Experimental Study of Forced Convection over Equilateral Triangle Helical Coiled Tubes

Abstract

This study presents an experimental investigation of an equilateral triangular cross-sectioned helical tube under uniform heat flux boundary condition. The experiments are carried out for nine helical coiled-tubes of different parameters. Different diameter ratio (D/a) ranged from 6.77 to 15.43 and pitch ratio (P/a) ranged from 1.127 to 3.062 are employed in the present study, The experiments covered a range of Reynolds number from 5.3X10 2 to 2.2X10 3 . Uniform heat flux is applied to the inside surface of the helical coil and air is selected as tested fluid. The experimental results obtained from the equilateral triangular cross-sectioned helical tube indicated that the parameters of the coil diameter and pitch of helical coil have important effects on the heat transfer coefficient. The Nusselt number increases with the increase of Reynolds number and coil diameter at constant pitch of the helical coil. Also, Nusselt number increases with the increase of Reynolds number and Pitch of helical coil at constant coil diameter tube. A comparison between the present experimental data with a previous work with circular cross-sectioned helical tubes have the same test conditions was achieved. From this comparison, it is clear that the average enhancement of Nusselt number for equilateral triangular cross-sectioned helical is about 1.12 ~ 1.25 times the circular cross-sectioned helical for all tested conditions. A general correlation of the average Nusselt number as a function in Re, D/a and P/a ratios is obtained to describe the forced convection from the equilateral triangle cross sectioned coiled tube. Key words : Forced convection; Helical coiled tubes; Coil diameter ratio; Pitch ratio