Influence of geometric parameters of alternate axis twisted baffles on the local heat transfer distribution and pressure drop in a rectangular channel using a transient liquid crystal technique

Abstract

This paper reports the effects of alternate axis twisted baffle geometric parameters on the heat transfer and flow characteristics within rectangular channels. In our experiments we used modified shapes of alternate axis twisted baffles according to relative pitch ratios (s/w) equal to 2-12 and twist ratios (y/w) equal to 1-5, under conditions where the angle of attack (a) was 90 and the relative blockage height (e/Dh) was at a constant value of 0.095. The results for the Reynolds numbers based on the duct hydraulic diameter ranged from 9000 to 24,000 at a constant Prandtl number, Pr = 0.707, using air as a working fluid. A 0.05 mm thick stainless-steel foil was used as a heater, and a thermochromic liquid crystal technique was used to obtain the local temperature distribution on the heated surfaces. Images were captured in areas with periodic, fully developed regions in the channel. The results show that rectangular channels equipped with alternate axis twisted baffles demonstrated 80%-185% greater heat transfer than rectangular channels with no baffles. Channels with alternate axis twisted baffles at higher twist ratios (y/w) and smaller relative pitch ratios (s/w) showed increased heat transfer, as well as pressure loss within the system, compared with other types of twisted baffles. The thermal enhancement factor of the rectangular channels equipped with alternate axis twisted baffles was higher than that for transverse baffles and smooth channels under similar operating conditions.