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Effect of agitation on the performance of an anaerobic sequencing batch biofilm reactor in the treatment of dairy effluents

PENTEADO, T. Z.; SANTANA, R. S. S.; DIBIAZI, A. L. B.; PINHO, S. C. de; RIBEIRO, R.; TOMMASO, G.
Fonte: IWA PUBLISHING Publicador: IWA PUBLISHING
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.99%
Agitation rate is an important parameter in the operation of Anaerobic Sequencing Biofilm Batch Reactors (ASBBRs), and a proper agitation rate guarantees good mixing, improves mass transfer, and enhances the solubility of the particulate organic matter. Dairy effluents have a high amount of particulate organic matter, and their anaerobic digestion presents inhibitory intermediates (e. g., long-chain fatty acids). The importance of studying agitation in such batch systems is clear. The present study aimed to evaluate how agitation frequency influences the anaerobic treatment of dairy effluents. The ASBBR was fed with wastewater from milk pasteurisation process and cheese manufacture with no whey segregation. The organic matter concentration, measured as chemical oxygen demand (COD), was maintained at approximately 8,000 mg/L. The reactor was operated with four agitation frequencies: 500 rpm, 350 rpm, 200 rpm, and no agitation. In terms of COD removal efficiency, similar results were observed for 500 rpm and 350 rpm (around 90%) and for 200 rpm and no agitation (around 80%). Increasing the system`s agitation thus not only improved the global efficiency of organic matter removal but also influenced volatile acid production and consumption and clearly modified this balance in each experimental condition.

Influência do tamanho da biopartícula e da agitação no desempenho de reatores anaeróbios operados em bateladas seqüenciais, contendo biomassa imobilizada, para tratamento de águas residuárias; Influence of bioparticle size and the agitation rate on the performance of anaerobic reactor operates in sequential batch containing immobilized biomass on the treatment of wastewater

Cubas, Selma Aparecida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 16/04/2004 PT
Relevância na Pesquisa
36.07%
O reator anaeróbio em batelada seqüencial é constituído por um frasco de vidro cilíndrico de volume total de cinco litros, envolvido por uma camisa de vidro, por onde escoa a água aquecida, permitindo a operação em temperatura controlada. A biomassa encontra-se imobilizada em partículas cúbicas de espuma de poliuretano (densidade aparente de 23 kg/'M POT.3', as quais estão colocadas em um cesto adaptado dentro do frasco cilíndrico. A mistura é promovida por três impelidores de 3,0 cm de diâmetro, distanciados 4,0 cm um do outro, situados ao longo do eixo vertical no centro do reator. O desempenho dessa nova configuração de reator anaeróbio foi avaliado sob diferentes condições os efeitos de transferência de massa nas fases sólida e líquida. Todos os ensaios foram efetuados à temperatura de 30 ± 1 grau Celsius. Cada batelada compreende três etapas: alimentação, reação e descarga. Para avaliar os efeitos da transferência de massa na fase sólida foram feitos quatro ensaios utilizando-se partículas cúbicas de espumas de poliuretano com tamanhos de 0,5 cm; 1,0 cm; 2,0 cm e 3,0 cm de lado, com impelidor tipo hélice e intensidade de agitação de 500 rpm, determinada através de um ensaio preliminar. Para avaliar os efeitos da transferência de massa nas fases sólida e líquida foram feitos experimentos com quatro tipos de impelidores: hélice...

Desempenho e homogeneidade de cultivos em meio sólido de Monascus sp. em biorreator do tipo tambor com agitação interna: efeitos do padrão de agitação.; Performance and homogeneity of Monascus sp. cultures in solid state fermentation in drum bioreactor with internal mixing: effects of mixing pattern.

