Microscale ion driven air flow
Ion-driven air flow is a novel method of pumping air at microscale dimensions using the concept of ion drag. Ions are generated in air using low voltage cold-cathode electron emitters that inject electrons into the air. Once in the air, the electrons generate ions by collision reactions. The ions are moved by a series of micro-fabricated electrodes that generate strong electric fields to pump ions through air. Ions collide repeatedly with neutral molecules, thus generating bulk motion of the gas. Meso-scale motion, flow on the order of millimeters, is obtained using a traveling electric field which is established by an array of electrodes. One application of this technology involves generation of air flow through microchannels or other micro-featured surfaces to create compact, high-flux heat sinks for electronics cooling. Analytical and numerical models of the fluid-ion-electric field interactions have been developed in the present work. First order analyses demonstrate the feasibility of implementing this concept into a heat sink with cooling rates as high as 40 W/cm2. More detailed models illustrate the basic mechanisms behind microscale ion driven air flow (MIDAF). Model results describe the body force interaction of the ions with the fluid, the location of the body force, the resulting velocity profiles, the stability of ion clouds and the important parameters that affect this flow. Experimental verification of the MIDAF concept is demonstrated by means of ion current measurements. Ion currents, as high as 50 nA, were established over a flat test section with pumping electrode spaced apart by 30 μm, operating at potentials of 0 to 35 V, and switching at a frequency of 1.4 MHz.
Fisher, Purdue University.
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