Coalescence Of Droplets Laden With Insoluble Surfactant

Energy saving and emission reduction are the inevitable requirements of the current development of industrial technology.Effective improvement of the heat transfer performance is one of the important measures.Dropwise condensation has become a potential and intensive heat exchange method,and the droplets coalescence process has a significant effect on the condensation droplets movement and heat exchange performance on heat exchange surfaces.In addition,the speed and effect of droplets coalescence are also important factors determining the quality of ink jet print and emulsifier polymerization.Therefore,it is extremely important to investigate the characteristics of droplets coalescence and main influencing factorsBased on the lubrication theory,the coalescence models of droplets containing insoluble surfactant on flat substrate,topographic substrate and inclined topographic base are established and the coalescence processes are simulated.The role of the surfactant and its inherent mechanism are investigated,and compared the impact of different parameters on the coalescence process.The main contents are as follows:(1)A model for the evolution of two droplets laden with an insoluble surfactant coalescing on a preset film is established according to lubrication theory,and the coalescence processes are simulated.The role of surfactant and inherent mechanism are investigated,the effects of the Marangoni number,the initial spacing between the two droplets on the coalescence and the preset liquid film thickness are examined.(2)A model for the coalescing evolution of two droplets laden with an insoluble surfactant on the topographic substrate is established,and the coalescence features are simulated numerically.The effects of spacing,wave number and base height on the characteristics of coalescing are revealed.(3)Based on the lubrication theory,the coalescence of two surfactant-containing droplets on inclined topographic substrate is modeled.The numerical simulation are compared with the experimental results,and the influence of surfactant and substrate on contact line movement is clarified.The effects of substrate tilt angle,preset film thickness and Bond number on the property of coalescing are discussed.