Abstract: An insert for air flow ducts includes a band (10) of a semi-stiff, although flexible character, a plurality of interspaced interflanges (11) along the band and spaced edge flanges (14) which are connected with the interflanges, the interflanges in pairs together with the band (10) and the edge flanges (14) delimiting consecutive cavities or pipes (12') along the band, the opposed ends of the cavities or pipes being open, the band being formed into a loop in which the band and the edge flanges are located tightly adjacent to each other and in which the pipes (12') are substantially evenly distributed.

Abstract: A particle separating arrangement includes a filter tube (1) that is made of electrostatically chargeable fibres, for instance electrete fibres, and through which an axial air stream can pass radially in a direction from within outwardly. Within the tube (1) an insert (2) is placed, including a carrier (3) which extends transversely to the tube, the carrier having a plurality of strip elements (4) arranged to be set in motion by the passing air stream and thereby be rubbed against each other in order to produce an electrostatically charged field in their environs. This field is used to automatically and continuously keep the chargeable fibres in the filter tube wall (1) electrostatically charged.

Abstract: A device for the removal of microscopic particles from air includes a tube which in a certain cross-section has a replaceable, suitably ionizing particle separation unit (4) with a multitude of threads or strips (10) which are held together in a common frame structure (11) extending across the tube. The strips (10) are arranged to be set in motion in relation to each other by the passing air, thereby generating static electricity for attracting micro particles from the air to the strips. The frame structure (11) is made of a flexible band formed into loops, the strips being affixed on the band, the frame structure also including a plurality of pipe- or tubeforming members located amongst the band loops, in order to distribute the air flow through the frame structure.