FLOW BOILING HEAT-TRANSFER IN VERTICAL TUBES CORRELATED BY AN ASYMPTOTIC MODEL

In flow boiling, the nucleate and convective components are superimposed by a very complex mechanism, which so far is not well understood. Two models exist in present literature, one by Chen [3] (1963), using addition of the two components with a suppression factor; and one by Shah [8] (1976), using the "greater of" the two components with a Bo-number simplified correlation. Neither model presents a satisfactory solution, as attested by the numerous methods published since then, mostly based only on regression analysis-derived correction factors. In this article a new model, based on asymptotic addition of the two boiling components, is introduced. It follows the established principles of flow boiling and converges correctly to the extremes of all parameters. Tested on the University of Karlsruhe data bank containing over 13,000 data points in vertical flow boiling, results superior to previous correlations are demonstrated.