Surface type evaporator with refrigerant as the refrigerant are called direct expansion evaporator. It is actually an evaporator in a refrigeration cycle, and its function is the same as a water-cooled surface cooler. When air passes between the evaporator tubes, heat exchange occurs with the refrigerant liquid in the evaporator tubes. The refrigerant liquid absorbs the heat of the air and evaporates into refrigerant vapor. The air loses its temperature and temperature.