Effect of wettability on viscous fluid impregnation in single-layer woven-fibre bundles driven by pressure difference

We investigate experimentally and numerically the effect of wettability on viscous-liquid impregnation into a single layer of woven fibers confined between the parallel plates. In our experiments, special attention is paid to the flow-front behaviors and the characteristic flow fields induced by the pressure difference attempted to the mold. We change the wettability between the fiber and viscous fluid by coating the bundles with fluorine-based coating agent. Correlation between the flow-front behaviors and void formation are indicated in terms of the capillary number Ca, and of so-called modified capillary number Ca^′ that incorporates the effect of the contact angle between the fiber and liquid, θ_f. Through our three dimensional multiphase simulations, the impregnation process is examined as functions of Ca and Ca^′ by varying either of the characteristic velocity, the surface tension, the viscosity, or the contact angle. We illustrate that the wettability is a crucial factor to dominate the impregnation and void formation processes, and that the modified capillary number does not apparently measure the formation of the macrovoids.