Influence of Lubricant on Horizontal Convective Boiling in a Micro-fin Tube
Influence of Lubricant on Horizontal Convective Boiling in a Micro-fin TubeNitin N. Sawant, Ph.D.Director: J. Steven Brown, Ph.D., P.E.The goal of this dissertation is to measure local convective boiling heat transfer coefficients in a micro-fin tube operating with pure R-410A and with R-410A/lubricant mixture and to develop a "user-friendly" correlation from these data so that it can be easily applied by designers, practitioners, and researchers in the heating, ventilating and air-conditioning industry. The motivation for this study is the fact that there is little documentation in the literature of the effect of lubricant on the flow boiling heat transfer of R-410A. This dissertation represents the first, and only, study of the effects of lubricant on the heat transfer rate of R-410A during flow boiling using a fluid heating technique. (Note: all of the other studies apply the electrical resistance heating technique, which has been shown by Kedzierski (1995) to strongly influence the measurement.) One of the objectives of this study, therefore, is to provide a source of data for the boiling of R-410A in a micro-fin tube with and without the addition of a Polyol ester (POE) lubricant. The evaporative heat transfer characteristics of R-410A and R-410A/POE were measured in a fluid-heated, 9.52 mm OD micro-fin tube. Data were measured for temperatures ranging from 7.2 0C to 10 0C. Baseline performance was established by measuring the convective boiling heat transfer of pure R-410A. In addition, measurements of an R-410A/POE (99.6/0.4 by mass) mixture were taken and then compared to the pure R-410A baseline. The mean degradation in the heat transfer performance with the addition of lubricant was approximately 6.7 %.A second objective of this study is to compare the experimental data to the existing NIST database of alternative refrigerants to determine the effect of the axial bulk lubricant concentration gradient on evaporative heat transfer. The experimental data were also compared with relevant correlations of R-410A and R-410A/lubricant mixtures.A heat transfer correlation was developed from the measured data and then compared to them. The correlation predicted 70 % of the experimental data within a deviation of + 30 %. The average and absolute average deviations of the model correlation are -3 % and 25.4 %, respectively.
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