Permeability of Aluminium Foams Produced by Replication Casting

Abstract

Abstract:The replication casting process is used for manufacturing open-pore aluminum foams with advanced performances, such as stability and repeatability of foam structure with porosity over 60%. A simple foam structure model based on the interaction between sodium chloride solid particles poorly wetted by melted aluminum, which leads to the formation of air pockets (or "air collars"), is proposed for the permeability of porous material. The equation for the minimum pore radius of replicated aluminum foam is derived. According to the proposed model, the main assumption of the permeability model consists in a concentration of flow resistance in a circular aperture of radius r min . The permeability of aluminum open-pore foams is measured using transformer oil as the fluid, changing the fractions of initial sodium chloride. Measured values of minimum pore size are close to theoretically predicted ones regardless of the particle shape. The expression for the permeability of replicated aluminum foam derived on the basis of the "bottleneck" model of porous media agrees well with the experimental data. The obtained data can be applied for commercial filter cells and pneumatic silencers.

The permeability of virtual macroporous structures generated by sphere packing models: Comparison with analytical models

“…It can be seen that the window radius more than doubles over the range of capillary radius investigated and that the coordination number increases much more significantly than for the very small change in packing fraction than would be predicted by the Nc expression in Eq 1 (although for constant capillary radius, changes in porosity lead to increases in coordination number that are consistent with those predicted by Eq 1). If Nc is determined from the porosity alone, using Eq 1 (from [6]), CFD predictions are still in reasonable agreement, overestimating the model by, on average, less than 20%. The model in [6] was found to underestimate experimental data for the permeability of structures made at low pressure (low capillary radius) and it is likely that neglecting the strong effect of capillary radius on the coordination number contributes strongly to this.…”

“…The model in [5] reduces to the same expression for permeability for the case of dense random particle packing if Nc = 6 (which is not atypical of this packing condition [7,8] Reasonable correlation between experimental measurements of permeability and the models was observed in both cases, with deviations attributed, in part, to the non-spherical nature of some of the salt particles used. Thus a strong dependence upon the size of the windows connecting the pores and the permeability is apparent and controlling the window size, through varying the infiltration pressure [6] has the capacity (for a given pore size) to vary the permeability by more than a factor of 10 and would be more convenient way to vary the permeability rather than by altering the packing (porosity) through additional and potentially costly processing steps. This paper aims to further test the "bottleneck" flow assumption and the accuracy of these models by simulation of fluid flow through virtual 3D structures that are accurate reproductions of real porous metals made by the infiltration route, but in which the structural characteristics can be controlled precisely, as demanded by the analytical models.…”

“…Simple permeability models for laminar flow have been developed [5,6] which could assist with the design of these porous metal structures to meet the requirements for specific applications. Both approaches use the same premise, considering the window between the pores to be a "bottleneck" to the flow through the structure.…”

“…Both approaches use the same premise, considering the window between the pores to be a "bottleneck" to the flow through the structure. The models consider different particle contact cases (loose packing [6] and packing enhanced through compaction [5]) with different approaches to including contributions from the window size and coordination number. The model to predict the permeability according to [6] is presented in Eq 1 where  is the porosity, Nc the coordination number, rw the window radius and rp the radius of the pore.…”

“…The models consider different particle contact cases (loose packing [6] and packing enhanced through compaction [5]) with different approaches to including contributions from the window size and coordination number. The model to predict the permeability according to [6] is presented in Eq 1 where  is the porosity, Nc the coordination number, rw the window radius and rp the radius of the pore. The coordination number and window radius are defined in separate equations, the coordination number as a function of the packing fraction (also shown in Eq 1), and the window radius in terms of the infiltration pressure and particle (pore) size.…”