Eduardo, Mariana de Paula
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 08/07/2010 PT
Relevância na Pesquisa
35.88%
Este trabalho teve por objetivo verificar a influência da agitação no cultivo em meio sólido, FES, quanto a crescimento microbiano, homogeneização do meio e remoção de calor. As correlações obtidas contribuem na definição de critérios para ampliação de escala da FES. O modelo adotado foi o cultivo do fungo Monascus sp. em arroz. Os experimentos foram conduzidos em reator tubular horizontal de 40 l, com agitação interna intermitente, camisa de resfriamento e vazão de ar de 2 l.min-1.Kgms-1. Os cultivos foram realizados com base num planejamento fatorial rotacional: 12 a 60 rotações das pás em 24 horas; 2 a 12 horas de intervalo entre os eventos de agitação. A intensidade do crescimento celular foi considerada com base no consumo de O2, produção de CO2 , concentrações de proteína e ergosterol. O consumo de O2 apresenta correlação de 81% com os padrões de agitação sendo que tanto o número de rotações quanto o intervalo entre os eventos de agitação influenciam negativamente o crescimento celular assim estimado. Por outro lado, a máxima velocidade de consumo de oxigênio, OUR, obtida por volta de 24 horas, em cultivos com menores intervalos entre os eventos de agitação...

Um estudo sobre as operações unitárias de agitação, troca de calor em tanques e mistura de pós

Razuk, Paulo Cesar
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Outros Formato: 143 f. : il.
POR
Relevância na Pesquisa
25.93%
De todas as operações, a agitação de fluidos, a troca de calor em tanques e a mistura de pós são, sem dúvida, as mais usuais, principalmente, na indústria de alimentos. Embora exigindo um estudo em separado, é comum estas operações unitárias estarem presentes, em instantes diferentes, no mesmo processo de fabricação. O propósito deste trabalho é enfatizar procedimentos de projeto para problemas práticos nas indústrias de processos envolvendo estas três operações. O modelo matemático proposto para a agitação de fluidos foi aplicado na substituição das tradicionais âncoras por impelidores de pás retas e inclinadas no processamento do suco concentrado de laranja. Observou-se que o tempo de permanência do suco no tanque de resfriamento caiu de quarenta para cinco minutos em decorrência da maior ação de mistura provocada pelas pás retas. O modelo proposto acompanha bem as exigências de potências requeridas pelo suco na medida em que é resfriado...(Resumo completo, clicar acesso eletrônico abaixo); In all operations, the fluid agitation, the heat tranfer in tanks and the solids mixing are, undoubtedly the more usual, mainly in the food industry. Although requering a present research, is usual this unitary operations to be process. The purpose of this work is to emphasize design project proceeding for practical problems in the process industry involving this three operations. The mathematical model proposed to fluid agitation...

Consumo de potência para impelidores rápidos aplicados em processos de agitação e mistura; Power consumption of high shear impellers in processes of agitation and mixture

Edimilson Souza
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 08/11/2011 PT
Relevância na Pesquisa
35.77%
O projeto de agitadores envolve um grande número de variáveis, além da necessidade de utilização das relações empíricas para que se possa elaborar um projeto eficiente. Em função do grande número de variáveis envolvidas, muitas opções ainda carecem de estudos científicos e bibliografias que deem segurança aos projetistas, como é o caso dos impelidores do tipo disco dispersor, para altas dispersões, com característica predominantemente de alto cisalhamento, também conhecidos como: impelidores dentados, dentes de serra ou simplesmente Cowles. O estudo passa inicialmente pelo entendimento amplo dos conceitos de agitação e mistura, tais como: regime de escoamento em tanques agitados, fluidos, nível de agitação, processos de agitação e mistura, geometrias de tanques, tipos e geometria dos impelidores, número de bombeamento e número de potência. Comparou-se resultados de número de potência obtidos nos ensaios com teoria de autores consagrados para impelidores de pás retas. Obteve-se de forma experimental as equações do torque em função da rotação e as curvas do número de potência em função do número de Reynolds para impelidores do tipo disco dispersores de diversas geometrias, trabalhando com dois métodos de medição de torque: transdutor de torque e parâmetros elétricos...

