Heat transfer coefficients for boiling mixtures: Experimental data for binary mixtures of large relative volatility

Abstract

In the process industries boiling is usually used to separate the components of a mixture. Notwithstanding, published correlations of heat transfer rates in boiling are almost always based on studies on pure substances and involve the tacit assumption that a pure compound and a mixture with the same average properties boil alike. The data presented here show that this assumption is untrue and unsafe. Heat transfer coefficients were measured in a pool boiler for fourteen binary mixtures. Included were systems which form ideal solutions and systems with strong positive and negative deviations from Raoult's law. The boiling range was larger than 170°F in all cases. In these systems with wide boiling range, boiling heat transfer coefficients are smaller, by up to thirty-fold, than the appropriate average of the coefficients for the two pure components. This is due to a diffusional resistance which appears when, as a consequence of boiling, the components are partially separated.