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在沉淀过程中,当进水的温度和浊度发生较大变化,常引起平流式沉淀池内水流的密度差异,使之呈分层流动状态,这种现象称为异重流。异重流导致水流的“短流”,降低沉淀池的容积利用率,从而降低处理水的沉淀效果。在此情况下,称水流为不稳定。反之,如沉淀池内不产生异重流现象,则称该水流的稳定性较好。常以弗罗德准数F_r作为衡量水流稳定性的指标。在平流式沉淀池中,F_r值应大于1×10~(-5)～3×10~(-5)为宜。F_r值越大,水流越稳定。至于为什么弗罗德准数能用来判别水流稳定性,其数值大小的根据何在,在有
In the precipitation process, when the temperature and turbidity of the influent water are changed greatly, the density difference of the water flow in the advection-type sedimentation tank is often caused, making it a stratified flow state. This phenomenon is called hetero-reflow. The concentric flow results in a “short flow” of the water flow, reducing the volumetric utilization of the sedimentation tank, thereby reducing the precipitation effect of the treated water. In this case, the flow is said to be unstable. On the contrary, if the sedimentation tank does not produce the phenomenon of gravity flow, the stability of the water flow is said to be better. The Freud criterion F_r is often used as an indicator of water flow stability. In the advection sedimentation tank, the F_r value should be more than 1×10~(-5)~3×10~(-5). The larger the F_r value, the more stable the flow of water. As to why the Ververdial can be used to determine the stability of water flow, the basis of its magnitude is