Refrigeration and Heat Pump Cycles
Stages of Refrigeration Cycle
Demonstrate understanding of basic vapor- compression refrigeration and heat pump systems.
Develop and analyze thermodynamic models of vapor-compression systems and their modifications
Sketch schematic and accompanying T-s diagrams.
Evaluate property data at principal states of the systems.
Apply mass, energy, and entropy balances for the basic processes.
Determine refrigeration and heat pump system performance, coefficient of performance, and capacity.
Compression: In this stage, the refrigerant enters the compressor as a gas under low pressure and having a low temperature. Then, the refrigerant is compressed adiabatically, so the fluid leaves the compressor under high pressure and with a high temperature.
Condensation: The high pressure, high temperature gas releases heat energy and condenses inside the "condenser" portion of the system. The condenser is in contact with the hot reservoir of the refrigeration system. (The gas releases heat into the hot reservoir because of the external work added to the gas.) The refrigerant leaves as a high pressure liquid.
Throttling: The liquid refrigerant is pushed through a throttling valve, which causes it to expand. As a result, the refrigerant now has low pressure and lower temperature, while still in the liquid phase. (The throttling valve can be either a thin slit or some sort of plug with holes in it. When the refrigerant is forced through the throttle, its pressure is reduced, causing the liquid to expand.)
Evaporation: The low pressure, low temperature refrigerant enters the evaporator, which is in contact with the cold reservoir. Because a low pressure is maintained, the refrigerant is able to boil at a low temperature. So, the liquid absorbs heat from the cold reservoir and evaporates. The refrigerant leaves the evaporator as a low temperature, low pressure gas and is taken into the compressor again, back at the beginning of the cycle.
Solved Example: 75-1-01
Heat is absorbed by a refrigerant during a refrigeration cycle in a: (RRB JE ME CBT Aug 2019)
B. Throttle valve
Correct Answer: C
Solved Example: 75-1-02
The lowest temperature during the cycle in a vapour compression system occurs after: (ISRO RAC 2019)
Correct Answer: B