The development of simulation models for food process operations.
The development of a simulation strategy and modelling algorithm with potential application to a
variety of food process operations, particularly to thermal processing of canned foodstuffs has been
A review of published work identified previous efforts in the development of mathematical models
for thennal process operations, including their limitations. The review showed that Finite
Difference methods have found wide application in modelling conduction heating of canned foods.
A similar model would be a useful numerical yardstick for validating any developments in this work.
The great diversity of food handling operations have been grouped into a more manageable small
number of classes. Such classification recognised that sets of related operations share common
characteristics and functions which are the basis for the development of mathematical models for
each class of operations. The strategy developed involved hierarchical decomposition of unit
operations into assemblies of basic modules and mathematical modelling of these basics. A model
of the operation can then be constructed simply by selecting and arranging the required basic units
with due consideration to the boundary conditions of the physical problem. For transient operations
with positional variation, these elementary modules have been termed "zones". The range of basic
zones to model representative units have been identified. This hierarchical zone-model simulation
has been demonstrated for heat transfer in a cylindrical container and for batch retort operation.
The repeated use of the same unit modules for different operations makes this a flexible and robust
The mathematics of zone-modelling has been developed for heat conduction in foodstuffs in
cylindrical containers. To ensure accuracy, the numerical integration steps were rigorously
monitored using mathematical procedures well-established for this purpose. The validity of the
model has been tested against the analytical and implicit finite difference solutions. Generally, zone
models agreed within 1 % of these standard yardsticks with the difference becoming negligible when
sufficiently small integration steps or zone sizes were used.
The effectiveness of zone-modelling as a simulation tool has been established using experimental
data and the various sources of discrepancy between the model and experimental data accounted for.
Thermocouple measurement errors have been found to have contributed most significantly to this
discrepancy. Detailed analysis and modelling of thermocouple measurement errors has been carried
out using zone-modelling to simulate the true experimental system which accounted for the presence
of a thermocouple. The result has been an improved agreement between experiment and the zonemodel,
and it also demonstrated the flexibility of the modelling technique. Further resuhs have
shown that the discrepancy varied with thermocouple size and type. The contributions to error of
temperature variability of, and of uncertainty in, thermophysical properties of the food were
The flexibility and robustness of zone-modelling have been further demonstrated using some
practical situations including heat transfer to foodstuff in flexible packaging - such as sausage rolls,
heat transfer in a food container with varying headspaces and the consequence of steam interruption
during processing. Examples have been discussed of other transient processes that could similarly
be modelled using this technique.
The main achievements of this work include the application of hierarchical simulation and zonemodelling
techniques to food processing and the development of a novel mathematical modelling
technique which is more flexible than finite differences. Moreover, the applications of zonemodelling
to the study of thermocouple errors, to the study of the consequences of steam
interruption during thermal processing, and to heat transfer in foods in flexible containers, are
developments of interest in food processing. It is concluded that the hierarchical simulation and
zone modelling algorithm are robust and flexible techniques with potential applications in food
process simulation .