NUMERICAL AND EXPERIMENTAL STUDIES ON MULTI-PHASE FLOWS IN MICRO-CHANNELS
Abdolali Khalili Sadaghiani
Mechatronics Engineering, MSc. Thesis, 2015
Assoc Prof. Ali Koşar (Thesis Advisor)
Assoc. Prof. Mehmet Yıldız
Prof. Dr. Yoav Peles
Assist. Prof. Gözde İnce
Assoc. Prof. Burç Mısırlıoğlu
Date & Time: 27th, 2015 – 14:30
Place: FENS L030
Keywords : Multiphase flows, Microchannel, Structured and coated-surfaces, Flow boiling, Nanofluid
Microchannels are considered as one of the key elements in thermal management of micro-systems. Despite the advantages of the micro-channels, understanding of the fundamental hydrodynamic and thermal transport mechanisms in multi-phase 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 multi-phase flows in order to be able to make use of them. Three types of multi-phase flows in micro-channels are investigated as (i) nanofluid convective heat transfer (ii) high-mass subcooled flow boiling (iii) flow boiling on structured and coated-surfaces.
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.