The effects of apparent wall slip on rheometric measurements of waxy gels are quantified for gels consisting of a macrocrystalline wax added in mineral oil in concentrations of 3.0 and 7.5 wt. %. The waxy gels are formed in situ in a stress-controlled rheometer, and rheological properties are then obtained. Seven different geometry configurations, including parallel plates, concentric cylinders, and vane, are employed. The surface roughness of the different geometries and wax crystals size are assessed to provide insight into the apparent wall slip phenomenon. In the presence of smooth surfaces, a decrease in approximately 80% in the measured yield stress value is observed in oscillatory tests, regardless of system composition. In addition, the storage modulus measurements are substantially different when obtained from smooth or grooved geometries. In creep experiments, the yield stress measurements decrease by 68%. As expected, apparent wall slip markedly affects the shape of the flow curves obtained, causing the appearance of kinks for smooth Couette geometry. Apparent slip velocities are calculated in the regime just above the yield stress, and it is found that for low concentrations apparent slip increases with concentration and decreases with the ratio between the shear stress and dynamic yield stress. The gathered results also demonstrate that the reproducibility of rheological measurements is improved by using geometries with grooved parts. By quantifying the effects of apparent wall slip on rheological measurements of waxy gels for different geometries, this work can provide useful information for the design of pipelines and oil transportation processes.

中文翻译：

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明显的壁滑效应对蜡状凝胶流变测量的影响

对于由以3.0和7.5wt。％的浓度添加到矿物油中的大晶蜡组成的凝胶，量化了表观壁滑对蜡状凝胶的流变学测量的影响。％。蜡状凝胶原位形成在应力控制的流变仪中，然后获得流变性质。采用了七种不同的几何构型，包括平行板，同心圆柱和叶片。评估了不同几何形状和蜡晶体尺寸的表面粗糙度，以提供对表观壁滑现象的洞察力。在存在光滑表面的情况下，无论系统组成如何，在振荡测试中均可观察到屈服应力值的测量值降低了约80％。另外，当从光滑或凹槽的几何形状获得时，储能模量测量值基本上不同。在蠕变实验中，屈服应力测量值降低了68％。正如预期的那样，明显的壁面滑移会显着影响所获得的流动曲线的形状，从而导致出现光滑的Couette几何形状的扭结。在刚好高于屈服应力的状态下计算表观滑移速度，发现对于低浓度，表观滑移随浓度的增加而增大，并随剪切应力与动态屈服应力之比的减小而减小。收集的结果还表明，通过使用带有槽形零件的几何形状，可以改善流变学测量的可重复性。通过量化表观壁滑对不同几何形状的蜡状凝胶流变学测量的影响，这项工作可以为管道和输油工艺的设计提供有用的信息。收集的结果还表明，通过使用带有槽形零件的几何形状，可以改善流变学测量的可重复性。通过量化表观壁滑对不同几何形状的蜡状凝胶流变学测量的影响，这项工作可以为管道和输油工艺的设计提供有用的信息。收集的结果还表明，通过使用带有槽形零件的几何形状，可以改善流变学测量的可重复性。通过量化表观壁滑对不同几何形状的蜡状凝胶流变学测量的影响，这项工作可以为管道和输油工艺的设计提供有用的信息。