Effect of Fluid Bypassing on the Experimentally Obtained Darcy and Non-Darcy Permeability Parameters of Ceramic Foam Fil
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rs (CFFs) are commonly used in various industries, including chemical, automotive, and metallurgy, for catalyst support, to control exhaust emissions, and for liquid metal filtration.[1–4] In general, solid foams can be divided into open and closed cell materials, where each material has a different structure, property, and application.[2,5,6] Depending on the type and production method, ceramic foams may possess adequately high mechanical properties such as high thermal and chemical resistance, high structural uniformity, and strength.[6] The open cell ceramic foams represent a net of voids where each and all voids are surrounded by and connected via a ceramic material,[2,7] as shown in Figure 1(a). Due to open pores, the foams have high permeability and, therefore, are able to capture solid particles. This makes CFFs suitable for filtration in metal production.[5,6] On the other hand, closed cell SHAHIN AKBARNEJAD, Ph.D. Candidate, MOHSEN SAFFARI POUR, Postdoctoral Fellow, LAGE TORD INGEMAR JONSSON, Researcher, and PA¨R GO¨RAN JO¨NSSON, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden. Contact email: [email protected] Manuscript submitted June 3, 2016. Article published online November 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
foams are polyhedron-like cells connected via a solid interface while each cell is isolated from the others,[2,7] as illustrated in Figure 1(b). Such structure creates a suitable material for thermal insulation, fire protection, gas combustion burners, etc.[5,6] In this research, the focus was on the open cell 30, 50, and 80 pores per inch (PPI) commercial alumina CFFs. In metallurgy, CFFs are used to remove undesired nonmetallic particles from molten metal before casting,[1,4,7–13] i.e., filtration. In order to prime the filters, the melt has to reach a certain pressure on the top of the filter to initiate passage through the filter.[9–12,14] To estimate, adjust, and maintain the required pressure and to regulate the melt velocity, it is essential to determine the Darcy and non-Darcy permeability coefficients of the filter.[8,9,15] The permeability coefficients can be obtained using permeametry experiments.[16–18] In general, permeametry is based on a gas or liquid flow through a porous media. Thus, the pressure drop DP (Pa) along the height of the porous media L (m) as a function of the superficial velocity Vs (m/s) needs to be measured. Thereafter, the Darcy and non-Darcy permeability coefficients k1 (m2) and k2 (m) can be estimated using the Forchheimer equation for incompressible fluids (Eq. [1]),[2,8,9,15,17,19–21] if the fluid dynamic viscosity l (Pa s) and fluid density q (kg/m3) values are known:
VOLUME 48B, FEBRUARY 2017—197
DP lVs qV2s ¼ þ L k1 k2
II. ½1
In the literature,[8,9,17,18,22–32] it has been stated that accurate pressure drop estimates only can be achieved when fluid bypassing is avoided. If the CFF samples are not fully sealed, fluid will flow through the filter as well as the gap between the filter and
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