An improved Müller-Steinhagen and Heck model for two phase pressure drop modelling at high reduced pressures

Abstract

A better understanding of the two-phase fluid behaviour is necessary to optimize the design models of the components containing a two-phase refrigerant especially in the light of the fact that more and more applications are sought in the region of high reduced pressure values, for instance a vapor generator, a key heat exchanger in Organic Rankine Cycle system or high temperature heat pump. Nowadays we seek implementations at high evaporation saturation temperatures where the refrigerant transformation to vapour occurs at temperatures higher than 90oC. However, a literature analysis shows that there is a gap in knowledge of the two-phase flow for synthetic refrigerants at high saturation temperatures. The reliable prediction of pressure drop in two-phase flows is an important prerequisite to accurate optimization of thermal systems. The total pressure drop of a fluid is due to the variation of potential and kinetic energy of the fluid and to the friction on the channel walls or between the phases (60-120oC) and moderate reduced pressures (0.2-0.5). In the paper a modification to the established Müller-Steinhagen and Heck (1986) model for two phase pressure drop in relation to high values of reduced pressures has been presented. Model validation has been done in comparison to a reliable experimental data due to Charnay et al (2015) for R245fa at reduced pressures above 0.5. Postulated in the paper modification exhibit a significant improvement to the calculations presented in the literature, also by the authors of experimental data.