20. An extruder barrel has a diameter of 5.0 in and a length-to-diameter ratio of 22. The viscosity of the polymer melt = 0.0020 lb-s/in2 . The pitch of the screw = 4.5 in and channel depth = 0.25 in. The screw rotates at 50 rev/min, generating a head pressure = 500 lb/in2 . What is the volume flow rate of plastic at the die end of the barrel? 21. An extrusion operation produces continuous tubing with outside diameter = 2.0 in and inside diameter = 1.7 in. The extruder barrel has a diameter = 4.0 in and length = 10 ft. The screw rotates