O processo de absorção do CO2 em soluções aquosas de alcanolaminas foi estudado em uma coluna de parede molhada empregando-se uma tela metálica, de 28 mesh, como promotor de película e operando em contracorrente. As alcanolaminas testadas nos diferentes experimentos foram: monoetanolamina (MEA), 2-amino-2-metil-1-propanol (AMP) e piperazina (PZ). Os experimentos de absorção foram realizados nas soluções aquosas individuais da MEA e AMP; e, nas misturas MEA:AMP e AMP:PZ; visando avaliar a velocidade de absorção do CO2 em diferentes vazões do líquido, a saber: 3.10-7, 6.10-7 e 10.10-7 m3/s. O presente sistema de absorção foi caracterizado através da determinação dos principais parâmetros de transferência de massa: área interfacial efetiva, coeficiente de transferência individual da fase gasosa e o coeficiente volumétrico global médio de transferência de massa. Determinou-se a área interfacial efetiva da coluna, por meio da absorção do CO2 diluído em ar em uma solução aquosa de NaOH, para as diferentes vazões de líquido, sendo os resultados obtidos igual a 106, 126 e 144 m2/m3, respectivamente. O coeficiente volumétrico de transferência de massa da fase gasosa foi determinado por meio da absorção de SO2 diluído em ar em uma solução aquosa de NaOH. Os resultados experimentais mostram que o coeficiente volumétrico individual de transferência de massa e a área interfacial são função da vazão do líquido. As velocidades de absorção do CO2 diluído em ar, em soluções de aminas e suas misturas foram determinadas experimentalmente para diferentes vazões de líquido, sendo os resultados expressos na forma de coeficientes globais de transferência de massa e parâmetros cinético-difusivos da fase líquida. As velocidades de absorção em MEA são bem superiores aos de AMP e NaOH. No caso das misturas foram obtidas velocidades superiores em comparação às das aminas individuais. A velocidade de absorção em AMP é fortemente incrementada na presença de PZ, mesmo em baixa concentração. / The CO2 absorption process in alkanolamine aqueous solutions was studied in a wetted wall column employing a film promotor of thin stainless steel woven wire, 28 mesh, which was operated in countercurrent. The tested alkanolamines were monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The absorption experiments were performed in individual aqueous solutions of MEA and AMP and the mixtures MEA:AMP and AMP:PZ, with the aim of evaluating the CO2 absorption rate in different liquid flow rates, namely: 3.10-7, 6.10-7 e 10.10-7 m3/s. This absorption system was characterized through determining of the main parameters of mass transfer: effective interfacial area, individual mass transfer coefficient of the gas phase and the average overall mass transfer volumetric coefficient. The effective interfacial area was determined by the absorption of CO2 diluted in air into an aqueous solution of NaOH for the different liquid flow rates, and the results obtained are 106, 126 and 144 m2/m3, respectively. The mass transfer volumetric coefficient of the gas phase was determined by chemical method of the absorption of SO2 diluted in air into an aqueous solution of NaOH. The experimental results show that the individual mass transfer coefficient and interfacial area are a function of liquid flow rate. On the other hand, the results of the performance of CO2 absorption into amine aqueous solutions were expressed in function of the average overall mass transfer volumetric coefficient and liquid phase diffusive kinetic parameters, which were measured experimentally for different liquid flow rates. The absorption rate in MEA are higher in comparison with AMP and NaOH. In the case of the blended, the absorption rate in AMP is enhanced by piperazine, even in low concentration.

