• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.297-302
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• 2005

Since the use of CFC and HCFC refrigerants are to be restricted due to the depletion of ozone layer, this experiment applies the $NH_3$ gas to study the performance characteristics of $NH_3$ refrigeration system by the superheat control for improving the energy efficiency. The experiments are carried out for the condensing pressure of refrigeration system from 1,500 kPa to 1,600 kPa and for degree of superheat from $0^{\circ}C\;to\;10^{\circ}C$ at each condensing pressure. As a result of experiment, when the degree of superheat is $0^{\circ}C$ at each condensing pressure, the refrigeration system has the highest performance.

• 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.

• Journal of the Korea Organic Resources Recycling Association
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• v.11 no.1
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• pp.138-148
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• 2003

In the study, current status of waste plastic recycling was investigated. Some factors to obstruct recycling of waste plastic was analyzed. These factors include the difficulty of obtaining location and man power, unclear marking of recyclable plastic and inefficient rate in producer and consumer deposit system. Life cycle assessment(LCA) study was performed to investigate the environmental impact of waste plastic(PET) recycling. When the recycled raw plastic material is used together with the virgin raw plastic material, all the environmental impact showed (-) value except ozone depletion impact category. The environmental avoided impact was the greatest in the global warming impact category. For active promotion of recycling activity, source separation system of waste plastic should be established first of all. Also, marking system of the recycling waste plastic should be made more clear so that consumers can understand it easily. Other strategies include the determination of decent rate for producer and consumer deposit system, establishment of infrastructure and information system for waste plastic recycling and citizen's cooperation through intensive public education.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.612-620
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• 2008

New alternative refrigerants have been developed due to the ozone layer depletion and global warming. For this reason, carbon dioxide is believed to be a promising refrigerant for use in air conditioners and heat pumps. Evaporative heat transfer characteristics and pressure drop of $CO_2$ with outer diameter of 5 mm in inclined ($45^{\circ}$) smooth and micro-fin tubes have been investigated by the experiments with respect to several test conditions such as mass fluxes, heat fluxes, evaporation temperatures in this study. The inclined ($45^{\circ}$) smooth and micro-fin tubes with length of 1.44 m were installed to measure the evaporative heat transfer coefficients of $CO_2$ and heat was supplied to the refrigerant by direct heating method where the test tube was uniformly heated by electricity. The tests were conducted at mass fluxes from 212 to $656\;kg/m^2s$, heat fluxes from 15 to $60\;kW/m^2$ and evaporation temperatures from -10 to $20^{\circ}C$. The heat transfer coefficients of $CO_2$ are slightly increased with increasing mass flux, and the heat transfer characteristics in the inclined ($45^{\circ}$) tubes are enhanced about $5{\sim}10%$ compared with those in horizontal or vertical tubes.

• Solar Energy
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• v.17 no.4
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• pp.23-33
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• 1997

In this paper, performance of various working fluids is evaluated for the closed Ocean Thermal Energy Conversion(OTEC) power plant operating on Rankine cycle. The evaporator and condenser are modeled via UA and LMTD method while turbine and pump are modeled by specifying isentropic efficiencies. R22, Propane, Propylene, R134a, R125, R143a, R32, R410A and Ammonia are used as working fluids. Results show that newly developed fluids such as R410A and R32 that do not cause stratospheric ozone layer depletion perform as well as R22 and ammonia. The superheat at the evaporator exit and subcooling at the condenser exit do not affect the performance of the simple OTEC power cycle. Turbine efficiency and heat exchanger size influence greatly the performance of the Rankine cycle. Finally, it was shown that closed OTEC power plants can practically generate electricity when the difference in warm and cold sea water inlet temperatures is greater than $20^{\circ}C$.

• International Commerce and Information Review
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• v.15 no.1
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• pp.97-116
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• 2013

The environmental problems such as global climate chage, global wamning, ozone depletion, environmental pollution have been caused by the rapid economic growth, increasing in use of fossil fuels for industralization and scientific technology development. Between Environmental Preservation and Economic Development, the new paradigm, "Sustainable Development" is presented to the world now. To achieve global environmental objectives, some multilateral envrionment mental agreements includes trade regulation. However Kyoto Protocol has no provisions to regulate trade and is not in force yet. By the effectuation of the Kyoto Protocol, Korea will be faced very serious situation because of her high Dependency on Foreign Trade and Fossil Fuel- intensive Industries. We must be able to gain a sense of ownership in the out come of the WTO/CTE discussions by contributing meaningfully to the creation of a constructive relationship between Trade and Environment concerns.

• 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.

• Journal of Korean Elementary Science Education
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• v.28 no.2
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• pp.142-153
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• 2009

The purpose of this study was to survey primary students' perception of the global and local environmental issues. The subjects were 853 fifth primary students in Seoul, Busan, Daejeon, Anyang, Gimpo and Cheongju. The results were as follows: First, the perception level of the global environmental issues were global warming (M=3.99), drinking-water pollution (M=3.92), acid rain (M=3.77), yellow dust (M=3.66), ozone depletion (M=3.57), deforestation in tropical areas (M=3.52), desertification (M=3.36), biodiversity (M=3.40) and their perception level of local environmental issues were waste disposal (M=3.87), air pollution (M=3.74), bad smell (M=3.70), noise (M=3.61), river pollution (M=3.57), soil pollution (M=3.44). Second, it was shown that the metropolitan students' perception levels of environmental issues were higher than the non-metropolitan students'. There wasn't a significant difference in the perception levels of two scale environmental issues and characteristics for sex (p>.05). Third, the result of analyzing on the effects between characteristics was that the factors like 'environmental interest' and 'impact on personal life' had a strong influence on the 'behavior will' to solve the global environmental issues, and 'environmental interest' and 'personal knowledge' had a strong influence on the 'behavior will' to solve the local environmental issues. Fourth, the result of analyzing on the characteristics according to the types of the environmental issues showed that 'personal knowledge', 'environmental interest' and 'behavior will' were high in the global environmental issues (p<.01) and 'virtual contamination', 'human responsibility' and 'impact on personal life' were high in the local environmental issues (p<.05).

• Tribology and Lubricants
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• v.35 no.4
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• pp.206-214
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• 2019

This study investigates alternative refrigerants and refrigerant oils as well as the tendency of protecting the global environment in view of automobile air-conditioning systems. Since decades, the R12 refrigerant is not used in automobile air-conditioners because of the ozone depletion potential (ODP) problem, and for the last 20 years, the ODP-free R134a refrigerant is leading the new automotive air-conditioning market. However, owing to its high global warming potential (GWP), the R134a refrigerant use in automobile air-conditioning system is also prohibited by law, and alternative refrigerants with a low GWP need to be proposed. Therefore, recently, the application of R1234yf, R152a, or other alternative refrigerants has started worldwide. By contrast, natural refrigerant R744 was introduced in the market several years ago by VDA (Verband Der Automobilindustrie), which is a German association in the automotive industry. This study also deals with refrigerant oils. For a long time, polyalkylene glycol (PAG) oil has been traditionally used with automobile air-conditioners, and polyolester (POE) oil is suitable for HEV, PHEV, and EV air-conditioning systems, where it is used by the electrically driven compressor owing to its excellent electrical insulation properties. Finally, PAG is an excellent lubricant for all the R134a, R152a, R1234yf, and R744 refrigerants, and has the advantage that it can be applied rapidly to alternative refrigerant air-conditioning systems.