Laminar flow heat transfer enhancement in square and rectangular channels having : (1) A wire-coil, axial and spiral corrugation combined with helical screw-tape with and without oblique teeth and a (2) spiral corrugation combined with twisted tapes with oblique teeth

Abstract

Heat transfer enhancement is a vital area of research as it helps to design heat exchangers of reduced sizes and improved heat transfer rates. Thus, there is a pressing need for techniques which result in significantly increased heat transfer over and above increased pressure drop. In this paper, the benefits of different compound techniques using (1) wire-coil inserts and helical screw-tape inserts with oblique teeth, (2) wire-coil inserts and helical screw-tape inserts without oblique teeth, (3) spiral corrugation and helical screw-tape inserts without oblique teeth, (4) axial corrugation and helical screw-tape inserts without oblique teeth, and (5) spiral corrugation and twisted-tape inserts with oblique teeth were studied experimentally for laminar flow in a non-circular duct (aspect ratio = 1, 0.5 and 0.33). Servotherm medium oil with Prandtl number ranging from 430 to 530 was used as working fluid. The experiment was conducted for a uniform heat flux boundary condition. The effect of geometric parameters of the inserts such as wire-coil diameter, wire-coil helix angle, tooth angle and tooth horizontal length of the screw tape and the twisted tape, corrugation height and corrugation pitch, etc. on heat transfer and pressure drop characteristics was presented. The influence of duct geometry (aspect ratio) on Nusselt number and friction factor was also studied. Correlations for Nusselt number and friction factor were developed and a performance evaluation was done.