On‐line Measurement of Residence Time Distribution in a Food Extruder

Abstract

A technique was based on electrical conductivity of material in a die, and used a series circuit consisting of a 5 mm dia die, a 10 ohm resistor, and a 15V dc power supply. Material conductivity was altered with addition of an electrolyte tracer at the feed inlet. Change in current flow was measured as a proportional voltage response across the resistor. Using a twin‐screw extruder, with L/D 32:1, the RTD of rice flour at 15% moisture was determined using sodium nitrate as tracer. Under steady state, the voltage across the resistor was measured. The on‐line results correlated well with the established erythrosine dye method. The effects of screw configuration, feed flow rate, and screw speed were precisely determined by the on‐line method.