GRADUATE SEMINAR - From Electrospinning to Thermal Management in Microelectronics, From Co-electrospinning to Nanofluidics, by Professor Alex Yarin, University of Illinois at Chicago

Education - Colloquium - WPI Only

Wednesday, January 23, 2013
2:00 PM-3:00 PM

Higgins Laboratories
HL 116

In the first part, a novel method of enhancement of drop and spray cooling for microelectronic, optical and
radiological elements and server rooms, which require extremely high heat fluxes, is discussed. The key
idea of the method is to cover the heat transfer surfaces with electrospun nonwoven polymer or metal-plated
“thorny devil” nanofiber mats. The experiments revealed that drop impacts on nanotextured surfaces of
nanofiber mats produce spreading similar to that on the impermeable surfaces. However, at the end of the
spreading stage the contact line is pinned and drop receding is prevented. All the mats appeared to be
dynamically permeable for coolant drops. The enhanced efficiency of drop cooling in the presence of nanofiber
mats observed experimentally results from full elimination of receding and bouncing of the drops,
characteristic of the current spray cooling technology. Therefore, the drops evaporate completely, and the
large cooling potential associated with the latent heat of evaporation is more fully exploited. This is
paradoxical: the best cooling can be provided by a "furry overcoat"! Using this approach very high cooling
rates of about 1 kW/cm2 were achieved and the anti-Leidenfrost effect was discovered.

In the second part, carbon nanotubes are synthesized and self-assembled via co-electrospinning,
emulsion electrospinning, or template electrospinning and subsequent carbonization. Then, controlled flows
through macroscopically long (~1cm) carbon nanotubes are demonstrated. It is shown that a higher flow rate
of liquid in a bi-layer gas-liquid system can be achieved as compared to the case when the same liquid flows
through the same tube subjected to the same pressure drop and occupies the whole bore. This means that it
is possible to release more liquid than predicted by the Poiseuille law, even though in the bi-layer flow
liquid does not occupy the whole cross-section. This paradoxical result is related to the fact, that the
less viscous gas layer can flow much faster than the underlying liquid layer and entrain the latter via a
significant shear stress. This quasi-giant-slip phenomenon occurs in relatively large nanotubes
of the order of 500 nm dia.) where the no-slip condition holds with sufficient accuracy. This phenomenon
can be beneficial in reverse osmosis systems. In addition, parallel bundles of these carbon nanotubes are
used as nanoreactors to polymerize sufficiently monodisperse thermo-responsive nanoparticles of the order
of 400 nm dia. at the rate of 107 particles per sec. Nanoparticles of this size are therapeutically
beneficial and can be used as drug carriers. Controlled release from them modulated by temperature variation
was demonstrated.

Suggested Audiences: College

Phone: 508-831-5459

Last Modified: January 16, 2013 at 10:12 AM

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