 |
|||
|
|
Capillarity and Wicking-2 Wicking in fabrics may occur in a range of conditions and situations. Researchers attempt to distinguish between two phenomena related to liquid transport in fabrics are · Wettability · Wickability Qualitative definitions of these terms can be found in the literature be found in the literature but parameters which quantify these properties are not available. According to Harnet and Mehta, Wickability is the ability to sustain capillary flow while, Wettability describes the initial behavior of a fabric, yarn, or fiber when brought into contact with water. While wetting and wicking are still argued to be separate phenomena, they can be described by a single process liquid flow in response to capillary pressure. More completely, in the absence of external forces, the transport of liquids in a porous media is driven by capillary forces that arise from the wetting of the fabric surface. Because capillary forces are caused by wetting, wicking is a result of spontaneous wetting in a capillary system. Hence, they are coupled and one cannot occur in the absence of the other. The spontaneous flow of moisture of wicking occurs due to a pressure differential or capillary action. Capillary action, or capillarity, can be defined as the macroscopic motion or flow of a liquid under the influence of its own surface and interfacial forces. The primary driving forces responsible for the movement of moisture along the fabric is the forces of capillarity. Capillarity describes the phenomenon when liquids in narrow tubes, cracks, and voids take on motion caused by the surface tension of the liquid. Capillarity is based on the intermolecular forces of cohesion and adhesion, if the forces of adhesion between the liquid and the tube wall are greater than the forces of cohesion between the molecules of the liquid, then capillary motion occurs. According to the laws of capillarity, fluid flow would be faster in a void with a large capillary radius than that in one with a small radius. Though that may be true, the smaller radius capillary can transport moisture to a greater height. Due to the mechanisms of capillarity, the moisture front moves from the larger pores to the smaller pores as height increases. This would indicate that the moisture flows from a region of low capillary pressure to a region of high capillary pressure. In general, the moisture begins in all the pores, but can travel only to certain heights in the larger pores where it then migrates to the smaller pores. So as the height increases, moisture held in the yarns of a fabric decreases because all pores are not filling. If the pores or capillaries do not fill, then they do not contribute in the transport or wicking of the moisture.
|
