Experimental data for the evaporation coefficients of water have indicated a scatter over four orders of magnitude. One source of uncertainty in the data is probably the temperature at the liquid-vapour interface; recently published results in an axisymmetric geometry show temperature jumps of several ℃ at the free surface of evaporating water, contradicting the established assumption of a unique temperature in the liquid and vapour phases at the interface. In an apparatus with a two-dimensional geometry, temperature profiles in both phases near the interface during steady state evaporation confirm the earlier measurements and indicate the suitability of the apparatus for measurements close to the interface.
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