Experimental investigation of heat transfer and friction factor characteristics in a circular tube with longitudinal strip inserts

Longitudinal strip inserts are used as a heat transfer enhancement tool for both retrofit and new design of shell-and-tube heat exchangers. This paper discusses and reviews the characteristics and performance of full-length longitudinal strip inserts inside a circular tube experimentally. The strips considered for heat transfer behavior in a circular tube have been of rectangular and square cross sections with different aspect ratios (AR). The heat transfer test section was maintained constant wall heat flux (CWHF) boundary condition by supplying electricity. The Reynolds number of the fluid lies in between 4000 to 10,000. The friction factor and Nusselt number correlations have been developed. High heat transfer rates are obtained for the longitudinal strip insert of aspect ratio, AR = 1 and at the same time pressure drop is higher. The enhancement of heat transfer as compared to a conventional bare tube at the same Reynolds number based on the equivalent diameter was found to be about a factor of 22 at Re <= 10,000, while the friction factor rise was about a factor of 3.5 at Re S 10,000. The following regression equation for the Nusselt number has been developed for longitudinal strip inserts: Nu = 0.02278Re(0.824)Pr(0.412)(AR + 1)(-0.253)(D-i/l)(0.055).