This work explores the hydraulic performance of a wastewater lagoon system located in San Antonio, Bolivia. The system consists of one facultative pond and two maturation ponds in series and is managed through a locally elected water committee. A tracer study was performed on the primary facultative pond and an analysis of the solids accumulation on the bottom of the facultative lagoon was also performed. The results were used to generate residence time distribution curves and provide an estimate of mean residence time in the system. The data was used to examine hydraulic efficiency as it relates to short-circuiting and dead zones. A sludge study accumulation study was performed using the white towel method and the resulting measurements were interpolated to determine a total estimated sludge volume of 169 m3 (which is 8% of the facultative pond volume). An orange study was also performed to assess the surface flow pattern in the system. The results were compared with a computational 2-d model. The 2-d model incorporated the estimated sludge distribution and provided a good fit for the tracer dye concentrations measured in the field over the 12 day study period. Simple models such as the Tanks in Series and the Completely mixed model were evaluated and abandoned because of their inability to model the physical behavior in the system. The Completely mixed model did however perform better than the Plug flow model. After comparing the tracer results from the reactor models that were considered: Tanks in Series, Completely mixed fluid, manual interpolation and the results from the 2-d cfd flow simulation, the results that provided the best fit for the data over 12 days was the manual interpolation method at a flow rate of 98 m3/day and configuration D at 60 m3/day. However, because of uncertainty as to what depth to obtain a representative area for the 2-d simplification and sensitivity to flow; all four configurations were considered for estimating the MHRT at the lowest measured flow rate of 60 m3/day. The results at a flow rate of 60 m3/day varied between 10.88 and 13.04 days for the MHRT with a hydraulic efficiency that varied between 33-51.6% (accounting for sludge volume). This is much shorter than the actual nominal retention time of 37 days and the design nominal retention time of 26 days. As a result it was concluded that short-circuiting was occurring in the facultative lagoon.

This thesis examines how the non-Newtonian characteristics of liquid hog manure affect the flow conditions within a steady-flow anaerobic digester. There are three main parts to this thesis. In the first part of this thesis, the physical properties of liquid hog manure and their variation with temperature and solids concentration are experimentally determined. Naturally¬¬-settled manure sampled from an outdoor storage lagoon is studied, and density, viscosity, and particle size distribution are measured. Hog manure with total solids concentrations of less than 3.6% exhibits Newtonian behaviour; manure between 3.6% and 6.5% total solids is pseudoplastic, and fits the power law; manure with more than 6.5% total solids exhibits non-Newtonian and time-dependent characteristics. The second part of this thesis investigates the flow of Newtonian and non-Newtonian fluids—represented by tap water and xanthan gum solution, respectively—within four lab-scale reactor geometries, using residence time distribution (RTD) experiments. The effect of reactor geometry, flow rate, and fluid viscosity are evaluated. In the third part of this thesis, flow conditions within lab-scale and pilot-scale anaerobic digester reactors are simulated using three-dimensional modeling techniques. The RTDs of lab-scale reactors as predicted by the 3D numerical models compare well to the experimental results. The 3D models are also validated using data from particle image velocimetry (PIV) experiments. Finally, the viscous properties of liquid hog manure at 3% and 8% total solids are incorporated into the models, and the results are evaluated.

This thesis examines how the non-Newtonian characteristics of liquid hog manure affect the flow conditions within a steady-flow anaerobic digester. There are three main parts to this thesis. In the first part of this thesis, the physical properties of liquid hog manure and their variation with temperature and solids concentration are experimentally determined. Naturally¬¬-settled manure sampled from an outdoor storage lagoon is studied, and density, viscosity, and particle size distribution are measured. Hog manure with total solids concentrations of less than 3.6% exhibits Newtonian behaviour; manure between 3.6% and 6.5% total solids is pseudoplastic, and fits the power law; manure with more than 6.5% total solids exhibits non-Newtonian and time-dependent characteristics. The second part of this thesis investigates the flow of Newtonian and non-Newtonian fluids—represented by tap water and xanthan gum solution, respectively—within four lab-scale reactor geometries, using residence time distribution (RTD) experiments. The effect of reactor geometry, flow rate, and fluid viscosity are evaluated. In the third part of this thesis, flow conditions within lab-scale and pilot-scale anaerobic digester reactors are simulated using three-dimensional modeling techniques. The RTDs of lab-scale reactors as predicted by the 3D numerical models compare well to the experimental results. The 3D models are also validated using data from particle image velocimetry (PIV) experiments. Finally, the viscous properties of liquid hog manure at 3% and 8% total solids are incorporated into the models, and the results are evaluated.

