Two-Phase Flow Pattern Map for Evaporation in Horizontal Tubes: Latest Version

Abstract

A two-phase flow pattern map was originally proposed by Kattan, Thome, and Favrat as part of a new flow pattern-based flow boiling model for predicting local heat transfer coefficients during evaporation in horizontal tubes in the fully stratified flow regime, the stratified-wavy regime, the intermittent flow regime, the annular flow regime, and for annular flow with partial dryout. Zürcher, Thome, and Favrat improved on this flow pattern map by empirically correcting two of the transition boundaries based on extensive new flow pattern observations for ammonia, but it still requires an iterative solution of numerous equations. Zürcher, Favrat, and Thome have since proposed an even more detailed method for predicting flow pattern transitions by taking into account the intertwined effects of void fraction on flow transition and flow pattern on void fraction, resulting in a map that is very effective but very complex to implement. In the newest version of this map, the goal of which was to simplify the method to avoid iterative calculations as much as possible while retaining its accuracy, the Rouhani and Axelsson void fraction equation is used in the transition equations rather than the original method of Taitel and Dukler in this map. This provides a simpler method for calculating the transitions and gives equivalent results. Simulated flow maps for R-134a, R-22, and R-410a are shown here, as well as the effect of tube diameter on the transition boundaries. Future directions in flow map developments are discussed, such as the application of this map to intube condensation.