THE EFFECT OF SURFACTANTS ON HEAT AND MASS-TRANSFER TO WATER DROPS IN AIR

Water drops doped with the soluble surfactants sodium stearate, sodium palmitate, sodium myristate and sodium laurate were suspended on fine glass fibres or thermocouples and evaporated under conditions of controlled temperature and humidity. The kinetics of evaporation followed those of pure water initially but then showed relatively abrupt transitions to lower evaporation rates. The behaviour of sodium stearate was described convincingly in terms of a diffusional resistance at the surface coupled with vapour pressure lowering due to the presence of the solute. However, the behaviour of the shorter-chain soaps could not be explained in the same terms. Heat transfer rates to the drops were unaffected by the surfactants.