Experimental Study of Single-phase Pressure Drop Characteristics in Horizontal Internal Helical Finned Tubes

Abstract

Due to the intense enhancement of the convective heat transfer, internal helical finned tubes are widely applied into the field of HVAC. An experimental setup was built for investigating single-phase flow characteristics of internal helical-rib roughness. The single-phase flow characteristics for water-ethylene glycol mixture in three internal finned tubes and a smooth tube were obtained. The nominal diameter of the two test tubes was 22.48mm and 16.662mm, the number of the fins was 60 and 38, the helix angle was 45 degrees and 60 degrees and the relative roughness was 0.022 and 0.053, respectively. The Prandtl number varied from 10.0 to 177 and the Reynolds number ranged from 185 to 40000. The friction factors were measured under the condition of thermal insulation. Experimental results showed that the smooth-tube results were compared to the Filonenko equation with satisfactory agreement. Transition for internal helical finned tubes occurred at lower Reynolds numbers than that of their smooth tube counterparts. The trend of the friction factor of the internal helical finned tube is remarkably different from that of plain tube in the transition regime. For Tube 2 and Tube 3, the flow turns into the fully turbulent flow at Re=14500, while Tube-4 at Re=9500, which is obviously different from that of the plain tube.