Dynamic modelling for a twin screw food extruder: analysis of the dynamic behaviour through process variables
1995
Cayot, N. | Bounie, D. | Baussart, H.
Food extrusion processes are multiple input, multiple output complex systems. In this paper, the extrusion cooker is simplified into a single input, single output dynamic system, even though multi-input tests have also been performed. Its dynamic characteristics are obtained with step tests on different operating variables: feed rate, moisture content and screw speed. The response is monitored on the following outputs: melt pressure, melt temperature and specific mechanical energy. The results show the following: -the behaviour of the extruder generally verifies the conditions of the BIBO (Bounded Input, Bounded Output) stability, -the process can be considered to be stationary and non-linear. The non-linearity of the system is highlighted by: -the variability of the steady state grain as a function of step magnitude, -the lack of superimposition of the gains when performing multi-input tests. The study of the transient behaviour shows that the systems exhibit a non-separable non-linearity. The observed dynamic characteristics are rising problems that must be taken into account in designing control systems for food extrusion.
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