污泥的滑移现象及其特性分析

Analysis on wall slip phenomenon and characteristics of sewage sludge

为了确定对于脱水污泥是否存在滑移现象以及影响壁面滑移的可能因素,采用平行板旋转流变仪(AR2000)并借助高速摄像机进行实验,采用直线标记法观察滑移现象,考察了应力应变数据对平行板间距的依赖性,同时研究阶跃应变扫描时间应力曲线的趋势。结果表明,剪切试验表明随着应变增大,含水率80%的污泥,剪切应力在某一处发生分叉,即剪切应力依赖于间距,说明发生了滑移现象,同时将其用来研究临界剪切应力以及计算滑移速度的大小,初步拟合出剪切应力和滑移速度的公式。而含水率90%的污泥应力应变污泥曲线重合较好,即没有滑移发生。同时对含水率80%的污泥在不同剪切速率下进行了5s和60s的扫描,5s与60s情况下剪切速率分别于大于10s-1和0.5s-1时时间应力曲线出现峰值情况,即均有滑移现象发生,故浓度、剪切速率和时间均对滑移有一定影响。

Wall slip of sewage sludge and possible slip in fluencing factors are studied experimentally by using a rotational rheometer with parallel plate fixtures and by high speed camera.The technique involves placing a straight line marker to monitor wall slip,checking the gap dependence of the stress-strain data and studying the time-stress data trend of strain stepped scanning.In the shearing flow it is found that,for sewage sludge of water content 80%,as the strain amplitude increases,the stress data starte to diverge at a certain strain amplitude,indicating that wall slip occurs.Meanwhile,it has been utilized for studying the critical shear stress and calculating the slip velocity,and the formulation of shear stress and slip velocity are fitted.But for sewage sludge of water content 90%,these curves are superimpose,indicating no slip occurs.While scanned sewage sludge water content 80% at different shear rates in 5 s and 60 s,it is found that under 5 s and 60 s,when the shear rate is greater than 10 s-1 and 0.5 s-1 respectively,peak appeas in time-stress curves,i.e.slip occurs.Therefore,concentration,shear rate and time have influence on wall slip.