Water and Air Permeability for Polyester Fabrics

Abstract

The water permeability was studied in comparison with the air permeability for a series of polyester fabrics. The experimental apparatus for the water permeability measurement is composed of a vertical cylinder at the bottom of which a specimen is attached. The water filled in the cylinder flows by its weight through the specimen. The water flow was measured as a function of time in the water pressure range from about 6.63 to 2.22 kPa. The water pressure drop by the specimen, obtained after correcting the water pressure drop inherent to the apparatus, changed in proportion to the water flow rate. The proportional coefficient of the pressure drop against the flow rate was defined as the water permeation resistance Rw. The air flowresistance Ra was measured by separate experiments. The water flow resistance Rw was proportional to the flow resistance of air Ra, and the flow resistance ratio Rw/Ra was 71.1. According to the Darcy's law the flow resistance ratio Rw/Ra equals the ratio of the water viscosity ηw to the air viscosity na. The value of the viscosity ratio nw / na , which is calculated with the viscosity values of 1.00 mPa*s for water and 18.1 uPa*s for air, is 55.2. This value of viscosity ratio nw / na agrees reasonably with the value of flow resistance ratio Rw/Ra obtained experimentally.