Conference Year
2016
Keywords
Carbon/Carbon, Flow Boiling, R134a
Abstract
With the increase of heat flux densities following the Moore’s law, electronic cooling challenge is focused on the high heat flux to be dissipated by the operating fluid and more and more efficient heat spreaders, dissipators, and compact heat exchangers are in great demand for various applications. Considering the device efficiency, the boiling heat transfer ensures very high heat transfer coefficients, which can even be improved via specific surface treatments that have been shown to be very effective. In particular, several authors, experimentally demonstrated the interesting enhancement capabilities of microparticles coatings on the Critical Heat Flux. Furthermore, the recent work on nanoscale domain has led to new concepts for surface modification. In the last decade, nano-structured materials (i.e. nanowires coatings, nanoporous layers, Carbon Nano Tube arrays, etc.) have been proved to enhance the boiling heat transfer. Unfortunately, almost all of this kind of surface treatments fail when scaled up to industrial implementation because of the relatively high costs and complex operations involved. Furthermore, compactness and lightness of cooling systems are becoming even more challenging design constraints leading the research efforts towards new light and efficient materials. In this scenario, the Carbon/Carbon material appears to be a viable option for future thermal management devices because it exploits interesting properties having a low density and a high thermal conductivity; moreover, it is already used in many industrial applications where it is shaped in various forms even complex. This paper presents the experimental measurements carried out during flow boiling heat transfer of R134a on a Carbon/Carbon surface. The test section with the Carbon/Carbon sample, is electrically heated from the bottom and it is instrumented with 18 wall thermocouples to monitor the temperature distribution at an imposed heat fluxes of 50 kW m-2, and refrigerant mass flow rates from 50 to 200 kg m-2 s-1, at constant saturation temperature of 30 °C. The sample is tested in a new experimental facility built at the Nano Heat Transfer Lab of the Department of Management and Engineering of the University of Padova especially designed to study the flow boiling heat transfer process on innovative materials and enhanced micro- and nano-structured surfaces.Â