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Food processing wastewaters and slurries typically contain high concentrations of biodegradable organic matter. Before the wastewater can be discharged the pollutant concentration must be reduced. One way to achieve this is through the use of a biological species (`biomass') that consumes the organic matter (`substrate').
We investigate biological reactor models in which the growth rate is given by a Contois expression with a variable yield coefficient. We investigate the reduction in pollutant concentration when wastewaters are passed through one of two reactor configurations: a single reactor and a two-reactor cascade. In the latter scenario the total residence time is fixed and the residence time in the first reactor is taken to be a design parameter. It is found that in many cases an optimal reactor cascade may outperform the single reactor by two orders of magnitude.
M.I. Nelson and H.S. Sidhu. Reducing the emission of pollutants in food processing wastewaters. Chemical Engineering & Processing 46(5), 429-436, May 2007.
The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1016/j.cep.2006.04.012.
We model the increase in temperature in compost piles or landfill sites due to micro-organisms undergoing exothermic reactions. The mode incorporates the heat release due to biological activity within the pile and the heat release due to the oxidation of cellulosic materials. The heat release rate due to biological activity is modelled by a function which is a monotonic increasing function of temperature over a particular range and followed by a monotone decreasing function of temperature. This functionality represents the fact that micro-organisms die or become dormant at high temperatures. The heat release due to the oxidation reaction is modelled by the usual manner using Arrhenius kinetics. The bifurcation behaviour is investigated for two-dimensional slab geometries to determine the critical sizes of the compost piles.
H.S. Sidhu, M.I. Nelson, T. Luangwilaiu and X.D. Chen. Mathematical Modelling of the Self-Heating Process in Compost Piles. Chemical Product and Process Modeling, 2(2), article 8.
This paper is available at http://www.bepress.com/cppm/vol2/iss2/8.
We model the increase in temperature in compost piles due to micro-organisms undergoing exothermic reactions. The model incorporates two types of heat release: one due to biological activity; and the other due to the oxidation of cellulosic materials. In this study we also include the consumption of oxygen. We investigate the bifurcation behaviour and compare the results obtained from models that includes and exclude oxygen consumption in both one- and two-dimensional geometries.
H.S. Sidhu, M.I. Nelson and X.D. Chen. A simple spatial model for self-heating compost piles. ANZIAM Journal E, 48, C135-C150, 2007.
This paper is available at http://anziamj.austms.org.au/ojs/index.php/ANZIAMJ/article/view/86
We revisit the analysis of a reactor network consisting of two coupled continuous stirred tank reactors (CSTRs) arranged in series (Chem. Eng. J. 59 (1995) 169.) The main idea proposed in this earlier work is to improve process conversion by generating periodic behaviour in the first reactor (by appropriate choice of design and operational parameters) which then `forces' the second reactor. The performance of this cascade system was shown to be greatly enhanced using the above strategy. In this paper we show some conceptual errors in the analysis in the original paper. We also show that by employing a systematic bifurcation analysis, including the use of a path following software, greater insights can be gained regarding the system's behaviour. Using these techniques we show that operation and design parameters can be readily identified to ensure that the cascade has a superior performance to a single CSTR.
H.S. Sidhu, S.D. Watt, M.I. Nelson and A.K. Ray. Performance improvement and dynamical behaviour analysis of a cascade of two CSTRs. International Journal of Chemical Reactor Engineering, 5: A13, 2007.
This paper is available at http://www.bepress.com/ijcre/vol5/A13.
Students commencing science and engineering degrees at the University of Wollongong are given mathematics skills test in the first and fourth weeks of session. An evaluation of the results from these tests indicate that the majority of students' basic mathematical skills were insufficient to adequately support the prescribed first year mathematics curriculum. To address this problem a pilot study was set up to develop video solutions. These solutions permit students to see the development of each solution in a step-by-step manner. An audio commentary on each worked solutions assists learning by providing students with an explanation of the developing solution. Two methods of video capture were investigated. The first used eBeam, a system to capture pen strokes from a whiteboard. The second method used a video camera mounted on a copy stand. We describe the process by which the video solutions were recorded and describe the educational environment in which students accessed them. A preliminary analysis of the impact of this tool on the achievement of students is also presented.
E. Aminifarp, A. Porter, R. Caladine and M.I. Nelson. Creating mathematical learning resources --- combining audio and visual components. ANZIAM Journal E 47, pp C934-C955, 2007.
This paper is available at http://anziamj.austms.org.au/V47EMAC2005/Aminifar/home.html.
