Dry Expansion Evaporators

In dry expansion evaporators, the exchange coil is designed to receive the exact amount of liquid refrigerant for the required thermal load. The fluid is fed by an expansion valve that fulfills the role of keeping the superheat constant so that all the refrigerant is vaporized before the end of the exchanger. As the expansion is just before the evaporator, the fluid entering the evaporator is a mixture of vapor and liquid at low pressure (saturated vapor) and not saturated liquid as desired, as a small fraction of this fluid is vaporized in the expansion valve to reduce The temperature of the refrigerant at design saturation temperature. Thus, at the end of the coil, as there is no more liquid, the only heat exchange that occurs is sensitive and not latent as expected, thus decreasing the efficiency of the evaporator.