1. CASE STUDY OF LIQUID SUCTION
HEAT EXCHANGER IN MECHANICAL
REFRIGERATION SYSTEM USING
ALTERNATIVE REFRIGERANTS.
PRESENTED BY: COORDINATED BY:
Samir Ghorasainee Keshav Acharya
Sampanna Dhakal Teaching Assistant
Sanam Sapkota Purwanchal Campus,
Sanchita Sapkota Dharan
2. Mechanical Refrigeration System
Mechanical refrigeration, often referred to as refrigeration or air
conditioning, is a process by which heat is removed from a location
using a human-made heat exchange system.
As the refrigerant circulates through the system, it is alternately
compressed and expanded, changing its state from a liquid to a
vapor.
3. Components of
Refrigeration Cycle
Evaporator : It absorbs heat from
refrigerating space.
Compressor : It increases the pressure
and temperature of refrigerant through
compression.
Condenser : It releases the heat into
surrounding.
Expansion Valve : It decreases the
pressure of the refrigerant.
4. Modification of the System
Many studies have been done to
modify and enhance the performance
and energy consumption of the
mechanical refrigeration system.
Using heat exchanger in the mechanical
refrigeration system is one of the
effective technique that can be used to
improve the energy performance of the
system.
A LSHX is a counterflow heat
exchanger in which the warm
refrigerant liquid from the condenser
exchanges heat with the cool refrigerant
vapor from the evaporator.
5. Modification of the System
Refrigerant type can also influence the
system performance, so it is a big
challenge to obtain matching between the
system modification and refrigerant type.
The performances of the alternative
refrigerants R600a, R134a and R22 while
using liquid suction heat exchanger are
studied.
R600a R22
R134a
6. Model Development
The liquid-suction heat exchanger is installed across the suction and
liquid lines.
7. Model Development
The Liquid Suction Heat Exchanger allows:
Subcooling for the condensed refrigerant.
Reducing the flash gas in the liquid line to ensure maximum capacity for the
thermostatic expansion valve.
Superheating liquid of refrigerant which is located in the suction line.
Prevention of liquid refrigerant entering the reciprocating compressor.
9. Thermodynamics Analysis of Subcooling
Subcooling reduces the flash gas in the liquid line to ensure maximum capacity for the
thermostatic expansion valve, which eventually increases the refrigeration effect.
It increases the amount of heat rejection from the condenser.
It also increases the enthalpy of refrigerant entering the evaporator from 4 to 4’ , which
increases the refrigeration effect.
The work to be done in the Compressor remains unchanged.
Since subcooling increases the refrigeration effect without changing the compressor input,
COP of the system can be increased significantly.
10. Thermodynamics Analysis of Subcooling
Increases Refrigeration effect
Doesn’t change the work input
More refrigeration with same work
input
11. Thermodynamic Analysis for Superheating
Superheating saves compressor from damage by preventing refrigerant liquid
droplets that may be flown with the gas from entering the suction line.
If superheating of refrigerant takes place due to heat transfer with the refrigerated
space then it is called as useful superheating as it increases the refrigeration effect.
On the other hand, it is possible for the refrigerant vapor to become superheated
by exchanging heat with the surroundings as it flows through the connecting
pipelines, which is called as useless superheating.
12. Thermodynamic Analysis for Superheating
Fig: P-h diagram of superheating Fig: T-s diagram of superheating
13. Thermodynamic Analysis for Superheating
Superheating increases the refrigeration effect of the system.
It also increases the work to be supplied to the compressor.
Thus, although increasing the refrigeration effect of the system it may
or may not increase the COP.
The change in COP depends upon the refrigerant used.
14. Results & Conclusion
Multiple simulations were run for wide range of conditions.
Refrigerants R600a, R134a and R22 were used in the system.
Two systems : Non-Modified and Modified with LSHX were examined.
All the results were obtained through Engineering Equation Solver.
15. Effects of Subcooling
The liquid-suction heat exchanger
improves the sub-cooling for three
types of refrigerants; R22, R134a and
R600a.
However, higher value of the sub-cool
temperature was achieved by R600a.
Fig : Effect of Liquid-Suction Heat Exchanger on Superheating at
Different Condenser Pressure and Different Refrigerants
16. Effects of Superheating
The LSHX effectively increased the
superheat temperature in the suction
line.
The figure also shows that the higher
value of the super heat temperature
was achieved by R600a and achieved
better performance. Fig : Effect of Liquid-Suction Heat Exchanger on Superheating
at Different Condenser Pressure and Different Refrigerants
17. Comparison between non-modified and
modified system
Non-Modified System Modified system
The following comparison shows the refrigerant effect at different Condenser pressure
and different refrigerants :
18. Comparison between non-modified and
modified system
Non-Modified System
R600a achieved highest value of
refrigerant effect
Refrigerant Effect: about 250kJ/kg
when the condenser pressure was
350 kPa
Modified System
R600a achieved highest value of
refrigerant effect
Refrigeration Effect: about 350
kJ/kg when the condenser
pressure was 350 kPa
20. Result & Conclusion
The Figure shows that the highest value of COP was achieved by the modified
system using R134a.
Which is about 7% and 12% higher than that of R600a and R22 respectively.
The COP can be improved and enhanced up to 20% based on the refrigerant type
and operating conditions while using LSHX.
The R600a is good replacement for other refrigerants but it has lower COP
compared with R134a due to its thermodynamic properties.
21. Acknowledgement
We thank Raid Ahmed Mahmood, School of Mechanical and
Electrical Engineering, University of Southern Queensland,
Australia for the research.
22. We thank you all for your time and coordination.
