Refrigeration and Liquefaction: Instructor: Engr. Caressa Marie Frial-De Jesus

Chapter :
Refrigeration and Liquefaction
INSTRUCTOR:
ENGR. CARESSA MARIE FRIAL-DE JESUS
Carnot Refrigeration
Operates on a Carnot cycle
Reverse of heat-engine
Work applied to the system
Cold Reservoir
Coefficient of performance of
refrigerator
System
Work
Hot Reservoir
Vapor-Compression Cycle
This is the most common thermodynamic cycle used in refrigerators, air-conditioners,
and heat pumps.

Carnot cycle operating in reverse
Rankine vs VCC
Rejects low temperature energy to a
cold region
Pump is used to increase the pressure
Rejects high temperature energy to a
hot region
Compressor is used
of the working fluid

Energy addition occurs in a steam
Occurs in an evaporator
generator
Accepts high temperature energy from a
hot energy source

Working fluid is expanded in a turbine
Accepts low temperature energy from a
cold region
Working fluid is expanded in a
throttling device
Process 1-2: Vaporization (Thermal
energy addition)
-Vaporization of refrigerant in the
evaporator. The refrigerant
absorbs heat at constant
temperature while changing its
state from wet to saturated vapor.
Heat absorbed in the evaporator
**Take note of the denotations.
Process 2-3: Compression
-Increase in T and P of the refrigerant
inside the compressor and leaves
as superheated vapor
-dashed line as isentropic process
Work of compressor
Process 3-4: Condensation (Thermal
energy rejection)
- Due to the state of the refrigerant, it
can now condense in a higher
temperature in the condenser and
releases heat to the system.
-The refrigerant leaves as saturated
liquid.
Heat rejected at the condenser
Process 4-1: Throttling (Expansion

valve)
-pressure reduction to state 1.
Coefficient of performance
Therefore,
Rate of circulation of refrigerant
Example 9.1:
A refrigerant space is maintained at 10degF and cooling water is available at
70degF. Refrigeration capacity is 120000Btu per h. The evaporator and
condenser are of sufficient size that a 10degF minimum temperature difference
for heat transfer can be realized in each. The refrigerant is tetrafluoroethane
(HFC-134a), for which data is given in Table 9.1 and fig G.2.
(a) What is the value of COP for a Carnot refrigerator?
(b) Calculate the COP and rate of circulation of refrigerant for the vapor
compression cycle if the compressor efficiency is 0.8.
Absorption Refrigeration
In vapor-compression refrigeration, the work of the compressor is usually from an electric
motor (source also a heat engine -> generator).
Ultimately, the work for refrigeration comes from heat at a high temperature level.
Direct use f heat as energy source is the basis for adsorption refrigeration.
Work required by a Carnot Refrigerator
Thermal efficiency
Figure 9.3: A twostage cascade

refrigeration
system.
But Carnot cycles cannot be achieved in actual practice
Figure 9.4: Schematic diagram of an absorption-refrigeration unit.
Absorber
-refrigerant vapor from the
evaporator is absorbed in a nonvolatile liquid solvent at the same
P.
-Heat is discarded to the
surroundings (denoted as TS)
Pump
-liquid solution (with high
concentration of refrigerant)
passes through with an increase in
P (the same as in the condenser).
Heat exchanger
-heat is transferred to the compressed
liquid solution.
-Increase in temperature evaporates
the refrigerant from the solvent.
Regenerator
-Further increase in temperature
-Refrigerant vapor passes through
and proceeds condenser
-Solvent is brought back to the
absorber by passing through the
heat exchanger.
Heat Pump
Device used for heating during the winter and cooling during the summer.
Heat Pump
Evaporation
-Refrigerants evaporates in coils placed underground or outside the
system.
Vapor compression
Condenser
-heat transferred to air or water or any fluid used for heating
Throttling
-working fluid must b compressed until refrigerant temperature is higher
than the required temperature of the building
For cooling, the refrigerant flows in a reversed cycle. Heat absorbed from
the building and rejected though the coils
Heat pump
Example 9.2: A house has a winter heating requirement of 30 kJ/s and a
summer cooling requirement of 60 kJ/s. Consider a heat-pump
installation to maintain the house temperature at 20degC in the winter
and 25degC in the summer. This requires circulation of the refrigerant
through the interior exchanger coils at 30degC in the winter and 5degC
in summer. Underground coils provide the heat source in winter and
heat sink in summer. For a year-round ground temperature of 15degC,
the heat-transfer characteristics of the coils necessitate refrigerant
temperature of 10degC in winter and 25degC in summer. What are the
minimum power requirements for winter heating and summer cooling?
Liquefaction Processes
Liquefaction results when a gas is cooled to a temperature in the two-phased
region.
Uses: liquid propane as domestic fuels, liquid oxygen as oxidizing agent in rocket
engines, liquid natural gas for ocean transport, liquid nitrogen and carbon
dioxide as refrigerants
3 several ways:
(1) By heat exchange at constant temperature
(2) By expansion process from which work is obtained
(3) By a throttling process
Low temperature, high pressure feed needed
Linde Liquefaction Process

Depends solely on throttling expansion.
After compression, gas is precooled to ambient temp.
Further cooling may be done; the lower the temp the grater the fraction
of gas is liquefied.
Claude Liquefaction Process

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Chapter :

Refrigeration and Liquefaction

and heat pumps.

Rejects high temperature energy to a

of the working fluid

hot energy source

Accepts low temperature energy from a

**Take note of the denotations.

Process 4-1: Throttling (Expansion

Rate of circulation of refrigerant

Figure 9.3: A twostage cascade

Figure 9.4: Schematic diagram of an absorption-refrigeration unit.

Linde Liquefaction Process

Claude Liquefaction Process

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