The focus of this investigation was to determine the effect of barrel rotation and screw rotation on the flow rate and viscous dissipation inside the screw pump-extruder The screw pump-extruder was built to allow for barrel rotation anti screw rotation independently. A Newtonian fluid, Polypropylene glycol, was chosen as the working fluid. The experimental results can be summarized by noting that the pumping capacity of the device was independent of which element was rotated at constant angular velocity and that barrel rotation generated higher temperature rise than screw rotation for the two screws evaluated. Also this analysis suggested that a large amount of viscous dissipation inside this extruder arises from the clearance flow. A new analytical model was proposed to evaluate the viscous dissipation for screw rotation. Calculations using this new mathematical model provided good agreement with the experimental data for both barrel and screw rotation.