Bubble formation and transport in T-junction for application to Liquid Composite Molding: Wetting effect

Abstract

The aim of this work is to underline the influence of the wetting behavior on bubble formation and transport during the impregnation of fibrous preforms for Liquid Composite Molding processes. The void prediction within the elaboration of composite material sparks off interest because it represents a significant issue to keep the expected mechanical properties of the final product. Voids or bubbles are mainly formed due to the resin flow competition inside and outside the tows. However, the experimental characterization of void formation and transport during the flow inside fibrous media remains delicate. Since the direct visualization of the liquid flow and the entrapped bubbles in a practical material is uneasy, we used model networks to study the formation of bubbles and their transport. Thus, our experimental study deals with a simple configuration of connected pores: two capillaries converging at a node perpendicularly (T-junction). We emphasized on microfluidic and millifluidic approaches where the wetting is significant during bubble formation mechanisms. For the same flow conditions, the experimental results reveal that the bubble lengths are higher for partially wetting liquids than for completely wetting ones. In a wetting case, it was demonstrated that the lubrication hypothesis can be a good approximation to describe the bubble transport in fibrous media.

Dynamic Wetting of Molten Polymers on Cellulosic Substrates: Model Prediction for Total and Partial Wetting

“…In literature, to the best of our knowledge, the majority of experimental works investigated the dynamic wetting using totally wetting liquids and via a visual method, observing the spontaneous spreading of a drop (the speed of the liquid front is not constant), especially at room temperature (Tanner, 1979;Schneemilch et al, 1998;Prevost et al, 1999;Le Grand et al, 2005;Kumar and Deshpande, 2006;Seveno et al, 2009;Duursma et al, 2010;Duvivier et al, 2011). Some works using microfluidic techniques proved that, with partially wetting liquids, established models in literature are no longer valid (Wielhorski et al, 2012;Abdelwahed et al, 2014). A recent work studied molten polymers but in a spontaneous regime of drop spreading (Zhang et al, 2017).…”

Temperature effect on dynamic wetting of cellulosic substrates by molten polymers for composite processing

“…Capillary forces coupled with the viscous ones play a dominant role in dynamic wetting during composite processing [1,2], that were expressed with the definition of the capillary pressure [3,4]. Moreover, a lot of experimental [5][6][7][8][9] and numerical [10,11] works mentioned that capillary and viscous effects lead to porosity formation, depending on local liquid velocity v in the heterogeneous fibrous preform and liquid properties, both included in the capillary number Ca: (1) where η and γLV are respectively the dynamic viscosity and the liquid surface tension. Dynamic wetting phenomena are described by a dynamic contact angle between the liquid-vapour interface and the solid surface (θd) and it is well known that θd exhibits a strong dependence on Ca.…”

Numerical Simulation of Bubble Formation and Transport in Cross-Flowing Streams

“…In our case, the film thickness is not measured directly but arises from the bubble and liquid velocities which have been deduced from the time evolution of both front positions. Then by taking into account the volume of lubrication film in the liquid volume conservation, the relation between the film thickness e and the relative bubble velocity is given by: (11) By fitting our experimental data for the wetting liquids, we obtain the following relation [58]:…”