Experimental research on refrigerant condensation heat transfer and pressure drop characteristics in the horizontal microfin tubes

Abstract

The condensation heat transfer characteristics and pressure drop for R410A were investigated in the horizontal smooth and microfin tubes. The 6.35-mm-OD, 7-mm-OD and 8-mm-OD tubes with active length 2 m were selected for condensation test cooled by the heat transfer fluid (water) circulated in a surrounding annulus. A refrigerant superheating 2–3 °C was set at the test section inlet and the mass flux range was 300–1100 kg·m−2·s−1. The heat transfer coefficient (HTC) of the microfin tube was about 1.63–2.29 times of that of the smooth one. The microfin one yields ~28.9% higher pressure drop than the smooth one. Large helix angle and fin height were beneficial to enhance heat transfer due to the centrifugal force and surface tension, but increased the pressure drop. 6.35-mm-OD tube produced both the higher HTC and pressure drop than the 7-mm-OD and 8-mm-OD tubes due to the increased effect of the surface tension and the sheer stress at the gas-liquid interface. It was necessary to optimize finned structure to enhance heat transfer. Experimental data were also compared with previous correlations proposed for smooth and microfin tube. It was necessary to collect more data source and make a generally-accepted and accurate correlation in future.