The current work has developed a CFD model to characterise a pseudo-annular photocatalytic bubble column reactor. The model development was divided into three stages. Firstly, hydrodynamic assessment of the multiphase fluid flow in the vessel, which incorporated residence time distribution analysis both numerically and experimentally for validation purposes. Secondly, the radiation distribution of the UV source was completed. The final stage incorporated the kinetics for the degradation the model pollutant, sodium oxalate. The hydrodynamics were modelled using an Eulerian-Eulerian approach to the multiphase system with the standard k- turbulence model. This research established that there was significant deviation in the fluid behaviour in the pseudo-annular reactor when compared with traditional cylindrical columns due to the nature of the internal structure. The residence time distribution study showed almost completely mixed flow in the liquid phase, whereas the gas phase more closely represented plug flow behaviour. Whilst there was significant dependence on the superficial gas flow rate the mixing behaviour demonstrated negligible dependence on the liquid superficial velocity or the liquid flow direction, either co- or counter- current with respect to the gas phase. The light distribution was modelled using a conservative variant of the Discrete Ordinate method. The model examined the contribution to the incident radiation within the reactor of both the gas bubbles and titanium dioxide particles. This work has established the importance of the gas phase in evaluating the light distribution and showed that it should be included when examining the light distribution in a gas-liquid-solid three-phase system. An optimal catalyst loading for the vessel was established to be 1g/L. Integration of the kinetics of sodium oxalate degradation was the final step is developing the complete CFD model. Species transport equations were employed to describe the distribution of pollutant concentration within the vessel. Using a response surface methodology it was shown that the reaction rate exhibited a greater dependency on the lamp power that the lamp length, however, the converse was true with the quantum efficiency. This work highlights the complexity of completely modelling a photocatalytic system and has demonstrated the applicability of CFD for this purpose.

Under de senaste årtionden har den svenska förskolan genomgått stora förändringar där barnantalet ökat i takt med att pedagogerna blivit tilldelade alltmer uppdrag utanför barngruppen. Samtidigt som förskolans läroplan ställer höga krav, där pedagogen har till uppgift att möta varje enskilt barn i ett socialt samspel och tillvarata det unika hos varje individ (Skolverket, 2016). Syftet med denna studie är att undersöka samspelstillfällen mellan barn och pedagog under en verksamhetsförlagd dag i förskolan, samt undersöka hur omgivningen kan påverka interaktionen däremellan. Studien är kvalitativ och materialet har inhämtats via skuggning av tio barn samt en gruppintervju med två verksamma pedagoger i förskolan. Resultatet visar på stora variationer mellan barnens samspelstid tillsammans med pedagog. Vidare framkommer det hur faktorer i omgivningen kan orsaka avbrott i samspelet, vilket i sin tur resulterar i kortare sammanhållande interaktionstider för det enskilda barnet. / <p>Fastställt via akademichefsbeslut HIG-STYR 2019/7 den 2019-01-07</p><p>Daniel Petterson, fil dr, univ. lekt Pedagogik och Erika Björklund, fil dr, univ. lekt Pedagogik går in som examinatorer på PEG700 under veckorna 1 till och med 3, 2019 då Peter Gill, prof. Pedagogik, gått i pension från och med 2019-01-01.</p>