Continuous flow reaction using micro-reactors is a valued technology due to its excellent mass and heat transfer performance, reduced reactor volume, handling capacity of hazardous reactions, and many other process intensifications. These intensifications opportunities interest the fine chemicals, pharmaceuticals producers and other multiphase reaction users who currently use batch processes or already use continuous flow. In this thesis, elements of passive and active mixing are investigated for the application of immiscible liquid-liquid systems. In the first study, the effects of geometrical arrangements of a residence time between mixing units on the interphase mass transfer rates are evaluated with four different immiscible liquid-liquid systems. A presentation of an algorithm for the optimal selection of a reactor and its operating conditions is given in order to enable easy and improved use of one’s micro-reactor. In the second study, the impact of a secondary pulse flow on interphase mass transfer is investigated. A coil without internal baffles is used as the oscillatory-flow coil reactor with a continuous active mixing source. The best application for the reactor is determined using a comparison to other complementary continuous flow platforms in the toolbox approach. The novel advancements presented here will help lead new molecular discoveries and connect the laboratory science scale to the process engineering production scale.

Esta pesquisa teve como objetivo estudar a hidrodinâmica, a transferência de massa e a inativação de microrganismos indicadores durante o processo de ozonização de esgoto sanitário tratado previamente em reator UASB. A pesquisa foi dividida em três grupos de ensaios, experimentos I, II e III, nos quais foram medidas as concentrações de bolhas de ozônio, os campos de velocidades instantâneos e médios, os diâmetros das bolhas de ozônio e realizados ensaios de desinfecção com ozônio para inativação de microrganismos indicadores - E. coli, colifagos e Clostridium perfringens - e remoção de DQO. Estes ensaios foram realizados tanto em batelada (experimento I e II) quanto em fluxo contínuo (experimento III), e as dosagens de ozônio aplicado foram de 10 e 20 mg/L e os tempos de contato de 5, 10, 15 e 20 minutos. As concentrações, velocidades e diâmetros das bolhas de ozônio foram proporcionais às vazões de ozônio aplicadas e variaram, respectivamente, de 0,23 a 5,26%, de 6,84 a 10,81 cm/s e de 0,260 a 1,781 mm. A quantidade de ozônio consumido variou entre 50,5% e 99,3%, em relação à dose de ozônio aplicado, e seu valor foi decrescente com o aumento da vazão de ozônio. Quanto à inativação dos microrganismos indicadores, C. perfringens apresentou-se como o mais resistente à ação bactericida do ozônio seguido por E. coli e colifagos. Foram inativados 1,7 log de C. perfringens (Ct = 80 mg.min/L); 6,1 log de E. coli (Ct = 133 mg.min/L); e 100% de colifagos (Ct = 38 mg.min/L). O controle das características de ensaios - dose e vazão aplicadas e tempo de contato -, bem como das características hidrodinâmicas das bolhas de ozônio podem otimizar o processo de ozonização de esgoto sanitário tornando-o atrativo técnica e economicamente. / This research had as objective study hydrodynamics, mass transfer and indicating microrganisms inativation during the ozonization process of sanitary sewer treated previously in UASB reactor. The research was divided in three groups of assays, experiment I, II e III, in which had been measured the concentrations, velocity and diameter of bubbles and carried through assays of disinfection with ozone for indicating microrganisms inativation - E. coli, coliphages and C. perfringens - and COD removal. These assays had been carried through in batch (experiment I and II) how much in continuous flow (experiment III), and the dosages of applied ozone had been of 10 and 20 mg/L and the times of contact of 5, 10, 15 and 20 minutes. The concentrations, velocity and diameters of ozone bubbles had been proportional to the applied ozone outflows and had varied, respectively, of 0,23 to 5,26%, of 6,84 to 10,81 cm/s and 0,26 to 1,781 mm. The amount of consumed ozone varied between 50,5 and 99,3%, in relation to the dosage of applied ozone, and its value was decreasing with the increase of the ozone outflow. For the indicating microorganisms inativation, C. perfringens was presented as most resistant to the bactericidal action of ozone followed for E. coli and coliphages. Had been inactivated 1,7 log of C. perfringens (Ct = 80 mg.min/L); 6,1 log of E coli (Ct = 133 mg.min/L); and 100% of colifphages (Ct = 38 mg.min/L). The control of the characteristics of assays - dosage and outflow applied and time of contact -, as well as of the hydrodynamic characteristics of the ozone bubbles they can optimize the ozonization process of sanitary sewer becoming it attractive technique and economically.

