a method is described of mixing fluid materials , including solids and gases . the materials to be mixed are introduced between two cylindrical rotors mounted in parallel on a motorized shaft . the rotors have arrays of cavities on their cylindrical surfaces and rotate within close proximity to the interior of a cylindrical shell . passage of the fluid between the rotating rotors and the interior surface of the cylindrical shell causes cavitation , which mixes the materials . the mixture is passed to outlets on the far sides of the rotors from the inlet . apparatus is described for extending the flow path of the materials and thus increasing exposure to the cavitation process .