1. Flooded type
2. Dry type
Flooded type -: In flooded type refrigeration system , there is a pool of refrigerant in the evaporator. In this system, the refrigerant level in the evaporator is maintained through the action of refrigerant flow control device. This system oprates at higher average suction pressure and operating cost is low with high efficiency. It also provides closer control of temperature. More liquid on low pressure side of tge system provides a greater area of wetted surface, and allows a higher rate of heat transfer through the evaporator walls and tubing.
Flooded type system are classified depending on the type of flow control device used -:
1. Low side float system
2. High side float system
3. Capillary tube or restrictor systems.
1. Low side float system -: In low type float system, the working of which is self- explanatory. Here the refrigerant charge used in system is not critical as any exess or over-charge will remain in the liquid receiver.
2. High side float system -: In this type of system , the flow of liquid refrigerant in this system is controlled by both the high side float in the liquid receiver and the pressure reducing valves at the evaporator to maintain differential pressure between the refrigerant in the liquid lines and the refrigerant in the evaporator, the refrigerant charge in the high side float system is very critical.
Excess charge will result in flood back and liquid refrigerant in that case will flow into suction line of compressor causing frost to appear and may damage compressor.
3. Capillary tube or restrictor systems -: This system is widely used because of low cost, trouble free opration, simplicity and achieving of hermetically sealed system. In this system, the amount of refrigerant allowed to flow is dependent upon the length and inside diameter of capillary tube provided between the filter and evaporator . Overcharge may result in floodback.
Dry type refrigeration system -: Dry type refrigeration system have only droplets of liquid refrigerant in the evaporator. In dry type system, the refrigerant passing through the valve is partially evaporated immediately after passing the orifice. The fine suspended droplets of liquid refrigerant are completely evaporated as they flow through the balance of the evaporator. Evaporator is generally made from one continuous length of tubing which ensure better control of liquid refrigerant when the flow control device is properly adjusted.
Dry type refrigeration system are classified in two types -:
1. Automatic expansion system
2. Thermostatic expansion valve system.
Automatic expansion valve system -:
This system uses a pressure operated refrigerant flow control device which when properly adjusted, keep the evaporator fully refrigerated .
Thermostatic expansion valve system -:
In thermostatic expansion valve system, thermostatic control is used to maintain evaporator outlet temperature in combination flow of with evaporator pressure by automatic expansion valve. It provides more accurate control of refrigerant in the evaporator.
No comments:
Post a Comment