Accurate experimental oxygen mass transfer coefficient, a measure of how quickly oxygen travels from a gas bubble to the bulk liquid, is important for comparing performance and for evaluating the oxygen transfer capability of a fermentor. Delays in probe response and changing gas volumes upon start-up of gassing affect the accuracy of oxygen transfer measurements. To mitigate these inaccuracies, a standard correction procedure for oxygen mass transfer data was established for highly oxygenated, well-mixed fermentation systems. Probe response time correction was generated by applying a second-order response model to dissolved oxygen probes and shown to be effective within 4%. By using a derived model for transient volume rise, the effect of changing gas volume at start-up was shown to cause very minimal error (1-2%) in kLa. The unsteady-state method of kLa determination was used to compare design aspects of a hypothetical fermentor, including gas sparging devices and locations, baffle geometries and quantities, and impeller configurations. It was shown that locating the sparging device in the center of the tank, directly below the drive shaft and bottom impeller, is optimal for oxygen mass transfer. Sparger type was shown to have little effect on oxygen mass transfer values, although an open-pipe sparger was shown to provide slightly more oxygen mass transfer than a ring sparger. The use of rounded baffles in place of traditional rectangular baffles resulted in a 67-80% decrease in oxygen mass transfer coefficient. A comparison of three and four traditional baffles showed that three baffles produced a higher oxygen mass transfer than four. Correlation of baffle ratio and oxygen mass transfer coefficient indicated that the optimum baffle ratio is approximately one. Radial impellers were observed to provide better mixing, and thus higher oxygen mass transfer coefficients than axial impellers. In seven of ten comparisons, an impeller quantity ratio of 1.33 instead of 1.00 provided significant improvement in kLa. Additionally, only two of ten comparisons showed a difference between traditional Rushton turbine impellers and Smith turbine impellers, indicating that the difference in oxygen mass transfer capability of the two is negligible.

Health care facilities, offices, as well as workshops and other commercial occupancies, require ventilation and air conditioning for thermal comfort and removal of contaminants and other pollutions. A good design of ventilation and air conditioning provides a healthy and comfortable environment for patients, workers, and visitors. The increasing developments of computational fluid dynamics (CFD) in the recent years have opened the possibilities of low-cost yet effective method for improving HVAC systems in design phase, with less experiment required. This work presents numerical simulations of thermal comfort and contaminant removal for two typical working spaces where these factors are critical: a hospital operating room with various configurations of inlet and outlet arrangements, and an office with two cases of air distribution systems: underfloor and overhead, also with alternative cases. The 2-D simulation approach was employed. Temperature, relative humidity, contaminant concentration, thermal sensation, predicted mean vote (PMV), and contaminant removal factor were computed and used for assessing thermal comfort and contaminant removal characteristics of the office room and operating room. The result shows good agreements with experimental data taken from related literature.

Hollow fibre and spiral wound membrane (SWM) modules are the most common commercially available membrane modules. The latter dominate especially for RO, NF and UF and are the focus of this study. The main difficulty these types of modules face is concentration polarisation. In SWM modules, the spacer meshes that keep the membrane leaves apart also help reduce the effects of concentration polarisation. The spacer filaments act as flow obstructions, and thus encourage flow destabilisation and increase mass transfer enhancement. One of the detrimental aspects of the use of spacers is an increase of pressure losses in SWM modules. This study analyses the mechanisms that give rise to mass transfer enhancement in narrow spacer-filled channels, and investigates the relationship between flow destabilisation, energy losses and mass transfer. It shows that the regions of high mass transfer on the membrane surface correlate mainly with those regions where the fluid flow is towards the membrane. Based on the insights gained from this analysis, a series of multi-layer spacer designs are proposed and evaluated. In this thesis, a Computational Fluid Dynamics (CFD) model was used to simulate steady and unsteady flows with mass transfer in two- and three-dimensional narrow channels containing spacers. A solute with a Schmidt number of 600 dissolving from the wall and channel Reynolds numbers up to 1683 were considered. A fully-developed concentration profile boundary condition was utilised in order to reduce the computational costs of the simulations. Time averaging and Fourier analysis were performed to gain insight into the dynamics of the different flow regimes encountered, ranging from steady flow to vortex shedding behind the spacer filaments. The relationships between 3D flow effects, vortical flow, pressure drop and mass transfer enhancement were explored. Greater mass transfer enhancement was found for the 3D geometries modelled, when compared with 2D geometries, due to wall shear perpendicular to the bulk flow and streamwise vortices. Form drag was identified as the main component of energy loss for the flow conditions analysed. Implications for the design of improved spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and filament profiles to reduce form drag are discussed.

