Experiments on Condensation Flow Pattern of R32 inside Horizontal 4mm Small–Diameter Microfin Tubes

Abstract

In this study, the condensation flow patterns of R32 in horizontal small–diameter microfin tubes with outer diameter of 4 mm were experimentally visualized. Two kinds of copper microfin tubes were used： HF40 had 40 fins, with fin height of 0.18 mm and helix angle of 17°； and LF50S had 50 fins, with fin height of 0.12 mm and helix angle of 25°. The experiments were carried out at mass velocities from 50 to 400 kgm^–2s^–1 at a saturation temperature of 35°C. The flow pattern of small–diameter microfin tube was classified as annular, wavy, and slug flows. It is also confirmed that the annular liquid film in the microfin tube swirled along the direction of the inner grooves. Comparing the results of the HF40 and LF50S, the transition from annular flow to wavy flow is similar to each other. The condensation flow pattern of the microfin tubes were compared with that of the smooth tube. The transition of smooth tube from annular to wavy flows occurred at higher mass velocity and lower wetness than the microfin tubes.