Single-Phase Heat Transfer and Pressure Drop of Developing Flow at a Constant Heating Flux Inside Horizontal Helical Finned Tubes

Abstract

An experimental investigation was carried out to determine the friction factor and heat transfer coefficients under the uniform heat flux boundary condition. Heat transfer and pressure drop data were obtained from two different types of internal helical finned tubes with diameters of 22.48 and 16.662 mm, a fin height to diameter ratio of 0.0222 and 0.0534, number of starts of 60 and 38 and helix angles of 45 and 60°. Reynolds numbers ranged between 300 and 30,000, while Prandtl number was in the order of 12.1 to 47.5. Results show that friction factors of single-phase flow in the internal helical finned tube were higher than the counterpart of the plain tube. The heating boundary condition has a significant effect on friction factors of internal helical finned tubes in the laminar and transition flow regions. Transitions of single-phase flow in the internal helical finned tube under uniform heat flux were delayed when compared with the adiabatic result. In turbulent region, heat transfer results showed an overall increase when compared with the smooth tubes. With the same Re or q, the heat transfer enhancement of tested tubes was in the range of 1.0–6.8 in the turbulent region and the heat transfer enhancement increase with Reynolds number.