In situ characterization of enhanced thermal performance by periodic nanostructures on the surface of a microchannel

In situ formation of nanofins (i.e. isolated and dispersed precipitation of nanoparticles) on flow conduits induces changes to the surface morphology for heat exchange, increasing effective surface area and enhancing their cooling performance. Furthermore, the existence of these nanostructures has a significant influence on heat transfer, as opposed to the thermo-physical properties (e.g. thermal conductivity) of cooling fluids enhanced by addition of nanoparticles. This study conducted an in situ analysis exploring the effects of nanoscale surface modifications on forced convective heat transfer and thermal performance. A numerical heat transfer analysis, based on the conductive/convective heat transfer between a fin base and deionized water (DIW), was performed with the assumption that periodic nanostructures existed on the heated microchannel surface. Predictions of enhanced thermal performance (between 37% and 143%) from the resultant increase in the effective heat transfer area were validated for flows over these nanostructures (artificial nanofins) fabricated by SFIL (step and flash imprint lithography) inside a microchannel. Polydimethylsiloxane microchannels are bonded to a silicon wafer containing thin-film thermocouple arrays deposited onto artificial nanofins, which had been fabricated a priori for the in situ characterization of thermal performance. It was found that the convective heat transfer Nusselt number (Nu) increased from 61% to 110%. Additionally, a theoretical analysis of the pressure drop was also successfully achieved for a comprehensive understanding of the heat transfer characteristics at the fluid-wall interface of a microchannel.