Analysis Of Secondary Splash Characteristics Of Continuous Impinging Jet Droplets On The Wall Surface

With formulation of the “Double Carbon” target,the biomass oil,as a novel liquid fuels,becomes increasingly important due to its advantages,such as renewable,high energy density,good fluidity,and zero carbon emission.As spray is still the dominate utilization of liquid fuel,the phenomena of the droplet break-up and splash caused by the impact of jet droplets on the wall are a typical pattern.The morphology of droplet break-up and splash and their behaviors have an important influence on the subsequent heat transfer,evaporation,and even combustion.This further indicates that it has significant importance for improving the clean utilization of biomass fuel.This paper is supported by the Natural Science Foundation of Zhejiang Province,China(Approval No.LY15E06007),the Innovation Ability Promotion of Small and Medium-sized Technology-based Enterprises in Shandong Province(Approval No.2021TSGC1339)and the Basic Scientific Research Business Fees of Universities in Zhejiang Province(Approval No.GK199900299012-020).The dynamic behavior and morphology of the continuous droplets impacting on the wall were experimentally studied in terms of our experimental setup of jet droplets.A novel model was developed for impact of jet droplets on the wall,and its simulation was carried out.The main research contents are as follows:(1)Preparation and physicochemical properties of mixed oil(camellia oil/gasoline).Including: a)Different(camellia oil/gasoline)blends are formulated in terms of the volume ratio of raw materials.b)Physicochemical properties of mixed oil(camellia oil/gasoline)under different proportions were analyzed,and the basic physical parameters,liking density,viscosity,surface tension,and wettability,were obtained.c)The influence of temperature and raw material ratio,etc.is analyzed.The results show that with the increase of camellia oil content,the density,viscosity,surface tension and contact angle of the(camellia oil/gasoline)mixture oil increase accordingly.The increase in temperature reduces the viscosity,surface tension and contact angle of the(camellia oil/gasoline)oil mixture.(2)Splash diffusion characteristics of jet droplets impacting on wall surface.The influences of driving pressure,impact height and wall size were analyzed.The experimental results show that the splash diffusion caused by the droplets impact on two walls is significantly different.For the flat impact surface,the maximum diffusion diameter of the impact splash gradually increases with increasing the impact height,and then slightly decreases.Wall size mainly affects the splash spread of droplets upwards.When the impact surface is spherical,the impact height has no obvious effect on the droplet breakage splash diffusion.The wall size mainly affects the maximum diameter of the droplet splash spread.On both impact surfaces,the greater the drive pressure,the greater the maximum diameter of the droplet splash spread.(3)Splashing droplet size characteristics of jet droplets impacting on wall.The particle size distribution of secondary droplets at different positions was analyzed in the splash region.The influence of driving pressure and impact height were analyzed by focusing on the size distribution of secondary droplets.The experimental results show that,for the flat impact surface,the secondary droplet size is below 100μm with its peak locating at 30-40μm,indicating a better impact spray effect.The further distance away from the impact point in the horizontal direction is,the smaller the secondary droplet size,and the smaller the particle size above the impact point.With the increasing driving pressure,the secondary droplet size the with the peak frequency distribution becomes smaller,whereas the distribution range of secondary droplet size becomes larger.Interestingly,for spherical impact surface,the overall particle size of the secondary droplet is relative smaller.(4)Spatter rate of the secondary droplets of the jet droplet impact on wall.The influences of driving pressure,impact height,wall size,and nozzle aperture were analyzed.The experimental results show that the droplets have a good spatter rate,and the highest spatter rate reaches to 71%.The spatter rate of secondary droplets increases with increasing the impact height.The spatter rate is highest when the drive pressure p= 0.5 MPa.The larger the wall size,the lower the splash rate of secondary droplets.The larger the nozzle aperture is,the higher the splash rate of the secondary droplets.For spherical impact surface,the influence of various factors on the secondary droplet spatter rate is similar to that of the flat impact surface.(5)A novel numerical model of break-up and splash of continuous droplet impact on the wall was established by adopting the volume-to-discrete phase model(VOF-toDPM)transition mechanism.According to the adaptive mesh refinement method,the development and break-up of the gas-liquid interface is predicted by VOF method,and the motion trajectory of secondary droplets was tracked by the DPM method.Compared with those of experimental results,the effectiveness and accuracy of the model were validated.Their results agree with each other very well.The highlights in present work are as follows: a)The splashing morphology along with its behavior of continuously jet droplets impact on the wall was firstly investigated.b)Variation rule of the splashing droplet was obtained.b)A novel numerical model of breakup and splashing of continuous droplet impact was established in terms of VOFDPM method.