The Rate of Drying of Fabrics

Abstract

It is frequently stated that one fabric dries faster than another, usually with reference to house hold conditions of drying on a line. However, the data of this report show that by and large all fabrics dry at the same rate under these conditions (rate being expressed as weight of water evaporating per unit area per unit time), but that the time of drying depends upon the amount of water originally held, so that some fabrics dry sooner than others. The main portion of the drying time shows this constant rate of drying, although there is a final period which is short compared to the main drying period, during which the rate of drying decreases. The water-holding capacity of a fabric depends upon how the fabric is supported (vertically or horizontally) and upon the mechanical treatment given to remove water. For simple drainage in the vertical position, the water-holding capacity of small samples is more closely correlated with fabric thickness than with fabric weight. The kind of fiber—i.e., wool or cotton-and large differ ences in moisture affinity, as shown with Vinyon, also affect the water-holding capacity. How ever, these factors have almost no effect on rate of drying, since this is controlled by the resistance of air layers to the passage of heat. The thickness of these air layers is sufficient under ordinary conditions to smooth-over the fabric surface irregularities, even when these are rather large, as in rib knits or in cellular or waffle fabrics. Increasing the hairiness of the surface in order to give more area for evaporation is sometimes proposed as a means of increasing the drying rate, but results show that this is without effect except for extremely high, open naps, for which the effect is the opposite-the thickness of the layers of still air is increased and the drying retarded.