A methodology for a heat and mass transfer analysis of a steam
sterilisation process in industrial size autoclave with inclusion of
products has been developed. A model of the heat and mass flows
around the products consisting of saline solution packed in bags
and placed onto stacked trays was developed and added to a previously
developed model of an empty autoclave. This allowed for
the predictions of the performance profiles, including the temperature
distribution in the products in a fully loaded autoclave during
the sterilisation cycle. Inputs required for solving of the model
were initial conditions and since the control of the autoclave was
also modelled, a transient target vessel temperature profile for the
simulated PI controller was taken from an actual operational
industrial sterilisation cycle. The assumption of uniform spatial
distribution allowed for a numerical solution to be achieved
within 5 min for simulating a process with a heating cycle time
of 1 h.
Excellent agreement with experimental measurements was
achieved in the transient vessel, water pool and product temperatures,
as well as vessel pressure profile was obtained with the
numerical model. Additionally, the prediction of cumulative
steam consumption being within 3% of the physical measurement
is a demonstration of validity and accuracy of the model. The
model also allows for estimation of the breakdown in energy consumption
by the various entities within as well as losses to the
ambient.
The very small computational processing time required to
obtain a solution allows the simulation of many combinations of
parameters to gain a deeper understanding of thermal energy consumption
within a steam sterilisation process. The insights to
potential thermal energy savings are valuable when making decisions
regarding equipment improvement and the design of new
autoclaves. It is shown that a total energy savings of 8% is possible
by insulating the outer walls.