Rajagopalan, Dilip
ABSTRACT
We discuss mathematical models of capillary flow in complex geometries representative of the void spaces formed between fibers in a textile yam. Moisture transport in textile yams and fabrics is an important factor affecting physiological comfort. We have extended an existing analytical model for capillary flow in circular tubes to more complex geometries. We validate this model using detailed computational fluid dynamics simulations of this flow. These models are used to understand the effect of geometric and material parameters on moisture transport. In vertical wicking in a bundle of filaments, the model predicts that as the nonroundness of the filaments increases, or the void area between the filaments decreases, the maximum liquid height increases while the initial rate of penetration decreases.
Moisture transport in textile fabrics is one of the critical factors affecting physiological comfort. Fabrics that rapidly transport moisture away from the human body make wearers feel more comfortable by keeping them dry. This enhanced moisture transport may also help wearers feel cool as the body provides latent heat to evaporate sweat at an enhanced rate. The comfort afforded by textile fabrics can be improved by understanding the key geometric and material parameters that contribute to moisture transport. Mathematical modeling of surface-tension-driven flow in yarns and fabrics could provide a way to develop such an understanding.
Capillary flow in yams and fabrics has been extensively studied (e.g., [5-7]), and the subject was reviewed by Kissa [9]. Fabrics are typically constructed by knitting or weaving textile yams, which are essentially bundles of several fibers or filaments. For movement of liquid in a fabric, the liquid must wet the fabric surface before being transported by capillary action through the fabric pores formed between fibers and yams. This capillary action is determined by the interaction of the liquid and the fabric material, by liquid properties such as viscosity and surface tension, and by the geometric structure of the pores. The size and shape of the fibers, as well as their alignment, determine the geometry of the void spaces or pores through which the liquid is transported. However, the complexity of a fabric structure makes it impossible to predict pore structure, and very difficult to arrive at a detailed structure experimentally. Furthermore, movement of liquid through the pores can cause shifting of fibers and changes in the pore structure. For some materials, the fibers can absorb liquid and swell considerably, thereby changing the pore structure even more. Thus, a detailed mathematical or computational model of capillary flow in fabric structures is not a reasonable goal.
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Manuscript received October 5, 2000; accepted December 17, 2000.
DILIP RAJAGOPALAN AND ARUN P. ANEJA
E. I. du Pont de Nemours and Company, Wilmington, Delaware 19880, U.S.A.
JEAN-MARIE MARCHAL
Fluent Inc., B-1348 Louvain-la-Neuve, Belgium
