outlet this is no more wet (no liquid) but dry (superheated) vapour.