Projetos de reatores para tratamento de águas de abastecimento e águas residuárias envolvem o conhecimento da hidrodinâmica do escoamento e das reações químicas e bioquímicas que ocorrem em seu interior. A variável hidrodinâmica pode interferir de modo significativo na eficiência da unidade, visto que ela influencia diretamente no desempenho da cinética das reações. Existem muitos reatores que operam em regime não-permanente de vazão, entretanto, são poucos os trabalhos disponíveis na literatura científica que sugerem o desenvolvimento de métodos para a avaliação da hidrodinâmica desse tipo de escoamento. A aplicação de modelos convencionais para avaliações hidrodinâmicas desses reatores é conceitualmente errada, visto que os mesmos são desenvolvidos considerando-se um regime permanente de vazão. Nesse contexto apresenta-se nesse trabalho um modelo matemático voltado para a avaliação hidrodinâmica de reatores que operam em regime não-permanente de vazão, com intuito de subsidiar as análises e previsões de seu comportamento. Foi utilizada a técnica DTR para levantamento de dados experimentais e um software de simulação numérica, o Vensim 6.3 da Ventana Systems, para auxiliar no desenvolvimento do modelo. Após a sua calibração e validação, com as devidas restrições, o modelo demonstrou ser comparativamente mais adequado para a avaliação do comportamento hidrodinâmico de reatores em condições de regime não-permanente com variação senoidal cíclica de vazão, principalmente para escoamentos que possuem tempo de detenção hidráulica relativamente baixo e amplitude de variação de vazão relativamente elevada. / Reactor designs for water supply and wastewater treatment require the knowledge of hydrodynamic and chemical reactions that occur in its interior. The hydrodynamics is very important as it interferes the efficiency of an treatment unit, since it directly influences the chemical reactions. There are many non-steady state reactors, but there are little studies about their hydrodynamic evaluation in the literature. The use of conventional models is conceptually wrong because they have been developed for steady state conditions. This work presents a mathematical model for hydrodynamic evaluation in non-steady state reactors to support analisys of these flows. The RTD technique to get experimental data and a numerical software simulation have been used as well as the Vensim 6.3 program, of Ventana Systems, to support the model development. After its the calibration and validation, the model proved to be suitable for the experimental conditions, especially for flows that have relatively low hydraulic retention time and relatively high amplitude of flow variation.

The impact of refrigeration systems on the environment can be reduced by the use of alternative reffigerants which are less harmful to the atmosphere and the optimisation of systems and control strategies to deliver increased levels of energy efficiency. Mathematical modelling offers the opportunity to test the performance of systems under different operating conditions and with alternative refrigerants. Dynamic models allow comparison of both transient and steady-state behaviour and this is of particular importance for liquid chillers, since these systems can operate under transient conditions for long periods. This thesis details the development of a general dynamic model for the simulation of liquid chillers. Mathematical models of the reciprocating compressor, expansion valve, evaporator and condenser are presented. The models are integrated to form the overall system model by passing conditions from one component to another. A series of steady-state and transient experimental tests were carried out on a liquid chiller and the model was used to simulate these tests. Validation was carried out by comparison of these measured results to those predicted by the simulation for both the steady-state and transient tests. Once validated, the model was used to investigate the steady-state and dynamic performance of liquid chillers operating with various refrigerants. The effect of the mass of the system refrigerant charge was examined for a number of refrigerants. The steady-state performance for a range of evaporator and condenser coolant temperatures was also investigated. Finally, the effect of different system refrigerants on start-up transients was examined and the losses in cooling capacity due to cycling quantified. The effect of the expansion valve's initial superheat spring setting on the dynamic response and transient losses was also investigated.

