Part II: Capillary Size Distribution

Abstract

The water holding capacity of a fabric is important in determining its pick-up of treating solutions, the amount of water which must be removed in drying it, and other aspects of its functional behavior. This capacity can be considered to be made up of the volume of a bundle of continuous capillaries of various radii, the volume of a noncon tinuous capillary system, and the sorption capacity of the fibers themselves.

A vertically suspended wet fabric develops a water concentration gradient from top to bottom which can be used to calculate the pore size distribution of the bundle of continu ous capillaries. The water gradient is given empirically by

where W_h is the water content at height h, a is the water held within the fibers and in noncontinuous capillaries, b is the maximum capacity of the continuous capillaries, and k is a constant which depends on the fabric. The number of capillaries of a given radius r is given by where ρ ₂ is fabric density in g./cm.², v is the surface tension of water in dynes/cm. and θ its contact angle with the fiber, ρ ₁ is the density of water, and g is the gravitational constant. This is approximately a log normal distribution.

For cotton printcloth, wool flannel, and nylon challis, the maxima in the radius fre quency distributions were found to be 11.1, 19.3, and 9.3 microns respectively.