Experimental Study On Enhanced Coalescence-induced Jumping Of Droplets And Condensation Heat Transfer By Concave Curved Surface

Condensation heat transfer is widely used in industrial and agricultural processes,and it can effectively save energy resources to improve condensation heat transfer efficiency.During condensation process on superhydrophobic surfaces,coalescence-induced droplet jumping make the condensing droplets break away from the limitation that the traditional hydrophilic surface can only rely on gravity to induce droplet detachment,which greatly accelerates the surface droplet update frequency and strengthens the transmission.However,the conditions for the coalescence-induced Jumping of droplets are relatively harsh,and their combined size and bounce speed have a significant impact on the final droplet shedding.Therefore,it is important to study the method of enhancing droplets and bouncing to improve heat transfer efficiency.Based on this,the influence of the concave curved surface structure on the combined bounce of droplets is studied.The relationship between the concave curvature and the shape of the liquid bridge and the bounce speed is systematically studied.Through the construction of steam condensing system,the basic experimental research on the condensation process of the concave curved array structure surface was carried out.details as follows:In order to explore the relationship between the curvature of concave surface and the bounce speed of droplets of different sizes,this study prepared semi-circular superhydrophobic structures with different radii of curvature,and performed equal-size droplet merging experiments on three different droplets with a radius of 0.5.The droplets of mm were subjected to a suspension experiment.The high-speed camera is used to record the droplet merging process,and the post-processing software of the image is used to obtain the bounce speed of the droplet,and the strengthening relationship between the curvature and the droplet merging speed is summarized.The growth model of the liquid bridge radius is obtained by fitting the experimental values of the suspended liquid bridge radius,and the length of the droplet spread on the concave curved surface is further compared with the growth model of the liquid bridge radius to obtain the liquid bridge morphology of the droplet combination process on the concave curved surface feature.The design and construction of a multi-functional steam condensation heat transfer and frosting process visualization experiment system.The system collects the temperature data in the heat transfer experiment through the thermocouple,and realizes the regulation,display,processing and preservation of the whole system parameters based on the Labview software.At the same time,it can meet the visual requirements such as side shot,overhead shot and upright shot.In order to explore the influence of concave curved surface on the condensation process,the super-hydrophobic surface of concave curved array was designed and the condensation experiment under different subcooling conditions was carried out.The dynamic characteristics of the droplets on this surface and the combined bounce phenomenon were analyzed.It is found that under low subcooling conditions,the concave curved surface array with small radius of curvature has a strengthening effect on the condensation heat transfer,and the concave curved surface array with large curvature radius has no obvious effect;when the high subcooling degree,the droplet wet state is toward the Wenzel state.The transformation,the droplet merge bounce phenomenon disappears,and the strengthening effect of the concave surface disappears completely.