Void fraction and two-phase pressure drops for evaporating flow over horizontal tube bundles

A study has been performed to assess the accuracy of several existing void fraction and pressure drop correlations for diabatic, two-phase, shell-side flow over a horizontal tube bundle. The void fraction predictions have been applied in the computation of the static and momentum components of the two-phase pressure drop and have been compared to measured data for diabatic, vertical, up-flow through a twenty-tube bundle evaporator for refrigerants R-134a, R-410A, and R-507A. The tests were made with bundles comprised of plain tubes, low- finned tubes, and enhanced boiling tubes. The recent correlation of Feenstra et al. [5] has been found to perform quite well. The void fraction predictions have also been compared to data for flow with oil in the refrigerant. The results show that the static pressure drop is much lower with oil due to the foaming of the refrigerant/oil mixture. Finally, by back calculating the expected frictional pressure drops from the measured data, the investigation has evaluated the leading method for predicting frictional losses for two-phase flow over tube bundles, and a new one has been proposed, applicable to low-mass velocities that are typical of flooded evaporators.