An apparatus and associated method is provided for injecting a processing fluid in a device that operably rotates a disc stack. A fluid injector has a nozzle defining an outlet sized to longitudinally span the disc stack to operably direct the processing fluid toward the disc stack. The nozzle also has a flow rate feature that operably directs a first flow rate of the processing fluid from the nozzle into a space adjacent a storage surface of a first disc of the disc stack and that directs a substantially different second flow rate of the processing fluid from the nozzle into another space adjacent a storage surface of a second disc of the disc stack.