<p>The objective of this work has been to study equilibrium and non equilibrium situations during high pressure gas processing operations with emphasis on utilization of the high reservoir pressure. The well stream pressures of some of the condensate and gas fields in the North Sea are well above 200 bar. Currently the gas is expanded to a specified processing condition, typically 40-70 bar, before it is recompressed to the transportation conditions. It would be a considerable environmental and economic advantage to be able to process the natural gas at the well stream pressure. Knowledge of thermodynamic- and kinetic properties of natural gas systems at high pressures is needed to be able to design new high pressure process equipment. </p><p>Nowadays, reactive absorption into a methyldiethanolamine (MDEA)solution in a packed bed is a frequently used method to perform acid gas treating. The carbon dioxide removal process on the Sleipner field in the North Sea uses an aqueous MDEA solution and the operation pressure is about 100 bar. The planed carbon dioxide removal process for the Snøhvit field in the Barents Sea is the use of an activated MDEA solution. </p><p>The aim of this work has been to study high-pressure effects related to the removal of carbon dioxide from natural gas. Both modelling and experimental work on high-pressure non-equilibrium situations in gas processing operations have been done. </p><p>Few experimental measurements of mass transfer in high pressure fluid systems have been published. In this work a wetted wall column that can operate at pressures up to 200 bar was designed and constructed. The wetted wall column is a pipe made of stainless steel where the liquid is distributed as a thin liquid film on the inner pipewall while the gas flows co- or concurrent in the centre of the pipe. The experiments can be carried out with a well-defined interphase area and with relatively simple fluid mechanics. In this way we are able to isolate the effects we want to study in a simple and effective way. </p><p>Experiments where carbon dioxide was absorbed into water and MDEA solutions were performed at pressures up to 150 bar and at temperatures 25 and 40°C. Nitrogen was used as an inert gas in all experiments. </p><p>A general non-equilibrium simulation program (NeqSim) has been developed. The simulation program was implemented in the object-oriented programming language Java. Effort was taken to find an optimal object-oriented design. Despite the increasing popularity of object-oriented programming languages such as Java and C++, few publications have discussed how to implement thermodynamic and fluid mechanic models. A design for implementation of thermodynamic, mass transfer and fluid mechanic calculations in an object-oriented framework is presented in this work. </p><p>NeqSim is based on rigorous thermodynamic and fluid mechanic models. Parameter fitting routines are implemented in the simulation tool and thermodynamic-, mass transfer- and fluid mechanic models were fitted to public available experimental data. Two electrolyte equations of state were developed and implemented in the computer code. The electrolyte equations of state were used to model the thermodynamic properties of the fluid systems considered in this work (non-electrolyte, electrolyte and weak-electrolyte systems).</p><p>The first electrolyte equation of state (electrolyte ScRK-EOS) was based on a model previously developed by Furst and Renon (1993). The molecular part of the equation was based on a cubic equation of state (Scwarzentruber et.al. (1989)’s modification of the Redlich-Kwong EOS) with the Huron-Vidal mixing rule. Three ionic terms were added to this equation – a short-range ionic term, a long-range ionic term (MSA) and a Born term. The thermodynamic model has the advantage that it reduces to a standard cubic equation of state if no ions are present in the solution, and that public available interaction parameters used in the Huron-Vidal mixing rule could be utilized. The originality of this electrolyte equation of state is the use of the Huron-Vidal mixing rule and the addition of a Born term. Compared to electrolyte models based on equations for the gibbs excess energy, the electrolyte equation of state has the advantage that the extrapolation to higher pressures and solubility calculations of supercritical components is less cumbersome. The electrolyte equation of state was able to correlate and predict equilibrium properties of CO₂-MDEA-water solutions