Determinação experimental do consumo de potência para impelidores âncora e helicoidal usando fluidos pseudoplásticos de alta viscosidade; Experimental determination of the power consumption for using helical impellers, anchor and pseudoplastic fluids of high viscosity

Ana Milena Torres Garavito
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/05/2013 PT
Relevância na Pesquisa
46.02%
Frequentemente os processos de agitação e misturas tão fundamentais são negligenciados na indústria como um todo petroquímico, farmacêutica, química, de alimentos, etc. No entanto, existem sistemas em que o desempenho desses processos depende fortemente do grau de homogeneidade conseguido durante a mistura. Quando o processo de mistura não está devidamente projetado e controlado, obtêm-se misturas com flutuações significativas nas suas características físicas e/o químicas, que no geral são indesejáveis e que suscitam perdas de lotes inteiros de produtos, aumentando o custo e o impacto ambiental do processo de produção. O custo final da energia utilizada no processo de agitação e mistura depende de vários fatores, sendo um deles o impelidor empregado. Para analisar um processo são considerados fatores de interesse como: melhor agitação, menor tempo de mistura e menor potência consumida. Este trabalho de pesquisa teve como objetivo a determinação experimental do número de potência em função do número de Reynolds nos regimes turbulento e laminar para impelidores de proximidade tipo âncora (reta e tubular) com e sem raspadores e para um impelidor do tipo helicoidal, usando como fluido pseudoplástico de alta viscosidade a carboximetilcelulose (CMC) diluída em água. Desta forma...

Mixing efficiency on plant cell growth and proteinase production in a stirred tank reactor

Raposo, Sara; Lima-Costa, Maria Emília
Fonte: Universidade do Algarve Publicador: Universidade do Algarve
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
Relevância na Pesquisa
35.78%
Mixing efficiency is one of the most significant factors in bioprocess productivity. The major role of agitation is to improve broth homogenization, mass and heat transfer inside the bioreactors.

Mass transfer coefficients in a hanson mixer-settler extraction column

Torab-Mostaedi,M.; Safdari,S. J.; Moosavian,M. A.; Maragheh,M. Ghannadi
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2008 EN
Relevância na Pesquisa
25.84%
The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

Dispersal of Aspergillus fumigatus from Sewage Sludge Compost Piles Subjected to Mechanical Agitation in Open Air

Millner, Patricia D.; Bassett, David A.; Marsh, Paul B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1980 EN
Relevância na Pesquisa
35.62%
Aerosolization of the thermophilous fungal opportunist Aspergillus fumigatus from mechanically agitated compost piles was examined at a pilot-scale sewage sludge composting facility and two other selected test sites. Aerosols of A. fumigatus downwind from stationary compost piles were insignificant in comparison with those downwind from agitated piles. These aerosols were generated by a front-end loader moving and dropping compost. Aerial concentrations of the fungus at distances downwind from the point of emission were used to determine an emission rate for A. fumigatus associated with the moving operations. The maximum emission rate, 4.6 × 106A. fumigatus particles per s, was used to calculate predicted concentrations in an unobstructed plume with restrictive, neutral, and dispersive atmospheric mixing conditions up to 1 km downwind from the emission source.

Computational fluid dynamics modeling of the paddle dissolution apparatus: Agitation rate, mixing patterns, and fluid velocities

McCarthy, Leonard G.; Bradley, Geoff; Sexton, James C.; Corrigan, Owen I.; Healy, Anne Marie
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Publicado em 08/04/2004 EN
Relevância na Pesquisa
35.83%
The purpose of this research was to further investigate the hydrodynamics of the United States Pharmacopeia (USP) paddle dissolution apparatus using a previously generated computational fluid dynamics (CFD) model. The influence of paddle rotational speed on the hydrodynamics in the dissolution vessel was simulated. The maximum velocity magnitude for axial and tangential velocities at different locations in the vessel was found to increase linearly with the paddle rotational speed. Path-lines of fluid mixing, which were examined from a central region at the base of the vessel, did not reveal a region of poor mixing between the upper cylin-drical and lower hemispherical volumes, as previously speculated. Considerable differences in the resulting flow patterns were observed for paddle rotational speeds between 25 and 150 rpm. The approximate time required to achieve complete mixing varied between 2 to 5 seconds at 150 rpm and 40 to 60 seconds at 25 rpm, although complete mixing was achievable for each speed examined. An analysis of CFD-generated velocities above the top surface of a cylindrical compact positioned at the base of the vessel, below the center of the rotating paddle, revealed that the fluid in this region was undergoing solid body rotation. An examination of the velocity boundary layers adjacent to the curved surface of the compact revealed large peaks in the shear rates for a region within∼3 mm from the base of the compact...

