• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.981-989
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) are measured on a low fin tube and Turbo-C tubes at the saturated vapor temperature of $30^{\circ}C$, $39^{\circ}C$, and $50^{\circ}C$ for R22, R410A, R407C and R134a with the wall subcooled at $3{\~}8^{\circ}C$. The HTCs of all refrigerants decreased as increasing the saturation temperature from $30^{\circ}C$ to $50^{\circ}C$. This trend is due to better thermodynamic properties of the liquid phase at low temperature Beatty and Katz's prediction yielded a $20.0\%$ deviation for the low fin tube data. The heat transfer enhancement factors for the 26 fpi low fin tube and Turbo-C tubes are 4.0${\~}$5.5 and 3.0${\~}$8.1 respectively for the refrigerants tested. Finally the performance of Turbo-C tube is better than that of the low fin tube.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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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.

• Journal of Power System Engineering
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• v.21 no.3
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• pp.45-50
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• 2017

This paper presents the Coefficient of performance(COP) and mass flow ratio of cascade refrigeration system with respect to refrigerants appling to high temperature cycle. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporating temperature, condensing temperature and internal heat exchanger effectiveness in high temperature cycle. The result of this study is as follows : The COP of cascade system increases with increasing degree of superheating and subcooling, compressor efficiency and internal heat exchanger effectiveness except increasing condensing temperature. The mass flow ratio of low and high temperature cycle increases with increasing evaporating temperature and condensing temperature, but decreases with increasing internal heat exchanger effectiveness, degree of superheating and subcooling. Also, the mass flow ratio has no correlation with compressor efficiency at high temperature cycle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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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.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.148-157
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• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.729-735
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) were measured on a horizontal smooth tube at the saturated vapor temperature of $30^{\circ}C,\;39{\circ}C,\;and\;50^{\circ}C$ for R22, R410A, R407C, and R134a with the wall subcooling of $3\~8^{\circ}C$. The HTCs of all refrigerants are the highest at $30^{\circ}C,\;39{\circ}C,\;and\;50^{\circ}C$ in order. This trend is due to its excellent thermodynamic properties of the liquid phase. The measured data of HTCs were compared with the calculated ones by Nusselt's equation for a smooth tube. Measured HTCs of R22, R134a, R410A are $4.2\~7.5\%$ higher than prediction respectively while those of R407C are $15.6\~28.9\%$ lower than the prediction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.569-580
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• 1998

In this study, condensation heat transfer coefficients(HTCs) of a plain tube, low fin tube, and Turbo-C enhanced tube for CFC-11, HCFC-123, CFC-12, HFC-l34a are measured and compared against each other. All data are taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling temperature 3~8$^{\circ}C$. Test results show that HTCs of a low vapor pressure refrigerant, HFC-123, for a plain, low fin, and Turbo-C tubes are 10.5~20.5%, 8.2~12.2%, 16.5~19.2% lower than those of CFC-11, respectively. On the other hand, HTCs of a medium vapor refrigerant, HFC-l34a, for a plain, low fin, and Turbo-C tubes are 20.6~31.8%, 0.0~8.0%, 13.2~20.9% higher than those of CFC-12, respectively. For all refrigerants tested, HTCs of Turbo-C tube are the highest among the three tubes showing almost 8 times increase in HTCs as compared to those of a plain tube. Nusselt's prediction equation for a plain tube yielded 12% deviation for all plain tube data while Realty and Katz's prediction equation for a low fin tube yielded 20% deviation for all low tube data.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.4
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• pp.188-198
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• 2003

R410A and R407C are considered to be alternative refrigerants of R22 for the air-conditioners. An experimental study is carried out to investigate the effect of the change of mass flow rate on the characteristics of heat transfer and pressure drop in three row slit finned-tube heat exchanger for R407C, R410A and R22. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation heat transfer coefficient was much lower than that of R22 and R410A. On the other hand, the condensation heat transfer coefficient of R410A, near-azeotropic refrigerant mixture, was a little higher than that of R22. R410A also showed the lowest condensation pressure drop across the test section. For all refrigerants, the condensation heat transfer coefficient and pressure drop increase as the mass flux increases. The condensation heat transfer coefficient correlation proposed by Kedzierski shows the best agreement with the experimental data within $\pm$20%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.564-571
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• 2001

The present study investigated the effect of key parameters on the performance of a cascade system using R-22 and R-23 refrigerants. Experimental data for the cascade system have been compared with simulation results using thermodynamic analysis. The cascade system tested at the evaporating temperature of $-80^{\circ}C $ and the condensing temperature of$40^{\circ}C $. The key experimental parameters were the evaporating temperature of the HTC(-35, -30, -25, -20, $-15^{\circ}C $) and mass flux of the HTC(200, 250, 300kg/$m^2$s). As the evaporating temperature and the mass flux of the HTC were increased respectively, the COP and the refrigerating efficiency were increased and then decreased while the volume flow rate per unit refrigeration capacity showed the opposite trend. The maximum COP and refrigerating efficiency were obtained at the evaporating temperature of the HTC of $-25^{\circ}C $ and the mass flux of 250 kg/$m^2$s.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.4
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• pp.306-317
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• 1993

In this study, a performance comparison of scroll compressor for various refrigerants(CFC-12, HCFC-22 and HFC-134a) has been numerically carried out. The thermodynamic properties have been calculated by using the recent experimental equations and the performance has been investigated qualitatively at the same geometric specifications and operating conditions of scroll compressor. The results are as follows; HFC-134a has the highest compression ratio of 5.40. The mass flow rate of HCFC-22, which affects the cooling capacity of refrigerant system, is higher than that of other refrigerants. HFC-134a has the highest adiabatic efficiency in comparison with CFC-12 and HCFC-22.