with a good precision. It was also able to correlate high pressure data of systems of methane-CO₂-MDEA and water. </p><p>The second thermodynamic model (electrolyte CPA-EOS) evaluated in this work is a model where the molecular interactions are modelled with the CPA (cubic plus association) equation of state (Kontogeorgios et.al., 1999) with a classical one-parameter Van der Walls mixing rule. This model has the advantage that few binary interaction parameters have to be used (even for non-ideal solutions), and that its extrapolation capability to higher pressures is expected to be good. In the CPA model the same ionic terms are used as in the electrolyte ScRK-EOS. </p><p>A general non-equilibrium two-fluid model was implemented in the simulation program developed in this work. The heat- and mass-transfer calculations were done using an advanced multicomponent mass transfer model based on non-equilibrium thermodynamics. The mass transfer model is flexible and able to simulate many types of non-equilibrium processes we find in the petroleum industry. A model for reactive mass transfer using enhancement factors was implemented for the calculation of mass transfer of CO₂ into amine solutions. The mass transfer model was fitted to the available mass transfer data found in the open literature. </p><p>The simulation program was used to analyse and perform parameter fitting to the high pressure experimental data obtained during this work. The mathematical models used in NeqSim were capable of representing the experimental data of this work with a good precision. From the experimental and modelling work done, we could conclude that the mass transfer model regressed to pure low-pressure data also was able to represent the high-pressure mass transfer data with an acceptable precision. Thus the extrapolation capability of the model to high pressures was good. </p><p>For a given partial pressure of CO₂ in the natural gas, calculations show a decreased CO₂ capturing capacity of aqueous MDEA solutions at increased natural gas system pressure. A reduction up to 40% (at 200 bar) compared to low pressure capacity is estimated. The pressure effects can be modelled correctly by using suitable thermodynamic models for the liquid and gas. In a practical situation, the partial pressure of CO₂ in the natural gas will be proportional to the total pressure. In these situations, it is shown that the CO₂ capturing capacity of the MDEA solution will be increased at rising total pressures up to 200 bar. However, the increased capacity is not as large as we would expect from the higher CO₂ partial pressure in the gas.</p><p>The reaction kinetics of CO₂ with MDEA is shown to be relatively unaffected by the total pressure when nitrogen is used as inert gas. It is however important that the effects of thermodynamic and kinetic non- ideality in the gas and liquid phase are modelled in a consistent way. Using the simulation program NeqSim – some selected high-pressure non-equilibrium processes (e.g. absorption, pipe flow) have been studied. It is demonstrated that the model is capable of simulating equilibrium- and non-equilibrium processes important to the process- and petroleum industry.</p>

Mass transfer processes in food systems, such as solute infusion, are poorly understood because of their complex nature. Food systems contain porous matrices and a variety of continuous phases within cellular tissues. Mass transfer processes are generally not pure diffusion: often convection, binding and obstructing diffusion will occur. Monte Carlo (MC) simulation has been increasingly used in life science and engineering to elucidate molecular transport in biological systems. However, there are few articles available discussing MC simulation in food processing, especially mass transfer. The main goal of this study was to show the inherent simplicity of the MC approach and its potential when combined with traditional experimental and theoretical approaches to better describe and understand mass transfer processes. A basic framework for MC random walk - simulation applied to a diffusion problem - is developed in this project. Infusion of two sizes of dextran macromolecules in fish muscle cells is used to apply the MC framework in combination with Fluorescence Recovery After Photobleaching experiments. Effective diffusivity coefficients within cells, considering the degree of obstruction due to the myofibrilar matrix, are assessed. Then, the results are used as input in a mathematical model