Abstract
In addition to the increase of thermal conductivity, heat transfer enhancement mechanism for nanofluids also includes the changes of the flow characteristics, therefore it is needed to take an in-depth research on nanofluids flow characteristics. In this paper, the flow characteristics of H2O and SiO2-H2O nanofluids in a rectangular convex channel (channel composed of continuous staggered rectangular convex platform) at the Reynolds numbers 2300, 2500, 3000 and 4000 are studied by the quantitative PIV method (Fig. 1a). The rectangular convex channel (Fig. 1b) has periodic perturbation effect on the fluid flow, so that the flow direction is changed for several times, and vortexes are generated, which makes turbulence enhanced. In this way, flow is in the intense turbulent state under a low flow rate. Results show that the flow fields becomes more chaotic by the addition of nanoparticles (Fig. 2 and 3). Both the number and the size of vortices increase observably. The vorticity of nanofluids is also enhanced compared with H2O, and with the increase of Reynolds number, the increased ratio in the vorticity magnitude is getting higher (Fig. 4). At different Reynolds number, the pressure loss of nanofluids increases by 2.27%, 2.23%, 1.5% and 14.7%, respectively. As shown the flow resistance does not increase significantly compared to base fluids, especially at low Reynolds number. It can be concluded that the interaction between nanoparticles and the basic fluid strengthens the flow field disturbance, which is benefit to the heat transfer of nanofluids.
