The document discusses the basic processes of a vapor compression refrigeration cycle including: evaporation of refrigerant absorbing heat from the refrigerated space; compression of the vapor requiring work input; condensation of the vapor releasing heat to the surroundings; and expansion of the liquid refrigerant. It also discusses engineering models and assumptions made in analyzing the cycle components, refrigeration capacity, coefficient of performance, use of pressure-enthalpy diagrams, multistage compression systems, flash gas removal, cascade systems, and psychrometric processes.

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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-phase
liquid-vapor mixture

3. ►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 41
in
hh
m
Q



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4. ►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
Compressor
Assuming adiabatic compression
12
c
hh
m
W



Condenser
32
out
hh
m
Q



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5. Expansion valve
Assuming a throttling process
34 hh 
Coefficient of Performance (COP)
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6. p-h Diagram
The pressure-enthalpy (p-h) diagram is a thermodynamic property diagram commonly
used in the refrigeration field
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7. Multistage compression refrigeration
systems
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8. 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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9. 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.

11. Psychometric Processes
 Sensible Heating
 Sensible Cooling
 Dehumidification
 Humidifying
 Adiabatic Cooling
 Adiabatic Mixing
 (Moist Air & Water Vapor)
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