Research On The Heat Transfer Characteristic Of Vapor Mixtures Marangoni Condensation Caused By Concentration Gradient

Steam condensationexists generally in nature and human’s life, and steamcondensation heat transfer is the common phase change heat transfer process in thefields of nuclear power, steam power, petrochemical, refrigeration and airconditioning. The so-called Marangoni condensation is caused by the localconcentration gradient. Marangoni condensation is different from the filmcondensation and dropwise condensation and the heat transfer may be greatlyenhanced in certain working conditions. In this paper, the characteristic curves ofMarangoni condensation heat transfer, the shape and unstable feature of condensatefilm, thethermal resistance of condensate film and vapor film and the effect of thenon-condensable gas on heat transfer were investigated.A condensation heat transfer experimental system with high air tightness wasestablished to obtain the Marangoni condensation heat transfer characteristics and thecondensate images. The characteristic curves of ammonia-water Marangonicondensation heat transfer showed a nonlinear variation along with the surfacesubcooling and had peak values. There was an optimal ammonia concentration rangenear0.38%that heat transfer coefficient (HTC) and heat flux reached maximu. Incertain surface subcooling range, the addition of a vary little amount of ammonia tothe steam could greatly enhance the condensation heat transfer. The HTC increasedalong with the vapor velocity and the surface subcooling corresponding to the peakvalues of HTC had nothing to do with the vapor velocity.The Marangoni condensation HTC and condensate mode were influenced by theconcentration and surface subcooling. The measurement and calculation on the dropsize of the ethanol-water Marangoni condensation revealed that the drop size was adiscontinuous variable and the drop size distribution showed a good agreement withthe Rosin-Rammler model. The nonlinear feature of the Marangoni condensation heattransfer characteristic curves was explained from the point of view of the liquid filmcoverage.The experimental results proofed that he HTC of ethanol-water binary systemwere higher than that of the ammonia-water binary system. It could be attributed tothe difference of condensate instability and the diffusion thermal resistance between the two binary systems. Through the quantitative calculation of condensate instabilityand diffusion thermal resistance of the two binary systems, the mechanism of theMarangoni condensation caused by the concentration gradient was analysised.The effect of non-condensable gas on the characteristic of Marangonicondensation heat transfer was studied. The results showed that the HTC couldgreatly decreased by a little bit increase of the non-condensable gas in the range of thelow concentration of non-condensable gas. The influence of the non-condensable gason the HTC was very obvious in the peak value range of HTC.