Experimental Studies on Heat Transfer and Friction Factor Through Isothermal Square Duct with Twisted Tape Inserts

Abstract

This work addresses Experimental investigations of heat transfer and friction factor characteristics in a concentric double pipe heat exchanger (square duct inner and circular tube outer) using full length twisted tapes of different twist ratios. The data were taken for Reynolds number well in the laminar region (Re =30-1100) with twisted tapes of twist ratios (y=2.66 and y=3.55). Experiments were carried out for constant wall temperature boundary condition using Ethylene glycol as working fluid; the results demonstrate that as twist ratio decreases, the twisted tape gives better heat transfer enhancement. Isothermal friction factors were found to be 6 to13 times the plain duct values. Mean Nusselt number for the twisted tapes are higher than those for the plain duct around 6.0 and 5.30 times for y=2.55 and y=3.66 respectively. The experimental result shows that Nusselt numbers are found to be 5.44 -7.49 and 2.46- 4.88 times the plain square duct forced convection values based on constant flow rate and constant pumping power criteria respectively, for y =2.66.