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Garamond} This paper presents an approach for modelling a commercial dinitrotoluene (DNT) production process using the CHEMCAD simulation software. A validation of the model was performed based on results of an experimental study carried out at Chematur Engineering AB, Sweden.  Important parameters such as fluid properties, temperature profile and other operating conditions for CHEMCAD steady state model were selected so as to obtain the crude DNT yield as well as the acid –and organic phase compositions within the same range as the reference values from the experimental study. The results showed that the assumption of the steady state model was correct, and that acid –and organic phase compositions were in good agreement, although with a slightly lower sulphuric acid concentration than that observed in the experimental study.  Also, a detailed study was carried out to analyse the effects of physicochemical conditions on the desired product yield. Both the results from the experimental study and the simulated model agree that the effects of mixed acids or heats of mixing acids contribute significantly to the energy balance.  For the appropriateness of the thermodynamics, a NRTL model was chosen and the reactor system was optimized by an equilibrium based approach, producing MNT in 99.8% yield and crude DNT in 99.9% yield. An 80.1/19.9 DNT isomer ratio of the main isomers was achieved and a reduction of by-products in the crude DNT shows a good agreement between the model and the experimental study. / p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.5px Garamond} I denna rapport presenteras en metod för att modellera en kommersiell nitreringsprocess för tillverkning av dinitrotoluen (DNT) med simuleringsprogrammet CHEMCAD. En validering av modellen gjordes baserat på resultat från en experimentell studie utförd hos Chimärer Engineering AB, Sverige.  CHEMCAD-modellen utgår från ”steady-state” drift av anläggningen. Viktiga parametrar såsom fluidegenskaper, temperaturprofil och andra driftsbetingelser i CHEMCAD-modellen valdes för att erhålla ett utbyte av DNT samt sammansättningar av såväl syrafas som organisk fas i god överensstämmelse med referensvärdena från den experimentella studien.  Resultaten visade att antagandena i modellen var korrekta och sammansättningarna för syrafasen och den organiska fasen överensstämde med data från den experimentella studien.  Det genomfördes också en detaljerad studie för att analysera effekterna av fysikalisk-kemiska betingelser på det önskade produktutbytet. Både resultaten från den experimentella studien och data från anläggning i drift överensstämde med den simulerade modellen avseende utspädningsvärmens bidrag till energibalansen.  För att erhålla en lämplig beskrivning av reaktionssystemets termodynamik valdes en NRTL-modell och reaktorsystemet optimerades, vilket gav 99,8 % utbyte av MNT och 99,9 % DNT utbyte. Ett förhållande på 80,1 / 19,9 mellan de två huvudisomererna av DNT uppnåddes och en minskning av biprodukter i DNT produktblandningen. Detta är två exempel på en bra överensstämmelse mellan modellen och experimentstudien.

I denna studie har jämförelse gjorts mellan Interacoustics Eclipse och GSI Audera i samband med Auditory Steady-State Respons (ASSR) mätningar. Syftet med studien var att undersöka ASSR som metod, att utvärdera dess tillförlitlighet i jämfö­relse med tonaudiometri för personer med normal hörsel och personer med hörsel­nedsätt­ning. Avsikten var dessutom att undersöka om elektrod­placering­ på örsnibb eller på mastoid påverkade mät­resultatet, försökspersonens upplevelse av instrumen­­t­ens ljudstimuli, om de estimerade ASSR-värdena påverkades av att mättillfället påbörjades eller avslutades med Interacoustics Eclipse samt undersöka tiden för mätningarna. En experimentell studie genomfördes. Mätningarna som utfördes var tonaudiometri och ASSR, den senare uppmättes med Interacoustics Eclipse och GSI Audera på (n=20) vuxna med normal hörsel och (n=4) vuxna med hörselnedsättning. För personer med normal hörsel påvisades en god överensstämmelse mellan estimerade ASSR-värden och tonaudiometri för Interacoustics Eclipse, något sämre överensstämmelse för GSI Audera. Genomsnittlig mättid för båda instrumenten var ca 40 min. Resultaten visade att elektrodplaceringen inte har någon påverkan på ASSR-värden för Interacoustics Eclipse. Hälften av försökspersonerna upplevde att Interacoustics Eclipse hade ett behagligare ljudstimuli att slappna av till och den andra hälften upplevde GSI Audera som behagligast. De estimerade ASSR-värdena påverkades minimalt beroende på om mättillfället påbörjades eller avslutades med Interacoustics Eclipse.

