The effect of two main vortexes generator on heat transfer enhancement in mini rectangular ducts of airborne thermoelectric conversion system

Abstract

To enhance the heat transfer process of supercritical pressure fluid in rectangular channels of the airborne thermoelectric conversion system, the combined effect of the Reynolds stress, properties variation and longitudinal fins on convective heat transfer process in ducts under supercritical pressure is investigated. Then, a method to induce the two main vortexes structure in rectangular ducts is proposed. Results show that, in smooth ducts, the two main vortexes structure is formed due to the effect of density variation. By comparing the flow and heat transfer process in the smooth duct and ridged duct with trapezoidal fins attached on the lower wall, it is found that, due to the effect of new vortexes induced by trapezoidal fins, the two main vortexes structure is inhibited, which makes local wall temperature increases about 50 K. Accordingly, the thermal performance enhancement factor of rectangular duct with trapezoidal fins is lower than 1. To enhance the two main vortexes structure, a method that using triangular fins to induce two main vortexes structure is proposed, and the duct with one triangular longitudinal fin attached on the upper wall is designed, which has better thermal performance than ducts with trapezoidal fins. Due to the effect of triangular fins, the dominant distance of two main vortexes structure increases by 416%. Accordingly, in ducts with triangular fins, local heat transfer coefficient is enhanced about 23.5%, and the maximum of thermal performance enhancement factor is about 1.29.