Modelling of mass transfer in packing materials with cellular automata
Date
2008-12
Authors
Engelbrecht, Alma Margaretha
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
The general objective for this thesis is to assess the ability of cellular automata to
model relatively complex processes or phenomena, in particular thermodynamic
scenarios. The mass transfer in packing materials of distillation columns was selected
as an example due to the sufficient level of complexity in the distillation process, and
its importance in a wide range of applications.
A literature survey on cellular automata that summarizes the information currently
available in formal publications and the internet is included to provide a general
overview on the basic theoretical principles and the application of cellular automata
models in the process engineering industry. The literature study was also used to
identify potential requirements for the new research project.
The study objective includes the construction of a cellular automata model that is able
to represent transition of solutes from the fluid on the micro-surfaces of packing
materials to the by-passing vapour stream, as well as the steady-state equilibrium
between evaporation and condensation. Iterated model parameters sufficient for the
realistic modelling of mass transfer as a result of thermodynamic driving forces, are
required to meet this objective. The model behaviour was compared and the
parameters subsequently adjusted according to the behaviour that is theoretically
expected from the system being simulated. Qualitative (although sometimes in a
quantitative format) rather than quantitative observations and comparisons were
made seeing that the model has not yet been calibrated.
The model that has been developed to date is not able to simulate the individual
effects of chemical and thermodynamic properties although a realistic simulation of
the cumulative effect exerted by these factors, or change thereof, on a system has
been achieved. The accuracy of the results that have been obtained by using iterated
parameters cannot be guaranteed for scenarios that deviate too much from the
systems that have already been modelled successfully.
The trade-off between the ability of the model to incorporate the effect of polarization,
its ability to represent separation, in particular the condensation of hydrophilic
substances, for strong hydrophilic packing materials and its ability to incorporate a
large number of species limits the range of scenarios that can be successfully
modelled.
The model is able to represent the effect of a declining driving force (difference
between the component vapour pressure of the gas phase and that of the liquid
phase) that is typical of a system which is allowed to reach equilibrium after an initial
disturbance. The model is also able to represent an additional driving force for
separation caused by the effect of intermolecular forces.
The model also displays the potential ability to represent the effect of different surface
structures of the packing material on the extent of separation achieved at steady
state as well as the rate at which such steady state conditions have been achieved.
The model must be correctly scaled to minimize inaccurate results.
Although several adjustments are needed to eliminate some limitations, the model
has proven itself worthy of further development due to its capability to represent the
basic characteristics of mass transfer in packing materials.
Description
Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008.
Keywords
Discrete modelling, Cellular automata, Intermolecular forces, Mass transfer, Dissertations -- Process engineering, Theses -- Process engineering