Experimental investigation of heat transfer characteristic of semi circular longitudinal vortex generators in rectangular channel

Abstract

The vortex generators in the form of semi circular winglets were used in the present study to investigate heat transfer characteristics. These vortex generators can be mounted on the flat surface by either welding, embossing or punching. In this experiment punched 45° inclined semicircular vortex generators were developed which were directly punched on longitudinal winglet. These vortex generators induced stream wise longitudinal vortices. These vortices disrupted the growth of the thermal boundary layer and results to heat transfer enhancement between the fluid and surfaces. In this experiment semi circular vortex without hole, with holes of 3, 5 and 7mm diameters at centroid were used in in-line position and results were compared with each other. Measurements were carried out for a rectangular channel of an aspect ratio of AR = 1.12, for a winglet transverse pitch (S) to a longitudinal winglet height (e) ratio of S/e = 0.59, and a winglet height (e) to a channel height (H) ratio of e/H = 0.24. The Reynolds numbers considered were ranged from 16458 to 41147. The results of punched semi circular longitudinal vortex generators with and without hole were compared with the smooth plate surface. The vortex generators with hole of 5 mm diameter at centroid show a more significant increase in heat transfer as compared to the vortex generators without hole and with 3 and 7 mm hole diameter. Results showed a 24.75-32.80% increase in heat transfer and 25-33% decrease in pressure drop due to the use of vortex generators with 5 mm hole at centroid position.