Microscopic forced-flow heat-transfer systems containing heat exchangers, flow channels, electrostatically driven peristaltic pumps, and related components have been proposed. These systems would be made largely of silicon, by use of micromachining processes similar or identical to those used to make integrated circuits. These microscopic heat-transfer systems could thus be made as integral parts of integrated circuits: For example, charge-coupled-device (CCD) imaging circuits in infrared cameras could be cooled very effectively by incorporating such systems to circulate cryogenic fluids within the CCD substrates.

Electrostatic Attraction would be used to pull the flexible membrane into, across, and along the channels: this would generate peristaltic waves in the membrane to pump a fluid along the channel.

The figure illustrates a dual-cavity push-pull embodiment of an electrostatically driven peristaltic pump. The pump channels would be etched into silicon substrates, which are bonded together with an electrically conductive flexible membrane sandwiched between them. The channels would be lined with electrically conductive strips covered with electrically insulating material and separated from each other by electrically insulating barriers. By applying a suitable voltage between the membrane and the conductive strips of each channel in succession, one would cause the membrane to be electrostatically pulled into the channel at successive positions along the channel. Dual interlaced and interlocked shift registers enable alternate inversions of bit-stream sequences and multiple membrane "bubbles" that move down the channel, pushing entrapped fluid in front of each membrane "wall" and pulling the fluid behind each membrane "wall." This pump architecture represents a true two-dimensional analog of a peristaltic mechanism that is valveless, impervious to gas-bubble entrapment, does not require priming, and is self purging. The device is a digital pump that may be single-stepped to function as a valve or, by counting the number of clocked bits, is a precision flowmeter.

A heat exchanger consisting of micromachined channels in a thermally conductive material would be designed to maximize heat-transfer surface area and to provide effective convective coupling of heat between the pumped fluid and the channel surfaces at the expected flow speeds. The use of microscopic channels would make it possible to achieve low conduction and convection losses, with consequent high thermal coupling and short characteristic times for decay of thermal transients.

This work was done by Frank T. Hartley of Caltech for NASA's Jet Propulsion Laboratory.

This is the invention of a Caltech/JPL employee, and a patent application has been filed. Inquiries concerning license for its commercial development may be addressed to

the inventor:
Frank Hartley
JPL
MS 125-177
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-3139

Refer to NPO-19093


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Microscopic heat exchangers, valves, pumps, and flowmeters

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This article first appeared in the July, 1998 issue of NASA Tech Briefs Magazine.

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