Answer: In the dryer, the reading of the evaporation temperature (evaporation pressure) cannot be used to replace the pressure dew point of the compressed air. This is because in the evaporator with limited heat exchange area, there is a non-negligible temperature difference between the compressed air and the refrigerant evaporation temperature during the heat exchange process (sometimes up to 4~6
). The temperature to which the compressed air can be cooled is always higher than the refrigerant evaporation temperature. The separation efficiency of the "gas-water separator" between the evaporator and the precooler cannot be 100%. There will always be a part of the fine water droplets that cannot be separated that will enter the precooler with the air flow and "secondarily evaporate" there to return to water vapor, increasing the water content of the compressed air and raising the dew point. Therefore, in this case, the measured refrigerant evaporation temperature is always lower than the actual pressure dew point of the compressed air.
