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

Abstract 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 °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 ∼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 ∼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.