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Experimental investigation of boiling heat transfer to R-134a refrigerant Podut, Alexandru Ion

Abstract

The aim of the present investigation was to improve the understanding of the boiling heat transfer to alternative refrigerants, specifically to tetrafluoroethane (R-134a). The refrigerants are mainly used in heat transfer applications, and due to environmental limitations, a need for assessing the suitability from a heat transfer efficiency perspective of new candidates has become a priority. The heat transfer coefficient that mainly controls the heat transfer phenomenon is very dependent on the operating conditions and on the geometry of the equipment and therefore an experimental assessments of proposed alternative refrigerants are required. In order to evaluate the performance of R-134a, a significant part of the project consisted in designing and building an experimental apparatus for the heat transfer study. A closed circulation loop with heat transfer and hydraulic equipment was constructed. The apparatus was equipped with state of art instrumentation, control and data acquisition equipment. Further, subcooled boiling experiments were pursued. These were carried out based on an experimental strategy that led to a significant amount of data, limited only by the maximum mass flow rate that could be achieved. Saturated boiling experiments that followed generated a limited data bank due to technical factors. For assessing the results, several theoretical methods for predicting the heat transfer coefficient were employed. Chen's (1966) correlation was used for both subcooled and saturated boiling data validation. A different method of extending Chen's correlation to subcooled boiling, when used for verifying experimental data was proposed. Liu and Winterton (1997) and Gungor and Winterton (1986 and 1987) correlations were also employed for validating the experimental data. This exercise confirmed that the measured vs. calculated heat transfer coefficients were within the range of accuracy claimed by correlations authors and/or acceptable from an engineering perspective. Discussions and conclusions for both subcooled and saturated boiling were part of the data analysis.

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