Thermohydraulic performance and entropy generation in heat exchanger tube with louvered winglet tapes

Abstract

The present article concerns with thermohydraulic performance, flow friction and entropy generation analysis in a heated tube contained with louvered winglet tape (LWT). The experiment was conducted in a uniform heat-fluxed test tube for turbulent fluid flow, Reynolds number (Re) ranging from 4760 to 29,260. The purpose of the LWT insert is to produce streamwise vortices assisting to induce impinging-jets onto the tube wall and to decline the pressure loss through the louver mounted on the winglet aside from providing rapid mixing of fluid flow. In the present experiment, the louvered winglets were mounted periodically on a double-sided straight tape with six different louver angles (θ = 0 ˗ 90°) and three winglet pitch ratios (PR = 1 ˗ 2) at a single relative winglet height (BR = 0.25) and a fixed attack angle (α) of 30°. There were two-types of LWT arrangements: inline and staggered louvered-winglet tapes (I-LWT and S-LWT). To examine the optimum thermohydraulic performance, an influence of θ at each PR on the rate of heat transfer and friction loss inside the tube was explored. The measured results disclosed that the Nusselt number (Nu) and friction factor (f) from using both types of LWTs rise considerably with the reduction of PR and θ. The entropy generation (S˙gen') was declined with the decrease in Re, PR and θ where the minimum S˙gen' was obtained for the I-LWT tube at PR = 1, θ = 0° and lowest Re. The peak thermal enhancement factors (TEF) of the S-LWT and the I-LWT were, respectively, around 2.22 and 2.18 at similar PR = 1, θ = 45°. The Nu, f and TEF correlations for using LWT insert were also reported.