ISSN Online: 2379-1748
ISBN Flash Drive: 978-1-56700-469-4
ISBN Online: 978-1-56700-470-0
Second Thermal and Fluids Engineering Conference
FALLING FILM EVAPORATION OF R410A OUTSIDE HORIZONTAL SINGLE TUBES AND A TUBE BUNDLE
Resumo
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].