Mems

Proceedings of ASME Turbo Expo 2003 Power for Land, Sea, and Air June 16-19, 2003, Atlanta, Georgia, USA

GT-2003-38866
MILLIMETER-SCALE, MEMS GAS TURBINE ENGINES
Alan H. Epstein Gas Turbine Laboratory Massachusetts Institute of Technology Cambridge, MA 02139 USA epstein@mit.edu several of which are marketed commercially [1, 2]. Gas turbines below a few hundred kilowatts in size generally usecentrifugal turbomachinery (often derivative of automotive turbocharger technology in the smaller sizes), but are otherwise very similar to their larger brethren in that they are fabricated in much the same way (cast, forged, machined, and assembled) from the same materials (steel, titanium, nickel superalloys). Recently, manufacturing technologies developed by the semiconductor industry haveopened a new and very different design space for gas turbine engines – one that enables gas turbines with diameters of millimeters rather than meters, with airfoil dimensions in microns rather than millimeters. These shirt-button-sized gas turbine engines are the focus of this review. Interest in millimeter-scale gas turbines is fueled by both a technology push and a user pull. The technology push isthe development of micromachining capability based on semiconductor manufacturing techniques. This enables the fabrication of complex small parts and assemblies – devices with dimensions in the 1-10,000 µm size range with submicron precision. Such parts are produced with photolithographically-defined features and many can be made simultaneously, offering the promise of low production cost inlarge-scale production. Such assemblies are known in the US as micro-electrical-mechanical systems (MEMS) and have been the subject of thousands of publications over the last two decades [3]. In Japan and Europe, devices of this type are known as “microsystems”, a term which may encompass a wider variety of fabrication approaches. Early work in MEMS focused on sensors and simple actuators, and manydevices based on this technology are in large-scale production, such as pressure transducers and airbag accelerometers for automobiles. More recently, fluid handling is receiving attention. For example, MEMS valves are commercially available, and there are many emerging biomedical diagnostic applications. Also, chemical engineers are pursing MEMS chemical reactors (chemical plants) on a chip [4].User pull is predominantly one of electric power. The proliferation of small, portable electronics – computers, digital assistants, cell phones, GPS receivers, etc. – require compact energy 1 Copyright ©2003 by ASME

ABSTRACT The confluence of market demand for greatly improved compact power sources for portable electronics with the rapidly expanding capability of micromachining technology hasmade feasible the development of gas turbines in the millimeter-size range. With airfoil spans measured in 100’s of microns rather than meters, these “microengines” have about 1 millionth the air flow of large gas turbines and thus should produce about 1 millionth the power, 10-100 W. Based on semiconductor industry-derived processing of materials such as silicon and silicon carbide to submicronaccuracy, such devices are known as micro-electro-mechanical systems (MEMS). Current millimeter-scale designs use centrifugal turbomachinery with pressure ratios in the range of 2:1 to 4:1 and turbine inlet temperatures of 1200-1600 K. The projected performance of these engines are on a par with gas turbines of the 1940’s. The thermodynamics of MEMS gas turbines are the same as those for large enginesbut the mechanics differ due to scaling considerations and manufacturing constraints. The principal challenge is to arrive at a design which meets the thermodynamic and component functional requirements while staying within the realm of realizable micromachining technology. This paper reviews the state-of-the-art of millimeter-size gas turbine engines, including system design and integration,...