Pressure drop during condensation at low mass fluxes in smooth horizontal and inclined tubes

Abstract

There are limited studies on pressure drops at low mass fluxes in smooth horizontal and inclined tubes. Thus, this paper presents the pressure drops during the condensation of R134a at low mass fluxes in smooth horizontal and inclined tubes with an internal diameter of 8.38 mm. Experiments were conducted at a saturation temperature of 40 °C at mass fluxes of 50, 75 and 100 kg/m2 s, and mean vapour qualities between 0.1 and 0.9. The temperature differences (between the mean saturation temperature and mean wall temperature) tested were 1, 3, 5, 8, and 10 °C. The pressure drops between the test section inlet and outlet over a length of 1.71 m were measured and were found to be temperature difference dependent. The flow patterns were captured concurrently with two high-speed video cameras positioned at the entrance and exit of the test section through sight glasses. The effect of the vapour quality, temperature difference, mass flux, and inclination angle on the measured and frictional pressure drop was analysed and discussed. It was found that the pressure drops increased with an increase in mass flux, temperature difference and vapour quality. Furthermore, the lowest and highest measured pressure drops were obtained during the downward and upward flows respectively. On the other hand, the opposite was found for the frictional pressure drops.