| Droplet impact on solid surfaces is a common phenomenon in many industrial technologies.Clarification of the dynamic characteristics of droplet impact and its influencing factors accompanied by heat transfer is of vital importance to its applications in related fields.In this paper,an experimental platform for droplet impact and heat transfer research was built up.Based on this platform,the dynamic evolution characteristics of droplets impact using deionized water,ethanol,1-butanol,and alcohol-water mixtures of different concentrations were studied.The influence of additive concentration,wall temperature and impact velocity on the impact dynamics is explored.The droplet impact characteristics in different heat transfer regimes are analyzed.The main work and conclusions of this paper are as follows.Experiments on the impact characteristics of three pure liquids,i.e.,deionized water,ethanol and 1-butanol were carried out.First,the influence of wall temperature and impact velocity on the droplet impact dynamic characteristics is analyzed.The results show that the droplet impact patterns can be categorized as deposition,deposition with boiling,rebound,rebound（break up） with atomization,and film rebound（break up） .Secondly,non-dimensional analysis was conducted to establish the impact regime maps of the three components,and to determine the variation of surface temperatures at the critical heat flux point(TCHF ) and Leidenforst point(TLFP ) with Weber number（We） .Finally,the time evolution of the droplet spreading factor βin each temperature region is analyzed,and the variation of the maximum spreading factor βmax is presneted along with the cloud diagram of the βmax distribution.It is found that the spreading characteristics of alcohol droplets are always better than deionized water in various temperature regions.The impact characteristics of ethanol solution droplets were also experimentally studied.Firstly,the influence of ethanol concentration,wall temperature and impact velocity on the dynamic characteristics is analyzed.The results show that ethanol additives significantly enhance the spreading,atomization and breakup characteristics in various temperature regions.Secondly,the dynamic characteristics distribution diagram of the ethanol solution droplets was established,and the variation of TCHF and TLFP was also determined.Compared with the deionized water,it is found that ethanol significantly improves the TCHF and TLFP of the mixture droplets.Finally,the evolution of the spreading factor βwas analyzed,and each influencing factor on the βmax of ethanol solution droplets was studied with established maximum spreading factor βmax cloud diagram.The analysis found that the βmax of ethanol solution droplets was always higher than that of deionized water at similar We.Therefore,it is concluded that the ethanol additives can effectively improve the droplet spreading performance.Last,experiments were conducted to study the impact characteristics of 1-butanol solution droplets.First,by analyzing the dynamic characteristics of the 1-butanol solution droplets,the distribution diagram of the dynamic characteristics was established.Compared with ethanol,1-butanol additive enhances the atomization and breakup more obviously in the transition boiling region.Secondly,the variation of TCHF and TLFP of 1-butanol solution droplets with We was also determined.Compared with ethanol,1-butanol increases the TLFP more significantly.Finally,the time evolution of βwas analyzed,and the effects of various factors on βmax of 1-butanol solution droplets were studied.Similarly,the maximum spreading factor βmax cloud diagram was established for the 1-butanol solution.It is shown from the analysis that the βmax value of 1-butanol solution droplets is always higher than ethanol solution and deionized water with similar We.It is concluded that the 1-butanol additive can effectively enhance the atomization and breakup ability,improve the spreading performance and the heat transfer ability between droplets and the solid surface. |
PDF Full Text Request