Analysis on wall slip phenomenon andcharacteristics of sewage sludge
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Abstract:
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.
