ANALYSIS OF SHEAR AND THERMAL HISTORY DURING CO-ROTATING TWIN-SCREW EXTRUSION

A computation procedure was developed for calculating contributions of frictional and viscous heat generation during co-rotating twin-screw extrusion. Application of energy balance to experimental data (mechanical energy input, feed rate, feed moisture, screw speed, die pressure, barrel wall and dough temperature profiles) indicated how conditions affected fill, filled length, shear and thermal energy inputs to the foods. Kneading blocks increased degree of fill in partially filled sections, and dissipated 4-6 times more viscous heat than conveying elements in completely filled sections. Energy input profiles along extruder screw axis clearly demonstrated how heat generation from shear and heat transfer between extruder and foods influenced total energy input.