Numerical and experimental study of flow through swelling porous media

Salokhe, Shivam Manohar (2022) Numerical and experimental study of flow through swelling porous media. Doctoral thesis, Northumbria University.

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Abstract

In Engineering studies, the flow through porous media is an active subject of research due to its practical applications. The applications include liquid composite moulding techniques, industrial wicks, hygiene products, industrial filtration etc. The computational modelling of flow through porous media is often based on a single-phase or multiphase continuum using Darcy’s law under rigid or swelling conditions. The computational models of fluid flow through porous media help to design and optimise for different engineering applications such as industrial wicks, baby diapers, paper towels, liquid composite moulding processes and heat pipes. The swelling of porous media as a result of liquid absorption by solid particles considerably affects the fluid flow through porous media. As a result, the resistance to fluid flow through porous media increases due to a reduction in the porosity and permeability of porous media.

Hence, the assumption of rigid porous media while developing the computational models is not always correct. The exclusion of swelling effects could lead to a serious error in the predictions from the developed computational model in terms of liquid front positions. Hence the inclusion of swelling effects in computational modelling is crucial and very few works are attempted to model such a flow condition. Further, for the computational modelling of capillary pressure effects, the available multiphase approaches are based on multiple fitting parameters. These parameters need to be measured experimentally or estimated analytically which makes it challenging to implement. The resulting computational model would not predict the liquid front accurately if the correct values of these fitting parameters are not known.

In this study, a novel methodological approach is proposed which allows us to account for the swelling and capillary pressure effects within the porous media. The novel combination of the Finite Volume Method and Volume of Fluid method (FVM-VOF) is used for the first-time to model the liquid absorption and swelling effects within porous media. The proposed methodological framework allows us to model the swelling and capillary pressure effects within porous media precisely with lesser fitting parameters. The use of the volume of fluid method helped to track the liquid-air interface accurately under different working conditions.

The computational models are developed for the different flow scenarios. For the case of flow-through non-absorbing swelling porous media, the modelling approach is first validated against the experimental data obtained from the literature. Further, 2D computational models for the liquid composite moulding process (LCM) are developed and studied. The results demonstrated the effects of permeability and the number of inlet gates on the mould fill times. The proposed methodology is further extended to model the flow through rigid porous media under absorbing conditions. A new analytical model predicting the liquid front locations under draining conditions is proposed. A novel boundary condition allowing us to model the liquid holdup within porous media is proposed. The effect of gravity and the size of the porous domain have a significant effect on the liquid front locations under different values of capillary pressures. The swelling behaviour of the cotton fabric is studied experimentally. A novel method of measurement of porosity changes as a result of swelling is proposed. The experimental results for the porosity changes highlighted the limitations of analytical models which are used to predict the porosity changes. The new correction factors for the existing analytical model are proposed and validated. These factors account for the inter-fibre interactions within the woven fabrics The results related to liquid absorption performance tests revealed that gravitational effects along with the swelling effects considerably affect the liquid absorption performance of fabrics. Finally, the computational models are developed for the case of flow-through swelling porous media under absorbing conditions. The model is developed using the data obtained from experiments. The model is further extended for the case of the flow-through single-layered and multi-layered diapers. It was observed that the changes in the permeability of layers considerably affect the liquid front shapes within the porous media. The outcomes from this study would help researchers to model the swelling and capillary pressure effects accurately with few basic input parameters. The proposed approach has demonstrated its ability to model the applications of forced imbibition in swelling conditions such as Liquid Composite moulding processes used to manufacture composites. The proposed approach can be used to model the applications such as industrial wicks, tissue papers, paper napkins, and hygiene products where flow is dominated by capillary forces and swelling effects in some cases.

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