Microfluidic Heat Engines for Recovery of Distributed Waste Heat

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Out of the 15 TW of power consumed on our planet, a majority is eventually rejected as heat to the ambient. One of the largest sources of renewable energy available today is therefore waste heat. This energy is however distributed in our homes, factories and cars, making it difficult to recuperate and reuse. Furthermore, temperatures are typically relatively low, which reduces the conversion efficiency of heat into useful work or electricity. We propose to develop micro heat engines driven by waste heat that can be fabricated in large planar arrays using batch fabrication approaches, such as MEMS-based microfabrication technologies. The micro heat engines will come in the form of sheets that can be directly integrated to the heat sources, such as hot automobile engine exhausts, walls of industrial process ovens, and drain pipes or chimneys rejecting hot gases or liquids. We have recently discovered unique behavior at the microscale that leads to uncommon thermodynamic cycles. Much better understanding of the dominant physics and their impact on the microfabricated device is however needed. The scope is composed of three main research objectives: 1) Understand the physics of explosive evaporation in confined microchannels and chambers; 2) Control the dynamic coupling between the heat transfer, fluid dynamics, and electromechanics; 3) Devise microfabrication approaches to batch fabricate microfluidic heat engines at low-cost and high volume. The methodology consists of a combination of experimental investigations using variants of miniature prototypes and test structures to explore and understand the dominant physics, along with analytical and numerical modeling. Microfabrication processes and prototypes will also be developed for experimental validation and demonstration. The outcomes will be the explanation of the novel thermodynamic cycles, an established knowledge base for the design of micro heat engines operating on these cycles, and training of HQP in the multidisciplinary fields of thermofluid sciences, electromechanics, design of complex systems, and microtechnologies.