Patent ID: 6986832

Claim:
A mixer comprising a tube, through which the first flow of the papermaking process is conveyed; and a feed opening which is in connection with the space limited by the tube and with a feed channel for mixing a second flow into the first flow through the feed opening; wherein a mixing zone has been formed in the tube, comprising at least one form part on an the inner periphery of the tube; the form part comprises control surfaces which extend a predetermined distance from the inner periphery of the tube towards the middle of the tube and which extend a predetermined circumferential distance that is less than the entire circumference of the inner periphery of the tube for generating turbulence in said flow in the mixing zone of the tube; the inner periphery of the tube and the control surfaces of the form part define the inner surface of the mixing zone; and the inner surface of the mixing zone is provided with one or more feed openings which is/are in connection with the feed channel and through which a second flow can be fed into the first flow, the first of the one or more feed openings for supplying the second flow being located at or after a front edge of the first form part in the direction of the first flow, wherein the axial middle of the tube is free of any feed opening.