Characteristic features of the evaporation of liquids

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Abstract
The evaporation rate variation of liquids (water, ethanol) is studied versus their vapour pressure. From measurements of liquid-vapour interface displacement versus time, the state change whose rate is vo at initial time-is seen to slow down before reaching a constant rate v1 under stationary working conditions. The difference between both rates increases as pressure decreases. In addition, whereas the vo(P) curves are monotonous and increasing from saturation vapour pressure to vacuum, the v1(P) curves have a typical shape, characterised by two extremums. From the simultaneous measurement of temperature to assess the endothermic character of state change, it is shown that the previous observations may be related to the occurrence of a thermal flow at interface level. The new profile of the v1(P) curves can neither be predicted nor explained from conventional expressions of evaporations rate. The present paper shows that a thermodynamic interface model involving coupling of mass and heat flows allows the features detected to be accounted for with out any ambiguity.

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