The Permeability of Dual-Sized Replicated Aluminum Foam

Abstract

The replicated aluminum foam technology implies impregnation of the water-soluble filler (NaCl) with a melt. Products made of replicated aluminum foam have a porosity range of 40–70% and a rather high prime cost; hence, they cannot be commercially competitive as a structural material with an aluminum foam with its porosity of 80–95% and low prime cost. Still, replicated aluminum foam is recognized as an excellent functional material for transferring liquids and gases, and products from it are used as filters. The operational life before cleaning is an important operation parameter of a filtering element. It is determined by porosity, which can be increased using filler multifraction beds. However, to predict the filtering element characteristics, the number of fractions was limited to two, which makes it possible to increase porosity by 10–15%. The size of fine filler fractions was 200–400, 400–630, and 1000–1600 μm in the proportion 30, 50, and 70%, and the coarse fraction was 2500–4000 μm in size. Preparing the filler bed consists in mixing two fractions in a certain proportion and heating up the filler bed in a box resistance furnace with subsequent filling it into a metal mold and pouring with AlSi melt. Impregnation of the filler with the melt was ensured by vacuuming the mold. After crystallization of the casting, it was machined by cutting out a cylindrical sample from the bottom of the composite casting, and then the filler was dissolved in water. The coefficient of permeability of dual-sized replicated aluminum foam was experimentally studied by the nonstationary method. The additive dependence of the permeability coefficient on the proportions and permeability coefficients of monofractions is shown. Permeability coefficients of monofractions are calculated using the model of concentration of single resistances. A review of dual-sized bed permeability models is performed, and it is shown that the Kazemi model is most consistent with the experimental data obtained. A discrepancy with the experiment is evident only at a significant difference of fraction sizes, with a small size of the fine fraction, which is caused by the loosening effect. The obtained results make it possible to design filtering elements with a higher porosity.