A flow-through cavitation device having an elongated housing with an inlet and an outlet. An inner annular body and an outer annular body are concentrically and nestingly disposed in the elongated housing. The outer annular body is fixed relative to the housing and the inner annular body is rotatable about a longitudinal axis of the housing. Each annular body has a plurality of channels that pass therethrough. Rotation of the inner body relative to the outer body provides for selective alignment or misalignment of the plurality of channels to control fluid flow from the inlet to the outlet. The device may have a plurality of pairs of inner and outer annular bodies as described.