• 대한기계학회논문집B
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• 제34권6호
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• pp.635-642
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• 2010

마이크로채널 열교환기에서 채널 굽힘 각도에 따른 R-134a의 증발열전달 특성에 관하여 실험적 연구를 수행하였다. 본 연구에서는 채널의 굽힘 각도가 $120^{\circ}$, $150^{\circ}$ 및 $180^{\circ}$인 마이크로채널 열교환기에서 R-134a의 증발온도와 Reynolds수 변화에 따른 열전달 특성을 대향류 조건에서 실험하였으며, 실험결과 마이크로채널 열교환기에서 증발열전달량과 증발열전달계수는 R-134a의 레이놀즈수 증가에 따라 증가하였다. 또한 채널의 굽힘각도가 $120^{\circ}$ 및 $150^{\circ}$인 마이크로채널 열교환기는 증발온도 $4.9{\sim}14.9^{\circ}C$ 에서 채널굽힘 각도가 $180^{\circ}$인 마이크로채널 열교환기와 비교하여 평균 약 17.1% 및 13.3%로 증발열전달량이 증가하였으며, R-134a의 증발열전달계수는 채널의 굽힘 각도가 작을수록 증발열전달계수가 증가하는 것으로 나타났다.

• 대한기계학회논문집B
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• 제35권7호
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• pp.743-748
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• 2011

R-134a 대체 냉매인 HFO-1234yf의 성능을 가정용 냉동/냉장고에서 평가하였다. AHAM(Associ- ation of Home Appliance Manufacturers) 규격에 의거하여 HFO-1234yf를 Drop-in하여 냉매 봉입량 시험, Pulldown 시험, 냉각속도 시험 그리고 소비전력 시험을 수행하였으며, R-134a 실험 결과와 비교하였다. $43^{\circ}C$ 고온 가혹 조건에 서도 시험을 수행하였다. 결과적으로 HFO-1234yf 냉매는 Cycle 성능면에서는 R-134a와 유사하나, 냉각속도는 모세관경을 더 크게 변경시켜야 한다.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1033-1041
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• 2003

Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and Rl23, The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube, 2m long with 10mm I.D., 1.5mm wall thickness. The obtained results are compared with the available various correlations for flow pattern. The flow pattern map of Hashizume was in good agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In this study, the flow pattern are simply classified into two groups; stratified(including intermittent, stratified and stratified-wavy) flow and annular flow. The transition quality from stratified to annular flow was obtained by modifying the liquid Froude number.

• 대한설비공학회지:설비저널
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• 제28권5호
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• pp.368-374
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• 1999

최근 세계적으로 환경보호에 대한 관심이 고조됨에 따라 기술개발 방향이 환경을 고려한 규정 및 장치에 제한을 받고 있다. 따라서 냉동 공조 기기에 사용되는 기존의 CFC계열 냉매가 오존층 파괴의 주 원임이 판명됨에 따라 환경 문제가 없는 HCFC계열인 R123와 HFC R134a로의 대체가 불가피하게 되었다.

• 설비공학논문집
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• 제7권4호
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• pp.589-599
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• 1995

The frictional pressure drop of a capillary tube flow is experimentally investigated for pure refrigerants such as R32, R125, and R134a and refrigerant mixtures such as R32/R134a(30/70 by mass percent), R32/R125(60/40), R125/R134a(30/70), and R32/R125/R134a(23/25/52). The binary interaction parameters for the calculation of viscosities of refrigerant mixtures are found based upon the data in the open literature. Several homogeneous flow models predicting the viscosity of two-phase region are compared to select the best model. Cicchitti's equation is known to be the most adequate for the prediction of the viscosity for refrigerant mixtures, which is used in the analysis of adiabatic capillary flows. A model for the prediction of the frictional pressure drop of single and two-phase flow is developed for refrigerant mixtures in this study. This model may be used to design and analyze the performance of a capillary tube in the refrigerating system.

