|Message from : SANJEEV KUMAR on 9/6 2021, EMail: Kumarsumit9804@gmail.com |
The term refrigeration means cooling a space, substance or system to lower and/or maintain its temperature below the ambient one (while the removed heat is rejected at a higher temperature).In other words, refrigeration is artificial (human-made) cooling.
Refrigeration cycle is a cycle of mechanical system in which transmission of heat allow from one place at a lower temperature (the source ) to another place at a higher temperature ( the sink or heat sink ) by continuously circulating, evaporating, and condensing a fixed supply of refrigerant in a closed system.
Or,Refrigeration cycle is thermodynamic cycle to generate refrigerating effect with the use of evaporator, compressor, condenser & expansion valve.
Thus, a heat pump is called as a "heater" if the objective is to warm the heat sink (as when warming the inside of a home on a cold day), or a "refrigerator" or “cooler” if the objective is to cool the heat source (as in the normal operation of a freezer).
In both case, the operating principles are close.Heat is removed from a cold place to a warm place.
Note :- Refrigeration cycle is also called heat pump cycle.
Diagram of refrigeration cycle.
Vapour compression cycle
Vapour Compression Refrigeration Cycle is the most widely used refrigeration system.
Vapor-compression cycle refrigeration is a process that uses the physics of phase change heat transfer and the unique properties of a refrigerant to transfer heat from a relatively cold source to a hot medium.
Basic Refrigetion cycle
The basic components of any refrigeration system working on the vapour compression cycle,are the compressor,condenser, expansion valve and evaporator and the refrigerant fluid which is alternatively vaporized and liquefied during the refrigeration cycle.
The temperature at which a fluid boils or condeses,is known as the saturation temperature and it varies with temperature.
Basic components of refrigeration cycle
The 4 main Components of Refrigeration cycle
1.Compressor :- The compressor in a refrigeration system in raising the pressure of the vaporizer refrigerant, causes its situation temperature to rise, so that it is a higher than that of the the sea water or air, cooling the condenser.The compressor also promotes circulation of refrigerant by pumping it around the system.
Notes :-Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.
Why compression takes place :- compression takes place to raise the temperature and refrigerant pressure
2.Condenser :- In the condenser the refrigerant is liquefied by being subcooled to below the saturation temperature relating to the compressor delivery pressure, by the circulating sea water or air for domestic refrigerator.
Latent heat, originally from the evaporator,is the transfer to the cooling medium. The liquid refrigerant, Still at the pressure produced by the compressor, passes to the receiver and then to the expansion valve
Notes :-After condensing, the refrigerant is a high-pressure, low-temperature liquid, at which point it’s routed to the loop’s expansion device.
What happen in condenser :- Heat is transferred from the refrigerant to a flow of water
3.Expansiin valve :- The expansion valve is the regulator through which the refrigerant flow from the high pressure side of the system to the low pressure side. Its throttling effect dictates the compressor delivery pressure which must be sufficient to give the refrigerant a saturation temperature which is higher than the temperature of the cooling medium.
The pressure drop through the regulator causes the saturation temperature of the refrigerant to fall so that it boil at low temperature of the evaporator.In fact, as the liquid passes through the expansion valve,the pressure drops makes its saturation temperature fall below its actual temperature.
Some of the liquid was boils off at the expansion valve taking latent heat from the remainder and causing it's temperature to drop.
The expansion valve throttles the liquid refrigerant and maintains the pressure difference between the condenser and evaporator, while supplying refrigerant to the evaporator at the correct rate.It is thermostatically controlled in modern systems.
What happen to refrigerant in Expansion valve :- When the refrigerant enters the throttling valve, it expands and releases pressure. Consequently, the temperature drops at this stage.
4.Evaporator :- The refrigerant entering the evaporator coil at a temperature lower than that of the surrounding Secondary coolant (air or brine ) receives latent heat and evaporates. Later the heat is given of In the condenser,when the refrigerant is again compressed and liquefied.
Notes :- refrigerant enters the evaporator as a low temperature liquid at low pressure, and a fan forces air across the evaporator’s fins, cooling the air by absorbing the heat from the spaces.
What happen to refrigerant in evaporator :- it evaporates and absorbs latent heat of vaporization.
For a small refrigerator the evaporator coils without forced circulation of secondary coolant.In larger installation, the evaporator cools air or bribe which are circulated as secondary refrigerants.