Single-Step Assembly of Homogenous Lipid-Polymeric and Lipid-Quantum Dot Nanoparticles Enabled by Microfluidic Rapid Mixing

Valencia, Pedro M.; Basto, Pamela A.; Zhang, Liangfang; Rhee, Minsoung; Langer, Robert; Farokhzad, Omid C.; Karnik, Rohit
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 23/03/2010 EN
Relevância na Pesquisa
25.86%
A key challenge in the synthesis of multi-component nanoparticles (NPs) for therapy or diagnosis is obtaining reproducible monodisperse NPs with a minimum number of preparation steps. Here we report the use of microfluidic rapid mixing using hydrodynamic flow focusing in combination with passive mixing structures to realize the self-assembly of monodisperse lipid-polymer and lipid-quantum dot (QD) NPs in a single mixing step. These NPs are composed of a polymeric core for drug encapsulation or a QD core for imaging purposes, a hydrophilic polymeric shell and a lipid monolayer at the interface of the core and the shell. In contrast to slow mixing of lipid and polymeric solutions, rapid mixing directly results in formation of homogeneous NPs with relatively narrow size distribution that obviates the need for subsequent thermal or mechanical agitation for homogenization. We identify rapid mixing conditions that result in formation of homogeneous NPs, and show that that self-assembly of polymeric core occurs independent of the lipid component, which only provides stability against aggregation over time and in the presence of high salt concentrations. Physicochemical properties of the NPs including size (35 to 180 nm) and zeta potential (−10 to +20 mV in PBS) are controlled by simply varying the composition and concentration of precursors. This method for preparation of hybrid NPs in a single mixing step may be useful for combinatorial synthesis of NPs with different properties for imaging and drug delivery applications.

Simple approach for the preparation of 15−15N2-enriched water for nitrogen fixation assessments: evaluation, application and recommendations

Klawonn, Isabell; Lavik, Gaute; Böning, Philipp; Marchant, Hannah K.; Dekaezemacker, Julien; Mohr, Wiebke; Ploug, Helle
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 04/08/2015 EN
Relevância na Pesquisa
35.62%
Recent findings revealed that the commonly used 15N2 tracer assay for the determination of dinitrogen (N2) fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared 15−15N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of 15−15N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add 15−15N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥ 5 min). Optionally, water can be degassed at low-pressure (≥950 mbar) for 10 min prior to the 15−15N2 gas addition to indirectly enhance the 15−15N2 concentration. This preparation of 15−15N2-enriched water can be done within 1 h using standard laboratory equipment. The final 15N-atom% excess was 5% after replacing 2–5% of the incubation volume with 15−15N2-enriched water. Notably, the addition of 15−15N2-enriched water can alter levels of trace elements in the incubation water due to the contact of 15−15N2-enriched water with glass, plastic and rubber ware. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn) increased by up to 0.1 nmol L−1 in the final incubation volume...

Growth dynamics and the proximate biochemical composition and fatty acid profile of the heterotrophically grown diatom Cyclotella cryptica

Pahl, S.; Lewis, D.; Chen, F.; King, K.
Fonte: Springer Science + Business Media B.V. Publicador: Springer Science + Business Media B.V.
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
35.76%
To investigate the nutritional value of the diatom Cyclotella cryptica as an alternative feed for aquaculture, its heterotrophic growth characteristics were studied. First, the proximate biochemical composition and fatty acid profiles were studied under a controlled heterotrophic growth condition. The approximate total ash, carbohydrate, lipid, and protein content were 245 mg g−1 (dry weight), 360 mg g−1, 165 mg g−1 and 260 mg g−1, respectively. Polyunsaturated fatty acids accounted for 24.5, 31.3, 45.1 and 17.3% of the total lipids in the phospholipid, sterol, free fatty acid and triglyceride classes. Secondly, the effect of aeration and agitation rates on the specific growth rate of C. cryptica under heterotrophic conditions was studied. The maximum specific growth rate was not significantly affected (P > 0.05) by the rate of agitation within the range of 100 to 160 rpm, but it was significantly affected (P > 0.05) by the rate of aeration. Optimal growth occurred when the aeration rate was within the range of 0.44 to 1.07 v/v/min. Viability measurements throughout the growth period showed that the C. cryptica cells remained viable in spite of the varied cultivation conditions. Hydrodynamic forces are an important parameter within biological systems...

