A mixer system comprising a sealed tube (2) provided with inlets and outlets (4,5) for a process fluid which is rotatable in arcs around the longitudinal axis of the tube (3) and contains one or more blades (11) mounted at each end on a blade carrier (10) supported within the tube (3) in a manner that allows the one or more blades (11) to rotate in the same direction and angular velocity (in degrees per second) as the tube (3) rotates in arcs and the use of such a system as a reactor and/or for mixing.