Single-Phase Heat Transfer Inside Internal Helically Ribbed Tubes

Abstract

Abstract. This study focuses on experimentally investigating the performance of two generations of internal helically ribbed tubes during single-phase heat transfer of water inside the tube, where boiling or condensation of refrigerant occurs outside the tube. The design parameters of the two generations of enhanced tubes include differences in internal helical rib height, helix angle, number of ribs per turn, and rib base thickness. This includes a smooth tube (Tube-1) as well as Tube-2 through Tube-8 representing the first generation of internal helically ribbed tubes from the 1990s, and Tube-9 through Tube-19 representing the second generation of internal helically ribbed tubes that are in widespread use now. With the maturity of tube manufacturing processes, the number of ribs per turn and the helix angle of the second generation of internal helically ribbed tubes have been increased. This helps in increasing the tube's heat transfer area and enhancing the turbulence intensity of the fluid. The increase in the number of ribs per turn also disrupts the development of the fluid boundary layer, reducing its thickness, thereby reducing its thermal resistance and further improving the heat transfer rate. Furthermore, based on previous single-phase empirical correlations, a novel heat transfer correlation capable of predicting the heat transfer factor of the 18 tested tubes with an uncertainty ranging from −20% to 20% has been successfully fitted to the experimental data. Results of this research should provide a reliable body of data for optimized design of heat exchangers used in a variety of industries and especially in high-temperature solar energy applications.