Prediction and simulation of two-phase pressure drop in return bends

In this paper, 325 pressure drop data points measured in return bends have been collected from the literature. The database includes 3 different fluids (R-12, R-134a and R-410A) from two laboratories. Based on this database, a new method is proposed for predicting the pressure gradient in return bends, which is the sum of the frictional pressure gradient that would be obtained in straight tubes (predicted by Müller-Steinhagen and Heck, 1986 correlation) and the singular pressure gradient (proposed equation). The proposed correlation includes only two empirical constants and exhibits the correct physical limits. Using the proposed equation, simulations have been performed to predict the effect of fluid, mass velocity and saturation temperature on the singular pressure gradient.