Heat transfer study on flowing liquid film of SiO2-water nanofluid with surfactant confined by metallic foam

To solve the urgent issue of rapid heat dissipation in narrow spaces of electronic devices, the nanofluid as coolant is an effective way, in the cases that the thermo-physical properties and stabilities of coolant solution can be improved by the dispersion of nanoparticles and surfactant in the base fluid, and scattering sodium dodecyl benzene sulphate (SDBS) as the surfactant and SiO2 nanoparticles, respectively, at different concentration ratios into the base fluid of water to form SiO2-SDBS-water (SSW) nanofluid in current research. In the liquid film of SSW nanofluid flowing across heating surface confined by porous metal foam, the effects of the concentration ratios of nanoparticles and surfactant on heat transfer and mechanism of heat transfer enhancement are analyzed in gradual heating and rapid cooling. The boiling and cooling performances can be improved in the SSW nanofluids with the proper concentrations of SiO2 nanoparticles as well as matching surfactant, and the deterioration in heat transfer occurs with the mentioned concentrations exceeding the critical values. In the cooling process, the variation of critical heat flux happens with the concentrations of SiO2 nanoparticles and sodium dodecylbenzene sulfonate in the SSW nanofluids, and the concentration ratio of SiO2 nanoparticles to surfactant should be optimized to enhance heat transfer. Specifically at constant SDBS concentration of 50 ppm, and the relative better heat transfer performances can be obtained at SiO2 concentration of omega(SiO2) = 100 ppm, in which the removed heat flux increased by 19%, the cooling time shortened from 8.1 to 5.7 seconds and the critical heat flux increased by 18% in comparison with deionized water. The optimized concentration ratio of SiO2 nanoparticles to SDBS to benefit heat transfer changes with variation of SiO2 nanoparticles in nanofluid at the relatively higher superheat temperature.