Composite industry increasingly uses natural fibres because of their environment-friendly advantages. These natural fibres may swell during the mould filling process when they absorb resin, and this swelling reduces the porosity and permeability of the preform. Hence, computational modelling of the flow in swelling porous media would be useful to model the different mould filling processes with the swelling effect. This paper demonstrates the possibility of using computational fluid dynamics to study the effect of swelling on liquid composite moulding mould filling in isotropic and orthotropic porous media. An empirical relation for local permeability changes is used to model the flow of resin under constant volume flow rate and constant injection pressure conditions. The flow front locations and inlet pressure predicted by the computational fluid dynamics simulations are in good agreement with the experimental data for 1D rectilinear flow case. Further, to capture the flow patterns, two different arrangements employing point injection are considered. It was observed that the volume fraction of resin in swelling porous medium is 6% less than rigid porous medium at any given time. It was also observed that the location of the inlet and outlet has a considerable effect on the flow front advancement.

In the first part of this two-paper series, published in the Journal of Porous Media in 2021, a novel framework based on the combination of finite volume method and volume of fluid method was proposed to model the flow through absorbing porous media under rigid conditions. The results from the model showed a promising correlation with the experimental and analytical predictions for the wicking height and radius. However, the framework did not include swelling porous media conditions. The swelling effect influences the porosity and permeability of the porous medium considerably, therefore causing errors in the flow front location predictions if the effects are not taken into account in the numerical models. Here, the framework is extended by including the swelling effects. The empirical relation for changes in permeability is included in the existing methodology to include the swelling effects. The predictions from the proposed model showed excellent agreement with the experimental data. The modeling approach is further extended to model the flow through single and multiple layer diaper geometries. The results showed notable patterns of liquid–air interface, demonstrating the ability of the present method to track the flow fronts in combined wicking and draining flow scenarios.

The performance of the absorbing porous media is an important factor in several practical applications such as hygiene industries. The primary goal of hygiene products is to absorb and retain a liquid. In these types of products, the liquid flow is often driven by a strong capillary force. Hence, computational modelling of the liquid absorption process within rigid porous media would be helpful to design or modify these products. This paper demonstrates the application of a newly proposed approach for modelling liquid absorption within rigid porous media. The proposed modelling approach uses fewer input parameters than previously used methods in literature which make it simple to implement. The wicking heights, predicted by computational fluid dynamics simulations, are in good agreement with the experimental and analytical data. The capability of the method to model the flow through absorbing porous media is explored by considering different flow cases. For the case where the flow front hits the walls of a porous domain, the results showed interesting patterns of the flow front under the action of gravity. It is observed that the nature of flow front propagation becomes 1D as time passes.Finally, the newly proposed cell zone condition to mimic the liquid hold up showed promising results by allowing only air to pass through the porous domain.

Design of hygiene products such as sanitary napkins, diapers, etc. is heavily dependent on the liquid absorption performance of fabrics. As fibres swell upon liquid absorption, their liquid absorption performance changes. Understanding the flow through porous media under swelling conditions has important implications for product design and has yet to be elucidated fully. The goal of our research was to study the effect of fibre swelling experimentally. Cotton is selected as the test fabric as it is commonly used in most hygiene applications. Under swelling conditions, the effect of swelling on individual fibres, porosity, permeability, and performance of the cotton fabric is analysed. Findings showed that upon water absorption, the fibre diameter increased by 10%, porosity decreased by 11%, and permeability decreased by 60% under fully swollen conditions. The porosity reduction is also predicted analytically using the data obtained from the fibre swelling measurements. In contrast, predictions of commonly used analytical models showed only a 30% reduction in the porosity. To correct this, two new correction factors to account for effects of inter-fibre interactions on the total swelling rate of fabric are proposed. The performance measures of cotton samples under swelling conditions indicated that advancement of the flow front on the lower face was more dominant than the upper face of the sample possibly related to gravity. These experimental data improve our understanding of wicking flow which can help to improve the design of hygiene products and to develop more realistic computational fluid dynamics models.