Residence time distribution and barrel fill in pet food twin-screw extrusion cooking

The residence time distribution and barrel fill of pet food in a twin-screw extruder was determined under conditions of a constant ratio of feed rate to screw speed. Specific feeding load was held constant at 0.16 kg/hr/ rpm while feed rate ranges were 24-56 kg/hr and screw speed ranges were 150-350 rpm. The residence time rapidly decreased as feed rate and screw speed increased. The spread of the residence time distribution (RTD) was smaller at higher feed rates and screw speed, however analysis of the normalized RTD indicated greater mixing. The barrel fill was constant at approximate to 50% throughout the range of experimental conditions.