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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

FALLING FILM EVAPORATION OF R410A OUTSIDE HORIZONTAL SINGLE TUBES AND A TUBE BUNDLE

P.H. Jin
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, 28 Xian Ning West Road, Xi'an 710049, China

C.Y. Zhao
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, 28 Xian Ning West Road, Xi'an 710049, China

J.X. Liu
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, 28 Xian Ning West Road, Xi'an 710049, China

Wentao Ji
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, Xi'an Jiaotong University, 28 Xian Ning West Road, Xi'an 710049, China

Wen-Quan Tao
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China

Abstract

This study investigated falling film heat transfer characteristics of mixture refrigerant R410A on horizontal copper tubes. A horizontal plain tube, an enhanced boiling tube and a triangular-pitch tube bundle comprised of 6 commercial boiling tubes were tested. Major results are as follows. For both plain and enhanced tubes, the effect of film Reynolds number on heat transfer coefficients is negligible at high film Reynolds number. As Reynolds number decreases to a certain value, heat transfer coefficients decrease sharply due to the occurrence of partial dryout on the outer surfaces. At the same saturation temperature, heat transfer coefficients increase with heat flux. At higher heat fluxes, the film flow rate below which dryout occurs and the related threshold film Reynolds number becomes larger. Heat transfer coefficients of the enhanced tubes are obviously higher than the plain tube. Effect of saturation temperature on heat transfer coefficients differs with heat flux. In the tube bundle, heat transfer deteriorates earlier for the tubes positioned at the lower part of the bundle due to insufficient film flow rate. Tubes of the middle column of the three columns own higher heat transfer coefficients. It is found out that for R410A, the smooth tube performs better compared with R134a while worse or comparable for the enhanced boiling tube. Heat transfer coefficients of the plain tube can be reasonably predicted by the empirical correlation of Zhao et al [14].

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