Air Flow Through Textiles at High Differential Pressures

Air flow through fabrics at relatively high differential pressures is studied both ex perimentally and theoretically. An extension of a previous model for fluid flow through a bed of fibers takes into account the geometric irregularities and deflection of the fibers, successfully predicting that the pressure drop across the fabric is a linear function of the air flow rate up to the pressure corresponding to critical flow conditions. It also correctly predicts values for the elastic moduli of the various fibers. The influence of fiber swelling induced by wetting on air permeability is examined. At high differential pressures (55 kPa), a decreased air flow rate is found only for wool fabrics. Under the conditions of the standard fabric air permeability test (differential pressure 12.3 Pa), water blocking the channels in the wet fabric is not removed, so the air permeability is much less than that for the conditioned fabric.