Determination of diffusion coefficient-vapor pressure product of some liquids from hanging drop evaporation

Drop evaporation experiments were performed in still air for 11 liquid drop s, and the results were expressed by using the drop half-life time method. This method was found to be useful to judge the importance of the related f actors such as vapor diffusion coefficient and vapor pressure of the liquid and the temperature decrease on the drop surface. (Drop weight)(2/3) versu s time plots were drawn and clearly linear plots over the drop half-life we re obtained. The product of diffusion coefficient and drop surface vapor pr essure DPv* was calculated from the experimental drop mass decrease data an d a proportionality was found between the DPv* product and the vapor pressu re of the drops at the ambient temperature. DPv* product is found to be a u seful parameter to determine the peripheral contact angle during following the evaporation of sessile or pendant drops on solid surfaces. The surface temperature of drops was calculated using DPv* product and by assuming the heat transfer is only by conduction. Considerable surface cooling was found for liquid drops having high vapor pressures. A new procedure is also prop osed to calculate the partial water vapor pressure during evaporation in hu mid air and the corresponding decrease in water drop surface temperature.