Design, Analysis and Fabrication of a Meso-scale Centrifugal Compressor

A gas or vapor compressor is one of the key components of many engineering systems, such as certain designs of vapor compression refrigeration systems, cryo-coolers, air handlers. For meso-scale systems with linear dimensions of a few centimeters, conventional designs do not work efficiently because of rather large relative tolerances, and hence these meso-scale systems require micro-fabricated components for efficient operation. This paper presents a meso-scale centrifugal compressor fabricated by photo-lithographic techniques. A preliminary design based on 1-D flow analysis using air as the working fluid shows that a 50 mm diameter centrifugal compressor with a blade height of 200 μm gives a static pressure ratio of 1.12. In this design, the impeller has 10 full blades and 10 splitter blades. Each blade has the NACA profile 9510 with the maximum camber at 50% of the chord. These impeller blades have exit angles 35 with exit flow angles of 60. A vaned diffuser having 20 equally spaced vanes with the same NACA profile is used to improve compressor efficiency. A 3-D compressible, viscous flow analysis has been done using a commercial finite volume software. The results of this analysis allowed the verification of the flow characteristics inside the meso-scale centrifugal compressor. The compressor has been fabricated using micro-fabrication techniques. The rotor and the stator are made by etching a silicon wafer by using DRIE (Deep Reactive Ion Etching) technique. A Pyrex wafer is then bonded to the stator for visual access inside the compressor. INTRODUCTION Advances in micro-fabrication capabilities over the last decades have facilitated a new era in miniaturization of engineering systems. Photolithography, thin-film deposition and anisotropic etching, the same techniques that have allowed the electronics industry to pack more and more memory and computing power into smaller and smaller chips, can be used to make compressors, pumps, valves, sensors, heat exchangers and chemical reactors at millimeter or smaller scales [1-2]. Miniaturization of thermal and chemical systems offers several advantages over their large-scale counterparts. (1) Transport processes, both thermal and chemical, rely on surface area of heat exchangers or reactors. Hence, the higher surface-tovolume ratios of a miniature system help to make more compact systems with higher volumetric transport coefficients. (2) For meso-scale systems, micro-fabrication provides better tolerances, leading to better performance. (3) Smaller size typically leads to better safety. (4) Use of micro-fabrication technology is expected to provide better cost efficiency. (5) Miniaturization makes newer engineering systems possible. (6) Smaller modular size leads to more options in usage. It is primarily the first two advantages that motivated the development of a meso-scale refrigerator. The two intended applications of this system are (1) an integrated heat removal system for electronics or photonic entities, and (2) an actively cooled jacket for personnel. The preliminary design requirements for the overall system have been set at [3-4] (1) evaporator temperature of 12 °C, (2) condenser exit temperature of 60 °C, (3) heat removal rate of 350 W with refrigerant R134a, (4) saturated vapor at