Inverted structurally inhomogeneous stepped agitators in a channel flow

Abstract

Homogeneous thin-film agitators used in a channel flow have shown enhanced thermal-hydraulic performances compared to a clean channel benchmark. In this study, an experimental study was carried out to explore the performances of three inverted structurally inhomogeneous stepped agitator designs in the same channel flow in order to further improve the overall thermal-hydraulic performance of a heatsink. The three agitator designs were constructed by connecting two sections of material with different lengths while maintaining the constant total length of 6 mm as in our previous study: a relatively thicker 125-μm material mounted on the channel wall as the trailing edge and a thinner 25-μm material as the free leading edge. The new designs were expected to maximize fluid mixing enhancement but minimize pressure loss due to the unique structure of the inhomogeneous materials. Experiments in this study covered a wide Reynolds number range from 300 to 9000. High-speed footage was used to capture the dynamic motion of the agitators. At the same time, a time-resolved particle image velocimetry (TR-PIV) system was used to characterize the vortex dynamics due to the motion of agitators in various flow conditions. A synthetic thermal-hydraulic performance factor, η, taking into consideration both the Nu number enhancement and friction factor increment, was used to evaluate the overall effects of the added agitator features in the channel flow compared to a clean channel benchmark. Results show that a maximum factor of about 1.5 has been achieved, and it stays above 1 under most of the test conditions in this study, indicating great benefits for enhanced thermal transport.