The electrokinetic pump works by having an electric field drive a fluid through a sintered glass disk. The electric field's strength controls the liquid's flow rate.
"It was a matter of scaling the volumes of liquid involved from what has already been demonstrated to make the pump practical," says Goodson, Cooligy's co-chief technology officer.
The pump consists of a small sintered glass filter disk as the active pumping structure, a catalytic gas recombiner, platinum electrodes, and Plexiglas machined parts (Fig. 3). The housing was made of Plexiglas in the prototype stage, but in production it will be made from glass, ceramic, or metal. An electric field drives the water that flows through the microchannel heat collector and then flows through the radiator. The radiator is a counter-flow type where the fluid and the air flow in different directions.
The pump has a high flow rate of more than 20 ml/minute with a 60-V/mm electric field. It's also silent. Most importantly, it's reliable since it has no moving parts. The flow rates can be scaled up to 200 to 300 ml/minute. The pumping structure has a diameter of 30 mm, is 2-mm thick, and has an effective pore diameter of 1 µm.
The pump requires only about 10% of the heat energy removed, which is about 10 W for 100 W of heat removed. Successful demonstrations of the pump have been performed on CPUs from Intel, Apple Computer, and Hewlett-Packard using buffered de-ionized water as the liquid. The water contains buffer chemicals to prevent growths in the water that could cause blockages.
COMMODITY PARTS
Keane points out that the commodity parts for Cooligy's pump are similar to parts that go into filters widely used in industry. The sintered glass, the key element of the electrokinetic pump, is used as a filter in beer and food processing (for much larger liquid volumes) and as a pump component in the biomedical field in microfluidic arrays (for very small liquid volumes).
Cooligy notes that each heat-exchange system it designs is custom-made to the specific application involved. The MEMS heat exchanger and the pump can then be optimized differently for different applications, depending on the chip that's being cooled.
Nevertheless, cost for a closed-loop system can range around $30 during the early stages of manufacturing, which should come down with volume manufacturing. In contrast, a heat-pipe system might cost between $15 and $25, while a fan/heatsink combo might cost about $12 to $20. But these other systems can't deliver the benefits of Cooligy's MEMS-based system, which is about 20% smaller, not to mention the resulting higher reliability and CPU performance gains.
COOLIGY INC.
www.cooligy.com
Andy Keane, (650) 417-0300, ext. 325