The effects of corrugation pitch on the condensation heat transfer coefficient and pressure drop of R-134a inside horizontal corrugated tube

The heat transfer coefficient and pressure drop of R-134a inside a horizontal smooth tube and corrugated tubes are experimentally investigated. The test section is a 2.0 m long counter-flow concentric double tube heat exchanger with refrigerant flowing in the inner tube and cooling water flowing in the annulus. A smooth tube and corrugated tubes having inner diameters of 8.7 mm are used as an inner tube. The corrugation pitches are 5.08, 6.35, and 8.46 mm, respectively. The corrugation depth of all corrugated tubes is fixed at 1.5 mm. The outer tube is made from smooth copper tube having an inner diameter of 21.2 mm. The test runs are performed at the saturation temperatures of 40, 45, and 50 °C, heat fluxes of 5 and 10 kW/m2, and mass fluxes ranging from 200 to 700 kg/m2 s. The results obtained from the corrugated tubes are compared with that of the smooth tube. It is found that the corrugation pitches have a significant effect on the heat transfer coefficient and pressure drop augmentations.