viscous impingement filter

viscous impingement filter

[′vis·kəs im′pinj·mənt ‚fil·tər]
(engineering)
A filter made up of a relatively loosely arranged medium, such that the airstream is forced to change direction frequently as it passes through the filter medium; the medium usually consists of spun-glass fibers, metal screens, or layers of crimped expanded metal whose surfaces are coated with a tacky oil.