Direct flow simulations of thixotropic liquids in agitated tanks

Abstract

Simulations of transitional and turbulent flows of purely viscous thixotropic liquids in stirred tanks have been performed. The simple thixotropy model employed is based on the notion of a network in the liquid with an integrity that builds up with finite rate under quiescent conditions and breaks down under liquid deformation. We solve a transport equation for the network integrity which is two-way coupled to the latticeBoltzmann-based flow solver. The liquid's time scale characterised by the dimensionless Deborah number demonstrates to have profound impact on the level of mobilisation and the flow patterns in the mixing tanks, especially if the time scale of the liquid is of the same order as the circulation time in the tank. It also is shown to what extent increasing the impeller speed improves mobilisation.On a effectué des simulations de courants transitoires et turbulents de liquides thixotropes purement visqueux dans des cuvesà agitation. Le modèle thixotrope simple employé est fondé sur la notion d'un réseau dans le liquide avec une intégrité qui s'accumuleà un taux fini dans des conditions quiescentes et se décompose lors d'une déformation liquide. Nous avons résolu uneéquation de transport pour l'intégrité du réseau qui est couplée de façon bidirectionnelle au résolveur de flux fondé sur Lattice Boltzmann. L'échelle de temps du liquide caractérisée par le nombre de Deborah sans dimension démontre une incidence profonde sur le degré de mobilisation et les modèles de courant dans les cuves de mélange, surtout si l'échelle de temps du liquide est du même ordre que le temps de circulation dans la cuve. On démontreégalement dans quelle mesure la vitesse de l'impulseur améliore la mobilisation.

Hydrodynamics in a stirred tank in the transitional flow regime

“…Ultimately, the full resolution of the time-dependent Navier-Stokes equations on an extremely fine 3-dimensional mesh would be desirable however such simulations require excessive com puting efforts, which may not be viable for practical engineering applications. As a result, there are very few studies in the literature that deal with the simulation of transitional flow in stirred tanks and almost ail of the available literature may be attributed ta a single author (Derksen, 2011(Derksen, , 2012a(Derksen, , 2012b(Derksen, , 2013Zhang et al, 2017). In his studies, Derksen has used the Lattice Boltzmann method ta perform direct numerical simulations (ONS) of flows with Reynolds numbers in the range 2000-12000.…”

Thixotropic Rheological Behavior of Maya Crude Oil

“…Thixotropy affects flow in mixers − and flow in pipes and pipelines and is particularly evident during restart operations following flow disruption, arising from gel formation, asphaltene precipitation, or maintenance, among other causes. Impacts are more likely and more severe at low temperatures.…”

Effect of Pressure on the Rheological Properties of Maya Crude Oil

“…Thixotropy can be responsible for order of magnitude changes in reported viscosity values. The impacts of thixotropic behavior are particularly evident during restart operations following flow disruption in a pipeline and during blending and mixing operations − and tend to become more significant at low temperatures . Although one can anticipate that the impact of increasing pressure is equivalent to the impact of decreasing temperature, there do not appear to be extant studies that report the effect of pressure on thixotropic properties of fluids, in general, or within the context of heavy oil and bitumen, in particular.…”