Thermodynamic Analysis of Cascade Refrigeration System using
CO
2
– NH
3
Refrigerant for Fish Cold Storage Application
Nazaruddin Abubakar
1,
Sutopo Purwono Fitri
1
1
Department of Marine Engineering, Faculty of Marine Technology, Technology Institute of Sepuluh Nopember, Surabaya
Keywords: Thermodynamic, cascade, refrigeration, cold storage, CO2, NH3
Abstract: The adverse effects on the earth's atmosphere due to the use of non-environmentally friendly
refrigerants have increased significantly which has resulted in an increase in Ozone Depletion
Potential (ODP) and Global Warming Potential (GWP). This phenomenon encourages
industries to use natural alternative refrigerants such as ammonia (NH
3
) and carbon dioxide
(CO
2
). The application of a cascade refrigeration system that uses CO
2
refrigerant on the Low-
Temperature Circuit (LTC) and NH
3
on the High-Temperature Circuit (HTC) becomes an
excellent alternative to the application of fish freezing at low temperatures. In this paper, a
cascade refrigeration system with CO
2
working fluid on the LTC and NH
3
on the HTC have
been analyzed. Design and operation parameters considered in this study include evaporation
temperature, a temperature difference in the cascade heat exchanger, condensation
temperature, suction and discharge pressure on the system.
.
1 INTRODUCTION
Refrigeration systems have played a very important
role in everyday life. The development of technology
in the field of refrigeration provides many benefits for
human needs. In the industrial world, refrigeration
systems are used for the storage and distribution of
food ingredients, so that the quality and freshness can
be maintained for several weeks until the time they
are needed to be distributed to consumers. One type
of food product whose quality and freshness needs to
be maintained is fishery products.
Fishery products are food that is easily damaged.
Post-harvest handling greatly determines the quality
and durability of the fish. According to reference
(Handayani et al, 2014), basically, handling and
processing of fish aim to prevent damage or decay.
Efforts are being made to extend the duration of
storing fresh fish which is stored in cold storage.
Cold storage is a room that is used to store fishery
products that require cold temperatures. Cold storage
has a larger room size than other refrigerators with
room temperature ranging from 15
o
C to -45
o
C.
This very low temperature range can be met by a
one-level refrigeration system with one compressor,
many pressurized systems that use more than one
compressor such as multilevel refrigeration systems
and a combination of two or more single refrigeration
systems (cascade), where the first system is a
High-
Temperature Circuit (LTC)
and others as Low-
Temperature Circuit (LTC)
. A cascade refrigeration
system is the best way to get power savings and
increase the coefficient of performance (COP). The
advantages of the cascade refrigeration system can
still be enlarged to produce very low temperature
conditions and save power. One way is to use
different types of refrigerants on each circuit.
Environmental problems related to Ozone
Depletion Potential (ODP) and Global Warming
Potential (GWP) caused by the use of synthetic
refrigerants (CFC's, HCFC's and HFC's) that have
occurred in recent decades, makes the effort to reuse
natural substances as refrigerants are rational. This
will be a better solution for using environmentally
friendly substances as alternative refrigerants in
170
Abubakar, N. and Fitri, S.
Thermodynamic Analysis of Cascade Refrigeration System using CO2 – NH3 Refrigerant for Fish Cold Storage Application.
DOI: 10.5220/0008544101700175
In Proceedings of the 3rd International Conference on Marine Technology (SENTA 2018), pages 170-175
ISBN: 978-989-758-436-7
Copyright
c
 2020 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

