Monday, October 16, 2017

3:00pm - 4:00pm

Hydrodynamic Focusing on Nano-Textured Surfaces and Spray Cooling of High-Power Microelectronics

Abstract A novel approach to enhancement of drop and spray cooling for microelectronic, optical and radiological elements and server rooms, which release 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 nano-textured 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 appear to be dynamically permeable for coolant drops, irrespective of their static wettability properties. For example, Teflon nano-textured surfaces are also dynamically wettable by water 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. The dynamic wettability phenomenon is linked to the hydrodynamic focusing effect, which is revealed in detailed experiments and described theoretically. It is shown that hydrodynamic focusing and spread-out drop pinning arise due to a dramatic disparity in sizes: D/d>>1, where D is the drop size (of the order of 1 mm, and d is the pore size in nano-textured surfaces, which is of the order of 1-10 micron).

BiographyMSc-1977, PhD -1980, DSc (Habilitation-1989), all in Physics and Mathematics. Affiliations: The Institute for Problems in Mechanics of the USSR Academy of Sciences, Moscow, The Technion-Israel Institute of Technology; Distinguished Professor at The University of Illinois at Chicago; The Fellow of the American Physical Society. The author of 4 books, 12 book chapters, 310 research papers, and 6 patents. Co-Editor of "Springer Handbook of Experimental Fluid Mechanics", the Associate Editor of "Experiments in Fluids". He was the Fellow of the Rashi Foundation, The Israel Academy of Sciences and Humanities, and was awarded Gutwirth Award, Hershel Rich Prize and Prize for Technological Development for Defense against Terror.