Barrel-valve Assembly: Its Influence on Residence Time Distribution and Flow Pattern in a Twin-screw Extruder

The effect of a barrel-valve assembly on the residence time distribution (RTD), degree of fill, and flow pattern in an intermeshing, co-rotating twin-screw extruder was studied at 300450 rpm screw speeds and 0.0026 to 0.0038 kg/rev specific feeding loads. Increasing the orifice plug size or decreasing the opening of the barrel valve slightly increases the mean residence time, RTD spread, and extruder fill level. The inclusion and variation of the barrel-valve assembly in the extruder does not change the dimensionless dispersion and flow behavior. Both residence time and RTD spread are decreased significantly (P < 0.001) with the increasing screw speed and specific feeding load, while degree of fill is decreased with the former but increased with the latter. The flow analysis indicated a 70~75% of plug-flow behavior was exhibited in the extrusion system. Regression models for predicting RTD parameters and extruder degree of fill were developed.