refrigeration systems (Dopazo et al, 2009). The
natural refrigerant is a substance that occurs through
a biochemical process and does not have an adverse
effect on the environment, but some of them have side
effects for users such as being exposed to high
toxicity and flammability. Natural refrigerants
commonly used are water, air, noble gases,
hydrocarbons, ammonia, and carbon dioxide.
As a natural refrigerant, ammonia is very suitable
to replace CFCs and HCFCs in modern refrigeration
systems. In terms of environmental aspects, ammonia
is the most acceptable refrigerant and a long-term
alternative, because its release into the atmosphere
has no impact on ozone depletion (ODP = 0) or
greenhouse effect (GWP = 0) (Jankovich & Osman,
2015). Whereas carbon dioxide has emerged as a
credible natural refrigerant to replace HFCs in retail
food applications. CO
2
is non-combustible and non-
toxic, it has no impact on ozone depletion (ODP = 0)
and negligible global warming potential (GWP = 1).
CO
2
has favorable thermophysical properties such as
high density, specific heat, volumetric cooling
capacity, latent heat and thermal conductivity
(Tsamos et al, 2017).
The application of natural refrigerants NH
3
and
CO
2
as working fluids in cascade refrigeration
systems is an excellent alternative to very low
temperature cooling applications. With a cascade
refrigeration system, NH
3
which is quite toxic will
separate from the cooling chamber so that it will
improve the safety of workers, property and
refrigerated products. The use of CO
2
is currently
well received in the industry and in large commercial
cooling systems where it is used as a refrigerant in the
NH
3
/CO
2
cascade refrigeration system with a
temperature range between -10ºC to -50ºC. CO
2
provides great electricity savings, excellent energy
efficiency, and has a good heat transfer coefficient.
Some researchers have evaluated the
thermodynamic performance of a cascade
refrigeration system. Getu and Bansal have
thermodynamically analyzed the cascade carbon
dioxide-ammonia refrigeration system (R744-R717)
to optimize the evaporation temperature of the R717
and its mass flow rate, which can provide a maximum
COP of the system (Getu & Bansal, 2008). Rawat et
al. analyzed thermodynamic cascade refrigeration
systems that use NH
3
on HTC and CO
2
on LTC, to
determine the effect of various types of design and
operating parameters which include condenser
temperature, evaporator temperature, coupling
temperature, compressor isentropic efficiency and
temperature difference in the cascade heat exchanger,
the influence of subcooling and superheating was also
investigated (Rawat et al, 2015). Messineo
thermodynamically analyzed the cascade
refrigeration system (R744-R717) based on operating
parameters, then the results were compared with the
thermodynamic analysis of a two-stage refrigeration
system using R404A refrigerant (Messineo, 2012).
However, there is still a lack of research analyzing the
effect of several operating parameters on the
coefficients of the performance of the system and the
work required by the compressor of each circuit.
Therefore, this study aims to analyze the effect of the
operating parameters of the cascade refrigeration
system on the COP cascade system and the work
required by the HTC and the LTC. The effect of
operating parameters on the mass flow rate of
refrigerant was also analyzed in this study.
2 SYSTEM DESCRIPTION
A schematic diagram of a cascade refrigeration
system for fish cold storage is shown in Figure 1.
This system consists of two units of vapor
compression refrigeration systems that work
separately with different refrigerants. The system
consists of several components such as a compressor,
evaporator, condenser, cascade condenser, cascade
evaporator, expansion valve, etc.
Low-Temperature Circuit (LTC) that using
Carbon dioxide as a refrigerant and High-
Temperature Circuit (HTC) that using Ammonia as a
refrigerant, are thermally connected by cascade heat
exchanger and it is assumed that the cascade heat
exchanger is perfectly insulated, kinetic energy and
potential is neglected. heat transfer from the fluid in
LTC must be the same as heat transfer to fluid on
HTC.
The Evaporator on HTC which has a relatively
higher temperature is used to absorb heat in the LTC
condenser so that the evaporator at LTC has a lower
temperature.
The cascade system is very effective when very
low temperature refrigeration is needed. The cascade
system allows the use of different refrigerants
depending on the work pressure and type of
compressor to be used.
Thermodynamic Analysis of Cascade Refrigeration System using CO2 – NH3 Refrigerant for Fish Cold Storage Application
171

