Study On Flow And Heat Transfer When Droplet Impact On Cylindrical Outer Surface With Airflow

Droplet impacts on heating surface widely exists in industrial and agricultural production process,because the process has a strong heat transfer and has an important influence on the effective operation of related equipment.At present,the academic circles on the droplet impacting at room temperature horizontal wall has been carried out comprehensive and in-depth research,but for the droplet impact on heating non horizontal wall,especially the research of droplet is influence by airflow and can not vertically hit the wall is very few,and the flow and heat transfer characteristics need to be further explored,Therefore,numerical simulation method is used to study the dynamic and heat transfer processes of droplet impacting on the outer cylindrical surface.The three-dimensional numerical simulation of droplet impacts on cylindrical surface is carried out by using the CLSVOF method and the phase transition model.The morphological changes and heat transfer characteristics of the droplet in the generatrix and the diameter direction are analyzed,and the reason of the droplet rupture was summarized As well as the relationship between the rupture position and the impact velocity.And the validity of the model is verified by comparing the simulation results with the experimental data.Based on the analysis of droplet velocity vector,morphological phase diagram,temperature distribution and wall heat flow diagram,it is concluded that droplet spreads at the three-phase contact line and the droplet rupture have large disturbance,which strengthen the heat transfer between the droplet and the wall,the two positions temperature rise fast.The effects of wall temperature,contact angle,impact velocity and curvature ratio on the spreading of the outer cylindrical surface and the evaporation heat transfer were analyzed.The results show that the influence of wall temperature on the evaporation of droplets is small,but the contact angle and impact velocity have a great influence on the droplet evaporation,and the smaller the contact angle is,the greater the impact velocity is The faster the evaporation rate is;The force analysis of the movement process of the droplet with different curvature ratio is carried out.It is pointed out that the greater the curvature ratio is,it is obvious that the gravity force of droplet itself promotes the spreading process which is benefit to heat transfer between droplet and surface,Especially the curvature ratio is 0.5,the heat transfer between them is much stronger than the other two sets of parameters.Three-dimensional numerical simulation of the droplet impact on outer cylindrical surface,Through the analysis of the droplet spreading process,we can get that the smaller the airflow velocity,the smaller the radial displacement of the droplet from the impact point,and the smaller the airflow,the effect of weak the reverse spreading is smaller which is helpful to droplet spread.In the case of heat transfer,the smaller the airflow velocity,the greater the wall heat flux density at the point of the three-phase contact point of the droplet and the highest point in the center of the droplet,and the larger the average heat flux.In summary,the smaller the airflow velocity,the more favorable the heat transfer between the droplet and the surface.