The Study On Heat Transfer And Spreading Characteristics During Droplet Impingement

Droplet impacting widely exists in life and industrial production,many engineering applications rely on it,and the dynamics and heat transfer characteristics of the droplets impacting will affect the efficiency of engineering applications.Studying the heat transfer and spreading characteristics of the droplets impacting is not only able to enrich the theory of gas-liquid flow with free interface and heat transfer,but also has guiding significance for related engineering applications.In this paper,aiming to improve the efficiency of oil-gas separators,taking oil droplets as the research object,taking numerical simulation as the main research method,combined with experimental and theoretical analysis,a systematic research was carried out to study the heat transfer and spreading characteristics during droplets impact on dry surface and liquid film.According to the different droplet viscosity,two formulas to predict maximum spreading coefficient are summarized by establishing a reliable numerical model and theoretical analysis,which can effectively improve the prediction accuracy for different droplets.By analyzing the heat exchanging amount and the temperature distribution during droplets impingement,it is found that the heat exchange amount mainly transform with the internal energy of the droplet when without phase change.The differenct temperature distribution of the droplets after heat exchange,changing the droplets' physical properties,is the reason why heat transfer characteristic has a influence on the spreading.By changing the wall temperature and the droplet temperature to study the spreading and heat transfer characteristics during the droplet impact the dry surface,it is found that spreading coefficient reduces when the temperature reduces;Compare to wall temperature,the droplet temperature has bigger influence on the droplet spreading pattern.The control variables were used to study the dynamic viscosity,surface tension coefficient,velocity gradient and contact angle of the droplets.It was found that for oil droplets,the viscosity-temperature characteristic is the main reason for the influence of heat transfer on spreading properties;When the droplet impact on the poor-invasive surface,the heat exchange rate is lower and the rebound phenomenon is more likely to occur.The spreading and heat transfer characteristics of droplets impinging on the liquid film were studied by changing the thickness of the liquid film,the temperature of the droplets and the temperature of the liquid film.The results show that when the droplet diameter and impact velocity are constant,as the thickness of the liquid film increases,the droplet spray,crown jet and wave motion will occur in sequence after the droplet impacts the liquid film.The thinner the liquid film thickness is,the higher the relative jet height is,the more obvious the jet is,but the smaller the heat exchange rate between the droplet and the liquid film is.When the droplet temperature decreases,the height and volume of the jet gradually decrease,and the proportion of jet which come from the droplet decreases.When the droplet temperature is lower,a part of the liquid film will be packed between the droplet and the wall surface.The lower the droplet temperature is,the larger the volume of the package is.As the temperature of the liquid film decreases,it gradually changes from a crown jet to a crushing motion after the droplets impact on the film.