BT-3 Boiling of Mixtures inside Vertical Tubes

J. W. Palen and C. C. Shin

This report presents HTRI work on boiling of mixtures inside vertical tubes in thermosiphon reboilers. The most important current theories from the literature on boiling of mixtures are briefly reviewed and are shown to be inapplicable in their present form for the design of reboilers. The HTRI approach is based on the mixture boiling range and is much more practical for industrial cases. A new formulation was obtained based on a physical model which is somewhat analogous to the Resistance Proration Method in condensation. The HTRI Method is compared to HTRI thermosiphon reboiler data for nine different mixtures with widely varying boiling ranges. Although prediction of the existing data by empirical correlation is good, this study emphasizes the great need for a better fundamental understanding of mixture boiling. Present knowledge, as shown by current literature, is very poor, even when compared to the still unresolved problems of mixture condensation. Basic experimentation on nucleate and convective boiling of multicomponent mixtures in simple geometries with typical industrial surfaces will be required for further progress. However, it now appears that a breakthrough in understanding of the processes involved is possible if present efforts along both experimental and theoretical lines are continued.

As in all HTRI design procedures, an attempt was made to correlate the mean of the data. Therefore, especially in such an uncertain area as mixture boiling, some safety factor should be applied in critical cases unless already present in some other form such as overly adequate fouling resistance.