The heat transfer performance in a square channel downstream of a representative shape memory alloy structure for microfluidics applications

Some of the largest heat densities that can be found in contemporary engineering applications are present in 3D chip stacks (~10³ W/cm³), and micro-fluidic systems have been proposed to cool these devices. As the chip heat flux is non-homogenous, hot spots exist which require greater local heat transfer coefficients 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, to regulate temperature by disturbing flow in a target location. In this work, the heat transfer coefficients downstream of a representative Shape Memory Alloy (SMA) structure were measured for low Reynolds numbers (90 - 200) in a ø4mm miniature channel, using a joule 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 area averaged heat transfer coefficients obtained in this work are useful parameters in the modeling and design of practical micro-fluidic cooling systems.