Influence of Foam Morphology on Effective Properties Related to Metal Melt Filtration

Abstract

In this article, a numerical study on the sensitivity, related to the performance of open-cell foams used for the depth filtration of liquid metals, on two characteristic morphological properties is presented. Therefore, simulations of fluid flow and particle transport inside an artificial foam structure are carried out, whose porosity and strut shape is varied within a certain expected range. For comparison purposes, however, the simulations are also performed for three typical ceramic foam filters (CFF) with pore densities of 20 and 30 PPI, whose geometries are obtained from CT scans. In order to allow for a comparison between the different structures, a reference length is introduced that relies upon the actual ratio of pores per volume. The evaluation is mainly based on the comparison of the hydraulic tortuosity, the viscous and the inertial permeability coefficients as well as the initial filtration coefficient for alumina inclusions, with their size ranging from of 10 to 40 mm at process conditions typically encountered during the aluminum filtration. It is shown that the ratio of filtration coefficient and pressure drop increases with the porosity, while the material distribution between the struts and the joints is less influential. Finally, the article also provides information on the anisotropy of CFFs and on the transition behavior from steady to unsteady flow in open-cell foams.

Experimental Investigations of the Depth Filtration inside Open‐Cell Foam Filters Supported by High‐Resolution Computed Tomography Scanning and Pore‐Scale Numerical Simulations

“…At first, hydrodynamic effective properties were determined to characterize the nature of the flow. For the hydraulic tortuosity, a value of 1.10 was determined, which is relatively low in comparison to the values reported for open‐cell foams, indicating a homogenous material distribution with few or no closed windows. This is also reflected by the Darcy and Forchheimer coefficients of 2.56 × 10 −7 m 2 and 3.97 × 10 −3 m, respectively, which align with the upper range of literature values .…”

“…[5] In this context numerical methods are often used, although modeling of the filtration process is considerably challenging due to its complexity and hence several simplifying assumptions are invoked. [6] The primary objective of all these approaches is to increase the filtration efficiency either by modifying the filter surface [7] or by improving the filter geometry with respect to the flow characteristics [8] and resistance to the melt flow. The present investigation on water-based model introduces the computed tomography as an important tool for characterization of particle separation inside CFF and provides detailed insight into the filtration efficiency for the first time.…”

Liquid Immiscibility and Thermodynamic Assessment of the Al2O3–TiO2–SiO2 System

“…In practice, Al 2 O 3 -based filter systems are currently being developed for aluminum-based melt filtration. [1,2] Oxide films and Al 2 O 3 particles formed during melting and alloying can be present as a suspension on the surface of the melt or inside the melt because of flow turbulence. Spinel inclusions appear due to the presence of magnesium ions in the aluminum melt, mainly coming from the refractories of the furnace.…”

Numerical Modeling of Flow Conditions during Steel Filtration Experiments

“…Hence, additional hydrodynamic interactions between the inclusions and the wall, such as the attenuation of the inertial impact due to the displacement of the liquid melt, as reported by Heuzeroth et al, [30] were neglected and a simple adhesion condition was employed. Detailed descriptions of the adopted particle tracking model and the determination of the filtration coefficient can be found in Werzner et al, [31,35] and hence are not presented here for the sake of brevity.…”