that was developed for theoretical simulation of mass transfer in the multi-cellular tissue. Diffusivity values obtained by the MC framework had an SD of ±0.02 [µm²/s] around the true value of 0.25 [µm²/s]. MC results for degree of obstruction were 0.29 and 0.34 for dextran FD1OS and FD2OS, respectively, and the Devalues were 23.7 and 11.2 [µm2/s]. The statistical error in the estimation of D was estimated to be [22.8-24.6] and [9.7-12.7] (95% CI), where average experimental values of 24.3 [µm²/s] for FD1OS and 11.4 [µm²/s] for FD2OS were captured by the respective interval. The theoretical model showed a significant influence of the cell membrane characteristics and tissue porosity in both the degree of solute penetration and the solute distribution between intra- and extra-cellular space. The combined approach was successfully applied to a diffusion problem. Overall, it is expected that the present work will contribute towards the application of MC simulation in the field of Food Science and Engineering. / Graduation date: 2006

Agglomerate formation is a common phenomenon that can cause operating problems in the fluid coking reactor. When agglomerates form they provide longer diffusion paths of the reaction products through the liquid layers and liquid bridges within the agglomerate, which leads to higher mass transfer resistance, trapping of the reaction products and increasing the undesired coke formation reactions. Surviving agglomerates in the reactor can also cause fouling of the reactor interior and defluidization of the bed. The ultimate coke yield was determined for agglomerates of Athabasca vacuum residue and solid particles by heating on Curie-point alloy strips in an induction furnace at 503 oC and 530 oC and in a fluidized bed reactor at 500 oC until all toluene-soluble material was converted. Coke yields from agglomerates were compared to the results from reacting thin films of vacuum residue. The average coke yield from the agglomerates was 23%, while the coke yield from thin films of 20 m thickness was 11%, which supports the role of mass transfer in coke formation reactions. The ultimate coke yield was insensitive to vacuum residue concentration, agglomerate size, reaction temperature and agglomerate disintegration. The temperature profile within agglomerates was measured by implanting a thermocouple at the agglomerate center, and a heat transfer model was used to describe the temperature variation with time. The effective thermal diffusivity of the agglomerates was 0.20 x 10-6 m2/s. Control experiments on reactions in thin liquid films confirmed that heating rates in the range of 14.8 to 148 K/s had no effect on the ultimate yield of coke

Many modeling studies have been carried out to simulate the current distribution across the channel and shoulder direction in a proton exchange membrane (PEM) fuel cell. However the modeling results do not show agreement on the current density distribution. At the same time, no experimental measurement result of current density distribution across the channel and the shoulder direction is available to testify the modeling studies. Hence in this work, an experiment was conducted to separately measure the current densities under the channel and the shoulder in a PEM fuel cell by using the specially designed membrane electrode assemblies. The experimental results show that the current density under the channel is lower than that under the shoulder except when the fuel cell load is high. Afterwards two more experiments were carried out to find out the reason causing the higher current density under the shoulder. The effects of the electric resistance of gas diffusion layer (GDL) in the lateral and through-plane directions on the current density distribution were studied respectively. The experimental results show that it is the through-plane electric resistance that leads to the higher current density under the shoulder. Moreover, a three-dimensional fuel cell model is developed using FORTRAN. A new method of combining the thin-film model and homogeneous model is utilized to model the catalyst layer. The model is validated by the experimental data. The distribution of current density, oxygen concentration, membrane phase potential, solid phase potential and overpotential in a PEM fuel cell have been studied by the model. The modeling results show that the new modeling method provides better simulations to the actual transport processes and chemical reaction in the catalyst layer of a PEM fuel cell.