Experimental investigation of water drop evaporation under moist air or saturated vapour conditions

Majority of studies on the drop evaporation phenomena have been realized in air atmosphere environment. Through the present experimental study, we attempt to underline the influence of the gas surrounding the drop during its evaporation in order to give some new physical elements for the modelling of drops or meniscus evaporation. This study has been motivated by the application of two-phase closed systems (heat pipes, loop heat pipes, pulsating heat pipes …), into which liquid and vapour phases are close to the saturation equilibrium state. A silicon wafer substrate, whose roughness does not exceed 3 nm, was selected for the water drop base in order to focus on the gas environment effect on the drop evaporation while reducing the roughness effect. The evaporation of a water drop put on a plane and horizontal silicon surface has been experimentally studied under atmospheric moist air and under saturated vapour conditions at 23 °C. The results show two different behaviours according to surrounding conditions, as well for the contact angle at the equilibrium state, than for the dynamic contact angle during the drop evaporation.