Direct-contact heat transfer involves the transfer of heat between two fluids by bringing them into intimate contact with each other. While one of the fluids involved is the continuous phase or the `quiescent phase', the other, which is intimately mixed with the former, is called as the `dispersed phase'. The advantage of direct-contact heat transfer is that it generates a very high value of overall heat transfer coefficient resulting in higher heat transfer efficiency. This overall heat transfer coefficient is maximum at the instant when the two fluids (phases) make their contact. The value of the heat transfer coefficient decreases rapidly due to the additional heat transfer resistances built up such as the condensate layer and so on. This rapid process has made experimental measurement of the initial heat transfer illusive. So far there has been only one analytic expression that has been derived to describe this initial process. The same authors also devised an experimental technique for measuring the direct contact heat transfer coefficient during this initial phase. However, while the experimental technique of the aforementioned authors was adequate, their analytical expression to evaluate the direct-contact heat transfer was incorrect. In this paper, five mathematical expressions have been presented for estimation of the direct-contact heat transfer coefficient for a condensing vapour bubble. Of these, three have been exclusively derived here and the other two are modifications from the already existing expressions. Comparisons have been made with the available experimental results and the physics revealed by the comparisons are described.
S. Karp, X.D. Chen and M.I. Nelson. Direct-contact heat transfer coefficient for condensing vapour bubble in stagnant liquid pool. Chemical Engineering Research and Design 85(A3), 320-328, 2007.
The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1205/cherd06030.
The increase in temperature in compost piles/landfill sites due to micro-organisms undergoing exothermic reactions is modelled. A simplified model is considered in which only biological self-heating is present. The heat release rate due to biological activity is modelled by a function which is a monotonic increasing function of temperature over the range 0<= T<= a whilst for T>= a it is a monotone decreasing function of temperature. This functional dependence represents the fact that micro-organisms die or become dormant at high temperatures. The bifurcation behaviour is investigated for 1-d and 2-d rectangular slab geometries. In both cases there are two generic steady-state diagrams including one in which the temperature-response curve is the standard S-shaped curve familiar from combustion problems. Thus biological self-heating, can cause elevated temperature raises due to jumps in the steady temperature.
This problem is used to test a recently developed semi-analytical technique. For the 2-d problem a four-term expansion is found to give highly accurate results - the error of the semi-analytical solution is much smaller than the error due to uncertainty in parameter values. We conclude that the semi-analytical technique is a very promising method for the investigation of bifurcations in spatially distributed systems.
M.I. Nelson, T.R. Marchant, G.C. Wake, E. Balakrishnan, and X.D. Chen. Self-heating in compost piles due to biological self-heating. Chemical Engineering Science 62(17), 4612-4619, 2007.
The DOI (Digital Object Identifier) link for this article is http://dx.doi.org/10.1016/j.ces.2007.05.018.
We investigate an experimentally verified model for the production of ethanol through continuous fermentation. Previous studies investigated this model using direct integration. Such integration is time consuming as parameter regions of interest can only be determined through laborious and repetitive calculations. Using techniques from nonlinear dynamical systems theory, in particular a combination of steady state analysis and path following methods, practical insights into operating strategies are found. We use the performance of the reaction scheme in one tank as a benchmark for comparing the performances of multiple tanks.
S.D. Watt, H.S. Sidhu, M.I. Nelson and A.K. Ray. Analysis of a model for ethanol production through continuous fermentation. ANZIAM Journal E (EMAC2007), 49, C85-C99, 2007.
This paper is available at http://anziamj.austms.org.au/ojs/index.php/ANZIAMJ/article/view/322.
We analyse a model for the activated sludge process occurring in a biological reactor without recycle. The biochemical processes occurring within the reactor are represented by the activated sludge model number 1 (ASM1). In the past the ASM1 model has been investigated via direct integration of the governing equations. This approach is time consuming as parameter regions of interest (in terms of the effluent quality leaving the plant) can only be determined through laborious and repetitive calculations. In this work we use continuation methods to determine the steady-state behaviour of the system. In particular, we determine bifurcation values of the residence time, corresponding to branch points, that are crucial in determining the performance of the plant.
H.S. Sidhu and M.I. Nelson. Mathematical analysis of the activated sludge process for domestic wastewater treatment. In Proceedings of the 35th Australasian Chemical Engineering Conference, CHEMECA 2007, pages 712-720 (on CDROM), Engineers Australia, 007. ISBN 0-858-25844-7.
