• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.47-51
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• 2017

Recently international cooperations are formed to deal with the environmental pollution of the atmosphere generated by the vapor compression refrigeration system. A refrigeration technique, which can replace existing CFC refrigerants that are the main cause of environmental contamination, has received greater attention. Magnetic refrigeration is a refrigeration technique using the magnetocaloric effect of the magnetic material, and is an eco-friendly refrigeration technology using the solid refrigerant instead of CFC refrigerants. Also it is regarded as an efficient refrigeration system to generate temperature difference between high and low sides using the temperature change of magnetic refrigerants according to the change of magnetic field, instead of using power-consuming and noisy compressor. In this paper, we introduce the magnetic refrigeration apparatus using concentric Halbach cylinder permanent magnets and the experimental results using the apparatus.

• Journal of Power System Engineering
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• v.19 no.6
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• pp.82-88
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• 2015

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

• 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.10 no.9
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• pp.2189-2194
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• 2009

The automatic hot gas by-pass technique is applied to control the capacity of refrigeration and air-conditioning system when operating at part load. In the scheme, the hot gas from the compressor is extracted and injected into the outlet of an evaporator through a hot gas by-pass valve. Thus, In this paper, the hot gas by-pass scheme for CO2 is discussed and analyzed on the basis of mass and energy conservation law. A comparative study of the schemes is performed in terms of the coefficiency of performance (COP) and cooling capacity. The operating parameters considered in this study include compressor efficiency, superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : the superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.286-296
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• 1991

The thermodynamic properties of R134a, the prospective R12 alternative, have been computerized using Martin-Hou equation of state and the coefficients given by Willson-Basu. Several experimental results in literatures for PVT data, saturated vapor pressure, saturated liquid density are compared with the calculated results to investigate the accuracy. The average deviation (max. deviation) is 0.13% (0.25%) for saturated liquid density, 0.25% (0.8%) for PVT data. Thermodynamic properties, enthalpy, entropy are compared with the NIST's. The maximum percent difference is 3% for saturated liquid enthalpy, 1.5% for saturated vapor enthalpy, 4% saturated liquid entropy, and 0.7% for saturated vapor entropy. Correction of W-B's coefficients and inclusion of the sixth term of M-H EOS for improvement of accuracy are recommended. R134a and R12 are compared with respect to refrigeration performance. COP's are different from each other within 3%. Refrigeration effect of R134a is superior to that of R12 but refrigeration capacity of R134a is inferior to that of R12 because the volumetric efficiency of the system using R134a is lower than that of the system using R12.

• The Journal of Korean Medicine
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• v.39 no.1
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• pp.22-34
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• 2018

Objectives: The purpose of this study is to investigate changes of the marker compounds and anti-inflammatory effect of Gamisoyo-san decoction (GMSYS) depending on storage temperature and periods. Methods: GMSYS was stored at room temperature or refrigeration for 12 months. According to storage temperature and periods, pH and sugar content of GMSYS were measured. To determine the marker compounds of GMSYS, high-performance liquid chromatography analysis was performed. To estimate the anti-inflammatory effect of GMSYS, LPS-induced pro-inflammatory mediators and cytokines were measured in RAW 264.7 cells. Results: There was no change in pH and sugar content depending on storage temperature and periods of GMSYS. The contents of gallic acid and mangiferin in both of room temperature and refrigerated decoctions reduced with increasing storage periods. Chlorogenic acid was time-dependently decreased in case of stored at room temperature. GMSYS significantly inhibited the LPS-induced production of nitric oxide, prostaglandin $E_2$ ($PGE_2$) and IL-6 in RAW 264.7 cells. These effects equally maintained up to 3 months at both of room temperature and refrigeration. Since 4 months, the inhibitory effect of GMSYS on LPS-induced $PGE_2$ production was time-dependently reduced, and the decrease in $PGE_2$ inhibitory effect of decoction stored at refrigeration was lower than that of stored at room temperature. Conclusions: Our results indicate that the anti-inflammatory effect of GMSYS are maintained up to 12 months, but it shows optimal efficacy up to 3 months. It is recommended to store in a refrigeration for short periods since some components decrease as storage periods becomes longer.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.2
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• pp.88-96
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• 2002

The present study was conducted to estimate the effect on fouling reduction in tubes of the condenser. It shows in detail how to calculate the fouling factor from the experimental results of refrigeration systems with or without the automatic cleaning system using sponge balls and to predict the variation of the factor with time. It also represents how to calculate the temperature and pressure decrease of the refrigerant vapor in the condenser and the load decrease of the compressor in the refrigeration system by fouling reduction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.329-340
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• 1995

Basic refrigeration effect and efficiency of a thermoacoustic refrigerator is studied. The refrigerator model for numerical simulation is composed of half wavelength resonator and appropriate stack of plate. Theoretical model for thermoacoustic refrigeration suggested by Swift et. al is adapted for numerical calculation. The model contains arbitrary viscosity effect of the gas filled in the resonator. The wave equation is integrated by using 4-th order Runge-Kutta algorithm to give pressure distribution along the stack of plate. Heat flux and COP are also calculated based on the energy flux equation. By analyzing the numerical simulation results, optimum values of design parameters for thermoacoustic refrigerator are obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.6
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• pp.482-489
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• 2001

The present study was conducted to estimate the effect on fouling reduction in tubes of the condenser. It shows in detail how to calculate the fouling factor from the experimental results of refrigeration systems with or without the automatic cleaning system using sponge balls and to predict the variation of the factor with time. It also represents how to calculate the temperature and pressure decrease of the refrigerant vapor in the condenser and the load decrease of the compressor in the refrigeration system by fouling reduction.