The Local Heat Transfer Performance Downstream of a Representative SMA Structure

Some of the largest heat densities that can be found in engineering applications are present in 3D chip stacks, and microfluidic systems have been proposed to cool these devices. As the chip heat flux is non-homogenous, hot spots exist and require a greater local heat transfer coefficient than the surrounding regions. To cool on-chip hot-spots, a passively actuated structure could be placed in the micro-channel and, deploying as necessary, regulate temperature by disturbing flow in a target location. In this work, the heat transfer coefficients downstream of a replica Shape Memory Alloy (SMA) structure were measured for low Reynolds numbers (90 to 200) in a diameter 4mm miniature channel, using an isoflux heated foil technique. The heat transfer coefficient was seen to increase with an increase in Re, and or a decrease in the valve opening ratio. Two peaks in the heat transfer coefficient were observed where the flow exited the valve. The local heat transfer coefficients obtained in this work are useful parameters in the modeling and design of microfluidic cooling systems.