• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.9
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• pp.744-750
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• 2003

The performance of adiabatic capillary tubes are measured to provide the database for a generalized correlation. Test conditions and capillary tube geometries are selected to cover a wide range typically observed in air-conditioning and heat pump applications. Based on extensive experimental data for R22, R290, and R407C measured in this study, a generalized correlation for refrigerant flow rate in adiabatic capillary tubes is developed by implementing dimensionless parameters for tube inlet conditions, capillary tube geometry, and refrigerant properties. The correlation yields good agreement with the present data for R22, R290, and R407C with average and standard deviations of 0.9% and 5.0%, respectively. In addition, approximately 97% of the data for Rl2, R134a, R152a, R410A, and R600a obtained in the open literature are correlated within a relative deviation of $\pm$ 15%.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.301-306
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• 2011

The paper presents an analysis of the heating cycle and discusses a desalination cycle that uses lowtemperature seawater. The basic heating cycle model is the heat pump cycle, and seawater desalination is usually performed by the indirect freezing desalination method. The low temperature of the seawater (below $5^{\circ}C$) acts as the heat source of the evaporator. R-134a, R-1234yf, R-600a are used as working fluids. In the 2-stage compression cycle, the compressor's work decreased by about 15.6% from that in the 1-stage compression cycle. Further, the COP in the 2-stage cycle was 17.6% higher than that in the 1-stage cycle. In the indirect desalination cycle, the energy per unit fresh water productivity in the 2-stage cycle was 19.8% lower than that in the 1-stage cycle.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.42-47
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• 2014

In this paper, the cycle performance analysis for the COP of supercritical heat pump using various refrigerants is presented to offer the basic design data for the operating parameters of the system. The working fluids are R134a, R22, R32, R290, R600, R600a, R1270 and R744. The operating parameters considered in this study include superheating degree of evaporator, temperature of gas cooler inlet and outlet, compressor efficiency and evaporating temperature in the supercritical heat pump system. The main results were summarized as follows : Superheating degree, temperature of gas cooler inlet and outlet, compressor efficiency and evaporating temperature of supercritical heat pump system have an effect on the COP of this system. With a thorough grasp of these effect, it is necessary to design the supercritical heat pump using R134a. And, in comparison of COP of supercritical heat pump using various refrigerants, R32 and R600 is the highest, and R744 is the lowest among other refrigerants. From these results, it is confirmed that the COP of supercritical heat pump using R744 is higher than that using freon refrigerants such as R32 and R134a.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.119-125
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• 2003

An experiment study on pressure drop was carried out for both an adiabatic and a diabatic two-phase flow with pure refrigerants R134a and Rl23 and their mixtures as test fluids in a uniformly heated horizontal tube. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. The measured frictional pressure drop was compared to a few available correlations. Homogeneous model considerally underpredicted the present data for mixture as well as pure component in the entire mass velocity ranges employed in the present study, while Friedel correlation was found to satisfactorily correlate the frictional pressure drop data as compared to other correlation.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.71-79
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• 2003

The goal of this paper is to measure and compare the performance of solar heat pump for refrigerants. To accomplish the goal, solar heat pump with aluminum roll bond type evaporator and indoor heat exchanged(condenser) was built. The test results showed that the COP and heating capacity of HFC-32/125/134a(23/25/52 wt%, $CH_2F_2/CF_3CHF_2/CF_3CH_2F$) were higher than those of HCFC-22$(CHClF_2)$. A study proved that best conditions to use heating system that is about $40m^2$ and $80m^2$. The COP range of the whole system was from 4 to 6 according to the solar collector's area variation. Hydrochlo-rofluorocarbon HCFC-22$(CHClF_2)$ is included in the compound to be controlled. HFC-32/125/134a(23/25/52 wt%, $CH_2F_2/CF_3CHF_2/CF_3CH_2F$) is the most suitable replacement HCFC-22$(CHClF_2)$ in solar heat pump application. The solar heat pump system was designed to show the best efficiency that the room temperature make $18\sim20^{\circ}C$ and $23\sim25^{\circ}C$ in Seoul during the fall season.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.581-584
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• 2007

