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takyon writes:

Purdue University researchers have come close to hitting a 1,000 W/cm² target for cooling computer chips specified by DARPA. The technique uses microchannel heat sinks built into chips with a liquid coolant (HFE-7100) flowing through them, but the width and length of the channels has been greatly reduced compared to previous designs. Better cooling performance is needed to enable stacked/3D chips:

Use of small microchannels is the key but doing so also complicates the process. "It's been known for a long time that the smaller the channel the higher the heat-transfer performance," said Kevin Drummond, one of the paper's lead authors and doctoral student. "We are going down to 15 or 10 microns in channel width, which is about 10 times smaller than what is typical for microchannel cooling technologies."

Although using ultra-small channels increases the cooling performance, it is difficult to pump the required rates of liquid flow through the tiny microchannels. The Purdue team overcame this problem by designing a system of short, parallel channels instead of long channels stretching across the entire length of the chip. A special "hierarchical" manifold distributes the flow of coolant through these channels.

"So, instead of a channel being 5,000 microns in length, we shorten it to 250 microns long," said Suresh Garimella, PI on the project, "The total length of the channel is the same, but it is now fed in discrete segments, and this prevents major pressure drops. So this represents a different paradigm." The channels were etched in silicon with a width of about 15 microns but a depth of up to 300 microns.

The team dissipated up to 910 W/cm², not 1 kW/cm² as specified by DARPA in its Intrachip/Interchip Enhanced Cooling (ICECool) program. W/m² is the SI unit for irradiance, or radiant flux.

This 2004 article mentions a Carnegie Mellon University team that managed to get to 300-400 W/cm² using "chip-scale squirt guns". In 2016, Lockheed Martin also hit the 1 kW/cm² target as well as 30 kW/cm² in "multiple local hot spots".

Also at Purdue University.

A hierarchical manifold microchannel heat sink array for high-heat-flux two-phase cooling of electronics (DOI: 10.1016/j.ijheatmasstransfer.2017.10.015) (DX)

Original Submission