Dynamic Modelling of a Cooking Extruder

A dynamic model of a twin-screw cooking extruder suitable for process optimisation and control purposes was implemented in MATLAB. The model is capable of predicting pressure, temperature and starch gelatinisation profiles, as well as the residence time distribution and the specific mechanical energy expended on the product. Two different rheological models were considered for their suitability in fitting experimental data. It was shown that the model proposed by Kulshreshtha et al. (1991) more accurately described the rheological behaviour of extruded starch than that used by Vergnes et al. (1987), although the latter model did provide a better prediction of the general trends observable in the data. The relevant model parameters were determined from experimental data using a least-square optimisation routine. The model predictions compared favourably with measured residence time distribution data.