(HFC(hydrofluorocarbon, 수소불화탄소)는 오존층 파괴 지수가 낮기 때문에 CFC(chlorofluorocarbon)의 대체 물질로 냉매와 발포제로 널리 사용되고 있는 물질이다. 하지만 HFC는 지구온난화 지수가 높은 기체이므로 대기중으로 방출되는 것을 막기 위해 분리/회수하여 재활용하는 것이 중요하다. 본 연구에서는 공기와 HFC의 혼합기체로부터 HFC만을 분리해 내는 방법으로 가스 하이드레이트 형성법을 제안하였다. 이 방법의 열역학적 타당성을 검증하기 위하여 질소+HFC-134a 혼합기체에 대하여 275-285 K의 온도 범위와 1-27 bar의 압력범위에 걸쳐서 가스 하이드레이트 상평형을 측정하였다. 질소는 가스 하이드레이트를 형성하기 위하여 0 $^{\circ}C$에서 150 bar 이상의 높은 압력이 필요한 반면 HFC-134a는 대기압에 가까운 낮은 압력이 필요하다. 두 기체의 평형 압력의 차가 크다는 것은 가스 하이드레이트 형성법을 이용할 경우 기체의 분리 효율이 매우 높다는 것을 나타낸다. 그리고, 본 실험을 통해서 얻어진 혼합기체의 하이드레이트상(H)-액상($L_W$)-기상(V)의 3상 평형선이 순수한 HFC-134a의 3상 평형선에 가깝게 위치하였다. 이는 가스 하이드레이트를 이용한 분리법이 낮은 압력에서 운전될 수 있음을 나타낸다. 이 분리법은 낮은 압력에서 운전되어 경제적일 뿐만 아니라 물 이외의 다른 매개체를 사용하지 않기 때문에 환경 친화적인 공정이라 할 수 있다.

• Journal of Hydrogen and New Energy
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• v.33 no.4
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• pp.413-418
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• 2022

This paper presents two-phase condensation heat transfer and pressure drop characteristics of R32 and R454B as an alternative refrigerant to R410A in a 9.52 mm OD microfin tube. The test facility has a straight, horizontal test section with an active length of 2.0 m and is cooled by cold water circulated in a surrounding annular space. The heat transfer coefficients of the annular space were obtained using the modified Wilson plot method. Average condensation heat transfer coefficient and pressure drop data are presented at the condensation temperature of 35℃ for the range of mass flux 100-400 kg/m²s. The average condensation heat transfer coefficients of R32 refrigerant are 35-47% higher than R410A at the mass flux considered in the study, while R454B data are similar to R410A. The average pressure drop of R32 and R454B are much higher than R410A and they are 134-224% and 151-215% of R410A, respectively. R32 and R454B have relatively low GWP and high heat transfer characteristics, so they are suitable as alternatives for R410A.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.39-49
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• 2000

This paper presents the modeling approach that can predict transient behavior of rotary compressor. Mass and energy conservation laws are applied to the control volume, real gas state equation is used to obtain thermodynamic properties of refrigerant. The valve equation is solved to analyze discharge process also. Dynamic analysis of vane and roller is carried out to gain friction work. From the above modeling, the performance of rotary compressor with radial clearance and friction loss is investigated numerically. The performance of each refrigerant is estimated, respectively by applying R12, R134a, and R290/ R600a mixture.

• Proceedings of the KAIS Fall Conference
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• 2012.05b
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• pp.583-586
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• 2012

현대의 지속적인 기술개발과 산업발전은 삶의 질을 향상시키는 긍정적인 시각이 있는 반면 심각한 환경문제를 안고 있다. 자동차 공조기술도 지구 환경보호라는 거대한 과제와 탑승자의 쾌적성 만족이라는 두 가지 다른 관점을 동시에 충족시켜야 하는 과제를 가지고 있으며, 이 분야 산업에 전문적인 지식으로 공조 열량계 운용에 대한 경험이 대학 교육과정에서도 강조되고 있다. 본 논문에서는 대학 교육과정 특성상 장비의 활용성, 경제성, 장비설치 및 취급의 용이성 등을 고려하여 교육용으로 적합한 간이 열량계를 제작하였다. 교육 및 연구용으로 제작한 간이 열량계의 타당성을 확인하기위해 현재 가장 많이 쓰이고 있는 R134a 자동차용 냉방시스템을 구성하여 압축기 회전속도, 실내 풍량, 냉매 충전량 등을 변수로 하여 열교환기 냉방성능을 평가한 후 비교하여 교육용 열량계의 유용성을 확인하였다.