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John O | October 2014

Can A Non-mechanical Thermal Control System Remake the World of Thermal Management?


a new pump type invented by brandon carpenter and jonathan wachob of fourier electric may create a new innovation set in the thermal management market.  originally conceived for nasa and satellites, their project was deemed not ready for prime time.  but now with first round money from golden knight capital and some guidance from blackstone launchpad, the fourier team is set to move forward to cool mri machines and more. [see end of this article for a video interview with jonathan wachob].

the teams invention, at its most basic level, involves changing the composition of the fluid in a pump used in liquid cooling and in doing so a pump's mechanical system could be removed.  such an approach has been discussed in the american physical society.  in their 2010 piece, "focus: fluid pump without moving parts", the authors note that:

microscopic pipes could soon move fluid around in a chemical-analysis chip or transport coolant around hot electronic circuits. in the 22 october physical review letters, a team from hong kong proposes a new type of fluid channel made of sections with different surface properties. their computer simulations show that heating at the seam joining the two sections could drive fluid flow in one direction, perhaps fast enough to cool computer chips using their own heat.

the techniques used to craft semiconductor chips can also be used to make tiny tubes for transporting liquid. at nanometer dimensions, though, fluid flow differs markedly from that at familiar scales. one big difference is that interactions between the liquid and the walls of the channel become much more important. over the years, researchers have proposed many ways to modify surface properties to manipulate fluid flow in channels without moving parts. but most of these schemes cannot easily move fluid in a complete circuit–for example, fluid might flow from hot to cold but not back, as would be required for cooling.


fourier_2_504

source:  c. liu and z. li, phys. rev. lett. 105, 174501 (2010)

performance under pressure. a nanoscale channel made of two sections
with different surface properties and heated in the center leads to
pressure differences throughout the channel, as shown in this simulation
(red is highest; blue is lowest). the fluid flows from right to left.


but note that in the work by c. liu and z. li, they focus on the surface properties of a channel.  as we write this, we don't know if mr. carpenter and wachob have leveraged that research along with their own, but, as the study shows, such non-mechanical pumps are possible.

but what about ferro fluids? 


nasa themselves invented such fluids in the 1960's as a way to non-mechanically pump fluid in space.  then, hur koser and colleagues of the university of georgia and massachusetts institute of technology created a pump that uses ferro fluids and magentics to pump fluid, for electronics cooling, without a mechanical mechanism.  as reported originally in physics world, 


the apparatus [ed. non-mechanical] comprises a closed fluidic loop built using pvc pipes bought at the local hardware store. the team added manual valves to the loop to stop the circulating flow whenever necessary as well as two pressure ports to measure the pressure created by the electrical windings – many turns of copper tape around the circumference of the tube – in a differential fashion. "we passed electrical current through the windings to create a magnetic excitation that travelled along the length of the tube on one arm of the fluidic loop. the currents were driven by a stereo amplifier, purchased from a local music store. the ferrofluid used was a cheap, commercially available formulation based on mineral oil and magnetite nanoparticles," says koser, explaining just how simply their device was built.


fourier_3_597


















computer rendered image of the koser-mao pump



the electromagnetic coils generate a magnetic field, which the researchers refer to as a "travelling wave". mao explains that these fields rotate the nanoparticles within the liquid. "we can control the strength, frequency and direction of the travelling waves, which in turn result in locally rotating magnetic fields within the ferrofluid. the field is set up to generate a gradient of nanoparticle rotation – those deeper inside the pipe rotate slower than those near the surface. this spin gradient sets up a shear gradient within the ferrofluid, propelling it linearly," he says. a large spin gradient means that each particle's rotations are highly coupled with those of its neighbours, while a zero-spin gradient means particle's rotations do not affect each other at all.


whatever the exact engineering approach the team at fourier electric are taking, its clear the science is there as a foundation to create a commercially viable way to bring innovation to thermal management.

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