Figure 1: Schematic diagram of a cascade refrigeration
system.
As shown in the T-s diagram in Figure 2, the
compressor's work decreases, and the amount of heat
absorbed from the refrigerated increases as a result of
cascading. Therefore, cascading improves the COP of
the refrigeration system.
Figure 2: Cascade refrigeration system cycles on T-s
property plots. [8]
3 NUMERICAL MODEL
3.1 Mathematical Modelling
The mathematical model of the cascade
refrigeration system has been designed to simulate
mass and energy balances on each one of the
components of the entire system.
Thermodynamic analysis of the cascade
refrigeration system is based on the assumptions
below:
1. The system is in a steady-state and steady-flow
state.
2. Changes in kinetic and potential energy are
negligible.
3. The compressor isentropic efficiency is constant.
4. The cascade heat exchanger and piping are
completely insulated.
Thermodynamic analysis of the cascade
refrigeration system in this study is based on the
cooling load (Q
E
) of cold fish storage that is equal to
76.21 kW, while for the operating parameters of the
designed cascade refrigeration system are as follows:
 evaporator temperature (T
E
= -30
o
C),
 condenser temperature (T
C
= 40
o
C)
 and cascade condenser temperature (T
CAS
= -5
o
C).
The temperature difference in the cascade condenser
is assumed to be (ΔT
CAS
= 5 K).
3.2 Thermodynamic Analysis
Thermodynamic analysis of a cascade refrigeration
system has been carried out by simulating the
thermodynamic state of the refrigerant.
The thermophysical properties of Ammonia and
Carbon dioxide refrigerants are calculated using
software called Engineering Equation Solver (EES)
(EES, 2013), which has a property function of many
types of refrigerants.
Simulations of various design parameters such as
evaporator temperature, condenser temperature, and
cascade condenser temperature variations are carried
out with parametric table features that can perform
calculations quickly and accurately.
Based on the assumptions that have been made
previously, the following is a series of calculations
used for thermodynamic analysis of a cascade
refrigeration system.
SENTA 2018 - The 3rd International Conference on Marine Technology
172

The capacity of the evaporator is determined from:
𝑄


𝑚

ℎ

ℎ

 (1)
Compressor power consumption for the HTC is
defined by:
𝑊


𝑚

ℎ

ℎ

 (2)
Whereas for the LTC, it is defined by:
𝑊


𝑚

ℎ

ℎ

 (3)
The rate of heat transfer in the cascade heat
exchanger is given by:
𝑄


𝑚


ℎ

ℎ


𝑚

ℎ

ℎ

 (4)
The mass flow ratio can be derived from Eq. (4):
𝑚

𝑚











(5)
The rate of heat rejection by the condenser is defined
by:
𝑄


𝑚

ℎ

ℎ

 (6)
The overall COP of the system is determined by:
𝐶𝑂𝑃 









(7)
4 RESULT AND DISCUSSION
4.1 Effect of Evaporator Temperature
The temperature of the evaporator (T
E
) was varied
from -25
o
C to -45
o
C by keeping the condenser
temperature and the cascade condenser temperature at
the operating design parameters.
Figure 3. System performance and compressor work with
variations in evaporator temperature.
Figure 3 shows the effect of the evaporator
temperature change on the work required by LTC
compressor (W
LS
), HTC compressor (W
HS
) and the
coefficient of performance (COP) of the cascade
refrigeration system.
As the evaporator temperature increases, the COP
of the system increases significantly, therefore the
work required by the LTC compressor decreases
significantly, but the work required by HTC
compressor is only slightly decreased.
Figure 4. Mass flow rate of refrigerant with variations in
evaporator temperature.
The effect of the temperature change of the
evaporator on the mass flow rate on the LTC and HTC
is described in Figure 4.
As the evaporator temperature increases, the mass
flow rate of the refrigerant on HTC decreases
constantly and significantly, while the mass flow rate
on the LTC initially decreases significantly but then
decreases slightly.
Thermodynamic Analysis of Cascade Refrigeration System using CO2 – NH3 Refrigerant for Fish Cold Storage Application
173

