R245fa vertical upward flow boiling heat transfer characteristics in enhanced tube with micro-nano porous coating
For the efficient utilization of of industrial waste heat,the R245fa flow boiling heat transfer characteristics was investigated experimentally in a vertically upward tube with a micro-nano porous coating.The effects of inlet vapor qualities,heat fluxes and mass fluxes on the heat transfer characteristics in the tube were analyzed,and the flow patterns were recorded by visualization.Experimental conditions were as follows:saturation pressure 0.6MPa,mass flux 199.68-701.81kg/(m2·s),heat flux 4.99-74.96kW/m2,and vapor quality 0.01-0.9.In addition,the heat transfer coefficient and friction pressure drop of the bare tube and enhanced tube were compared.The enhanced tube had an obvious effect of enhancing boiling heat transfer,and the maximum heat transfer enhancement factor could reach 2.12 times.With the increasing inlet vapor qualities and heat flux,the heat transfer enhancement factor showed a trend of initially increasing and then decreasing.The variation trend of the performance evaluation parameter aligned closely with that of EF.The visualization showed that the strong wettability of the enhanced tube accelerated the diffusion of R245fa liquid on the tube wall surface and facilitated rapid rewetting.In comparison to the bare tube,the transition to annular flow occurred earlier in the enhanced tube.
R245faenhanced tubevertical upflow patternheat transfer characteristics
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