Effect of droplet size on the jet breakup characteristics of n-butanol during impact on a heated surface

Jet breakup during droplet impacted on heated surface has received wide concerns due to its regularity.The Weber number(We)is a common used dimensionless parameter to classify and analyze the phenomenon,but it is unable to summarize all detailed phenomenon variations and related theory.Thus,the effect of droplet size on jet breakup was investigated by considering its significant difference in various scenarios.The behavior of n-butanol droplets with diameter range from 1.71 mm to 2.84 mm impacts a heated surface with jet breakup was recorded by backlit technology.Three parameters,the jet breakup time,the jet breakup length and the jet ligament diameter,were analyzed to illustrate the phenomenon.The results showed that these parameters are affected by the droplet size largely at 10<We<35,but affected lightly at higher Weber numbers.The sub-droplet diameter reduces with Weber number for all initial size droplets while the larger initial droplet corresponds to larger sub-droplet.The breakup time,breakup length and jet liga­ment diameter increase with the initial diameter.The time of jet breakup versus agrees well with the theory of Rayleigh instability regardless of droplet diameter.In addition,the jet breakup phenomenon was observed to evolve into pancake bouncing with an ultrafine high-speed jet when the We was above 50.