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The Forchheimer Effect and Non-Darcy Flows in Liquid Composite Molding Processes



In liquid composite molding (LCM) processes, the infiltrating resin has been assumed to have low velocity and low Reynolds number, where Darcy’s law can accurately describe the flow. In this creeping flow regime, viscous interactions are the dominant sources of pressure gradients. However, with the need to reduce cycle time and increase the production rate of composite parts there is considerable interest in the high pressure resin transfer molding (HP-RTM) process. The potential for high velocity resin flows in HP-RTM can result in an inertial pressure loss produced from the acceleration and deceleration of the fluid and a corresponding nonlinear relationship between pressure and velocity. This inertial pressure loss warrants the need for an additional second order term in Darcy’s law commonly referred to as the Forchheimer Equation. In this study, previous work related to non-Darcy flows and the Forchheimer Equation were reviewed and criteria for defining the point at which Darcy’s law is no longer valid were identified. To investigate non-Darcy flows during LCM processing, high flow rate experiments were conducted to measure the relationship between flow rate and pressure drop. The measurements were made with a test fixture used determine the in-plane saturated permeability of fibrous preforms. The study was conducted with tackified and non-tackified IM7-4HS preforms. Unfortunately, inertial effects and the transition from Darcy to non-Darcy flow could not be determined with the test fixture used in the present study due to leakage within the cavity of the test fixture due to high inlet pressure.

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