Effect of trapezoidal louvered winglets on increased heat transfer and exergy in tubular heat exchanger

Abstract

The effect of inserting a trapezoidal louvered winglet tape (TLWT) into a uniformly heat-fluxed tube on its thermal effectiveness was studied experimentally. The exergy and entropy analyses for turbulent flows, as well as frictional loss and thermal features, were highlighted as key aspects of the experimental finding for the Reynolds number which measured between about 4700 and 30,000. Because fixing baffles to the curved shape of tube wall presented a challenge, the baffles were consequently positioned on double surfaces of a flat tape. Six values of the louver angle (θ1 = 0°, 25°, 30°, 45°, 60°, and 90°) and three values of the relative pitch of winglet (PR = 1.0, 1.5, and 2.0) were employed in the arrangement of TLWTs, with the V-apex oriented upstream (V-up). Each of these had only a fixed height (BR = 0.25) and angle of attack (α = 30°). The winglets were utilized to induce streamwise vortices which can hinder the boundary layer formation, while the louvered openings were adopted to lessen pressure drop without significantly impacting the primary vortices. The experiment results disclosed that the smallest θ1 and PR produced the largest relative friction factor (fR) and NuR, which were about 13.57 and 4.04 times higher, while PR = 1 and θ1 = 45° provide the greatest TEF of about 2.27. The greatest exergy efficiency (ηEx) resulting from the TLWT was reached at θ1 = 0°, but the generation of entropy (S˙g′) dropped with lowering θ1 and Re. A further examination, however, showed that the best scenario with α = 60° and staggered arrays is more desirable since it yields the largest TEF of 2.45 at θ1 = 45° and PR = 1. For the range of parameters under consideration, the Nu and f correlations were additionally established.