• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.10
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• pp.895-900
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• 2004

With the phaseout of CFC and HCFC refrigerants, refrigeration and heat pump systems must be redesigned to match and improve system performance with alternative refrigerants. A generalized flow model for predicting mass flow rate through short tube orifices is derived from a power law form of dimensionless parameters generated by Pi-theorem. The database for developing the correlation includes extensive experimental data for R12, R22, R134a, R407C, R410A, and R502 from the open literature. The correlation yields an average deviation of $0.3\%$ and a standard deviation of $6.1\%$ based on the present database. In addition, rating charts for predicting refrigerant flow rate through short tube orifices are generated for R12, R22, R134a, R407C, R410A, and R502.

• Proceedings of the SAREK Conference
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• 2007.06a
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• pp.228-228
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• 2007

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.20-20
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• 2004

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.3
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• pp.158-167
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• 2004

Condensation heat transfer experiments were conducted with a oblong shell and plate heat exchanger without oil in a refrigerant loop using R-134a. An experimental refrigerant loop has been developed to measure the condensation heat transfer coefficient $h_r$ and frictional pressure drop ${\Delta}p_f$ of R-134a in a vertical oblong shell and plate heat exchanger. Four vertical counter flow channels were formed in the oblong shell and plate heat exchanger by four plates having a corrugated sinusoid shape of a $45^{\circ}$ chevron angle. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature and vapor quality were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. The results indicate that the condensation heat transfer coefficients and pressure drops increase with the vapor quality. A rise in the refrigerant mass flux causes an increase in the $h_r\;and\;{\Delta}p_f$. Also, a rise in the average heat flux causes an increase in the $h_r$. But the effect of the average heat flux does not show significant effect on the ${\Delta}p_f$. On the other hand, at a higher saturation temperature, both the $h_r\;and\;{\Delta}p_f$. found to be lower. Based on the present data, the empirical correlations are provided in terms of the Nusselt number and friction factor.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.93-103
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• 1998

The nucleate boiling heat transfer experiments are performed using a ternary refrigerant R407C which is a candidate of alternatives of HCFC 22. The boiling phenomena of R-32, R-125 and R-134a which are the constituent refrigerants of R407C are also investigated. The nucleate boiling heat transfer coefficients of R407C are less than those of HCFC 22 which have the similar physical and transport properties. In our experimental pressure range, which is similar to the operational pressure of air conditioning system, the deterioration of boiling heat transfer coefficients of mixture refrigerant R407C does not appear for moderate wall superheat region. Since nucleate boiling heat transfer coefficients cannot be obtained from ideal mixing law of mixture, Thome's method was used to predict. To account for the heat flux effect and system pressure in Thome's method, the correcting factor, a(P.L1T), was introduced and obtained from experiments for ternary refrigerant R407C.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.175-183
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• 2002

Flow Condensation heat transfer coefficients (HTCs) of Rl2, R22, R32, Rl23, Rl25, R134a, R142b were measured experimentally on a horizontal plain tube. The experi- mental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water-glycol loop. The test section in a refrigerant loop was made of a copper tube of 8.8 mm inner diameter and 1000 mm length respectively. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. All tests were performed at a filed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, 300 kg/$m^2$s. The experimental result showed that flow condensation HTCs increase as the quality, mass flux, and latent heat of condensation increase. At the same mass flux, the HTCs of R32 and R142b were higher than those of R22 by 35~45% and 7~14% respectively while HTCs of R134a and Rl23 were similar to those of R22. On the other hand, HTCs of Rl25 and Rl2 were lower than those of R22 by 28 ~30% and 15 ~25% respectively Finally, a new correlation for flow condensation HTCs was developed by modifying Dobson and Chato's correlation with the latent heat of condensation considered. The correlaton showed an average deviation of 13.1% for all pure fluids data indicating an excellent agreement.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.40-40
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• 2011

특정한 엔진부하 조건에서 배기가스 및 흡입공기 대해서는 물 또는 에탄올이 R134a에 비하여 시스템 효율이 상대적으로 더 높게 나타났고, 냉각수에 대해서는 R134a가 다른 냉매에 비하여 회수되는 일률이 상대적으로 더 컸다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.3
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• pp.139-148
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• 2010

A centrifugal compressor for HFC-134a has been newly designed and developed. Flow analysis using commercial programs was used to evaluate performance and internal flow of the impeller, inlet guide vane and diffuser etc. The purpose of this study is to establish the design theory necessary to the development of HFC-134a centrifugal compressors and to supply basic data related to design by reviewing design values and experimental values through the performance test. The compressor for HFC-134a was also investigated experimentally to check compression performance. The calculated data coincide the test results of compressor. The data obtained in the present study are useful for design of HFC-134a centrifugal compressors.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.672-677
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• 2001

This study has been conducted to design the high efficiency centrifugal compressor for a HFC-134a. The 2-stage centrifugal compressor consists of inlet guide vanes, two impellers with splitters, a deswirler, a vaneless diffuser and a volute casing. We have designed the high efficiency centrifugal compressor by applying the repeated design procedure including a meanline design, a 3D geometry generation of 1st and 2nd impellers etc. Also, a fluid dynamic calculation of impellers and deswirler have been conducting using a commercial code STAR-CD.

• 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.