Dans l’optique de produire de maîtriser les conditions d’expansion ex vivo de greffons hématopoïétiques produits à partir de sang périphérique en homéostasie, l’objectif de ce projet a été de caractériser fonctionnellement, métaboliquement et transcriptomiquement les cellules souches hématopoïétiques (CSH). Compte tenu de l’impossibilité technique de sélectionner spécifiquement les CSH humaines, nous avons utilisé un modèle cellulaire enrichi en CSH, le modèle Side Population(SP). Dans un premier temps, nos travaux ont confirmé que les CSH du sang périphérique étaient majoritairement dans la population SP et qu’elles possédaient des caractéristiques fonctionnelles proches des CSH des autres compartiments hématopoïétiques. Nous avons également démontré l’implication des basses concentrations d’O2 sur le maintien des CSH du sang périphérique. Dans un second temps, nos résultats ont prouvé que les CSH du sang périphérique utilisaient à la fois la glycolyse et la phosphorylation oxydative pour produire l’énergie nécessaire à leur maintien. Enfin, ce projet a permis d’apporter des résultats préliminaires concernant les régulations transcriptomiques des CSH du sang périphérique. Ces données montrent donc que le sang périphérique en homéostasie pourrait constituer une source potentielle de cellules pour la production de greffons hématopoïétiques tout en apportant les premiers éléments de compréhension de la physiologie de ces cellules, afin, dans un plus long terme de maîtriser leur maintien ou leur différenciation ex vivo. / To evaluate the possibility to control ex vivo expansion conditions, a key point to produce hematopoietic graft from steady state peripheral blood (SSPB), the objective of this project to characterize the functional properties, the metabolism and the transcriptomic regulations of hematopoietic stem cell (HSC) from SSPB. Due to the lack of strong HSC’s marker in human, we choose to use the Side Population (SP) model, previously described as enriched in HSC in other hematopoietic compartments. In a first part of our work, we showed that HSC from SSPB are mainly inside the SP population. Indeed, SP cells from SSPB exhibit functional properties very closed from HSC. In addition, we found they strongly affected by low O2 concentrations, as HSC from bone marrow. In a second part, our results showed that HSC from SSPB use as much glycolysis as oxidative phosphorylation to produce energy they need to maintain their properties. All together, these data give some interesting information about HSC regulation and needs. They also suggest that HSC from SSPB could be considering as a potential source of hematopoietic graft for therapy.

The ageing population has become more active and live longer, these patients require hip replacement surgery at a younger age. Artificial hip implants, consisting of the acetabular cup and femoral head, affect the lives of many people, and the longevity of these implants pose significant concerns (rarely longer than 17 years). To help understand the lubricating performance of such a system, a hip joint model was built based on the Reynolds equation; the model developed simulated hydrodynamic lubrication. A steady-state angular rotation model was built whereby it was concluded that such motion would not support any load due to the anti-symmetric nature of the resultant pressure distribution (anti-symmetric about the axis of rotation). The pressure distribution from the steady-state rotation simulation contained a pressure source and sink which converged to the centre of the cup and whose pressure value increased in magnitude, as the eccentricity ratio increased. Infeasible results were obtained when the intermediary pressure constraint, allowing only positive pressure values, was implemented. The results obtained were not representative of the problem and it is recommended that this constraint not be implemented. The transient walking cycle model showed that a fluid with viscosity of 0.0015Pa.s is not sufficient to support a load in the walking cycle under conditions representative of hydrodynamic lubrication. Increasing the fluid viscosity promoted better results in the hydrodynamic model. Increasing the femoral head radius and decreasing the radial clearance between the components also improves the possibility of hydrodynamic lubrication. It is recommended that the model should be extended to investigate elasto-hydrodynamic lubrication. If possible, the effects of a boundary lubrication model should be investigated, as it is believed to be a major contribution to the lubrication of hip joints. / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Biological remediation of Cr(VI) contaminated soil and groundwater is an emerging field. In this study, the in situ bioremediation technology for treating Cr(VI) contaminated groundwater aquifers was evaluated using a laboratory microcosm system. The study was conducted using columns with five equally spaced intermediate sampling ports along the length to facilitate finite difference modelling of the Cr(VI) concentration profile within the column. Cr(VI) concentration was continuously measured