John P. Leonard

Cooling Performance of Nanofluids in a Microchannel Heat Sink

This paper describes an experimental study on microchannel heat sink performance where ZnO nanoparticle suspended fluids are used as coolant. The microchannel heat sink has 65 parallel microchannels branched out from an inlet reservoir and then collected into an outlet reservoir. Its fabrication process is based on the standard photolithographic microfabrication technology. A main feature of the heat sink has an array of on-chip temperature sensors on the channel bottom surface along the channel. Thus, the channel wall temperatures are directly measured. Heat transfer coefficient for the nanofluid is measured and compared with that of DI water as reference. The experiments show that the heat transfer coefficient of the ZnO nanofluid is 13% higher than that of the base fluid at the Reynolds number of 3.8, although it is comparable with that of DI water at lower Re numbers. The experiments also show that the heat transfer coefficient as well as the Nusselt number increases as the Reynolds number increases.Copyright

Suppression of Dewetting in Pulsed Laser Melting of Thin Metallic Films on SiO 2

Pulsed excimer laser projection irradiation has been successfully applied to completely melt and resolidify encapsulated elemental metal films of Au, Cu, Cr, and Ni directly on amorphous SiO 2 substrates. A combination of narrow irradiated lines and appropriate SiO 2 capping layers was used to obtain films that do not dewet when fully melted. Detailed processing maps were generated for Au and Ni, while equivalent trends for Cu and Cr were also noted. These systems were analyzed for common behaviors, and from these the principle factors, a basic process map is proposed to describe adequately these four systems. Experimental parameters and sample preparation criteria are presented to realize such resolidification studies in other metal systems.

Microstructural Evolution during Post Deposition Annealing of Pulsed Laser Deposited Fe(100-x) Pdx Thin Films

FePd belongs to a group of L10 - intermetallics with attractive uniaxial hard-ferromagnetic properties. In this study thin films of different composition FeXPd1-X, X= 50, 60, were deposited by pulsed laser deposition (PLD) on amorphous SiO2 and Si3N4. We characterized the microstructural evolution during the different order/disorder phase-transformations during post-deposition annealing relative to the as-deposited state in terms of morphology, grain size, texture and presence of short-range order using SEM, XRD and TEM. VSM measurements were used to monitor magnetic properties. Differences in these microstructural parameters are due to different ordering reactions FCC to L10 ordering and concomitant phase separation of ?-Fe vs. FCC to L10 ordering upon heat treatment. The relationships of the different phase transformation products to properties are discussed. Support from NSF-DMR-Metals is gratefully acknowledged.