Numerical Investigations Into the Local Behavior of Condensing R134a Flows in a Horizontal Pipe

Abstract

The local characteristics and behavior of condensing R134a flows in a horizontal pipe, at mass fluxes of 100, 200, and 400 kg m−2 s−1, saturation temperature of 40 °C, and mean vapor qualities of 0.25, 0.50, and 0.75, are investigated numerically. The local results demonstrate an increase in condensate film thickness from a particular angular position, which is influenced by the vapor quality of the flow to the bottom of the pipe. The heat transfer coefficient decreases around the pipe circumference from the top to the bottom of the pipe. The results indicate the existence of a particular angular position where the film thickness and the heat transfer coefficient change significantly due to the stratified condensate layer. Furthermore, the velocity profiles of the condensing flows are noted to be asymmetrical due to the stratified condensate layer at the bottom of the pipe. The mean flow velocity and the heat transfer coefficient decrease along the condensation length. The local results demonstrate that the heat transfer coefficient is not merely affected by the condensate film thickness but also by the effective thermal conductivity of the flow. The findings demonstrate the capacity of local measurements in capturing fine features of condensing flows.