O processo de pasteurização tem como objetivo garantir a segurança e qualidade nutricional do alimento e aumentar sua vida de prateleira. O conhecimento da distribuição do tempo de residência (DTR) do alimento em cada etapa do processo contínuo é importante para uma avaliação adequada do processo e das alterações que causa no alimento. Este trabalho tem como objetivo estudar a DTR em um processo de pasteurização contínuo assistido por micro-ondas aplicado a alimentos líquidos e propor modelos de escoamento para representá-la. Para isso, foram realizados experimentos de estímulo-resposta com alimentação tipo pulso por técnica condutimétrica utilizando uma solução saturada de NaCl como traçador. Com isso, foram obtidas as curvas de DTR do sistema completo, dos trocadores de calor das seções de pré-aquecimento e resfriamento, de seis tubos de retenção com diferentes diâmetros e comprimentos (volumes entre 40 e 125 mL) e do sistema de aquisição de dados de condutividade elétrica. Os experimentos foram realizados em quatro vazões volumétricas (0,5, 0,7, 0,9 e 1,1 L/min), a temperatura ambiente (19 a 26 °C) e como fluido de trabalho foi utilizada uma corrente de alimentação de água com concentração 0,5 g/L de NaCl para estabilizar a leitura de condutividade elétrica. Foram realizadas três repetições por vazão para o processo completo, trocadores de calor e tubos de retenção, e cinco repetições por vazão para o sistema de aquisição de dados, dada a maior sensibilidade. Observou-se a necessidade de realizar o procedimento de convolução numérica para avaliar a distorção na curva de DTR do processo causada pelo escoamento na célula do sistema de aquisição de dados. Foram testados cinco modelos de escoamento: dispersão axial, compartimentado PFR+CSTR, tanques em série, convecção generalizada e y-laminar. O critério de ajuste dos modelos foi a minimização do erro quadrático entre valores experimentais e calculados da curva E(t). Os modelos de dispersão axial e y-laminar foram o que apresentaram melhor ajuste para os tubos de retenção e o modelo de convecção generalizada apresentou melhor ajuste para os trocadores de calor. O regime de escoamento durante os experimentos variou entre laminar e de transição (valores de Reynolds entre 1259 e 4238). Os resultados para o sistema completo e trocadores de calor foram satisfatórios, para os tubos de retenção foi observada uma grande incerteza nos valores dos parâmetros e foi observada a importância da convolução numérica em sistemas de pequeno volume. / Pasteurization process aims to ensure the safety and nutritional quality of the food and increase its shelf life. The knowledge of residence time distribution (RTD) of the food in each step of continuous processes is important to evaluate the process and changes that it causes in foods. This work aims to study the RTD in a continuous pasteurization process assisted by microwave applied to liquid foods and propose flow models to represent it. For this reason, stimulus-response experiments by pulse injection were conducted by conductimetric technique using a saturated solution of NaCl as a tracer. Thus, it was obtained the RTD of the complete process, heat exchangers of preheating section and cooling section, six retention tubes with different diameters and lengths (volumes between 40 and 125 mL) and of the electrical conductivity data acquisition system. The experiments were carried out at four volumetric flow rates (0.5, 0.7, 0.9 and 1.1 L/min), at room temperature (19 to 26 °C) and water with 0.5 g/L of NaCl was used as the work fluid to stabilize the electrical conductivity reading. Three repetitions per volumetric flow rate were performed for the complete process, heat exchangers and holding tubes, and five repetitions per volumetric flow rate were performed for the data acquisition system, given the higher sensibility. It was observed the need to apply the numerical convolution procedure to evaluate the distortion in the RTD curve of the process caused by the flow through the data acquisition system. Five flow models were tested: axial dispersion, PFR+CSTR association, tanks in series, generalized convection and y-laminar. The adjustment criterion of the parameters was the minimization of the quadratic error between experimental and calculated E(t) values. The axial dispersion and y-laminar models provided the best adjustments for the holding tubes and the generalized convection model provided the best adjustment for the heat exchangers. The flow regime during the experiments varied between laminar and transition (Reynolds values between 1259 and 4238). The results for the complete system and heat exchangers were satisfactory, for the holding tubes was observed a great uncertainty in the parameters values and was observed the importance of numerical convolution in small volume systems.

