Browsing by Author "Mare, Esmari"

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    Geometric versus kinetic modelling approach for characterizing porous metal foams
    (WIT Press, 2019) Mare, Esmari; Woudberg, Sonia
    Knowledge of the geometric and kinematic parameters of porous foams are of great importance since it is used in a wide variety of industrial multiphase flow applications that require optimal functionality, e.g. gas filters, heat exchangers and catalyst supports. The large external surface area and high porosity of metal foams provide good chemical resistance, enhanced heat and mass transfer properties and low pressure drops. Four generic geometric models will be considered to characterize the metal foam geometry, namely the cubic unit cell, tetrakaidecahedron, dodecahedron and rectangular representative unit cell (RUC) models, as well as three kinetic approaches from the literature in order to predict the specific surface area (SSA). Two sets of experimental data from the literature will then be compared to the SSA model predictions of the geometric approach and to the SSA values obtained from the kinetic approach. A comparative analysis reveals that the most geometrically complex tetrakaidecahedron model indeed provides the best correspondence with the experimental data for the SSAs, followed by the geometrically simplest RUC model. The latter model, in addition, provides accurate results for the kinetic approach. The advantage of the RUC model is that it is the only geometric model that provides both a geometric and kinetic approach, and, as a result of its relatively simple geometry it is geometrically adaptable towards anisotropy. The Klinkenberg effect will also be considered to determine the influence on the predictions of the SSAs dependency on the permeability coefficients for different fluid phases.
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    Investigating correlation among geometrical parameters of isotropic and anisotropic fibrous porous media
    (Stellenbosch : Stellenbosch University, 2020-12) Mare, Esmari; Fidder-Woudberg, Sonia; Stellenbosch University. Faculty of Science. Dept. of Mathematical Sciences. Division Mathematics.
    ENGLISH ABSTRACT: In this study four main geometrical models available in the literature that approximate the micro-structure of metal foams (i.e. the cubic unit cell model, the tetrakaidecahedron model, the dodecahedron model and the rectangular three-strut Representative Unit Cell (RUC) model), are outlined. Furthermore, an anisotropic two-strut RUC model is discussed in order to accommodate predictions of the morphological and transport properties of fibre-like materials due to its geometric model structure representing fibres more closely than metal foams. Equations for the prediction of the specific surface area in terms of the pore diameter and the porosity for each of the model geometries are presented and the predictions are compared to experimental data from the literature. Comparison of the model predictions show that the tetrakaidecahedron, dodecahedron and RUC models give similar results and correspond well with the experimental data. A kinetic approach is also considered where the transport properties, such as the experimental permeability obtained from the pressure drop, and porosity data of fibrous media are used to determine the specific surface area. Thereafter, a combined geometric and kinetic approach is investigated which combines the use of the transport properties of the fibrous media and the geometrical models that represent the fibrous media in order to determine the specific surface area. The two-strut and three-strut RUC models receive special attention in this study due to the advantage that the rectangular geometry allows for relatively simple geometric adaptations. Equations predicting the permeability and the specific surface area of the existing isotropic threestrut and anisotropic two-strut RUC models, as well as the compressed three-strut and two-strut RUC models, are proposed and compared to experimental data obtained involving foams and fibres. The isotropic and anisotropic RUC models are furthermore adapted to account for the Klinkenberg effect, an effect that accounts for the increase in gas permeability, compared to liquid permeability, and its influence on the specific surface area predictions are investigated. The model predictions are compared to a variety of available experimental data for fibrous media from the literature and the correspondence proves to be satisfactory. It is also shown that the permeability prediction of the two-strut model is more accurate for compressed layered fibrous media consisting of the stacking of fibres into parallel sheets than the compressed three-strut model, as expected. The analytical modelling approach presented adds value to this field of study in comparison with the empirical studies in the literature which mostly comprise of curve fitting procedures together with the introduction of empirical coefficients into the permeability equations to obtain correlation with experimental data.