A 2.4 mm-scale rotary engine has been redesigned, fabricated and partially assembled to operate as a compressed gas expander. The micro-expander is a multilayered stack of bonded components that are fabricated from single crystal silicon using bulk micro-machining techniques. This research is a continuation from previous work initiated by the MEMS Rotary Engine Power System (REPS) research group at UC Berkeley. The goal of the MEMS REPS project is to develop an autonomous, portable power system capable of producing electrical power on the order of milliwatts with an energy density better than conventional batteries. Such system was designed to generate power from an internal combustion 2.4 mm rotary engine integrated with an external millimeter-scale electrical generator. A compressed gas micro-expander represented a simplified test bed for the engine concept without dealing with the complexities of operating an internal combustion engine. Further research and particular applications for a micro-scale compressed gas expander sustained its evolution from a proof-of-concept idea into a device of its own.
The micro-expander device contains a 2.4 mm rotor, epitrochoid housing, top/bottom gear cover plates and fluidic porting/ducting plates. A compressed gas is supplied into the expander through a set of modified intake/exhaust ports; it then expands inside the housing chambers continuously supplying a driving pressure to spin the rotor. The proposed dual intake/exhaust ports configuration offer advantages over previous designs such as a constant power output and self-starting capabilities. The mechanical work is converted into electrical power by means of electromagnetic induction, accomplished by a "shaft-less" coupling between an external electrical generator and soft magnetic poles integrated on the engine rotor.
A reliable process to fabricate and assemble the components for a micro-expander has been developed and fully characterized. The micro-fabricated parts exhibit features within the design specifications and meet the surface quality requirements for the assembly and operation of a fully functional compressed gas expander. Different types of bonding techniques for the assembly of micro-devices were developed with exceptional results. Although the completion of a fully assembled micro-expander unit was not possible, the bonding sequences developed will be carried out in a flip chip bonder tool with sub-micron precision alignment tolerances, which are critical both during the micro- expander assembly and operation. A preliminary experimental setup has been devised to test the micro-expander units once the assembly stage is completed. Testing of stand- alone devices and also with electrical generator is proposed using different gases. Other research initiatives at UC Berkeley can eventually leverage this promising technology once completely characterized and optimized.
July 30, 2005
Rosario-Rosario, J. D. (2005). Fabrication and Assembly of a 2.4 Mm Compressed Gas Rotary Expander: A Report. United States: University of California, Berkeley.