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ACRC Technical Report 84PDF


Title:Evaporative Heat Transfer and Pressure Drop Characteristics of Refrigerant-Oil Mixtures
Author(s):Shimon, R.L.
Contributor(s):Chato, J.C.; Villaneuva, T.C.; DeGuzman, N.M.; Ponchner, M.; Sweeney, K.A.; Rhines, N.L.; Allen, D.G.; Hershberger, T.T.
Subject(s):geometric variables
R-22 alternatives
refrigerant-side evaporation condensation studies
Abstract:This study investigates flow boiling heat transfer and pressure drop characteristics of mixtures of R-134a and an ester based lubricant. Nominal oil concentrations of 1 %, 3%, and 5% are tested. Experimental heat transfer coefficients and pressure drops are collected over a wide range of flow conditions. The two-phase flow regime is observed visually. The oil has a significant impact on both heat transfer and pressure drop. Small concentrations of oil enhance the heat transfer coefficient. The enhancement is observed for all oil concentrations tested; however, the enhancement is decreasing at an oil concentration of 5%. The enhancement is attributed to several factors including the promotion of an annular-type flow pattern at low to moderate flow rates, the degradation of the nucleate boiling contribution at the same flow rates, and foaming at higher flow rates. The presence of small amounts of oil also increases the pressure drop. This increase is seen at all oil concentrations tested. The magnitude of the increase continues to rise with oil concentration. Factors influencing the pressure drop are the increase in the mixture viscosity, the promotion of an annular-type flow pattern, and foaming. Mixture properties are used in both a heat transfer correlation and a pressure drop correlation to determine the effects of the thermophysical property changes of the mixture. The results indicate that in order to accurately predict refrigerant-oil data, effects other than just property variations must be taken into account. General correlations must properly account for the flow regime effects and foaming.
Issue Date:1995-08
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-84
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Center Project 37
Date Available in IDEALS:2009-04-20
Identifier in Online Catalog:3929451

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