Time-resolved PIV measurement and thermal-hydraulic performance evaluation of thin film self-agitators in a rectangular channel flow

This study experimentally investigates the vortex dynamics induced by thin film self-agitators in a rectangular channel and the resultant thermal-hydraulic performance due to the disruption of the thermal boundary layer. Four channel flow features are compared: a clean channel without any agitators, a channel with double rectangular-shaped self-agitators in thicknesses of 25 µm and 125 µm, and a channel with double fishtail-shaped self-agitators in thickness of 25 µm. The effect of the self-agitator motion on the dynamic vortex shedding is characterized by employing time-resolved particle image velocimetry (TR-PIV) at the midspan of the agitator within a Reynolds number range of about 1300–6800 in a customized single channel. The instantaneous and time-averaged flow field are quantified in terms of velocity magnitude, vorticity contour, and turbulence intensity distribution. Results show that the added self-agitator designs all have positive effects on the flow mixing, especially during the flapping mode region. Near wall flow dynamics measurements quantitatively confirm the enhancement of flow boundary layer disturbance. In addition, an off-the-shelf multi-channel heatsink with an identical cross-section profile is tested under the same flow conditions to quantify the heat transfer enhancement as well as the pressure loss penalty for the four channel design features. A dimensionless synthetic thermal-hydraulic performance factor η is used to evaluate the overall benefits of the three self-agitator designs compared to the clean channel. A maximum enhancement factor of approximately 1.42 can be achieved while keeping above 1 for most of the test conditions. Therefore, there is great potential for integrating this external-energy-free vibration motion into plate fin heat exchanger applications.