Experimental investigation of pressure-drop characteristics across multi-layer porous metal structures

This study investigates the effect of airflow (in the range of 0–70 m s-1) on the pressure-drop characteristics for a novel multi-layered, nickel-based porous metal, as a function of thickness (affected by sectioning) and density (affected by compression). In addition to generating unique data for these materials, the study highlights the need for precise pinpointing of the different flow regimes (Darcy, Forchheimer and Turbulent) in order to enable accurate determination of the permeability (K) and form drag coefficient (C) defined by the Forchheimer equation and to understand the complex dependence of length-normalised pressure drop on sample thickness

Tailoring the pressure-drop in multi-layered open-cell porous inconel structures

This study investigates the pressure-drop behaviour associated with airflow through bulk and structurally tailored multi-layered, open-cell porous Inconel structures over a wide airflow velocity range (0–50 m s-1). The effect of airflow velocity on the pressure-drop behaviour as a function of the sample thickness is presented and related to the flow behaviour corresponding to the relevant flow regimes (Darcy, Forchheimer, Turbulent and Postturbulent). Entrance effects are highlighted as a source of the pressure-drop increase for porous structures with air gaps, regardless of their sizes, as long as they are larger than those generated by loosely-stacked structures. The pressure-drops for gapped porous structures and the mathematical-summation of the pressure drop for the corresponding individual components, were in very good agreement, at lower airflow velocities. The potential for mass-efficient porous structures, providing a high pressure drop, was demonstrated using multiple thin porous laminates separated by air gaps

Brinkman-extended Darcy flow in metal foam: analysis and experiment

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Fluid flow in porous media is found in numerous processes and applications of vital engineering interest, e.g., storage of nuclear waste, heat exchangers, ground water pollution and chemical reactors. Often, the porous medium is confined by solid boundaries for containment. These impermeable boundaries give rise to shear stress and boundary layers. The Brinkman-extended Darcy equation governs the momentum transport due to Newtonian fluid flow in such porous-media flow situations. Metal foam, especially aluminum-based, has gained a lot of academic and industrial interest over the past few years. The significance of metal foam is due to its low density (or, high porosity: 75 % to 95 %.), high thermal conductivity, interconnectivity of its solid ligaments and large surface area density. Metal foam applications include heat exchange system and chemical reactors. In these systems, the foam is usually cylindrical in shape and is contained in a cylindrical tube. The fluid flow in such systems is needed for further engineering and performance analysis of such systems. The flow field may be described by the Brinkman-extended Darcy equation. This equation is solved analytically in a cylindrical system, employing an existing fully-developed boundary-layer concept particular to porous media flows. As expected, the volume-averaged velocity is found to increase as the distance from the boundary increases reaching a maximum at the center. The friction factor is defined based on the mean velocity and is found to be inversely proportional to the Reynolds number, the Darcy number and the mean velocity. In order to check the validity of the Brinkman-extended Darcy flow model for the high-porosity metal foam, experiments were conducted on commercially-produced 20-ppi (pores per inch), i.e., 8 pores per centimeter using an-open loop wind tunnel. In the Darcy flow regime, reasonably good agreement is found between the analytical and the experimental friction factors. The implication of the results of this paper is that they can be applied in further engineering analysis that require knowledge of the velocity field and pressure drop, i.e., convection heat transfer and chemical reactors

Modifying of expansive clay soils using alkali activated ESKOM dump ash

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Flow regimes in foam-like highly porous media

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Metal foam is a relatively new class of porous media. The internal morphology of the foam is composed of connected cells each having many ligaments that form a web. In addition, metal foam has very high porosity (often greater than 90%) and a large surface area density. These properties are exploited in many applications, e.g., filtration, heat exchange and reactors. Flow regimes, and transition from one to another, are critical for understanding energy dissipation mechanisms for flow through the foam. While this topic is well studied in traditional porous media, e.g., packed beds, it is not well understood for foam-like porous media such as metal, graphite and polymeric foams. The choice of an appropriate characteristic length for metal foam has also varied among researchers. Pressure drop characteristics such as the permeability and form/inertial drag coefficient are very divergent for metal foam. The current study is to shed some light on the above issues. In particular, a large set of experimental data for pressure drop of water flow in commercial aluminum foam having 20 pores per inch and a porosity of 87.6% was collected. The range of flow Reynolds number covered a few important flow regimes. The current data correlated very well using the friction factor based on the square root of the permeability (measured in the Darcy regime) as a function of Reynolds number based on the same length scale. It is shown that the same foam exhibits different values of its permeability and Forchheimer coefficient in different flow regimes. The finding of this study can help in numerical and analytical work concerning flow and heat transfer in foamlike porous media.cf201

Measurement and simulation of pressure drop across replicated porous aluminium in the Darcy-Forchheimer regime

Experimental measurements of the pressure drop across porous metals have been compared with computational fluid dynamics simulations, for the first time, for structures typified by large pores with small interconnecting “windows”. Structural information for the porous structures was obtained from X-ray computed tomography and a robust methodology for developing a representative volume element is described. The modelling approach used was able to reliably predict the pressure drop behaviour within the Forchheimer regime. The methodology was extended to simulate flow through geometrically-adapted, “semi-virtual” pore structures and this approach could prove to be an invaluable tool in the design of porous metal components for applications involving fluid flow

Pore-scale numerical investigation of pressure drop behaviour across open-cell metal foams

The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier–Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier–Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value