Authors Geißler, P. ; Domurath, J. ; Ausias, G. ; Ferec, J. ; Saphiannikova, M.
Title Viscosity and dynamics of rigid axisymmetric particles in power-law fluids
Date 01.01.2023
Number 60529
Abstract The addition of rigid axisymmetric particles, like spheroids or rods, to a liquid leads to a noticeable increase of the viscosity of the mixture. The stress tensor in such suspensions can be described by the transversely isotropic fluid (TIF) equation. The TIF equation depends on three rheological parameters which are functions of the particle aspect ratio. Exact analytical solutions of the rheological parameters are only known for spheroidal particles in a Newtonian fluid. For rods only approximations are available.<br />In this contribution, we provide a mini-review of our recent numerical simulations to compute the rheological coefficients in the dilute regime. For spheroids in a Newtonian fluid we obtain the same result as Lipscomb et al. In the case of rods in a Newtonian fluid, we found that the slender body approximation of Batchelor considerably underestimates the first rheological coefficient. If the suspending fluid becomes non-Newtonian, the magnitude of all three rheological coefficients decreases significantly. Furthermore, an additional dependence of the first rheological coefficient on the particle orientation is found.<br />Additionally, we investigated the instantaneous angular velocity of spheroids and rods in the power-law suspending fluid. We found a very small influence of the shear thinning exponent, which is opposite for oblate and prolate particles. In overall, it is shown that the rotational dynamics of highly anisometric particles is well described by Jeffery´s equation even in a strongly thinning suspending fluid.
Publisher Journal of Non-Newtonian Fluid Mechanics
Citation Journal of Non-Newtonian Fluid Mechanics 311 (2023) Article Number: 104963

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