Characterization of bubble mobility during flow through fibrous porous media

Abstract

Multiphase flow through porous media is a common phenomenon during the processing of composite materials in which viscous liquid thermoset resin containing small bubbles due to entrapped air is injected into reinforcing porous fibrous media. The composite part is formed once the resin cures. Entrapped bubbles cause porosity, which is characteristic of materials fabricated by this technique and results in reduced mechanical properties. Hence, the reduction in porosity during the processing stage remains a critical issue. To investigate this, an experimental study was conducted to characterize the movement of bubbles within the pore network of the fabric’s weave architecture representing the porous media. Bubble dynamics, as the simulated resin impregnated the fibrous network, were observed in transparent molds for three fabric architectures, with bubble diameter and velocity being measured as they traversed through the fabric. A dimensionless number is introduced to correlate the fabric weave architecture to the bubble size, revealing that higher bubble mobility (indicating how fast the bubble moves compared to the pore averaged resin velocity) is observed in tighter weaves and with larger bubbles. To predict bubble mobility based on bubble size and fabric weave, two physics-based models are introduced. The predicted results are compared with the experimental data, facilitating void minimization by regulating bubble mobility.