• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.534-541
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• 2008

This paper deals with the heat transfer characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for evaporating. The experimental apparatus has been set-up as conventional vapor compression type refrigeration and air-conditioning system. The test section is a horizontal double pipe heat exchanger. Evaporating heat transfer measurements were performed for smooth tube with the outer diameters of 12.70, 9.52 and 6.35 mm and micro-fin tube 12.70 mm, respectively. For the smooth and micro-fin tubes measured in this study, the evaporating heat transfer coefficient was enhanced according to the increase of the mass flux and decrease of the tube diameter. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Also, the evaporating heat transfer coefficients of R-22 in the tube diameter of the 12.70 mm smooth and micro-fin tube were compared. Generally, the local heat transfer coefficients for both types of tubes increased with an increase of the mass flux. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 1.9 to 2.7 in all experimental conditions.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.590-595
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• 2006

This paper presents the friction and anti-wear characteristics of nano-oil with a mixture of a refrigerant oil and carbon nano-particles in the thrust slide-bearing of scroll compressors. Frictional loss in the thrust slide-bearing occupies a large part of total mechanical loss in scroll compressors. The characteristics of friction and anti-wear using nano-oil are evaluated using the thrust bearing tester for measuring friction surface temperature and the coefficient of friction at the thrust slide-bearing as a function of normal loads up to 4,000 N and orbiting speed up to 3,200 rpm. It is found that the coefficient of friction increases with decreasing orbiting speed and normal force. The friction coefficient of carbon nano-oil is 0.015, while that of pure oil is 0.023 under the conditions of refrigerant gas R-22 at the pressure of 5 bars. It is believed that carbon nano-particles can be coated on the friction surfaces and the interaction of nano-particles between surfaces can be improved the lubrication in the friction surfaces. Carbon nano-oil enhances the characteristics of the anti-wear and friction at the thrust slide-bearing of scroll compressors.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.29-38
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• 2004

The Condensation heat transfer coefficients of R-22 and R-l34a were measured in smooth horizontal copper tubes with inner diameters of 1.77. 3.36 and 5.35 mm. respectively. The experiments were conducted in a closed loop. which was driven by a magnetic gear pump. They were Performed for the following ranges of variables: mass flux (200 to $500\;kg/\textrm{m}^2{\cdot}s$) saturation temperature $30^{\circ}C$ and quality (0 to 1.0). The main results obtained are as follows Condensation heat transfer coefficients in the small diameter tubes (ID < 7 mm) were observed to be strongly affected by inner diameter change and to differ from those in the large diameter tubes. The heat transfer coefficients in the small diameter tubes were 20 ~ 40 % higher than those in the large diameter tubes as the inner diameter of the tube was reduced. Also. it was very difficult to apply some well-known previous predictions (Cavallini-Zecchin's. Haraguchi's and Dobson's correlation) to small diameter tubes. Based on an analogy between heat and mass transfer the new correlation is Proposed to predict the experimental data more accurately.

• 설비공학논문집
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• 제10권6호
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• pp.732-742
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• 1998

Prediction method for heat transfer coefficients in a horizontal smooth tube with forced convection condensation is proposed. In this paper, the analogy between momentum and heat transfer was applied to an annular flow regime and the logarithmic velocity distribution is applied to describe the velocity profile within the liquid film. Prediction results are compared with those of experimental ones. The test refrigerants are R113, R22, R134a, R407C(R33/R125/R134a, 23/25/52 wt%), R410A(R32/R125, 50/50 wt%) and R134a＋R123(R134a/R123, 85.5/14.5 wt%) which are used under operating conditions in a condenser of air-conditioner. The proposed prediction method shows good agreement with experimental data within$\pm 30%$ for pure refrigerants. For the mixture refrigerants including the ternary mixture refrigerant R407C, condensation heat transfer from this study are higher than those from experiments. By correcting the constant in two-phase frictional multiplier, the predicated heat transfer coefficients become similar to the experimental results.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.410-413
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• 2005

Drop-in tests were conducted using R290/R32 (31:69) mixture in an ice-cream maker for possible replacement of R-502 and R-404A. Optimum refrigerant charge and TEV opening were obtained through a series of experiments. At the standard outdoor condition ($35^{\circ}C$ DT, $24^{\circ}C$ WT), the time required for initial ice-cream making was 6'22", which was approximately the same as that of R-404A. The electric energy consumed was 660 kJ, which was about 10% higher than that of R-404A. The compressor outlet temperature ($8^{\circ}C$) and pressure (2.52 MPa) were higher than those ($60^{\circ}C$ and 1.48 MPa) of R-404A. The reason could be the usage of the same R-404A compressor although the specific volume of R290/R32 is much larger.

• 대한기계학회논문집B
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• 제22권7호
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• pp.980-991
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• 1998

In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m$\^$2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.

• 설비공학논문집
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• 제17권9호
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• pp.816-823
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• 2005

This paper deals with the heat exchange performance prediction of a counter flow type double-tube condenser for natural refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane in a smooth tube and a micro-fin tube. The local characteristics of heat transfer, mass transfer and pressure drop are calculated using a prediction method developed by the authors. The total pressure drop and the overall heat transfer coefficient are also evaluated on various heat exchange conditions. The calculated results of the natural refrigerant mixtures are compared with HCFC22. In conclusion, natural refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane are appropriate candidates for alternative refrigerant from the viewpoint of heat transfer characteristics.

• 대한기계학회논문집B
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• 제21권5호
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• 에너지공학
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• 제20권1호
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• pp.26-29
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• 2011

일반적인 냉각 과정에 적용되는 이차 냉매로서 아이스슬러리 적용 기술이 최근 개발되고 있다. 아이스슬러리는 액체와 거의 동일한 특성을 가지고 있고, 단위 체적당 아이스슬러리의 에너지용량이 얼음 입자의 잠열로 인해 냉각수나 브라인에 비해 상당히 높지만 파이프를 통해서 잘 유동시킬 수 있다. 아이스슬러리를 적용하는 냉각시스템의 설계를 위한 기초 결과를 제시하기 위하여, 쇼케이스의 냉각 코일에 아이스슬러리를 적용하는 실험을 수행하였다. 냉각 코일 입구에서의 아이스슬러리의 온도가 R22에 비하여 적어도 $5^{\circ}C$ 정도 높지만, R22를 적용하는 냉각시스템에 비하여 동등한 열적 성능을 가지고 있었다.

• 공업화학
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• 제28권2호
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• pp.171-176
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• 2017

염화이불화메탄($CHClF_2$) 냉매를 완전하게 분해하여 회수하기 위한 질소 플라즈마 열분해 공정이 연구되었다. 과열증기를 공급하여 분해가 보다 원활히 이루어질 수 있도록 스팀 발생기가 부착되었다. 60 A, 9.0 kW 이상의 운전 조건에서 94% 이상의 높은 분해율을 보이지만 탄소 성분의 완전 연소를 위해서는 같은 전류 대비 더 높은 power와 specific energy density를 갖춰야 함이 확인되었다. 60 A, 12.6 kW급 이상의 운전 조건에서는 $O_2$/R-22 ratio가 specific energy density에 비례하여 증가하였을 때 더 높은 분해율을 획득할 수 있었다. 반응물인 산소를 주입하는데 있어서 air를 단독으로 과량 주입하는 것보다는 산소를 air와 혼합하여 주입하는 것이 더 유용함이 밝혀졌다.