• 설비공학논문집
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• 제25권4호
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• pp.201-207
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• 2013

The performance of automobile air conditioning systems of R1234yf was evaluated and compared with that of R134a. In particular, the performance evaluation was carried out by installing an internal heat exchanger in order to improve the performance of the system used in R1234yf. A performance comparison between the R1234yf and R134a for automotive air conditioning revealed that the cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively.

• 대한기계학회논문집B
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• 제25권2호
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• pp.180-186
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• 2001

The condensation heat transfer coefficients of pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube were investigated. The experiment apparatus consists of a refrigerant loop and a water loop. The main components of the refrigerant loop consist of a variable-speed pump, a mass flowmeter, an evaporator, and a condenser(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flowmeter. The condenser is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal copper tube of 3.38mm outer diameter and 1.77mm inner diameter. The length of test section is 1220mm. The refrigerant mass fluxes varied from 450 to 1050kg/(㎡$.$s) and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main results were summarized as follows ; in the case of single-phase flow, the heat transfer coefficients increase with increasing mass flux. The heat transfer coefficient of R-410A was higher than that of R-22 and R-134a, and the heat transfer for small diameter tubes were about 20% to 27% higher than those predicted by Gnielinski. In the case of two-phase flow, the heat transfer coefficients also increase with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22 and R-134a. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2823-2828
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• 2007

Numerical simulation on the two-stage centrifugal compressor with Low Solidity Vaned Diffuser LSVD) for HFC-134a Turbo-chiller was performed using a commercial code. The comparative study with experimental results from other compressor was also investigated to testify the simulation schemes. The numerical analysis was separately simulated for each stage of the compressor and the effect of impeller-diffuser flow interaction was considered. Setting angle of the diffuser vane changed in the range of 15 deg. and the effects on its variation were discussed in detail including the flow analysis in the passage of the compressor. The vane setting angle obtained from the preliminary design was slightly adjusted to the optimal value by the performance enhancement in terms of pressure recovery and flow characteristics.

• 한국산학기술학회논문지
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• 제17권6호
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• pp.18-25
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• 2016

대형 압축식 냉동기의 증발기 전열관으로는 그간 평활관이 주로 사용되어 왔으나 최근들어 비등 성능이 우수한 성형 가공관을 많이 사용하고 있다. 증발기는 관군으로 구성되고 따라서 증발기 내 위치에 따라 냉매 상태가 다르다. 특히 R-11, R-123과 같은 저압 냉매는 압력변화에 따른 포화온도 변화가 크므로 위치에 따라 포화온도가 다르게 된다. 따라서 증발기를 적절히 설계하려면 증발기 내 각 위치에서의 냉매의 상태를 적절히 예측하여야 한다. 본 연구에서는 대형 냉동기의 만액식 증발기를 모사할 수 있는 컴퓨터 프로그램을 개발하였다. 이 프로그램은 증발기를 미소 체적으로 구분하고 각 미소 체적에 적절한 관 내외측 열전달 및 압력손실 상관식을 적용하여 해석을 수행하였다. 본 프로그램을 R-123을 사용하는 T사의 만액식 증발기 해석에 적용한 결과 만족할 만한 결과를 얻었다. 이 프로그램을 이용하여 신 냉매인 R-123, R-134a를 사용하는 만액식 증발기의 해석을 수행하였고 특히 관군 세장비의 영향을 검토하였다.

• 설비공학논문집
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• 제13권8호
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• pp.692-700
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• 2001

Flow boiling heat transfer coefficients(HTCs) of R22, R134a, R407C, and R410A were measured experimentally for a horizontal plain and a microfin tube. Experimental apparatus was composed of 3 main parts: a refrigerant loop, a water loop and a water-glycol loop. The test section in th refrigerant loop was made of a copper tube of 9.52 mm outer diameter and 1 m length for both tubes. The refrigerant was heated by passing hot water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of $5^{\circ}C$ with mass fluxes of 100~300 kg/$m^2$s. Test results showed that at similar mass flux the flow boiling HTCs of R134a were similar to those of R22 for both plain and microfin tube. HTCs of R407C were similar to those of R22 for a plain tube but lower than those of R2 by 25~48% for a microfin tube. And HTCs of R410A were higher than those of R2 by 20~63% for a plain tube and were similar to those of R22 for a microfin tube. In general, HTCs of a microfin tube were 1.8~5.7 times higher than those of a plain tube.

• Journal of Advanced Marine Engineering and Technology
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• 제31권3호
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• pp.224-234
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• 2007

Large diameter tubes have been used until comparatively lately. However, small diameter tubes are largely used because of their high efficiency in heat transfer and low cost, recently. This study focuses on the experimental research of the heat transfer coefficients during evaporation process of R-22 and R-134a in small diameter tubes. The evaporation heat transfer coefficients were measured in smooth horizontal copper tubes with ID 1.77, 3.36 and 5.35 mm. The evaporation heat transfer coefficients in the small diameter tubes (ID <7 mm) were observed to be strongly affected by the size of tube diameters and to differ from those of general predictions in the large diameter tubes. The heat transfer coefficients of ID 1.77 mm copper tube were higher by 20 and 30 % than those of ID 3.36 mm, ID 5.35 mm copper tubes respectively. Also, it was found that it was very difficult to apply some well-known previous predictions (Shah's, Jung's. Kandlikar's and Oh-Katsuda's correlation) to small diameter tubes. Based on the data, the new correlation is proposed to predict the evaporation heat transfer coefficients of R-22 and R-134a in small diameter tubes.

• 설비공학논문집
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• 제16권5호
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• pp.444-451
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• 2004

Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A were measured on horizontal plain and microfin tubes. The experimental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water/glycol loop. The test section in the refrigerant loop was made of both a plain and a microfin copper tube of 6.0∼6.16 mm inside diameter and 1.0 m length. Refrigerants were cooled by passing cold water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, and 300 kg/m2s. Test results showed that at similar mass flux the flow condensation HTCs of R134a were similar to those of R22 for both plain and microfin tubes. On the other hand, HTCs of R407C were lower than those of R22 by 4∼16% and 16∼42% for plain and microfin tubes respectively. And HTCs of R410A were similar to those of R22 for a plain tube but lower than those of R22 by 3∼9% for a microfin tube. Heat transfer enhancement factors of a microfin tube were 1.3∼1.9.

• 설비공학논문집
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• 제19권8호
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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.

• Tribology and Lubricants
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• 제35권4호
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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.

• 설비공학논문집
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• 제13권5호
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• pp.411-421
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• 2001

The purpose of this study is to investigate the performance of an autocascade refrigeration system by simulation and experiment using refrigerant mixtures of R744/134a and R744/290 as working fluid. Variations of mass flow rate of refrigerant, compressor work refrigeration capacity and COP with respect to mass fraction of R744/134a and R744/290 mixture were presented under different operating conditions. Performance test has been executed by ASRAE standard. Experimental results show as the composition of R744 in the refrigerant mixture increases, heating and coling capacity are enhanced, but COP trends to decrease. Experimental results are compared with those from the simulation.