An experimental study into the evaporation heat transfer and flow characteristics of R-134a refrigerant flowing through corrugated tubes

The effects of corrugation pitch on the evaporation of R-134a flowing inside horizontal corrugated tubes are investigated. The test section is a tube-in-tube heat exchanger with refrigerant flowing in the inner tube and hot water flowing in the annulus. Smooth and corrugated tubes having similar inside diameters are used as the inner tube. Three corrugated tubes having a corrugation depth fixed at 1.5 mm and corrugation pitches of 5.08, 6.35 and 8.46 mm are examined. The data obtained from smooth tube are plotted and compared with the flow pattern map established by Censi et al. (2003) and Zurcher et al. (2002). The effects of average vapour quality, equivalent Reynolds number and corrugation pitch are discussed. The maximum ratios of heat transfer enhancement factor to pressure drop penalty factor (Nuc/Nus)/((ΔP/L)c/(ΔP/L)s) is approximately 1.2.