Evaporation Rate of Water from Glass Surface Under Natural and Forced Convection

This article discusses the question of calculating of evaporation rate of water from glass surface at the final stages upon natural and forced convection at atmosphere pressure in isothermal conditions. Petri dish was used as glass surface. At the end of evaporation of single-component liquid (water) position of experimental points in the liquid weight–evaporation time plot deviates from linear dependence. This deviation characterizes gradual decrease in amount of evaporated moisture per equal time intervals and does not imply decrease in evaporation rate. The evaporation rate corresponds to the rate of mass transfer expressed in kg/(m2 ·s). Water placed into Petri dish is referred to wetting moisture (free moisture), its evaporation rate equals to evaporation rate of water from free surface. Initial evaporation surface is the same as the surface of the water mirror placed into Petri dish. During evaporation water does occupy not the entire surface of the bottom of the Petri dish, but only a certain part of it, wherein evaporation surface (mass transfer surface) is the surface of water bordering on the air. Article accepted that relative variation of mass transfer surface area is proportional to relative variation of moisture weight with certain coefficient of proportionality. The proposed dependence in the first approximation is accepted to be linear. Calculated decrease in water weight in time with consideration for the introduced adjustment agrees with experimental data obtained under natural and forced convection. Evaporation rate increases during water heating and remains constant during overall evaporation process.