• Journal of Power System Engineering
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• v.21 no.1
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• pp.24-29
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• 2017

Studies in liquid-vapor ejector, which performs a great efficiency in refrigeration cycle is highly concerned. This paper is based on basic refrigeration cycle and three ejector refrigeration cycles and the comparison and contrasts about when 6 different refrigerants are applied to such refrigeration cycles. All cycles had a percentage increase of COP from 4 to 74% when ejector was applied, and the source of increasement was the decrease of total work done due to ejector's pressure recovery function. When R-245fa is applied to cycle (d), results showed that COP was the most superior in such cycle, R-245fa showed high volume entrainment ratio in all cycles. Future studies in refrigeration cycles will require more knowledge and experiments on ejector's appliance to refrigeration cycles and the actuation of such functions.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.613-618
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• 2006

The 1st International Conference on Magnetic Refrigeration at Room Temperature was held at Montreux, Switzerland during September 27-30, 2005. The conference was the first of its kind to bring together about 140 scientists and engineers interested in magnetic refrigeration in one place. The magnetocaloric effect was discovered in 1881, however, magnetic refrigeration at room temperature was demonstrated to be viable in 1997 Since then, R&D efforts toward magnetic refrigeration have been on the rise around the world, in both areas of systems and materials. The conference reflected the recent R&D trend in magnetic refrigeration at room temperature, which includes the use of permanent magnet instead of superconductor magnet, switch from reciprocating to rotary magnetic refrigeration system, development of magnetic materials based on transition metal elements besides rare earth materials such as gadolinium(Gd).

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.4
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• pp.175-181
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• 2007

A computer model of a high efficiency refrigeration system equipped with heat storage for reverse cycle-hot gas defrost (the stored heat is used during defrost cycle of the system) is presented. The model was developed based on both theoretical and empirical equations for the compressor, evaporator, condenser and the heat storage equipment. Simulations of the prototype system were carried out to investigate refrigeration system performance under various operating conditions during refrigeration cycles. The simulations of the evaporator during defrost cycles at 30 and $40^{\circ}C$ hot gas refrigerant temperature were also performed which resulted on shorter defrost time but only slight increase in defrost efficiency. These information on energy efficiency and the defrost time required are important in order to avoid excessive parasitic load and temperature rise of the refrigerated room.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.24-29
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• 2012

In this paper, an analysis on performance and exergy of R404A refrigeration system using R744 secondary refrigerant was performed numerically to optimize the design for the operating parameters. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporation and condensation temperature in the R404A refrigeration cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : The COP(coefficient of performance) of R404A refrigeration system increases with increasing evaporation temperature. The evaporation capacity of R744 as secondary refrigerant increases with the increase in evaporation pressure of R744 secondary refrigeration. And the enthalpy in the evaporator outlet of R744 increases with the increasing evaporation pressure of R744 secondary refrigeration. Therefore, it is important to analysis for the relationship between COP of R404A refrigeration system and refrigeration capacity of R744. As cascade evaporation temperature increase, the exergy loss of condenser and compressor using R404A is the largest among all components. Therefore, the exergy loss in the condenser and compressor using R404A must be decreased to enhance the COP of R404A refrigeration system with R744 secondary refrigerant.

• 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.15 no.5
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• pp.3327-3335
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• 2014

In this study, comparison works have been performed for single-stage and multi-stage refrigeration cycle using propane as a refrigerant in order to cool down the natural gas stream. A comparative analysis has been performed for a single, two, three and four stage refrigeration cycle using propane as a refrigerant for cooling the natural gas stream. For the simulation, natural gas feedstock properties supplied by KOGAS were utilized and Peng-Robinson equation of state model was used. As the number of compression stages increase, the condenser heat duty is decreased. The refrigeration heat duty for a four-stage refrigeration cycle is decreased by 20.36% compared to that for a single-stage refrigeration cycle. Moreover, the total refrigerant circulation rate for a four-stage refrigeration system is was reduced by 14.53% compared to the single stage refrigeration cycle. The total compression power for a four-stage compression was reduced by 41.61% compared to the single stage compression.

• 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.

• Journal of Power System Engineering
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• v.18 no.1
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• pp.57-62
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• 2014

This paper present the performance characteristics of R404A two-stage compression refrigeration system. The operating parameters considered in this study include evaporating and condensing temperature, subcooling and superheating degree, compressor efficiency. The main results were summarized as follows: The COP of two-stage compression refrigeration system using R404A has an effect on the variation of evaporation temperature, condensation temperature, subcooling degree and compressor efficiency, but not an effect on the superheating degree. R404A two-stage compression refrigeration system is unstable because COP of this system is significantly changed when evaporating temperature and compressor efficiency decreased. In particular, when compressor efficiency decreased, COP is significantly decreased. This is inefficient for long-term use.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.585-590
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• 2005

It can be said that refrigeration and air-conditioning technology in Korea dates back to the ancient Shilla dynasty, all the way up to the Sokkuram(700s) and Seokbinggo(1700s). But modem refrigeration and air-conditioning technology was first developed in and introduced to Korea in the 1960s with the modernization of Korea. Today it is at a level which meets that of advanced countries in both the industrial and domestic fields. 62 million units of refrigeration and air-conditioning machinery and equipment were produced in 2003, worth a total of 7.7 trillion won(about 7.7 thousand million US$). As of 2003, there were about 700 companies that owned cold storage / freezing / refrigeration facilities, with cold storage capacity of about 2 million ton and capacity per company of about 3 thousand ton. This facilities most are continuously expanding and automatizing their facilities.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.88-94
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• 2007

This study deals with on-line fault detection and diagnosis for heat exchanger of variable speed refrigeration system. Conventional studies about fault of heat exchanger in refrigeration system have used temperature and pressure information. The temperature and pressure are able to be used valuably for faults detection of constant speed refrigeration system. However in case of variable speed refrigeration system, the temperature and pressure are no longer useful information for fault detection due to compensation effect of feedback controller. While current information is possible to detect faults of variable speed refrigeration system. The current information was detected in an inverter, it was used after transforming rms value. The faults of variable speed refrigeration system are divided into electrical faults and mechanical faults. We performed fault detection and diagnosis about heat exchanger among mechanical faults such as condenser fouling and evaporator fan fouling through some experiments.