UCLA

In the present paper, rectangular channels with six types of elliptic scale-roughened walls for heat transfer enhancement are numerically studied. Heat transfer and fluid flow characteristics for sixteen different scale-roughened models (with the scale height varying in the range from 1mm to 2.5mm) are numerically predicted using commercial CFD code, Ansys CFX. The turbulent model employed is the k-ω based Shear-Stress-Transport (SST) model with automatic wall function treatment. In the performance evaluation, we use a “universal” 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 to the circular scale-roughened channels. Results indicate that the scale-shaped roughness strongly spins the flow in the spanwise direction, which disrupts the near wall 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 scale-roughened channels is observed.