4.2 Effect of Condenser Temperature
The temperature of the condenser (T
C
) was varied
from 30
o
C to 50
o
C by holding the evaporator
temperature and the cascade condenser temperature at
the operating design parameters.
The effect of the condenser temperature changes
on the work required by the LTC compressor and the
HTC compressor has been analyzed (see Figure 5).
Figure 5: System performance and compressor work with
variations in condenser temperature.
As the condenser temperature increases, the work
required by the HTC compressor increases
significantly, while the COP of the cascade system
decreases significantly, while the condenser
temperature changes have no effect on the work
required by the LTC compressor.
Figure 6: Mass flow rate of refrigerant with variations in
condenser temperature.
Figure 6 shows the effect of changes in the
temperature of the condenser on the mass flow rate on
the LTC and the HTC.
The mass flow rate of refrigerant on the HTC
increases significantly as the condenser temperature
increases, while the mass flow rate of refrigerants on
the LTC is not affected by changes in condenser
temperature
4.3 Effect of Cascade Condenser
Temperature
The temperature of the cascade heat exchanger (T
CAS
)
has varied from 5
o
C to -5
o
C by keeping the
temperature of the evaporator and the condenser
temperature at the operating design parameters.
Figure 7: System performance and compressor work with
variations in cascade condenser temperature
The effect of changes in the cascade heat
exchanger temperature on the work required by the
LTC compressor and the HTC compressor illustrated
in Figure 7. The results show that as the cascade heat
exchanger temperature increases, the work required
by the LTC compressor increases, while the work
required by HTC compressor tends to decrease.
therefore, the cop of the cascade system decreases.

Figure 8: Mass flow rate of refrigerant with variations in
cascade condenser temperature.
SENTA 2018 - The 3rd International Conference on Marine Technology
174

The effect of the cascade condenser temperature
changes on the mass flow rate is shown in Figure 8.
As the cascade condenser temperature increases, the
mass flow rate on the LTC increases while the mass
flow rate on the LTC decreases.
5 CONCLUSIONS
In this study, thermodynamic analysis of the cascade
refrigeration system presents the use of Carbon
dioxide (CO
2
) on the LTC and Ammonia (NH
3
) on
the HTC. This analysis leads to the following
conclusions:
1. An increase in the temperature of the evaporator
produces an increase in the COP and decreases
both the work required by the compressor and
the mass flow rate.
2. An increase in condenser temperature results in
a decrease in COP and an increase in the mass
flow rate and work required by the compressor
on the HTC.
An increase in the cascade heat exchanger
temperature results in an increase in the mass flow
rate and work required by the compressor on the LTC
but decreases the mass flow rate and the work
required by the compressor on the HTC. Therefore,
the COP cascade system tends to decrease.
REFERENCES
Bansal, P. K. & Getu, H. M., 2008. Thermodynamic
analysis of an R744–R717 cascade refrigeration
system, Volume 31, p. 45–54.
Cengel, Y. A. & M. A. Boles, 2015. An Engineering
Approach. 8th ed. McGraw-Hill Education. New York.
Dopazo, J. A., Fernandez-Seara, J., Sieres, J., Uhia, F. J.,
2009. Theoretical analysis of a CO2–NH3 cascade
refrigeration system for cooling applications at low
temperatures, 29(8–9), p. 1577–1583.
EES., 2013. Engineering Equation Solver, s.l.: fChart
Software Inc.
Handayani, A., Alimin, A., Rustiah, W. O., 2014. Effect of
Storage at Low Temperature (Freezer -3oC) on Water
Content and Fat Content in Lemuru Fish (Sardinella
longiceps), 2(1), p. 64–75.
Jankovich, D. & Osman, K., 2015. A feasibility analysis of
replacing the standard ammonia refrigeration device
with the cascade NH3/CO2 refrigeration device in the
food industry, 19(5), p. 1821–1833.
Messineo, A., 2012. R744-R717 cascade refrigeration
system: performance evaluation compared with a HFC
two-stage system. s.l., s.n.
Rawat, K. S., Kshetri, R., Khulve, H., Pratihar, A. K., 2015.
Parametric study of R744-R717 cascade refrigeration
system, Volume 2.
Tsamos, K. M., Y. T. Ge., Santosa, I., Tassou, S. A.,
Bianchi, G., Mylona, Z., 2017. Energy analysis of
alternative CO2 refrigeration system configurations for
retail food applications in moderate and warm
climates, p. 822–8.
Thermodynamic Analysis of Cascade Refrigeration System using CO2 – NH3 Refrigerant for Fish Cold Storage Application
175