Experimental hydrodynamics of high-porosity metal foam: Effect of pore density

Commercial open-cell metal foam has very high porosity (often greater than 90%) and a large surface area density. The open flow area is copious compared to the ligament size. These properties are exploited in many applications, e.g., heat exchanger, reactors and filters. Pressure drop, flow regimes, and transition from one to another, are indispensable for any application involving flow of a fluid through the foam, and for heat transfer rates or reaction paces. These topics are not well-agreed on for foam-like porous media such as metal, graphite and polymeric foams. Pressure drop parameters such as permeability and form/inertial drag coefficients are very divergent for metal foam; the same can be said about flow regime boundaries. This paper presents experimental data for pressure drop for water flow in two commercial open-cell aluminium foams having 10 and 40 pores per inch (ppi). The two foams have similar porosities (88.5%). The wide range of flow Reynolds number covered all known flow regimes in porous media: pre-Darcy, Darcy, Forchheimer and turbulent. Flow regimes and transition between them were identified and compared. The friction factor based on the square root of permeability (measured in the Darcy regime) and the Reynolds number based on the same characteristic length were used. It is shown that the same foam exhibits different values of its permeability and Forchheimer coefficient in different flow regimes. A previously-tested foam having 20 pores per inch and a porosity of 87.6% was included in the comparisons. The basic finding of this study will inform numerical and analytical work concerning flow and heat transfer in foam-like highly-porous porous media.