Experimental investigation of dynamic evaporation characteristics of liquid droplet on heated surface

Using high-speed video imaging system,the evaporation and nucleation of 5ml water droplet on copper,aluminum and stainless steel plates with temperature from 50℃ up to 112℃ were observed.The time-dependent height,wetting radius and contact angle of the droplet were measured.In film evaporation regime,the evaporation process could be divided into two stages.In the fist stage,the height and contact angle of the droplet continuously decrease,but the wetting radius of the droplet hardly alters.In the second stage,the contact angle remains constant as the preceding one,and the wetting radius rapidly approaches zero.In nucleate boiling regime,the nucleation and dynamics of the bubbles inside the droplet are strongly dependent on the surface superheat.It was found that the linear relationship between the mean heat flux of the surfaces and the temperature of the heated surfaces holds true for both regimes,and their different slopes indicate their different heat transfer mechanism.