Experimental Study Of Vapour Condensation On Different Cold Surfaces

The steam condensation heat transfer process exists in many fields such as energy utilization,desalination,chemical in dustry,energy and water conservation and nuclear industry.However,due to the characteristics of the phenomenon itself and the limitations of available equipment,experimental studies of steam condensation are relatively rare,and the understanding of the condensation process is not yet deep and comprehensive.Therefore,in this paper,the phase change process of vapour condensation on different cold surfaces,the growth process of droplets and the heat transfer process are investigated and analysed from an experimental point of view.Based on the above analysis,this paper focuses on the following aspects of research:(1)Study and analysis of droplet morphology and size under different conditionsThe DSA-30 Droplet Surface Analyser was used to visualise the phase change condensation process of droplets on cold surfaces and to analyse the changes in droplet morphology and size at different cold surfaces(Plexiglas(PMMA)and copper plates)and different substrate temperatures(274.15 K,280.15 K,286.15 K,292.15 K and 304.15K).It was found that the steam on the surface of Plexiglas could form bead-like droplets with distinct particles,and small irregularly shaped droplets of different sizes were formed at the initial stage of condensation on the surface of the purple copper plate,but the droplets rapidly formed a film on the cold surface as the amount of steam increased;the droplet diameter was positively correlated with the condensation time,and the lower the substrate temperature,the higher the condensation rate,and vice versa.(2)Analysis of droplet area rate and contact angle under different conditionsThe area rate and contact angle of single droplets on cold surfaces were measured using image-j image analysis software,and the curves of single droplet area rate and droplet contact angle were plotted to analyse the changes under different cold surface conditions and different substrate temperatures.The lower the substrate temperature,the larger the area rate and the larger the contact angle,and the droplet contact angle varies within a certain range under a specific temperature condition,with the average droplet contact angle ranging from28.334° to 30.010° on the purple copper surface and 78.459° to 93.540° on the Plexiglas surface.93.540°.(3)Study and analysis of droplet condensation numbers under different conditionsUsing Photoshop image analysis software,the number of droplets condensed by the vapour on different cold surfaces and at different substrate temperatures was calculated as a function of time.The study shows that the number of droplets is negatively correlated with the substrate temperature,that the number of droplets is normally distributed as the condensation proceeds,that the second generation droplets re-nucleate in the interstices of the first generation droplets and that a double peak phenomenon occurs as the condensation proceeds.(4)Study and analysis of droplet morphological evolution parameters under different conditionsThe dynamic evolution of the droplet in the condensation process on different cold surfaces and at different substrate temperatures was analysed and summarised through the changes in the dynamic dimensional parameters of the droplet during the condensation process,and the variation of the dimensionless parameter bowing coefficient with respect to the phase transition time was summarised to analyse the variation of the droplet diffusivity on cold surfaces.It is found that the diffusivity of droplets on cold surfaces is positively correlated with the substrate temperature,but the diffusivity of droplets on metallic surfaces of purple copper plates is greater than that on polymeric material Plexiglas(PMMA)surfaces at any of the studied temperatures.