Post on 14-Apr-2017
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Refrigeration and Air Conditioning
NME:604Unit2
Presented byMr Naphis AhmadAssistant professorJETGI Barabanki
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The processes of this cycle are
Process 4-1: two-phase liquid-vapor mixture of refrigerant is evaporated through heat transfer from the refrigerated space.
Process 1-2: vapor refrigerant is compressed to a relatively high temperature and pressure requiring work input.
Process 2-3: vapor refrigerant condenses to liquid through heat transfer to the cooler surroundings.
Process 3-4: liquid refrigerant expands to the evaporator pressure.
Two-phaseliquid-vapor mixture
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►Engineering model:
►Each component is analyzed as a control volume at steady state.
►Dry compression is presumed: the refrigerant is a vapor.
►The compressor operates adiabatically.
►The refrigerant expanding through the valve undergoes a throttling
process.
►Kinetic and potential energy changes are ignored.►Applying mass and energy rate balances
Evaporator 41in hhmQ
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►The term is referred to as the refrigeration capacity, expressed in kW in the SI unit system
►A common alternate unit is the ton of refrigeration which equals about 211 kJ/min.
inQ
►Applying mass and energy rate balances
CompressorAssuming adiabatic compression
12c hhmW
Condenser
32out hhmQ
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Expansion valveAssuming a throttling process
34 hh
Coefficient of Performance (COP)
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p-h Diagram The pressure-enthalpy (p-h) diagram is a thermodynamic property diagram commonly used in the refrigeration field
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Multistage compression refrigeration systems
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Use of flash chamber for flash gas removal
In this system, instead of passing refrigeration vapour from the low stage
compressor through the flash tank, vapour from the flash chamber blended
with the vapour coming from the low stage compressor .Thus the inlet
condition to the high stage condition will be superheated.
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This is P-H diagram for flash removal
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Cascade refrigeration systems
Very low temperatures can be achieved by operating two or more vapor
compression systems in series, called cascading. The COP of a refrigeration
system also increases as a result of cascading.
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Psychometric Processes Sensible Heating Sensible Cooling Dehumidification Humidifying Adiabatic Cooling Adiabatic Mixing (Moist Air & Water Vapor)
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