• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.411-421
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• 2001

The purpose of this study is to investigate the performance of an autocascade refrigeration system by simulation and experiment using refrigerant mixtures of R744/134a and R744/290 as working fluid. Variations of mass flow rate of refrigerant, compressor work refrigeration capacity and COP with respect to mass fraction of R744/134a and R744/290 mixture were presented under different operating conditions. Performance test has been executed by ASRAE standard. Experimental results show as the composition of R744 in the refrigerant mixture increases, heating and coling capacity are enhanced, but COP trends to decrease. Experimental results are compared with those from the simulation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.880-890
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• 1999

The purpose of this study is to investigate the performance of an autocascade refrigeration system using the refrigerant miktures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) as working fluids by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions in the range of from 10/90 to 30/70 by weight percentage. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results show similar trend with those from the simulation.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.191-196
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• 2017

Owing to the harmful environmental effects of HCFC and CFC refrigerants discovered in the late 20th century, the need for environmentally friendly refrigerants such as $CO_2$ in cooling systems has increased. Air-source $CO_2$ heat pumps that utilize ambient heat in cold winter are less efficient because of a higher evaporation temperature, and it is difficult to manufacture the components of the heat pump owing to a super critical pressure of over 130 bar. This research aims to overcome these disadvantages and improve energy efficiency by introducing a new lower-pressure $CO_2$ auto-cascade heat pump system. $CO_2$-R32 zeotropic refrigerants were considered for two-stage expansion and effective cooling heat exchanging system configurations of the new auto-cascade heat pump. The results indicated that the efficiency of the two-stage expansion system was higher than that of the original one-stage expansion system. Furthermore, the two-stage expansion system showed significant performance improvements when the two-stage expansion stage from highest pressure of 70bar, intermediate expansion pressure of 25bar, and final low pressure of 10bar is applied. The COP of the new two-stage auto-cascade system (2.332) was 43.15% higher than that of the present simple auto-cascade system (1.629). Refrigerants having an evaporation temperature of $-10^{\circ}C$ or lower can be obtained that can be easily evaporated in an evaporator even at a low temperature.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.182-188
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• 2011

In this paper, analysis on the performance characteristics of R744-R404A cascade refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, compressor efficiency, and condensing and evaporating temperature in R404A high- and R744 low-temperature cycle, respectively. The main results were summarized as follows : It was observed that the highest COP of the system is achieved by higher superheating degree in R744 cycle than that in R404A cycle. The COP of the system increased by giving the subcooling degree in both cycles. The COP of the cascade system is the highest value when the system is operated at an optimum evaporation temperature.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.189-195
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• 2011

In this paper, prediction and comparison on COP(coefficient of performance) of R744-R404A cascade refrigeration system are presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, compressor efficiency, and condensing and evaporating temperature in the R404A high- and R744 low-temperature cycle, respectively. The main results were summarized as follows : The prediction for performance of R744-R404A cascade refrigeration system have been proposed through multiple regression analysis and compared with other researcher's correlations. As a result, prediction proposed in the study shows disagreement with existing equations. Therefore, it is necessary to propose the more accurate correlation predicting the COP of R744-R404A cascade refrigeration system through an addition experiments.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.6
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• pp.575-581
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• 2013

In this paper, the influences of several factors, such as subcooling, superheating degree, internal heat exchanger efficiency, and etc. to the optimal amount of refrigerant charge are investigated for the case of R744-R404A cascade refrigeration system. Refrigerants used in the cascade refrigeration system are R404A in high temperature cycle and R744 in the low temperature cycle. The main results are summarized as follows : The mass flow rate ratio decreases with increasing subcooling, superheating degree and internal heat exchanger efficiency in the high temperature cycle, and evaporating temperature and compression efficiency in the low temperature cycle. And the mass flow rate ratio decreases with decreasing temperature difference of cascade heat exchanger and evaporating, condensing temperature in the high temperature cycle, and subcooling, superheating degree and internal heat exchanger efficiency in the low temperature cycle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.2
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• pp.81-86
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• 2015

Performance of freezing and refrigeration systems in supermarket, which utilized $CO_2$ as a refrigerant, was investigated by using the Pack Calculation II. The configuration of simulated systems was basic parallel refrigeration system, cascade system, and two-stage system. The $CO_2$ cascade system showed higher COP than basic parallel R404A system by 13% for MT and 62% for LT, respectively. Among the $CO_2$ cascade systems, R717(MT)-$CO_2$(LT) showed the highest performance. Open-type intercooler method showed higher performance than liquid injection for the two-stage $CO_2$ systems.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1123-1128
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• 2009

In this paper, the cycle performance characteristics of a cascade refrigeration system with internal heat exchanger using natural refrigerants is presented to offer the basic design data for the operating parameters of the system. This system considered in this study is consisted of a high temperature cycle using a carbon dioxide(R744) and low temperature cycle using refrigerants such as R290, R1270, R600a and Ethane. The main results were summarized as follows : The COP of the cascade refrigeration system of R600a with internal heat exchanger is the highest grade in low temperature cycle using refrigerants such as R290, R1270, R600a and Ethane. The COP of the cascade refrigeration system with internal heat exchanger only in high temperature cycle is the highest value among three type cycle, such as only low temperature cycle, only high temperature cycle and all the cycle.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.38-43
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• 2012

This paper describes an analysis on performance of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporating and condensing temperature in the R744 low- and R404A high-temperature cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : COP of cascade refrigeration system increases with the increasing of compression efficiency, but decreases with the increasing temperature difference of cascade heat exchanger. Also, the COP increases with the increasing of internal heat exchanger efficiency in high-temperature cycle, but decreases with that in low-temperature cycle. Therefore, internal heat exchanger efficiency, compressor efficiency and temperature difference of cascade heat exchanger on R744-R404A cascade refrigeration system have an effect on the COP of this system.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.6
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• pp.526-533
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• 2009

In this paper, cycle performance analysis of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system with internal heat exchanger is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree and gas cooling pressure and evaporating temperature in the propane (R290) low temperature cycle and the carbon dioxide (R744) high temperature cycle. The main results were summarized as follows : The COP of cascade refrigeration system of $CO_2-C_3H_8$ (R744-R290) increases with the increasing subcooling degree, but decreases with the increasing superheating degree. The COP of cascade refrigeration system increases with the increasing evaporating temperature, but decreases with the increasing gas cooling pressure. Therefore, superheating and subcooling degree, compressor efficiency, evaporating temperature and gas cooling pressure of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system have an effect on the COP of this system.