COP
2
stg
¼ 1.73
Single-stage Coefficient of Performance:
COP
1
stg
¼
_
m
ref
ð
h
2
h
1
Þ
_
m
ref
ð
h
1
h
4
Þ
¼
h
2
h
1
h
1
h
4
(2)
COP
1
stg
¼ 1.30
Splitting the refrigeration cycle into two stages and sub-cooling
resulted in 33% increase in COP from 1.30 to 1.73.
10. Simulation model of the two stage system
A steady state simulation model of the two-stage system was
developed to analyse the performance of the refrigeration System
using the Engineering Equation Solver
[33]
package to optimise the
system for maximum efficiency. The main model was based on
individual components including Compressors, condensers, evap-
orators etc. using equations and correlations from the open
literature.
10.1. Compressor model
The low and high stage compressors were modelled by the
method proposed by Popovic and Shapiro (1995), where the
geometry of both the low and high stage compressors was identical
(bore, stroke, rpm etc.). The refrigerant mass flow rate is calculated
by:
_
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