• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.64-67
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• 2006

Drop-in tests were conducted using R290/R32 (31:69) or R290/DME (65:35) mixture in a ice-cream maker for possible replacement of R-502 and R-404A. At the standard room temperature ($20^{\circ}C$), the time required for initial ice-cream making was 4'7' for R290/32, 4'39' for R404A and 4'59' for R290/DME. The electric energy consumed was 436 kJ for R290/32, 425 kJ for R404A and 439 kJ for R290/DME. The mass flow rate as well as the temperature and pressure data are also provided.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.730-740
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• 1996

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW$^2$. Mass fluxes are set to 424 ~ 742kg/m$^{2}$s for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/m$^{2}$s for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.719-725
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• 2017

Frozen milk products are commonly made in small refrigeration machines. R-502 has long been used as a refrigerant for soft ice cream machines, but it is being replaced with R-404A due to the issue of ozone layer depletion. However, R-404A has high global warming potential, so it also needs to be replaced. In this study, a mixture of R-290 and R-32 was considered as a new refrigerant. An optimization and performance evaluation of the mixture were conducted for a freezer volume of 2.8 liters. The focus of the optimization was the appropriate refrigerant charge and the opening of the expansion valve. At the optimized conditions, ice cream was produced in 6 minutes and 24 seconds with the mixture, and the COP was 0.83. For R-404A, the ice cream production time was 6 minutes and 22 seconds, and the COP was 0.90. The results may be used for the design of food refrigeration machines and to optimize other refrigeration cycles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.1
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• pp.47-53
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• 1994

Cycle simulation of the air-conditioner was carried out using a number of candidate alternatives to R22;R32/R125/R134a(30/10/60, by mass percent), R32/R125/R134a(10/70/20), R32/R134a(25/75), R32/R134a(30/70), R32/R125(60/40), R290(propane) and R134a. In this study, we considered only the basic parts of the air-conditioner such as the compressor, the evaporator, the condenser and the capillary tube, for the purpose of analysis. The performance characteristics of alternatives considered here were examined by comparing with the case using R22 at the constant volumetric flow rate condition. The results of our analysis revealed that the use of refrigerant mixtures, R32/R134a(30/70) and R32/R125/R134a(30/10/60), was appropriate for the alternatives to R22 in view of the cooling capacity and the COP. For the case of using R134a and R290, the COP was observed to increase under the same volumetric flow rate condition, but the cooling capacity was substantially decreased. Therefore the use of R134a and R290 should be accompanied with increasing considerably the size of compressor in order to maintain the same cooling capacity of R22.

• Proceedings of the SAREK Conference
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• 2005.11a
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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.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.268-273
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• 2005

Because of environmental issues caused by CFC, HCFC or HFC refrigerants, new alternative refrigerants has gained a significant attention. This paper presents experimental information on heat transfer coefficient and pressure drop behavior during evaporation process of R32/290 mixtures in a horizontal smooth tube. A smooth tube with outer diameter of 5 mm and length of 5 m was selected as a test tube. Heat transfer coefficients and pressure drop characteristics were measured for a range of mass fluxes from 497 to 994 $kg/m^2s$, heat fluxes from 12 to 20 $kW/m^2$ and for several mixture compositions(100/0, 75/25, 58.4/41.6, 2s/75, 100/0 by wt% of R32/290). The differences of measured heat transfer characteristics among various R32/290 refrigerant mixtures were analyzed for various compositions.

• Journal of Hydrogen and New Energy
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• v.32 no.5
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• pp.356-364
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• 2021

During the hydrogen fueling process, hydrogen temperature inside the compressed tank were limited below 85℃ due to the allowable pressure of tank material. The chiller system to cool compressed hydrogen used R407C, greenhouse gas with a high global warming potential (GWP), as a refrigerant. To reduce greehouse gas emission, it should be replaced by refrigerant with a low GWP. This study proposes a chiller system for fueling hydrogen with R290, consisted in propane, by applying the C3 pre-cooled system use d in the LNG liquefaction process. The proposed system consisted of hydrogen compression and cooling sections and optimized the operating pressure through exergy analysis. It was also compared to the exergy efficiency with the existing system at the optimal operating pressure. The result showed that the optimal operating pressure is 700 kPa in 2-stage, 840 kPa/490 kPa in 3-stage, and the exergy efficiency increased by 17%.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.10.2-10.2
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• 2005

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.2
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• pp.254-266
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• 1996

Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

• 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 $20^{\circ}C$.