An experimental investigation on flow boiling heat transfer enhancement using Cu-TiO2 nanocomposite coating on copper substrate

Flow boiling heat transfer performances of Cu-TiO2 nanocomposite coated copper surfaces have been studied experimentally in this work for its potential use in heat transfer applications. Experimental studies are performed in a bottom surface heated minichannel with DI water as the coolant. Thin Cu-TiO2 nanocomposite coated copper surfaces are developed using electrocodeposition technique. Coated surfaces developed through this technique have varied surface properties such as wettability, porosity, crystallinity, etc. The developed coated surfaces are characterized with respect to porosity, mean pore diameter, roughness, contact angle, and coating thickness. Flow boiling heat transfer experiments are performed at different mass fluxes in an experimental setup developed for this purpose. The results obtained with bare copper surface are used as the reference data for comparing the performances of the coated surfaces. The Cu-TiO2 coated copper surfaces are found to augment single-phase heat transfer coefficient slightly, whereas the enhancement in the two-phase region is up to 94% depending on the mass flow rate of coolant and heater surface temperature. The critical heat flux (CHF) also augments for the nanocomposite coated surfaces up to 92%. The augmentation in CHF and heat transfer coefficient of Cu-TiO2 coated surfaces is due to the enhanced surface roughness, wettability improvement, and presence of high-density active nucleate site on the surface. In order to have appreciation of the results obtained in present work, the boiling curves and CHF against mass flux for the bare and coated surfaces are compared with previously published experimental results. Thus, the arrangement of the minichannel and porous surface offers a capable choice for compact small size cooling devices due to decreased wall superheat temperature, high CHF, and high heat transfer coefficient.