The operating condition of a submerged propeller has a significant impact on flow field and energy consumption of the oxidation ditch. An experimentally validated numerical model, based on the computational fluid dynamics (CFD) tool, is presented to optimize the operating condition by considering two important factors: flow field and energy consumption. Performance demonstration and comparison of different operating conditions were carried out in a Carrousel oxidation ditch at the Yingtang wastewater treatment plants in Anhui Province, China. By adjusting the position and rotating speed together with the number of submerged propellers, problems of sludge deposit and the low velocity in the bend could be solved in a most cost-effective way. The simulated results were acceptable compared with the experimental data and the following results were obtained. The CFD model characterized flow pattern and energy consumption in the full-scale oxidation ditch. The predicted flow field values were within -1.28 ± 7.14% difference from the measured values. By determining three sets of propellers under the rotating speed of 6.50 rad/s with one located 5 m from the first curved wall, after numerical simulation and actual measurement, not only the least power density but also the requirement of the flow pattern could be realized.
Making good use of vertical axis wind turbines (VAWTs) is an attractive and potential way to deal with the energy and environmental issues due to the unique superiorities of it. Computational Fluid Dynamics (CFD) technology is a useful tool for the design process of VAWTs. Various turbulence models have been developed and available for turbulent flow simulations. Currently, there have been few researchers studying on meshing strategies and turbulence model selections of VAWT simulations. In this paper, 2D unsteady models under 4 meshing strategies and 6 turbulence models were established and simulated to investigate the effect of the above two aspects on numerical simulations of VAWTs. The numerical results were compared with the experimental data of Oler et al. (“Dynamic stall regulation of the Darrieus Turbine,” SAND Report No. 83–7029, Sandia National Laboratories, Albuquerque, 1983, pp. 67–96) and the analytical solution of Deglaire et al. (Eur. J. Mech., B: Fluids 28(4), 506–520 (2009)). The results reveal that a mesh of 213 656 grids is sufficient to meet the requirements of grid independence with the help of boundary layer and size function techniques. Besides, the realizable k-ε model enables the closest CFD simulation of the experimental data and shows better prediction performance than the analytical model of Deglaire et al. and other turbulence models.
Phosphorylated chitosans were synthesized as templates to manipulate hydroxyapatite (HA) crystal nucleation, growth and microstructure. Two kinds of insoluble phosphorylated chitosan were soaked in saturated Ca(OH)2 solution for 4 d and in 1.5× SBF (simulated body fluid) solutions for 14 d at 37 °C for biomimetic mineralization. A lower [P]-content of phosphorylated chitosan promoted greater mineralization than higher [P]-content. Phosphorylated chitosan inhibited osteoblast proliferation and differentiation in vitro, while calcium phosphate phosphorylated chitosan composites did not.
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