Three-Dimensional Simulation of Transient Resin Non-Isothermal Flow Across a Porous Reinforcement with a Sink Term: Capillary Number Evaluation in RTM Process.

Resin Transfer Molding (RTM) is a broadly applied composite fabrication technique in which liquid resin is injected into a sealed mold housing a fibrous preform. This technique enables the industrial-scale production of large, complex-shaped components while ensuring high quality and excellent material properties. A notable phenomenon in the Resin Transfer Molding process, particularly when vegetable fibers are used as reinforcement, involves resin absorption by the fibers during the filling process, which causes a deceleration of the fluid flow front, leading to an increase in mold filling time. This phenomenon has been scarcely investigated in the scientific literature, particularly under non-isothermal situations. In this context, this paper focuses on the resin injection in a closed and heated mold, emphasizing the evaluation of the capillary number of the fluid flow. The model incorporates a transient, radial, and 3D flow, variable resin viscosity, and includes the effect of resin absorption by the fibers. Simulations were carried out using CFD techniques, evaluating the effect of fixed injection gauge pressure (2.0 bar) or volumetric flow rate (3.5 × 10-8 m3/s) on the infiltration transient behavior. The numerical results of the capillary number of the flow, resin viscosity, and resin superficial velocity as a function of radial position were analyzed. Based on the analysis of the capillary number field, with the sole objective of minimizing the potential formation of voids in the manufactured composite, optimal operating parameters were identified, namely, a mold heating temperature of 30 °C and an optimal resin injection condition consisting of a constant volumetric flow rate of 3.5 × 10-8 m3/s. Further, the volumetric fraction, pressure, and temperature fields are presented and examined. The numerical modeling used builds upon a previously validated numerical framework and extends its application by evaluating the potential generation of voids through the analysis of the capillary number field.