In boiling mixtures it is possible that the maximum nucleate boiling heat flux exceeds that of the components considerably. This effect has been ascribed to a slowing down in the bubble growth rate.
New measurements on binary organic mixtures with differences in surface tension are reported now. The experimental results show the intluence of this difference on the 9-values. They are obtained with a platinum heating wire in a Dewar boiler without supplementary heat supply. The influence of the surface tension difference in "positive" systems is ascribed to a stabilisation of the bubbles on the heating wire as a consequence of the Marangoni effect.
This Marangoni effect is already acting in positive systems of low relative volatility. However a high increase of qmax in a negative system of high relative volatility makes it clear that the Marangoni effect is not the only extra phenomenon in mixtures.
Under the experimental conditions used here it was found that the superheating of the bath at nucleate boiling decreased to O*l"C when the load was increased to the maximum value. The maximum heat flux proved to be independent of an artticial increase of the superheating of the bath.