A full three-dimensional finite element analysis of the non-isothermal flow of generalized non-Newtonian fluids in counter-rotating tangential twin screw extruder is presented. Previous studies of the simulation of processing in tangential twin screw extruders have focused solely on the twin screw extruder whereas here the coupled flow and heat transfer occurring in the integrated geometry of the extruder connected to a die are considered. The FEM based numerical simulation of the coupled momentum-mass-energy conservation equations allowed the determination of the effects of some of the important system parameters, including the power law index and the staggering angle of the screws, on the pumping and pressurization capability of the extruder and the associated degree of fill in the extruder.