A presentation on Expansion valve and Compressors M

A presentation on “Expansion valve and Compressors” M. E. Thermal Engineering(021) Mahatma Gandhi Institute of Technical Education and Research centre Navsari

CONTENT • EXPANSION VALVE • TYPES OF EXPANSION VALVE • COMPRESSORS • TYPES OF COMPRESSORS

EXPANSION VALVE • 1. Hand –operated Expansion valve This is the most simple type of expansion valve but it requires an operator to regulate the flow of refrigerant to the evaporator manually. The conical –shaped needle valve extends down into the valve port and restricts the flow area though the port. When closed, the valve rests on its conical seat. The use of hand –operated valve is limited to systems operating under nearly constant loads for long periods of time, such as in ice making plant and cold storages.

2. Automatic Expansion valve The automatic expansion valve is also known as constant pressure expansion valve. , because it maintains constant evaporator pressure regardless of the load on the evaporators. Its main moving force is the evaporators pressure. It is used with dry expansion evaporators where the load is relatively constant.

3. Themostatic expansion valve • The thermostatic expansion valve is the most commonly used expansion devices in commercial and industrial refrigeration system. This is also called a constant superheat valve because it maintains a constant superheat of the vapour refrigerant at the end of the evaporator coil, by controlling the flow of liquid refrigerant though the evaporator.

compressors 1. Reciprocating compressors The compressors in which the vapour refrigerant is compressed by the reciprocating (back and forth) motion of the piston are called reciprocating compressors. The two types of reciprocating compressors and in general use are single acting vertical compressors and double acting horizontal compressors.

2. Hermetic sealed compressors When the compressors and motor operate on the same shaft and are enclosed in a common casing. They are known as hermetic compressors. These type of compressors eliminate the use of crankshaft seal which is necessary in ordinary compressors in order to prevent leakage of refrigerant. The hermetic unites are widely used for small capacity refrigerating systems such as in domestic refrigerators. Home freezers and window air conditioners.

3. Rotary compressor • In rotary compressor, the vapour refrigerant from the evaporator is compressed due to the movement of blades. The rotary compressors are positive displacement type compressors. Since the clearance in rotary compressors is negligible , therefore they have high volumetric efficiency. These compressors may be used with R-12, R-22, R-114 and ammonia.

4. Centrifugal compressors • This compressors increases the pressure of low pressure vapour refrigerant to a high pressure by centrifugal force. The centrifugal compressors is generally used for refrigerants that require large displacement and low condensing pressure , such as R-11 and R-113 However , the refrigerant R-12 is also employed for large capacity application and low temperature application.

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