• 태양에너지
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• 제19권3호
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• pp.101-113
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• 1999

Thermodynamic performance of a simple Rankine cycle, regenerative Rankine cycle, and Kalina cycle for Ocean thermal Energy Conversion(OTEC) is evaluated under the same condition with various working fluids. The evaporator and condenser are modeled by a UA and LMTD method while the turbine and pump are modeled by considering isentropic efficiencies. As for the working fluids, R22, R134a, R32, propylene, ammonia are used for the Rankine cycles while ammonia/water and R32/R134a mixtures are used for Kalina cycle. Calculated results show that newly developed fluids such non-ozone depleting refrigerants as R134a and R32 perform as well as R22 and ammonia. The regenerative Rankine cycle showed a 1.2 to 2.8% increase in energy efficiency as compared to the simple Rankine cycle while the Kalina cycle with ammonia/water mixture showed a 1.8% increase in energy efficiency. The efficiency of the Kalina cycle with R32/R134a mixtures is the same as that of a simple Rankine cycle using R22. Therefore, the regenerative Rankine cycle turns out to be best choice for OTEC applications.

• 설비공학논문집
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• 제11권2호
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• pp.262-269
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• 1999

The application of hydrocarbon refrigerant mixtures in a hermetic reciprocating compressor for dehumidifier is investigated. The selected refrigerants are R12, R134a, HC-Blend (R290/R600a), CX(R152a/R600a) and OS-l2a. Both theoretical and experimental investigations have been performed for the selected refrigerants. The test results of hydrocarbon refrigerants have been compared to traditional refrigerant(R12) and R134a. The results show that hydrocarbon refrigerant mixtures(HC-Blend, CX and OS-l2a) are very good alternatives in the refrigeration system for R12 and R134a.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권1호
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• pp.39-49
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• 2001

Investigation of the performance of an autocascade refrigeration system using the refrigerant mixtures of R744 (carbon dioxide) and R134a (1,1,1,2-tetrafluoroethane) has been carried out by simulation and experiment. Cycle simulation using a constant UA model in heat exchangers has been performed for R744/134a mixtures of the compositions ranging from 10/90 to 30/70 by weight. Variations of mass flow rate of refrigerant, compressor work, refrigeration capacity and COP with respect to mass fraction of R744/134a mixture were presented. Performance test has been executed in the autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Experimental results match quite well with those obtained from the simulation.

• 대한기계학회논문집B
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• 제34권2호
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• pp.113-120
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• 2010

마이크로채널 열교환기에서 R-134a의 증발열전달 특성에 관하여 실험적 연구를 수행하였다. 마이크로채널은 금속박판인 SUS304에 포토에칭 공정으로 식각되었으며, 13개의 금속박판은 차례로 적층되어 확산접합공정을 통하여 접합되었다. 본 연구에서는 R-134a의 증발온도, 질량유속 그리고 물의 입구온도의 변화에 따른 열전달 특성을 대향류 조건에서 실험하였다. 실험결과 R-134a와 물의 입구온도차가 클수록 증발열전달량은 증가하였으며, 증발열전달계수는 0.67 kW/$m^2{\cdot}^{\circ}C$에서 6.23 kW/$m^2{\cdot}^{\circ}C$이었다. 아울러 마이크로채널 열교환기에서 R-134a와 물의 열교환에 따른 증발열전달 특성에 영향을 미치는 Reynold수와 무차원 온도비 $\Theta$를 도출하여 Nusselt수에 관한 실험적 상관식을 제안하였다.

• 설비공학논문집
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• 제19권5호
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• pp.403-410
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• 2007

In this study, natural refrigerants and their mixtures that can supplement and replace R12 and R134a in automobile air-conditioners are studied. R134a is currently used as the refrigerant in new motor vehicle air conditioners, replacing the ozone depleting refrigerant R12. Although R134a has no ozone depletion potential, it has a relatively large global warming potential, approximately 1300 times that of $CO_2$ over a 100 year time horizon. For this reason, performance of natural refrigerants and their mixtures containing R152a, RE170 (Dimethylether, DME) and R600a (Isobutane) are measured under 2 different temperature conditions. They were tested in a refrigerating bench tester with an open type compressor. The test bench provided about 4 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. Test results show that the coefficient of performance (COP) of these refrigerants is up to 21.55% higher than that of R12 in all temperature conditions. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for automobile air-conditioners.