Particle-resolved simulations of liquid fluidization of rigid and flexible fibers
- PDF / 5,137,883 Bytes
- 11 Pages / 595.276 x 790.866 pts Page_size
- 86 Downloads / 164 Views
O R I G I NA L PA P E R
J. J. Derksen
Particle-resolved simulations of liquid fluidization of rigid and flexible fibers
Received: 6 July 2020 / Revised: 22 August 2020 / Accepted: 21 September 2020 © The Author(s) 2020
Abstract Particle-resolved, three-dimensional, time-dependent simulations of rigid and flexible cylinders fluidized by a liquid flow in fully periodic domains have been performed by means of the lattice-Boltzmann method supplemented with immersed boundaries. The solids volume fraction ranges from 0.10 to 0.48 and the length-over-diameter aspect ratio of the cylinders from 4 to 12. The bending stiffness of the cylinders is the third major input parameter. The resulting Reynolds numbers based on the average slip velocity of the cylinders and their equivalent diameter range from 6 to 70. It is shown that increasing the flexibility—that is, decreasing the bending stiffness—reduces the Reynolds number, an effect that is most pronounced for low solids volume fractions and long cylinders. As for rigid cylinders, the distribution of the orientation relative to the direction of gravity of the flexible cylinders is a pronounced function of the solids volume fraction and the aspect ratio. Flexibility tends to somewhat randomize the orientation distribution, which could explain the effect of flexibility on the slip velocity and thus the Reynolds number.
1 Introduction Fiber suspensions are encountered in a number of process engineering applications. Two examples are pulp processing for paper production [1] and processing of bagasse—which is a fibrous residue from the production of sugar from sugarcanes—for, e.g., making biofuels [2]. Fiber suspensions are complex systems. In order to characterize them, one needs an extensive number of parameters and properties such as the fiber volume fraction, the size distribution of the fibers as well as their mechanical and surface properties. In principle, all these have an impact on the processability of the suspensions. Being able to anticipate the flow behavior of specific fiber suspensions has relevance for process design and optimization. In this paper, we make an attempt to quantify fiber suspension flow by means of numerical simulation. In the simulations, the objective is to account for the suspension properties in as much detail as possible. The main fiber properties we consider in the simulations are their shape that we quantify as the length over diameter aspect ratio and their bending stiffness. The continuous-phase fluid the fibers are suspended in is assumed to be a Newtonian liquid. The applications we have in mind concern non-Brownian fibers with diameters typically in the range from 0.1 to 1 mm. On these length scales, solids and fluid inertia is appreciable with fiber-based Reynolds and Stokes numbers significantly larger than 1. There is significant experimental and computational literature on fibers with (sub)micrometer diameters suspended in liquids, mostly inspired by biological applications, for which inertia is not significant—see the excellent
Data Loading...
