Flow boiling, along with single phase heat transfer performance in a micro-channel that its inner surface has been coated by SiO 2 nanoparticles was investigated experimentally in this thesis. Flow boiling in a vertical capillary micro-channel with enhanced wettability due to nanoparticles deposition on inner surface of micro-channel showed augmented critical heat flux (CHF). Experiments were performed in a single capillary micro-channel having internal diameter of 1.07mm and 200mm long using vertical upward de-ionized (DI) water flow. Electrical elements installed on the outer of surface of micro-channel were used to apply heat to the test section. Inlet sub-cooled temperature of DI-water was 30?C, and different mass fluxes of 275, 469 and 698 kg/m 2 .s and heat fluxes up to 270 kW/m 2 were used in the experiments. The effect of mass and heat fluxes on single phase and flow boiling heat transfer coefficient (HTC) and critical heat flux in micro-channel with bare surface were evaluated. Convective heat transfer coefficient of single-phase water flow in micro-channel increased with the heat flux mass flux. In flow boiling region, heat transfer coefficient increased with heat flux at first, passed through a maximum and decreased afterwards. Heat transfer coefficient was almost independent of mass flux for the two values of 469 and 698 kg/m 2 s investigated in this thesis. Critical heat flux increased with mass flux. The inner surface of micro-channel was modified by depositing SiO 2 nanoparticles during flow boiling of nanofluid with volumetric concentration of 0.1%. Results from the micro-channel with bare surface are used as reference data. Nanoparticles deposited surface was found effective in enhancing the critical heat flux and up to 24% enhancement in critical heat flux was observed in the highest mass flux (698 kg/m 2 .s) used in this study. The flow boiling heat transfer coefficient reduced about 10% in nanoparticles deposited micro-channel compared to the bare micro-channel. Critical heat flux was almost the same in bare and nanoparticles deposited micro-channel in low superficial mass flux of 275 kg/m 2 .s.
