• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.890-894
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• 2015

Recently, research on high-efficiency refrigeration cycles that apply an ejector to basic cycles has progressed actively. The role of the ejector and the performance of refrigeration cycles are subordinate to ejector locations. In this study, the performance of three refrigeration cycles with different ejector locations is compared and analyzed. The results showed an increased COP in all cycles due to the application of the ejector, with the highest increase of 44% compared to a basic refrigeration cycle. The ejector refrigeration cycle proposed in this study presents the highest COP, 3.47. Moreover, the decrease in condensation capacity in Bergander's cycle, Xing's cycle, and our proposed ejector refrigeration cycle went up to 21%. In refrigeration cycles applying the ejector, the pressure ratio of the ejector, the vapor fraction of discharge, and compression ratio are important factors for COP enhancement. For this reason, detailed and accurate control of these is significant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1548-1554
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• 2013

This paper presents the analysis on performance characteristics of R744-R410A cascade refrigeration system to offer the basic design data for the operating parameters of this system. The performance of cascade refrigeration system is analyzed by using EES program. The operating parameters include compressor efficiency, and condensing and evaporating temperature in R410A high- and R744 low-temperature cycle, respectively. The COP of this system increases with the decrease of condensing temperature, and increases with the increasing evaporating temperature. And the COP of this system increases with the compression efficiency. Therefore, it can be seen that the compression efficiency, and evaporating and condensing temperature of R744-R410A cascade refrigeration system have an effect on the COP of this system. Also, it can be known that the cascade evaporation temperature with the highest efficiency in each parameter is present. Thus, it is an important to design R744-R410A cascade refrigeration system by considering these parameters.

• Journal of the Korean Institute of Gas
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• v.14 no.1
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• pp.1-7
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• 2010

In this paper, cycle performance analysis of $NH_3-CO_2$(R717-R744) two-stage 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 the ammonia(R717) high temperature cycle and the carbon dioxide low temperature cycle. The main results were summarized as follows : The COP of two-stage cascade refrigeration system increases with the increasing subcooling degree, but decreases with the increasing superheating degree. The COP of two-stage cascade refrigeration system decreases with the increasing condensing temperature, but increases with the increasing evaporating temperature. And the COP of two-stage cascade refrigeration system increases with increasing the compressor efficiency. Therefore, superheating and subcoolng degree, compressor efficiency, and evaporating and condensing temperature of $NH_3-CO_2$(R717-R744) two-stage cascade refrigeration system have an effect on the COP of this system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.1013-1019
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• 2011

In this paper, simulation works for a multi-stage cascade refrigeration cycle using propane, ethylene and methane as refrigerants have been performed for the liquefaction of natural gas using Peng-Robinson equation of state built-in PRO/II with PROVISION release 8.3. The natural gas feed compositions were supplied from Korea Gas Corporation and the flow rate was assumed to be 5.0 million tons per annual. Supply temperature for propane refrigerant was fixed as $-40^{\circ}C$, that for ethylene refrigerant as $-95^{\circ}C$, and that for methane refrigerant as $-155^{\circ}C$. For the multi-stage refrigeration cycle, three-stage refrigeration was assumed for propane refrigeration cycle, two-stage refrigeration for ethylene refrigeration cycle and three-stage refrigeration for methane refrigeration cycle. Natural gas was finally cooled and liquefied to $-162^{\circ}C$ by Joule-Thomson expansion. Conclusively, 91.71% by mole of the natural gas liquefaction ratio was obtained through a cascade refrigeration cycle and Joule-Thomson expansion and 0.433 kW of compression power was consumed for the liquefaction of 1.0 kg/hr of natural gas.

• Journal of the KSME
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• v.35 no.2
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• pp.154-166
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• 1995

냉동\ulcorner공조기의 성능을 높이기 위해서는 정상상태 운전시는 물론 증발기 열부하 등 각종 작동 조건의 변화에 대응하여 운전의 평형점(balance point) 추이를 적절하게 조정함과 동시에 냉동 사이클 각부의 냉매 상태량을 과도적으로도 제어해야 한다. 이 글에서는 냉동\ulcorner공조기의 자동 제어에 있어서 가장 중요한 요소중의 하나인 냉매계통의 모델화와 냉동 사이클의 응답 및 제어 등에 관해서 서술하고자 한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2195-2201
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• 2009

This paper considers the influence of suction-line heat exchangers on the efficiency of a refrigeration cycle using hydrocarbon refrigerants such as R290, R600a and R1270. These suction-line heat exchangers can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analyze the performance characteristics of refrigeration cycle with suction-line heat exchanger. The influence of operating conditions, such as the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, to the performance of the cycle is also analyzed in the paper. Results showed that the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle of hydrocarbon refrigerants using suction-line heat exchanger.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.353-362
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• 2019

Thermodynamic analysis of cascade refrigeration systems has attracted considerable research attention. On the other hand, a system evaluation based on thermodynamic analyses of the individual parts, including the evaporator, condenser, intercooler, expansion valve, etc., has received less attention. In this study, performance analysis was conducted on a cascade refrigeration system, which has an individual cooling and refrigeration evaporator, and equips the intercooler and air-cooled condenser in a series in a lower cycle. The thermo-fluid design was then performed on the major components of the system - upper condenser, lower condenser, cooling evaporator, refrigeration evaporator, intercooler, compressor, electronic expansion valve - of 15 kW refrigeration, and 8 kW cooling capacity using R-410A. A series of simulations were conducted on the designed system. The change in outdoor temperature from 26 C to 38 C resulted in the cooling capacity of the lower evaporator remaining approximately the same, whereas it decreased by 9% at the upper evaporator and by 63% at the intercooler. The COP decreased with increasing outdoor temperature. In addition, the COP of the cycle with the intercooler operation was higher that of the cycle without the intercooler operation. Furthermore, the increase in the upper condenser size by two fold increased the upper evaporator by 4%. On the other hand, the lower evaporator capacity remained the same. The COP of the upper cycle increased with increasing upper condenser size, whereas that of the lower cycle remained almost the same. When the size of the lower condenser was increased 2.8 fold, the intercooler capacity increased by 8%, whereas those of upper and the lower evaporator remained approximately the same. Furthermore, the COP of the lower cycle increased with an increase in the lower condenser. On the other hand, the change of the upper condenser was minimal.

• 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.33 no.8
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• pp.1144-1151
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• 2009

Refrigeration systems can be incorporated with non-adiabatic capillary tubes to improve their efficiency. The non-adiabatic capillary tube is constructed by joining the capillary tube with suction pipe to allow heat transfer between them, which is called capillary tube-suction line heat exchanger(SLHX). There are various joining methods and they may influence the characteristics of the refrigeration cycle. The present work aims to analyze the effect of widely-used two joining methods on the refrigeration cycle. The results show that soldered SLHX has much less thermal resistance than tapered SLHX but slightly outperforms in terms of coefficient of performance(COP) and cooling capacity. The soldered SLHX increased COP and cooling capacity of a refrigerator by 5.09% and 14.77% while the tapered SLHX did by 5.05% and 14.75%, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.8
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• pp.3106-3111
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• 2010

In this study, a comparative study was performed between one- and two-stage refrigeration system to cool the natural gas temperature down to $-40^{\circ}C$ using propane as a chilling medium. As a thermodynamic model, Peng-Robinson equation of state equation was applied and PRO/II with PROVISION release 8.3 at Invensys company was utilized for the simulation of the refrigeration system. Through this study, optimization work showed that two-stage refrigeration system was proven to save about 33.5% refrigeration power consumption compared to the one-stage refrigeration cycle.