In this paper we model the thermal behaviour of compost heaps in the presence of micro-organism undergoing oxidative exothermic reactions. For simplicity we consider a spatially uniform model in which oxidative reactions of the cellulosic components is ignored. We use singularity theory to investigate the generic properties of the model. We show that there are two generic steady-state diagrams including one in which the temperature-response curve is the standard S-shaped curve familiar from combustion problems. Such a steady-state diagram contains an elevated temperature branch, which is the feature of practical interest in facilities such as industrial compost heaps and municipal tips. Thus biological self-heating can cause jumps in the steady-temperature. We outline a procedure by which reasonable values of the kinetic parameters can be estimated.
M.I. Nelson, H.S. Sidhu and X.D. Chen. A spatially uniform model of oxidative self-heating in compost piles. In Proceedings of the 35th Australasian Chemical Engineering Conference, CHEMECA 2007, pages 1673-1683 (on CDROM), Engineers Australia, 2007. ISBN 0-858-25844-7.
We investigate a model for the production of ethanol through continuous fermentation. Earlier studies have shown that by using continuous fermentation, rather than other methods such as centrifuges and settling tanks, the productivity can increase markedly. Recently, we showed that in a single tank the biochemical model possess a rich variety array of dynamical behaviour, ranging from oscillations, period-doubling to chaotic behaviour. We use path-following software to gain insights into the behaviour of the system when a cascade of either two or three continuously stirred reactors is used. In particular, we identify design parameters that optimise the productivity of the system in the different reactor configurations.
S.D. Watt, H.S. Sidhu, M.I. Nelson and A.K. Ray. Improving ethanol production through continuous fermentation. In Proceedings of the 35th Australasian Chemical Engineering Conference, CHEMECA 2007, pages 1862-1869 (on CDROM), Engineers Australia, 2007. ISBN 0-858-25844-7.
Modern technologies provide new approaches to tertiary education and will be an increasing component of the educational experience in the future. Their use in education poses a significant challenge to the design and delivery of teaching and learning as many teachers and students are unfamiliar with them in this context. Over the last decade there has been a very rapid expansion in the capability and usage of Information and Communication Technologies (ICTs) in teaching and learning. To them effectively there is a need to understand how different ICTs can be applied to learning and teaching. Videoconference, Access Grid and Web Conference Applications (WCAs) are now available for use in higher education. The technologies are compared with a view to recommending which ones to implement for teaching and learning.
E. Aminifarp, R. Caladine, A. Porter and M.I. Nelson. Beyond Videoconference: Increased Functionality to Enhance Media-Rich Interactions in Teaching and Learning. In G. Richards (Editor), Proceedings of World Conference on E-Learning in Corporate, Government, Healthcare, and Higher Education 2007, pages 6985-6990, Association for the Advancement of Computing in Education, Chesapeake, VA, USA, 2007.
A wide variety of research techniques have been applied to gain insights into the processes governing self-heating of coal. These range from fundamental investigations investigating the the oxidation mechanism of coal through to research methods that are used to provide rankings of the propensity of different coals to self-heat to topics of mining interest such as the detection and suppression of self-heatings. In this article we review the gamut of experimental work relating to self-heating and spontaneous combustion of coal. Although we do not cover mathematical modelling, we include reviews of experimental techniques that have been used to obtain kinetic parameters for coal oxidation: an essential input into any mathematical model.
M.I. Nelson and X.D. Chen. Recent experimental work on the self-heating and spontaneous combustion of coal, in G.B. Stracher (editor), Wild Coal Fires: Case Studies from Around the World, Geological Society of America Reviews in Engineering Geology v, XVIII, p 31-83, 2007. http://dx.doi.org/10.1130/2007.4118(04).
Access Grid Rooms (AGR) are rooms that draw together suites of technologies that enable collaboration and sharing across the internet. The sharing is of video images, interactive whiteboards, sound, document cameras, files and other applications. These rooms can be used to deliver lectures and subjects from one campus to other campuses at the same institution or to share subjects with other institutions across the country or with international partners. With no experience in teaching mathematics through the new medium the commitment to engage in teaching via an AGR was a leap of faith into one or many visions of the future of Mathematics Education. In this paper we examine the first 24 months from conception to a plan to install and use an AGR for teaching research and collaboration in mathematics and the reality of what transpired. The paper reports on student and staff experiences in using the technology to take and deliver honours level subjects across three universities in Australia.
A. Porter, M.I. Nelson, E. Aminifarp, G. Williams, and R.Caladine. Access grid rooms: the plan, the reality. In C.S. Lim, S. Fatimah, G. Munirah, S. Hajar, M.Y. Hashimah, W.L. Gan, and T.Y. Hwa, editors, Proceedings of the 4th East Asia Regional Conference on Mathematics Education 2007 (EARCOME 4), pages 285--291. School of Educational Studies, Universiti Sains Malaysia, 2007. ISBN 978-983-2700-45-46.