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.