• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.8
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• pp.555-562
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• 2007

In this study, condensation heat transfer coefficients (HTCs) of R22, R134a, R245fa and R123 are measured on a horizontal plain tube. All data are taken at the vapor temperature of $39^{\circ}C$ with a wall subcooling temperature $3-8^{\circ}C$. Test results show the HTCs of newly developed alternative low vapor pressure refrigerant, R245fa, on a plain tube are 9.5% higher than those of R123 while they are 3.3% and 5.6% lower than those of R134a and R22 respectively. Nusselt's prediction equation for a plain tube underpredicts the data by 13.7% for all refrigerants while a modified equation yielded 5.9% deviation against all data. From the view point of environmental safety and condensation heat transfer, R245fa is a long term good candidate to replace R123 used in centrifugal chillers.

• Journal of Energy Engineering
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• v.18 no.3
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• pp.203-211
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• 2009

Vapor pressure of HFC-404a and polyol ester system were measured at 56 points from 263.15 to 323.15 K and from 0 to 90 mass %polyol ester. It was found that below 273.15 K, the effect of the polyol ester on the vapor pressure was negligible up to 30 mass % polyol ester. The vapor pressure of the system significantly decreased as the mass fraction of polyol ester increased over 50 percent. Raoult's model and Flory-Huggins model were tested for data reduction. Empirical vapor pressure equations were obtained in terms of temperature and mass fraction of polyol ester.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.435-449
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• 1995

In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.

• Journal of the Korean Solar Energy Society
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• v.33 no.1
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• pp.15-23
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• 2013

In this study, thermodynamic performance of R435A is examined both numerically and experimentally in an effort to replace HFC134a used in the refrigeration system of domestic water purifiers. Even though HFC134a is used predominantly in such a system these days, it needs to be phased out in the near future in Europe and most of the developed countries due to its high global warming potential. To solve this problem, cycle simulation and experimental measurements are carried out with a new refrigerant mixture of 20%R152a/80%RE170 using actual domestic water purifiers. This mixture is numbered and listed as R435A by ASHRAE recently. Test results show that the system performance with R435A is greatly influenced by the amount of charge due to the small internal volume of the refrigeration system of the domestic water purifiers. With the optimum amount of charge of 21 to 22 grams, about 50% of HFC134a, the energy consumption of R435A is 11.8% lower than that of HFC134a. The compressor discharge temperature of R435A $8^{\circ}C$ lower than that of HFC134a at the optimum charge. Overall, R435A, a new long term environmentally safe refrigerant, is a good alternative for HFC134a requiring little change in the refrigeration system of the domestic water purifiers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.2
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• pp.109-117
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• 2009

In this study, thermodynamic performance of R430A is examined both numerically and experimentally in an effort to replace HFC134a used in the refrigeration system of domestic water purifiers. Even though HFC134a is used predominantly in such a system these days, it needs to be phased out in the near future in Europe and most of the developed countries due to its high global warming potential. To solve this problem, cycle simulation and experimental measurements are carried out with a new refrigerant mixture of 76%R152a124% R600a using actual domestic water purifiers. This mixture is numbered and listed as R430A by ASHRAE recently. Test results show that the system performance with R430A is greatly influenced by the amount of charge due to the small internal volume of the refrigeration system of the domestic water purifiers. With the optimum amount of charge of 21 to 22 grams, about 50% of HFC134a, the energy consumption of R430A is 13.4% lower than that of HFC 134a. The compressor dome and discharge temperatures and condenser center temperature of R430A are very similar to those of HFC134a at the optimum charge. Overall, R430A, a new long term environmentally safe refrigerant, is a good alternative for HFC134a requiring little change in the refrigeration system of the domestic water purifiers.

• Korean Journal of Environmental Biology
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• v.17 no.1
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• pp.1-9
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• 1999

Numerous observations revealed strong evidence of increased middle ultraviolet radiation or UV-B (280 ~ 320 nm) at the earth's surface resulting from stratospheric ozone depletion. UV is the waveband of electromagnetic radiation which is strongly absorbed by nucleic acids and proteins, thus causing damage to living systems. It has been recorded in the East Sea, Korea that solar UV-B impinging on the ocean surface penetrates seawater to significant depths. Recent researches showed that exposure to UV-B for as short as 2h at the ambient level (2.0 Wm$^{-2}$) decreased macroalgal growth and photosynthesis and destroyed photosynthetic pigments. These may suggest that UV-B could be an important environmental factor to determine algal survival and distribution. Some adaptive mechanisms to protect macroalgae from UV-damage have been found, which include photoreactivation and formation of UV-absorbing pigments. Post-illumination of visible light mitigated UV-induced damage in laminarian young sporophytes with blue the most effective waveband. The existence of UV-B absorbing pigments has been recognized in the green alga, Ulva pertusa and the red alga, Pachymeniopsis sp., which is likely to exert protective function for photosynthetic pigments inside the thalli from UV-damage. Further studies are however needed to confirm that these mechanisms are of general occurrence in seaweeds. Macroalgae together with phytoplankton are the primary producers to incorporate about 100 Gt of carbons per year, and provide half of the total biomass on the earth. UV-driven reduction in macroalgal biomass, if any, would therefore cause deleterious effects on marine ecosystem. The ultimate impacts of increasing UV-B flux due to ozone destruction are still unknown, but the impression from UV studies made so far seems to highlight the importance of setting up long-term monitoring system for us to be able to predict and detect the onset of large -scale deterioration in aquatic ecosystem.