US Patent 9291177 Duct having flow conducting surfaces

A duct in which a fluid can be conducted is bound by duct walls, wherein the duct walls have an inlet opening and an outlet opening through which the fluid can enter the duct and exit the duct. The fluid has a flow velocity which is smaller along the duct walls than at the duct middle, so that a zone of higher flow velocity and a zone of lower flow velocity can be formed in the duct. A flow guide surface is arranged in the duct by means of which a portion of the fluid can be taken from the zone of higher flow velocity and can be mixed into the zone of lower flow velocity.