Vapour compression refrigeration

VAPOUR COMPRESSION REFRIGERATION

Principle

In the Vapour Compression Refrigeration System, Freon-12 or Freon-22 is used as the Refrigerant. A Compressor does work on the refrigerant vapour to increase its pressure and temperature.

The refrigerant is circulated through the system. It alternately undergoes a change of phase from vapour to liquid and again liquid to vapour during the cycle. The latent heat of vaporization is used for absorbing the heat at low temperature from the refrigerated space. A constant temperature can be maintained in this space.

Description

See Fig. 1. Vapour Compression Refrigeration System consists of the following parts:

1. Condenser

2. Receiver

3. Expansion Valve (Capillary Tube)

 4. Evaporator

5. Compressor

1. Condenser

The delivery side of the Compressor is connected to a Condenser. Air or water is used as the cooling medium in the condenser. Air is used for refrigerators and window air conditioners. Water is used for large centralized air conditioning systems.

2. Receiver

Receiver is a vessel used to store the condensed liquid refrigerant coming from the condenser.

3. Expansion Valve (Capillary Tube)

The Receiver is connected to an Expansion Valve. The pressure of the liquid passing through the expansion valve drops for reuse in the evaporator. Low capacity systems like Refrigerators, Window air conditioners, etc., use a Capillary Tube as an expansion valve. Solenoid valve is used as expansion valve in large capacity systems.

4. Evaporator

An Evaporator consists of coiled tubes. The substance to be cooled is placed in the evaporator. It is the coldest region or space in the refrigerator and serves as the Refrigerated Space or Freezer Compartment.

5. Compressor

 The evaporator tube is connected to the suction side of the Compressor. The compressor is driven by an electric motor.

Working

 The refrigeration effect is produced at the Evaporator. The refrigerant enters the Evaporator at Low Pressure Low Temperature (LPLT).

The LPLT Liquid Refrigerant is evaporated and changed into vapour refrigerant at the Evaporator. Here, the refrigerant absorbs its latent heat of vapourization from the substances kept around the evaporator, thus cooling them at the Refrigerated Space.

The LPLT Vapour Refrigerant from the Evaporator is drawn by the suction side of the Compressor. It is compressed to High Pressure High Temperature (HPHT) and discharged to the Condenser through the delivery side of the Compressor. Electric Power is supplied to the motor to run the compressor. Note that power consumption is the major operating cost of the system.

 In the Condenser, the latent heat of the refrigerant is removed by circulating either atmospheric air or water. Thus, the HPHT Vapour Refrigerant is cooled and condensed into liquid form.

The High Pressure (HP) Liquid Refrigerant from the Condenser is collected in the Receiver. The High Pressure Refrigerant passes through an Expansion Valve and expands to Low Pressure. The Expansion Valve is a Capillary Tube in small (domestic) refrigerators. The function of the Capillary Tube is to throttle the refrigerant to Low Pressure Low Temperature. This LPLT Vapour Refrigerant enters the Evaporator. The cycle is repeated.

Thermostat Switch: The required low temperature is maintained in the refrigerator by a Thermostat. The Thermostat is used to switch ON or OFF the compressor motor by a relay.

Uses: Vapour Compression is used in domestic refrigerators, water coolers, air System conditioners, etc.