ASHRAE Journal - April 2023 - 49

TECHNICAL FEATURE
FIGURE 5 The available percentage increase of COP as a function of the dimensionless
number ξ.
102
Water
Ammonia
101
C02
R-410a
100
R-134a
of superheating and sub-cooling should be explored in
future work. Also, the method used for the calculation
of the hot and cold reservoirs resulted in temperatures
that may not represent realistic operating conditions
for some applications. The present work should not be
used for comparing the feasibility of the refrigerants
but rather a comparison of the relative energy
available for each refrigerant while using the proposed
method and a comparison of refrigerant performance
based on actual operating conditions recommended
for future studies.
Finally, R-134a and R-410A, considered in this study,
will be retired soon due to their high GWP values.
Therefore, future studies should focus on low GWP
hydrofl uoroolefi ns or their alternatives to promote the
expander technology.
10-1
ξ
Conclusions
The compressor-expander-fusion concept considered
here using fi ve different working fl uids proves to be
promising in improving the coeffi cient of performance
(COP) of both refrigeration and heat pump cycles. The
maximum possible improvements corresponded to the
compression process that is tangential to the vapor saturated
line, indicating a critical point for improvements.
The COP was increased more for fl uids that have a shallow
slope on the saturated vapor line on the T-s diagram.
This was due to an increased amount of heat transfer
available before the superheated vapor from the compressor
condenses into saturated vapor. Since natural
refrigerants are more likely to have shallow vapor lines,
they received more improvement from the compressorexpander-fusion.
The increase makes natural refrigerants
a more viable solution in future work.
Although the proposed cycle has theoretical advantage
over isentropic compression, the feasibility of such a
fusion confi guration must be considered in any future
work. Specifi cally, the ability of the fused compressorexpander
unit to have the required theoretical heat
transfer as well as the durability of the expander operation
should be tested experimentally.
The current analysis was an idealized scenario with
saturated vapor at the inlet of the compressor and
saturated liquid at the inlet of the expander; the effects
100
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