Segment V5.2: Shop Vac Filter

(Related to Textbook Section 5.1 - Conservation of Mass - The Continuity Equation)

For incompressible flow through a device, the volume flowrate (flow area times the average normal velocity) is constant.

The air velocity at the inlet nozzle of a shop vac is quite large (about 100 ft/s) and the flow area is relatively small (about 1.5 square in.). Within the vacuum cleaner the air passes through a large-area, folded paper filter (about 1500 square in.) with a small average velocity (about 0.1 ft/s). The filter provides a large particle collection surface with a small velocity and pressure drop across it.