| Summary: | Heat exchangers are devices that facilitate thermal energy transfer between two or more mediums and which function as key components in many industrial processes, such as steam power plants, refrigeration, chemical plants, nuclear plants, refineries, and next-generation renewable energy storage processes. Recent advancements in power generation techniques and heat engine cycle structures offer potential improvements to the efficiency of each process but require components capable of operating in increasingly demanding environments. Specifically, the shift to high-temperature, high-pressure thermodynamic cycles for improved efficiency has offered a new opportunity for device-level innovations, including producing a heat exchanger that supersedes classical material and design operating limits. Previous work has attempted to infiltrate this new market by developing heat exchangers using costly metal materials in mature architectures that achieve low power densities. Silicon carbide, while well known as a high-temperature material, has rarely been used under such loading conditions due to its low resistance to fracture and high tensile stress concentrations featured in existing heat exchanger designs.
In this thesis, we present the design, structural modelling, and initial characterization of a multiscale ceramic heat exchanger, capable of operating in extreme environments with high power densities and a safety factor against mechanical failure. The heat exchanger device is evaluated for a supercritical CO2 Brayton cycle, using air and sCO2 as working fluids at 80 bar, 1300 °C and 250 bar, 300 °C, respectively. A multiscale channel design, enabled by ceramic co-extrusion, results in a counterflow heat exchanger core with both high thermal performance and high mechanical strength during steady state operation. For coupling this core to typical power-cycle tubing we designed manufacturable ceramic headers, whose geometry was optimized to minimize both pressure loss and flow maldistribution of the working fluids. To evaluate prototypes of our design, we constructed a test setup and experimentally quantified the performance of initial heat exchanger core components. Our design offers a practical solution to address the material limitations imposed by high-temperature, high-pressure thermodynamic cycles while predicting efficiency and performance improvements compared to current state-of-the-art heat exchanger alternatives.
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