Condensation heat transfer in horizontal three dimensional two-layer two-side enhanced tubes

摘要

Condensation heat transfer characteristics of near-azeotropic refrigerant R410A inside the horizontal copper and stainless steel EHT series tubes were measured. All three dimensional two-layer two-side enhanced tubes have deep-textured surface structures composed of petal-shaped background patterns and dimpled protrusions or boat-shaped cavities. Tests were conducted at an average saturation temperature of 45 degrees C; over a mass flux range of 100-450 kg/(m(2).s); with an inlet quality of 0.8 and outlet quality of 0.2. Condensation heat transfer coefficient of the copper 1EHT1 tube is about 39-47% higher than that of a stainless steel one, showing a beneficial effect of high thermal conductivity material. Effects of saturation temperature and tube diameter on the copper 1EHT tubes were also discussed. Compared with a smooth tube, the heat transfer enhancement ratio of these stainless steel EHT tubes is up to 1.19. As expected, the 1EHT1 tube exhibits the highest condensation heat transfer coefficient due to its larger dimpled protrusions. In addition, the heat transfer performance of 1EHT2 and 3EHT tubes are similar. An explanation could be the condensate retention in boat-shaped cavities on the bottom of the 3EHT tube. (C) 2018 Elsevier Ltd. All rights reserved.