Os trocadores de calor tubulares são muito utilizados para o processamento térmico de alimentos líquidos viscosos por possuírem um maior diâmetro hidráulico em comparação aos trocadores de calor a placas. O cálculo da letalidade neste tipo de trocador está diretamente relacionado ao perfil de velocidade e à distribuição do tempo de residência (DTR). Para escoamento laminar de fluidos viscosos, Newtonianos e não-Newtonianos, geralmente adota-se um perfil de velocidade laminar e de lei de potência, respectivamente. No entanto, algumas características do equipamento como irregularidades na tubulação, a corrugação do tubo ou as curvas podem modificar o perfil de velocidade ideal. Esse desvio da idealidade pode ser caracterizado através da determinação experimental da distribuição do tempo de residência do processo. Este trabalho teve como objetivo a determinação experimental da DTR de fluidos viscosos em um equipamento bitubular de processamento térmico e o ajuste do perfil de velocidade associado. Modelos clássicos de DTR foram ajustados aos dados, assim como foram propostos e testados novos modelos generalizados de DTR, a fim de caracterizar o escoamento laminar não ideal em tubos. A determinação da DTR experimental foi realizada para vazões entre 10 e 50 L/h utilizando água, solução de carboximeticelulose 1,0% (pseudoplástico) e mistura glicerina/água 80%. Os dados de DTR foram obtidos através de duas técnicas: condutimétrica e colorimétrica. A primeira técnica baseia-se na injeção de solução saturada de cloreto de sódio e detecção online por um condutivímetro, porém, não apresentou resultados satisfatórios mostrando que o método não é adequado para fluidos viscosos. Já a segunda técnica utilizada se baseia na injeção de corante e posterior detecção em espectrofotômetro. Os modelos que melhor se ajustaram aos dados experimentais para os três fluidos estudados foram os modelos generalizados y-laminar e exponencial. A letalidade foi calculada a partir da distribuição de temperatura no trocador de calor em estado estacionário e do tempo médio de residência obtido experimentalmente e permitiu detectar o sobreprocessamento no processo estudado. / Tubular heat exchangers are widely used for thermal processing of viscous liquid foods because they have larger hydraulic diameters than the plate heat exchangers. The calculation of lethality in this type of exchanger is directly related to velocity profile and the residence time distribution (RTD). For the laminar flow of viscous fluids, Newtonian and non-Newtonian, generally laminar and power law velocity profiles are used, respectively. However, some features of the equipment as irregularities in the pipe, the corrugation of the pipe or the presence of curves can change the ideal velocity profile. This ideality deviation can be characterized through the experimental determination of the residence time distribution of the process. The aim of this work was the experimental determination of the RTD of a viscous fluid in a bitubular thermal processing equipment and the determination of the associated velocity profile. Classic models of RTD were fitted to the data, as well as were proposed and tested new generalized models of RTD, in order to characterize the non ideal laminar flow in tubes. The experimental determination of RTD was performed to volumetric flow rates between 10 and 50 L/h using water, carboximeticelulose solution 1,0% (pseudoplastic) and glycerin/water mixture 80%. The RTD data were obtained through two techniques: conductimetric and colorimetric. The first technique is based on injection of saturated solution of sodium chloride and online detection with a conductivimeter however, unsatisfactory results showed that the method was not suitable for viscous fluids. The second technique is based on the injection of dye and subsequent detection with a spectrophotometer. The best fitted models to the experimental data for the three studied fluids were: ylaminar and exponential generalized models. The lethality was calculated from the temperature distribution in the heat exchanger at steady state and average residence time obtained experimentally and allowed the evaluation of the overprocessing of this process.

É apresentado um estudo de distribuição do tempo de residência nas etapas de um processo de pasteurização contínuo por trocador de calor a placas (aquecimento, resfriamento, regeneração e retenção). Para o estudo experimental, foi adotada a técnica condutimétrica usando cloreto de sódio em solução aquosa como traçador. Foram verificadas as influências da vazão, da configuração do trocador de calor a placas (número de passes para o arranjo em série) e do tipo de tubo de retenção (tubo em \"S\" e tubo helicoidal). Modelos de distribuição foram usados para representar o comportamento experimental (dispersão axial, tanques em série, laminar modificado, combinado PFR+CSTR). Este estudo foi aplicado para as condições de pasteurização HTST de leite, visando a futura implementação de uma modelagem matemática rigorosa do processo, para otimização do projeto e operação do processo. / It is presented a study of residence time distribution in the steps of a process of continuous pasteurization by plate heat exchanger (heating, cooling, regeneration and holding). For the experimental study, it was adopted a conductimetric technique using sodium chloride in aqueous solution as a tracer. It was also studied the influence of the flow rate, the configuration of the plate heat exchanger (number of passes in series arrangement) and the type of holding tube (\"S\"- shaped tube and helicoidal tube). Distribution models were used for representing the experimental behavior (axial dispersion, tank in series, modified laminar, combined PFR+CSTR). This study was applied for the conditions of HTST pasteurization of milk, targeting the future implementation of a rigorous mathematical modeling of the process, which can be applied for the process operation and optimization of the project design.