in the influent, in five equally spaced intermediate ports within the column and in the effluent port. The change or the shift in microbial community within the inoculated column was also monitored due to exposure to toxic conditions after seven weeks of operation using the 16S rRNA genotype fingerprinting method. The effect of introducing a natural carbon source (sawdust) in inoculated columns in comparison with the performance of sterile controls under various loading conditions was also evaluated. Near complete Cr(VI) removal was achieved in an inoculated carbon source reactor, whereas only 69.5% of Cr(VI) removal was achieved in an inoculated column without an added carbon source after 4 days of operation at 20 mg/L. In a sterile control reactor less than 2% of Cr(VI) was removed after 4 days of operation at 20 mg/L. Experimental cores demonstrated a successful Cr(VI) reduction process in the simulated microbial barrier system that was evaluated internally. The model that simulates Cr(VI) removal and transport in the subsoil environment was developed. The Cr(VI) mass balance model across the reactor that accounts for the flow characteristics and biological removal mechanism successfully captured the trends of Cr(VI) response profiles under quasi-steady state conditions for different loading conditions. This study demonstrate the potential of applying effective Cr(VI) reducers in the reactive barrier systems to contain or attenuate the spread of Cr(VI) contaminant in groundwater aquifer systems. The finite difference model developed in this study to evaluate the behaviour of Cr(VI) in the reactor could contribute towards improved designs of future in situ bioremediation systems that can be implemented for remediation of Cr(VI) on site. / Dissertation (MSc)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

The steering arrangement of a 6x6 off-road military vehicle was investigated, with the aim to determine if a variable steering ratio between the first and second steering axle of the vehicle will make an improvement in the steady and transient state handling of the vehicle. Low speed manoeuvring was evaluated, comparing the vehicle steering geometry with Ackerman geometry. For steady state handling, a bicycle model was developed, and constant radius simulations at various track radii, vehicle speeds and steering ratios (ratio between the first and second steering axle) was performed. For transient dynamic simulations, a mathematical model was developed that included a simple driver model to steer the vehicle through a single lane change, again at various speeds and steering ratios. The vehicle was instrumented, and actual constant radii tests, as well as single lane change tests were performed. The measurements enabled the comparison of simulated and measured results. Although basic mathematical models were used, acceptable correlation was obtained for both steady state and transient dynamic behaviour. The results indicated that for this specific vehicle geometry, where the centre of mass is above the second axle, no marked improvement would be obtained by implementing a variable ratio steering system. The mathematical model was changed to simulate a vehicle with longer wheelbase and different centre of mass. With the new geometry, theoretical slip angles (and therefore tire wear) reductions were more noticeable It was concluded that a variable ratio system between the front and second axle would not be an economically viable improvement for this vehicle, since the improvement achieved will not warrant the additional cost and complexity added to the vehicle. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / MEng / unrestricted

Hydroelectricity plays an important role to balance the stability of grid network.  In order to improve the stability of presently high loaded grids, hydropower plants are being operated over a wide range of operations and experiencing frequent start-stop, load rejection, and load acceptance. The turbines need to sustain sudden change in their operating condition to balance the grid frequency. Francis turbines have been widely used because of their wider operating range and higher stability in operation during rapid load variation. This has resulted in severe damage to the turbines as they are not normally designed to operate under such transient conditions. Several low and high frequency pressure fluctuations prevail during transients operating conditions. Generally, wall pressure measurements are performed which may not provide sufficient information to investigate the flow instabilities related to these fluctuations. Thus, the main objective of the present work is to simplify and perform optical measurements in a turbine during transient operating conditions to investigate the flow field. The measurements have been performed at the Water Power Laboratory using a high head model Francis turbine. The turbine is a 1:5.1 scale down model of a prototype operating at the Tokke Power Plant, Norway. The model runner diameter, net head, and discharge at the best efficiency point (BEP) were 0.349 m, 12 m, and 0.2 m3 s-1, respectively. A total ten pressure sensors were mounted at different locations namely, turbine inlet, vaneless space, and draft tube. The data were acquired at a sampling rate of 5 kHz. The instruments and sensors have been calibrated according to guidelines available in IEC standards. The determined total uncertainty in the measurement of hydraulic efficiency was ±0.15% at BEP condition. The velocity measurements in the draft tube cone were performed using a 2D PIV system and the images were sampled at a rate of 40 Hz.      