No abstract

No abstract

No abstract

Gelation and breakage of model wax−oil systems is investigated using microscopy, densitometry, rheometry, and XRD. Various model waxy oils are prepared, including 1 to 20 wt % (w/w) macrocrystalline wax in dodecane, 1 to 20 wt % microcrystalline wax in dodecane, and 5 wt % macrocrystalline wax in Primol 352. The influence of shear history, thermal history, and fluid composition is ascertained. A novel gel breakage model is introduced which spans the entire mechanical response of wax gels from initial Hookean behavior at low strains to equilibrium slurry flow at the infinite strain limit. The local rheology model will benefit shut-in and restart processes of waxy crude pipelines via application of standard fluid mechanics relationships.

No abstract

A 3-D axisymmetric model is developed to predict pressure wave propagation processes during gelled waxy oil pipeline restart operations. A finite volume method is implemented on a staggered grid. An iterative predictor-corrector algorithm provides solutions to the combined parabolic-hyperbolic set of governing equations. A new shear-historydependent thixotropic rheology model is proposed for pressure wave propagation computations. Moderate Reynolds number flows within the laminar regime are computed, demonstrating the impact of inertial effects. The results clearly illustrate the important mechanisms of pipeline restart. The nature of pressure wave propagation is governed by gel strength as well as overall fluid compressibility. Three sequential pressure wave propagation regimes are dominated by inertial, viscous, and gel degradation phenomena, respectively. The viscous and gel degradation regimes are effectively coupled by imposed deformation conditions. For initially homogenous thixotropic gels, strain tends to localize near the pipeline wall, playing a central role in assuring the pipeline restart.

An experimental investigation of waxy oil gelation behavior is performed using the methods of rheometry, optical analysis, tensiometry, and microscopy. Thermal history, shear history, asphaltene content, and chemical additives influence the gelation process. Consequently, the final gel state is strongly correlated to the gelation conditions. Various model wax−oil systems are prepared, including 5 wt % microcrystalline wax or 5 wt % macrocrystalline wax in dodecane, as well as 5 wt % macrocrystalline wax in Primol 352. Real waxy crude oils UL-YS1 and Se-7-E06 are also investigated. A new yield stress model is developed on the basis of experimental results and a modified Eyring theory to provide gel strength predictions for petroleum transport pipelines. In the absence of shear during gelation, the yield stress can be correlated with the thermal history. However, for non-quiescent gelation conditions, the gel strength is also dependent upon the imposed shear history during the gelation process. The imposed shearing influences the growth process of a volume-spanning crystal network. Finally, pressure wave propagation calculations are performed following the Rønningsen convention, highlighting the impact of yield stress on startup lag times associated with wax gelation in field transport pipelines.

Rinsing with the essential oil mouth rinse can have long-lasting effects in reducing anaerobic bacteria overall as well as Gram-negative anaerobes and VSC-producing bacteria. The significant reductions in numbers of these bacteria produced by the essential oil mouth rinse, both in plaque and on the dorsum of the tongue, can play a key role in explaining the essential oil mouth rinse's effectiveness in reducing supragingival plaque and gingivitis as well as its effectiveness in controlling intrinsic oral malodor over prolonged periods.