The hydrodynamic and heat transfer behavior downstream of a channel obstruction in the laminar flow regime

Micro-fluidic systems have been proposed as potential solutions for the cooling of next-generation Integrated Circuits (ICs) and Photonics Integrated Circuits (PICs). For PICs, integration of micro-fluidics may enable greater laser-bar array densities and, consequently, greater transmission bandwidth. To cool the μm scale hot-spots produced by the laser-bars, a passively actuated structure situated in a micro-channel could regulate temperature by disturbing flow in a target location as required. To this end, a proof-of-concept passive structure was developed from a Shape Memory Alloy (SMA), and demonstrated at the millimeter scale in previous work. The objective of this study is to measure the heat transfer augmentation at a target surface downstream of the obstruction. Two experiments were performed to measure the flow field and heat transfer downstream of the test pieces in a square miniature channel for a range of obstruction Reynolds numbers (Re ≈ 50-170) and opening area ratios (β ≈ 0.2-0.5): using Particle-Image Velocimetry (PIV) and infrared (IR) thermography of a Joule-heated foil respectively. A 50% improvement was observed in the foil area averaged heat transfer coefficient (relative to the unobstructed channel) for Rew=176 and β=0.19. A correlation was developed to interpolate Nusselt number (Nu) from a given Re and β for the studied geometry, and analysis of the correlated exponents showed an improvement in heat transfer relative to a simple pillar obstruction. This was attributed to the wake that formed downstream of the test pieces. The findings of this work are relevant to the modeling and design of practical micro-fluidic systems for targeted hot-spot cooling in future integrated circuit packaging.