污水土地处理系统中管网铺设率对流态的影响与CFD模拟

污水土地净化系统的水力特性直接影响污染物的处理效果,研究不同管网铺设率对水流流态的影响,可为设计参数的选择及反应器结构优化提供依据.因此,运用示踪-应答技术,以停留时间分布(RTD)理论为基础,对反应器中水流的状态进行分析.同时,借助计算流体力学(CFD)软件Fluent进行数值模拟.RTD分析和CFD模拟结果互补分析发现,底部的碎石层具有布水功能,而表面的水层具有集水的作用:水流在承托层中水平流动,竖直流经填料层,最后在水层中水平流入集水管网.在有承托层和水层的情况下,系统采用不同管网铺设程度的布水和集水方式对填料中水流的流态影响不大,然而管网孔口布水效果不均.各管网铺设率反应器的体积效率均在90％以上,但都有一定的无效体积或滞留区.半网布水、集水的反应器体积效率最高,流态接近推流形式.无因次平均停留时间为1.09,轴向扩散系数为0.037.

Flow pattern and CFD simulation in wastewater land treatment system with various kinds of net-pipe

The hydrodynamics of wastewater land treatments system has a direct influence on the removal efficiency of pollutants. By studying the effect of net-pipes, a solid basis will be provided for design and optimization purposes. On the basis of residence time distribution (RTD) theory, the flow pattern in a land treatment reactor was analyzed using tracer-response technology. Computational fluid dynamics (CFD) software Fluent was utilized to simulate the flow pattern of water. By combining the results of tracer experiment with CFD simulation, the bear-layer was clearly shown to have the function of distributing water and the water-layer was clearly capable of collecting water from the whole water-carrying section. After flowing horizontally through the bear-layer, the water passed through the packing vertically before finally reaching the collection net-pipe in the water-layer. The net-pipe distribution was shown to have a negligible influence on the flow pattern in the absence of bear-layer and water-layer. However the water distribution of net-pipe holes was uneven. Even though the volume efficiency was all above 90%, there were parts of useless or stagnant zone. The highest volume efficiency was obtained in the reactor with half distribution and collection net-pipe, where the flow pattern was different from the plug flow. The dimensionless mean residence time was 1.09, and the degree of dispersion was only 0.037.