Investigation of flow of food materials in extrusion dies

Extrusion dies play an important role in shaping and imparting textural characteristics to extruded products. Designs of food extrusion dies have been mainly performed on an empirical basis, and there is little data available describing flow phenomena within the die. This research attempts to address this problem by studying transport phenomena in flows of food materials in extrusion dies by a combination of computational and experimental methods.; Commercial finite element software was used to carry out the numerical aspect of this study. Results from the software were validated with known theoretical analyses before it was used to predict design and flows in more complex extrusion dies. The software was modified by incorporating a viscosity subroutine, which enabled it to compute typical food flows.; Finite element analyses of flow of food materials in different dies were carried out. The geometries included an annular diverging die and a converging die. Flows of Newtonian and non-Newtonian food materials were investigated, along with conjugate thermal transport within the die walls. Results showed that the predictions for the Newtonian material matched very well with both analytical and experimental results. The numerical predictions of mass flow rate for non-Newtonian materials showed reasonable agreement with the experimental data. Characteristic curves for these dies were obtained, along with pressure, temperature and shear rate contours. The effect of cooling due to the flow of coolant in cooling jackets of the diverging die was also studied. Conditions under which conjugate effects were important were determined.; Experimental studies were performed to identify key factors and their influence on flow distribution in an annular food extrusion die. The objective in this section of the study was to determine the effects of die geometry, food material and operating parameters on flow distribution in the annular die. Corn syrup, cornstarch, cornmeal and wheat flour were extruded through the die using a twin-screw extruder at varying mass flow rates. It was found that perfect geometrical alignment had the strongest effect in achieving flow uniformity, and should be considered as the critical factor in practical applications.