Design, fabrication, and characterization of a microturbopump for a rankine cycle micro power generator

Abstract

A microfabricated turbopump has been designed, fabricated and experimentally characterized as the core component of a micro steam turbine power-plant-on-a-chip, which aims to implement the Rankine thermal cycle for micro power generation. The device consists of a four-stage radial planar type turbine and a spiral groove viscous pump supported on gas-lubricated bearings. The device is composed of five wafers: one glass wafer, one SOI wafer, and three silicon wafers. The silicon and SOI wafers are patterned using shallow and deep reactive ion etching (total of 14 masks), while the Pyrex glass wafer are ultrasonically drilled. Anodic bonding, fusion bonding and manual assembly with alignment structures were then used to complete the device and enclose the 4 mm diameter rotor. In a test using compressed air to drive the turbine, the rotor was spun up to 116,000 rpm, which corresponds to 25m/s in tip speed producing 0.073 W of mechanical power, and the pump pressurized water by 88kPa with a flow rate of 4mg/s. The pump performance chart was also completely characterized for speeds up to 120,000 rpm. A 1-D pump model based on lubrication theory has shown close agreement with the data and predicted 7.2% of maximum pump efficiency over the range of operating speeds.