Experimental investigation of refrigerant condensation heat transfer characteristics in the horizontal microfin tubes

The condensation heat transfer characteristics for refrigerant R22 and near-azeotropic mixture, R410A are investigated in the horizontal smooth tube and microfin tube, respectively. The 9.52-mm-OD tube with active length 3.4 m and 5-mm-OD tube with 5 m are selected for condensation test cooled by the heat transfer fluid (water) circulated in a surrounding annulus. A refrigerant superheating 4-7 degrees C is set at the test section inlet and the mass flux range is 100-400 kg m(-2) s(-1) for 9.52-mm-OD tube, and 300-550 kg m(-2) s(-1) for the 5-mm-OD tube. The heat transfer coefficient (HTC) of the microfin tube is around 1.65-2.55 times of that of the smooth one. The microfin one yields similar to 30% higher pressure drop than the smooth one. A lower condensation saturation temperature can generate a higher HTC and a higher pressure drop. 5-mm-OD tube produces both the higher HTC and pressure drop than the 9.52-mm-OD one due to the increased effect of the surface tension and the sheer stress at the gas-liquid interface. R22 performs marginally better for HTC than R410A and the former has a similar to 40% higher pressure drop. In addition, it is necessary to collect more data source and make a generally-accepted and more accurate correlation in the near future. (C) 2017 Elsevier Ltd. All rights reserved.