Cooling bubbles dissipate heat.

Purdue University researches are hot on the trail of a cooling technology that dissipates enormous amounts of heat. It could be used in the design of future fusion reactors, to produce more efficient medical equipment, and to make smaller, lighter electronics.

"In many devices, from fusion reactor components and rocket nozzles to X-ray machines and computer chips, there is an enormous amount of heat being produced and a very limited area for that heat to escape from," points out Issam Mudawar, professor of mechanical engineering. "If you don't have an effective cooling technology, such highly concentrated heat can produce failure."

The amount of heat a device can be subjected to before it burns out is known as critical heat flux. For instance, a nuclear reactor exceeding its critical heat flux can trigger a catastrophic meltdown. Critical heat flux also is a major design obstacle for very small and complex electronic devices, such as computer chips, that can be damaged or destroyed if they get too hot.

Mudawar's solution is to force boiling liquid at high pressure through tiny channels the size of hypodermic needles, a process called microchannel flow boiling. Flow boiling is different from other systems that use liquid coolants because two phases of the coolant flow through the system, both liquid and vapor, instead of just the liquid phase. Two-phase cooling allows much larger increases in heat dissipation than single-phase cooling.

"When you boil liquid, you create little bubbles, like heating water in a pot. In the case of microchannels, the walls of these channels are hot because they are in contact with a heat-producing device. As we pass liquid through the channels, the liquid becomes heated...