Numerical and experimental studies on multi-phase flows in microchannels

Official URL: http://risc01.sabanciuniv.edu/record=b1615029 (Table of Contents)

Microchannels are considered as one of the key elements in thermal management of microsystems. Despite the advantages of the microchannels, understanding of the fundamental hydrodynamic and thermal transport mechanisms in multiphase flows in them is far from satisfactory. Therefore, in this thesis using numerical and experimental approaches, it is aimed to focus on the understanding of phase change phenomena in order to be able to make use of them. In the first study, convective heat transfer of alumina/water nanofluids in a microtube is presented using a numerical approach. The effects of nano-particle size and concentration on convective heat transfer are studied. Next, the effect of MWCNTs (multi-wall carbon nanotubes) on convective heat transfer was experimentally studied. The effect of MWCNT concentration on thermal performance is presented. In the second study, high mass flux subcooled flow boiling of water in microtubes is investigated. Both experimental and numerical approaches are implemented to investigate high mass flux flow boiling in micro scale. Heat transfer coefficients are obtained as a function of mass flow rate, heat flux, and vapor quality. In the third study, the effects of surface wettability and roughness on flow boiling in a rectangular microchannel are presented. Micro and nano-structured and nano-coated surfaces are integrated into the channel to investigate the effect of surface characteristics on flow map, bubble formation and release and boiling heat transfer.