The basic understanding of mixing in the process of polymer melt extrusion by twin screw extruder is limited by their geometrical complexity and the interactions of the process parameters. Mixing and flow in a 100mm diameter, trapezoidal channeled, intermeshing co-rotating twin-screw extruder have been characterised by determination of residence time distribution (RTD) and of the paths taken by tracers added to the melt. The axial mixing and the effects of varius parameters on it were established by studying RTD using tracer techniques. As the tail of the distribution is of paramount importance, the reproducibility of the RTD curve was extensively studied. Radioactive NnO2 was used as a tracer and detected by gamma ray spectroscopy giving more reproducible results than added barytes estimated gravimetrically after ashing. Shock cooling of the extruder and sectioning of the solidified compound in the screw channels was used to-study the flow mechanism. The maximum throughput achieved, polymer melting mechanism, filled volume and axial mixing Are interrelated, and are dependent on the configuration and position of segmented mixing discs present in the screw profile. In the upstream position these act as melting discs and their efficiency is increased in a closed configuration. Initial melting is achieved over a remarkably short distance along the screw profile. The screw speed affects the axial mixing which is shown to be related to the net relative pressure change at the screw tips. A flow model is proposed such that the overall material flow taking place in an anticlockwise direction along the screw channel comprises two separate flow regimes. The upper regime rotates anti-clockwise and is made up of main and small tetrahedron flow and calender flow. The lower flow regime rotates clockwise and is made up of main and small side leakage flows and a portion of the main tetrahedron flows together with a central flow. The flow studies show conclusively that the melt from a particular site ahead of the intermeshing zone occupies a predestined site after passing through the intermeshing zone.

L’objectif de ce travail de thèse est la compréhension du mode de fonctionnement des co-malaxeurs, outils de mélange dont la connaissance est lacunaire par rapport à d’autres types de mélangeur comme l’extrudeuse mono-vis ou bi-vis. Ce manuscrit porte sur plusieurs études expérimentales relatives au co-malaxeur. L'influence de la vitesse de vis et du débit a été explorée par des mesures de distribution des temps de séjours (DTS), de température matière, de pression, de taux de remplissage, ainsi que de dispersion de fibres de verre. L'influence de la viscosité du polymère à l'état fondu sur la distribution des temps de séjour, la pression filière et la température à l'intérieur du co-malaxeur, a également été traitée, par variation de la température de régulation ou de la masse molaire du polymère. La distribution des temps de séjour ne dépend pas de la viscosité, malgré des différences de pression filière et de température matière. L'influence du profil local sur la DTS a été étudiée par des expériences interchangeant localement les types d'éléments (transport et mélange). Une méthode de mesure de la pression par extrusion micro-capillaire aux emplacements de doigts le long du fourreau a été développée, les gradients de pression sont similaires à ceux obtenus en extrudeuses bi-vis. Enfin une série d'expériences a porté sur la gélification du PVC, déterminée de façon qualitative et quantitative, et a montré l'influence primordiale de la température matière sur l’état de gélification / The aim of this PhD work is to gain a better understanding of the co-kneading process, whose knowledge is still lacking compared to other types of mixer such as the single screw extruder or the twin-screw extruder. This manuscript features several experimental studies about the co-kneader. The influence of screw speed and throughput was explored by measurements of the residence time distribution, material temperature, die pressure, filling rate, as well as dispersion of glass fibers. The influence of the viscosity of the polymer melt on the residence time distribution, die pressure and temperature within the co-kneader, was also investigated by varying the barrel temperature or the molecular weight of the polymer. The RTD is similar regardless of the viscosity, despite differences in pressure and material temperature. The influence of the screw profile on the RTD was obtained by experiments interchanging locally the types of elements (conveying and mixing). A method of measurement of the pressure along the barrel by micro-capillary extrusion through the location of pins in the barrel was developped, pressure gradients are similar to those obtained in twin-screw extruders. Finally, a series of experiments was dedicated to the gelation of PVC evaluated both qualitatively and quantitatively, and showed that the temperature governs the gelation rate