Basic refrigeration cycle .

Basic refrigeration cycle

1. Basic Refrigeration Cycle Presented by JISHNU U S5 MECHANICAL NO :35

2. Introduction A major application area of thermodynamics is refrigeration, which is the transfer of heat from a lower temperature region to a higher temperature one . Devices that produce refrigeration are called refrigerators , and the cycles on which they operate are called refrigeration cycles . The most frequently used refrigeration cycle is the vapour compression refrigeration cycle in which the refrigerant is vaporized and condensed alternately and is compressed in the vapour phase. Another well-known refrigeration cycle is the gas refrigeration cycle in which the refrigerant remains in the gaseous phase throughout

3. Principles of Refrigeration Liquids absorb heat when changed from liquid to gas(latent heat of vaporization) Gases give off heat when changed from gas to liquid.(latent heat of condensation)

4. Four basic processes 1-2 isentropic compression (in a compressor) 2-3 constant pressure heat rejection ( in a condenser ) 3-4 isentropic expansion ( in a metering device such as throatling valve) 4-1 constant pressure heat addition ( in a evaporator)

5. The cycle of cooling

6. Compressor The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then moves out of the compressor as a high-pressure gas.

7. Condenser The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to the outside air

8. Expansion Valve / Metering Device The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid, and lowers its pressure as it leaves the expansion valve.

9. Ev a po r a t o r The low-pressure liquid then moves to the evaporator, where heat from the inside air is absorbed and changes it from a liquid to a gas.

10. Compressor As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is repeated

11. Coefficient of performance (COP) The performance of refrigerators and heat pumps is expressed in terms of coefficient of Performance, defined as COP = desired output / required input Or COP = Cooling effect/ work input = QL/ Wnet,input A rule of thumb is that the COP improves by 2 to 4 percept for each °C the evaporating temperature is raised or the condensing temperature is lowered .

12. Selecting the right refrigerant There are several types of refrigerants such as CFCS, ammonia, hydrocarbons,( propane, ethane, ethylene etc.), Carbon dioxide, air( in the air conditioning of aircraft) and even water ( in the applications above the freezing point). The right choice of refrigerant depends on the situation at hand The industrial and heavy-commercial sectors were very satisfied with ammonia, and still are, although ammonia is toxic but due to its several advantages like higher COPs, low cost, no effect on ozone etc .