A MEMS Turbopump for High Temperature Rankine Micro Heat Engines—Part I: Design and Fabrication

We report the design and microfabrication of a MEMS turbopump with thermal insulation, as the core component of a steam power plant-on-a-chip for waste heat recovery based on the Rankine thermodynamic cycle. Based on a first-generation microturbopump for ambient temperature operation, this second-generation device introduces materials for thermal insulation and design improvements to the rotordynamic components for operation at high temperatures. Thermal management is required to prevent water boiling in the pump and vapor from condensing in the turbine, bearings and seals. The device is a five-wafer stack that encloses a 4-mm diameter rotor disk with microturbine blades on one side and a viscous micropump on the other. This second-generation microturbopump implements unique thermal insulation strategies to isolate the pump from the surrounding hot flows. An out-off-plane thick molded glass embedded into the rotor prevents heat conduction from the turbine to the pump. In addition, an in-plane thick array of oxidized trenches prevents heat conduction from the thrust bearing region to the pump. The assembled microturbopump is fabricated and tested, resulting in the first MEMS turbopump demonstrated at high temperature. Design and fabrication are covered herein, whereas experimental demonstration and characterization are presented in Part II of this two-part paper.