A Numerical Investigation of Turbulent Flow and Heat Transfer in Rectangular Channels With Elliptic Scale Roughened Walls

Abstract

In the present paper, rectangular channels with six types of elliptic scaleroughened walls for heat transfer enhancement are numerically studied. Heat transfer and fluid flow characteristics for sixteen different scaleroughened models (with the scale height varying in the range from 1 mm to 2.5 mm) are numerically predicted using commercial computational fluid dynamics (CFD) code, Ansys cfx. The turbulent model employed is the k–د‰ based shear–stress transport (SST) model with automatic wall function treatment. In the performance evaluation, we use a “universalâ€‌ porous media length scale based on volume averaging theory (VAT) to define the Reynolds number, Nusselt number, and friction factor. It is found that heat transfer performance is most favorable when the elliptic scales are oriented with their long axis perpendicular to the flow direction, while the scales elongated in the flow direction have lower Nusselt numbers and pressure drops compared with the circular scaleroughened channels. Results indicate that the scaleshaped roughness strongly spins the flow in the spanwise direction, which disrupts the nearwall boundary layers continuously and enhances the bulk flow mixing. With the flow marching in a more intense spiral pattern, a 40% improvement of heat transfer enhancement over the circular scaleroughened channels is observed.