A COPPER MICROCHANNEL HEAT EXCHANGER FOR MEMS-BASED WASTE HEAT THERMAL SCAVENGING

The growing necessity for increased efficiency and sustainability in energy systems such as MEMS devices has driven research in waste heat scavenging. This approach uses thermal energy, which is typically rejected to the surrounding environment, transferred to a secondary device to produce useful power output. This paper investigates a MEMS-based micro-channel heat exchanger (MHE) designed to operate as part of a micro-scale thermal energy scavenging system. Fabrication and operation of the MHE is presented. MHE operation relies on capillary action which drives working fluid from surrounding reservoirs via micro-channels above a heated surface. Energy absorption by the MHE is increased through the use of a working fluid which undergoes phase change as a result of thermal input.In a real-world implementation, the efficiency at which the MHE operates contributes to the thermal efficiency of connected small-scale devices, such as those powered by thermoelectrics which require continual heat transfer. This full system can then more efficiently power MEMS-based sensors or other devices in diverse applications. In this work, the MHE and micro-channels are fabricated entirely of copper with 300μm width channels. Copper electro-deposition onto a copper substrate provides enhanced thermal conductivity when compared to other materials such as silicon or aluminum. The deposition process also increases the surface area of the channels due to porosity. Fabrication with copper produces a robust device, which is not limited to environments where fragility is a concern.The MHE operation has been designed for widespread use in varied environments. The exchanger working fluid is also non-specific, allowing for fluid flexibility for a range of temperatures, depending on the thermal source potential. In these tests, the exchanger shows approximately 8.7 kW/m2 of thermal absorption and 7.6 kW/m2 of thermal transfer for a dry MHE while the wetted MHE had an energy throughput of 8.3 kW/m2. The temperature gradient maintained across the MHE bottom plate and lid is approximately 30 °C for both the dry and wetted MHE tests though overall temperatures were lower for the wetted MHE.Copyright © 2014 by ASME