The yield stress is a key rheological parameter of thick paste and critical design parameter of the high pressure pipeline system. Take coal slurry as an example, whether using vane method or curve extension method, the yield stress both exponentially increase with concentration increasing, but the data of yield stress in two methods is different. For pipes with different diameters, the yield stress showed in pipeline transportation varies during the extension of rheology curves. By contrasting the results of curve extension method and vane method using pipelines with different diameters, it comes that with a certain concentration and a certain range of diameter, yield stress with vane is bigger than that with curve extension, due to the effect of wall slip in pipe flow test.
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