ABSTRACT
A common gas-flow test for filter papers and nonwoven cloths is called the Frazier, in which an upstream air gauge pressure of 0.5 lbf/in
(psi) is applied to a 2-inch diameter disk of the filter medium as the downstream face is exposed to the atmosphere (0 gauge pressure). The airflow from the downstream face is reported as ft
/min·ft
. Some writers have referred to that measurement as permeability. Alternatively, the resistance is reported, say, in mm of water, to an approach velocity of, say, 10.5 ft/min. In these tests the investigator assumes he or she is in the viscous flow range: that range where the ratio of flow rate to driving pressure is constant for somewhat smaller and larger driving pressures. Setups for panel filters are described in ASTM F778.
