Dry-type Evaporator and Flooded Evaporator for Large Ice Machine Factory

     Ammonia refrigeration system adopts flooded evaporator .However ,fluorine uses dry-type evaporator. Our cube ice machine and other ice machine use dry-type evaporator, So what is dry-type evaporator and what are its advantages and disadvantages ?and fluorine ?

    

    Dry expansion evaporator refrigerant lines in the tube evaporator , the evaporator superheat outlet end is usually about 5 of 5至10 K , the expansion valve places the ball to detect temperature superheat required to adjust the evaporator refrigerant flow .

    Advantages of dry expansion evaporator unit : mostly in the temperature-sensitive expansion valve (TXV) is throttling device , able to adapt to changes in load , good controllability , and the construction is easy and inexpensive . The refrigerant flowing through the tube , due to large velocity, the speed by means of a gaseous refrigerant back directly to the refrigeration compressor oil .

    Disadvantages: superheated refrigerant vapor accounts for about 20 percent of the evaporator heat transfer area , but it can only provide a small amount of refrigerant enthalpy , the lower the total evaporator heat transfer efficiency. TXV refrigerant flowing through a pressure differential must be maintained to ensure that the system refrigerant circulation amount and cooling capacity . Usually water into the cooling water temperature is set to the high voltage control (Head Pressure Control) to maintain a pressure differential of 30 ℃ , but such control is required to maintain a certain mode of the system pressure, the high pressure side when the operating condition is less than the design conditions or at part load , the system efficiency can not be increasing. Multi- compressor systems , refrigerant circulation independently unloading after some idle can not use the heat exchange area , so the part load performance of the system is limited.

    

    Flooded evaporators are often associated with centrifugal compressors or screw compressors used in conjunction with medium and large ice machine, the system efficiency is good, higher manufacturing costs and technical difficulty . Refrigerant lines in tube evaporation can borrow high side or low side level controller ( such as float valve ) to regulate the flow of refrigerant evaporator required , the level of liquid is able to completely cover the evaporator drain tube is principle , boiling refrigerant heat transfer fluid can completely wetted surface , which can have a better heat transfer efficiency.

    The advantage is flooded evaporator : complete wetting of the heat transfer surface , increase the efficiency of the evaporator , improve system low side pressure. Liquid refrigerant in the evaporator shell side boiling , pressure loss is small compared temperature uniformity ; and due to the suction side of the nearly saturated gaseous vapor into the compressor , it can increase the compression efficiency and the mass flow rate of the compressor. Since the multi- compressor units can share an evaporator and condenser at part load can still effectively use the heat transfer area , it can have a high part load efficiency.

Note : a liquid -gas separator to be able to most of the space and the liquid refrigerant separated from the gaseous , liquid refrigerant may cause a large number of entering the compressor , resulting in liquid compression .