| Droplet impaction on hot surface is a common basic phenomenon in the field of industrial technology,in which droplet property,solid surface morphology and other wettability related parameters have a key impact on droplet boiling behavior and development.Relevant research will strengthen the understanding of droplet dynamics,bubble dynamics,boiling heat transfer characteristics and complex interface phenomena,which is of great significance for practical production.In this paper,a droplet impingement and boiling experimental platform was built,surfaces with different roughness were obtained by means of wire cutting technology and grinding and polishing,and dynamic wall impingement characteristics of droplet of alcohol-water mixture of deionized water and ethanol were explored,the influence of ethanol concentration,roughness and wall temperature on droplet impingement characteristics was explored,and wall impingement characteristics of droplet corresponding to different roughness were systematically analyzed.The bubble dynamics characteristics of the central jet phenomenon are discussed in depth,and the influence of roughness combined with macroscopic surface geometric constraints on the droplet spreading characteristics is explored.The main work and conclusions of this paper are as follows:(1)The influence of roughness and concentration on droplet dynamics was studied:The surface of the slow-moving wire was obtained by electric spark wire cutting,and the droplet dynamics distribution of five kinds of ethanol aqueous solution with molar concentration of 0%,20%,40%,60%and 80%on the slow-moving wire was systematically analyzed.The bubble dynamics of the central jet mode was explored,and the influence of concentration and temperature on jet parameters was systematically and quantitatively studied.The results show that the increase of ethanol concentration can promote the droplet breaking characteristics and reduce the LFP under the same roughness.The central jet flow phenomenon is divided into three stages,and the jet intensity index is proposed.The results show that the range of jet temperature increases first and then decreases with the increase of concentration.For the same type of droplets,the jet intensity increases first and then decreases with the increase of temperature.(2)The influence of geometric constraints combined with roughness factors on the spread and boiling life of the droplet in the nuclear boiling region was explored.The contact boiling phenomenon of droplets in aqueous solution was investigated experimentally by using V-shaped groove/plane obtained by two processing methods:fast wire and slow wire.The results show that there are two kinds of droplet dynamics in the V-shape:bubble coalescence and spreading mode.The superheat interval of bubble coalescence mode in V-shaped groove is narrowed by fast-moving wire processing.In particular,droplets have anti-gravity adhesion phenomenon in the spreading mode on the surface of V-shaped groove in fast-moving wire processing.Under the same structure,the life of droplets on the surface of fast-moving wire is shorter than that of LS,and the bubble aggregation and superheat range are narrower.In bubble coalescence mode,the life of V40 droplets is the shortest.The maximum spreading coefficient of V40 is the highest in bubble convergence mode,the maximum spreading coefficient of V90 is the highest in droplet spreading mode,and the lowest in contact boiling process. |
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