Steady state measurements were carried out considering the realistic design and off-design operating conditions of the prototype turbine. Therefore, the angular speed of the runner was maintained constant for all steady state conditions during the measurements. The maximum hydraulic efficiency (92.4%) was observed at nED = 0.18, QED = 0.15, and a = 9.8º, which is named BEP. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space, runner, and the draft tube. The fluctuations due to rotor-stator interaction (RSI) were observed to be most dominating at high load condition, however, fluctuations due to the rotating vortex rope (RVR) at part load (PL) condition. Two different modes (synchronous and asynchronous) modes of vortex rope are observed at PL condition of the turbine. An asymmetry in the flow leaving the runner was detected at both design and off-design conditions, with a stronger effect during off-design operating condition. Numerical simulations of the model turbine were carried out at PL operating condition. The simulations were performed using two turbulence models, standard k-ε and SST k-ω, with high-resolution advection scheme. The numerical pressure values obtained with both standard k-ε model and SST k-ω showed a small difference with the experimental values. The amplitudes of numerical pressure values were higher (~2.8%) in the vaneless space and lower (~5.0%) in the draft tube than the experimental values. The frequencies of the RSI and RVR were well captured in the turbine but the amplitudes were overestimated.   During load rejection from BEP to PL, the plunging mode of the vortex rope was observed to appear first in the system than that of the rotating mode. Whereas during the load acceptance from PL to BEP, both the modes were observed to disappear simultaneously from the system. In the velocity data, the axial velocity only contributed to the development of the plunging mode and radial velocity to the rotating mode. The region of low velocity, stagnation point, flow separation, recirculation, oscillating flow and high axial velocity gradients were well captured in the system during the transients. The induced high-velocity gradients during the load acceptance from BEP to HL was observed to develop a vortex core in the draft tube. During startup and shutdown, the guide vanes angular position was moved from one to another steady state condition to achieve the minimum load condition of the turbine. At this condition, the generator of the turbine was magnetized at the synchronous speed during startup and shutdown, respectively. The frequency of wave propagation was observed to vary with the runner angular speed during startup and complete shutdown of the turbine. Comparatively high-pressure fluctuations in the draft tube were observed during the guide vane movement from the high discharge conditions. Some unsteady phenomena such as the formation of dead velocity zone, backward flow, and flow oscillations were observed during startup and shutdown of the turbine.   The current work has been also used to continue a series of workshops, i.e., Francis-99. The first workshop was held on December 2014 with the cooperation of LTU and NTNU. The measurements performed in this work were used for the second workshop which was held on December 2016. The investigations presented in this thesis will be further explored in the third workshop scheduled for December 2018.

We study diffusion-reaction-advection models describing population dynamics of aquatic organisms subject to a constant drift, with reflecting upstream and outflow downstream boundary conditions. We consider three different models: single logistically growing species, two and three competing species. In the case of a single population, we determine conditions for existence, uniqueness and stability of non-trivial steady-state solutions. We analyze the dependence of such solutions on advection speed, growth rate and length of the habitat. Such analysis offers a possible explanation of the "drift paradox" in our context. We also introduce a spatially implicit ODE (nonspatial approximation) model which captures the essential behavior of the original PDE model. In the case of two competing species, we use a diffusion-advection version of the Lotka-Volterra competition model. Combining numerical and analytical techniques, in both the spatial and nonspatial approximation settings, we describe the effect of advection on competitive outcomes. Finally, in the case of three species, we use the nonspatial approximation approach to analyze and classify the possible scenarios as we change the flow speed in the habitat.