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

Abstract: 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 1.5mm and corrugation pitches of 5.08, 6.35 and 8.46mm are examined. The data obtained from smooth tube are plotted and compared with the flow pattern map established by and . 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. [ABSTRACT FROM AUTHOR]