Answer: When the compressed air is cooled in the evaporator, a large amount of condensed water is precipitated. If the refrigerant evaporation temperature is too low, the surface temperature of the evaporator copper tube is lower than the freezing point of water under load conditions, and the condensed water will freeze in the evaporator. In severe cases, it will block the air flow channel and paralyze the air supply pipeline. In order to prevent this from happening, the refrigerant evaporation temperature must be controlled. The simple and effective measure is to add a hot gas bypass valve between the condenser and the evaporator. The pressure measuring tube of the hot gas bypass valve is directly connected to the evaporation pressure. When the evaporation pressure is low to a certain extent, the hot gas bypass valve opens, and the high-temperature refrigerant vapor in the condenser directly enters the evaporator, raising the evaporation temperature and avoiding ice blockage.
Since the reduction in evaporation temperature is often caused by the low load of the cold dryer, and the high-pressure vapor in the condenser is always pressed out when the compressor is fully loaded, the use of a hot gas bypass valve can prevent the trouble caused by the low evaporation temperature within a certain range, but it is not an energy-saving measure. In large-scale cold dryers, methods such as compressor unloading or frequency conversion speed regulation are often used to limit the evaporation temperature from being too low.
