The pressure required to pass air bubbles through the mesh (covered by a test liquid) is measured. The average aperture size is then calculated by taking into account surface tension, liquid density, temperature and immersion depth. See- "absolute micron retention" See- "glass bead test"
A method used to test the average aperture size. The pressure needed for air bubbles to pass through the mesh, which is covered by a test liquid, is measured, and surface tension, liquid density, temperature and immersion depth are taken into account in the calculations.