Engineering considerations for process development in mammalian cell cultivation

Zhang, H.; Wang, W.; Quan, C.; Fan, S.
Fonte: Bentham Science Publ Ltd Publicador: Bentham Science Publ Ltd
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
35.82%
Mammalian cell cultivation plays a great role in producing protein therapeutics in the last decades. Many engineering parameters are considered for optimization during process development in mammalian cell cultivation, only shear and mixing are especially highlighted in this paper. It is believed that shear stress due to agitation has been over-estimated to damage cells, but shear may result in nonlethal physiological responses. There is no cell damage in the regions where bubbles form, break up and coalescence, but shear stress becomes significant in the wake of rising bubbles and causes great damage to cells in bubble burst regions. Mixing is not sufficient to provide homogeneous dissolved oxygen tension, pH, CO2 and nutrients in large-scale bioreactors, which can bring severe problems for cell growth, product formation and process control. Scale-down reactors have been developed to address mixing and shear problems for parallel operations. Engineering characterization in conventional and recently developed scale-down bioreactors has been briefly introduced. Process challenges for cultivation of industrial cell lines in high cell densities as well as cultivation of stem cells and other human cells for regenerative medicine, tissue engineering and gene therapy are prospected. Important techniques...

An investigation into mathematical modelling of integrated biosystems for operational control and management.

Shamim, Khalid
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
35.77%
The South Australian Research & Development Institute (SARDI) and the Environmental Biotechnology Cooperative Research Centre (EBCRC) undertook a project “Commercial Scale Integrated Biosystems for Organic Waste and Wastewater Treatment for the Livestock and Food Processing Industries”, for which this research forms a part. The Integrated Biosystems (IBS) project laboratory was set up at the Roseworthy campus of The University of Adelaide, South Australia. The major objective of this project was to develop an Integrated Biosystems (IBS) on a commercial scale for the treatment of wastewater by applying the stages of anaerobic digestion and bioconversion stages involving algae, zooplankton and fish. The IBS developed could be used in both rural and urban settings for efficient waste disposal and generation of energy in the process. The overall aim of this research was to develop a mathematical model of an IBS for operational control and management. The objectives of this research were to: 1. Develop a mathematical model for the anaerobic digestion system. 2. Use an existing model to simulate the aquaculture stages of the IBS and to test its suitability for a commercial scale IBS for effective control and management. 3. Conduct a sensitivity analysis on the parameters of the aquaculture model. 4. Develop an automatic calibration program to validate the aquaculture model with real time field data. The major contribution from this research was to elucidate the key parameters required to simulate the integrated IBS model. The data was collected through a series of rigorous experimentation for both the anaerobic digestion and aquaculture modules of the IBS. The data obtained was used to parameterise a coupled anaerobic digestion-hydrodynamic ecological model. The resulting model adequately simulated key processes within the IBS...

Avaliação do Efeito da Agitação e Mistura no Processo de Produção do Biodiesel de Mamona via Transesterificação Metílica; Evaluation of the Effect of Agitation and Mixing in the Production Process Biodiesel Castor by Methyl Transesterification

Nazário, Jaelson de Lima
Fonte: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL Publicador: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL
Tipo: Dissertação
POR
Relevância na Pesquisa
85.92%
Most part of the energy demand on the planet is derived from petroleum, a nonrenewable energy source that releases large amounts of greenhouse gases in the atmosphere. Many researches have been devoted to the development of renewable energy sources that are less agressive to the environment. Biodiesel is a renewable, non-toxic and less polluent fuel, thus being a potential alternative to mineral diesel. It is produced from vegetable oils or animal fats. The transformation of vegetable oil into biodiesel by transesterification reaction consisting of a reaction between triglyceride oil and a lower alcohol, usually methanol or ethanol. The soil and climate in BR is attractive to a diversity of oil plants that can be used in biodiesel production. Among them, it can mentioned the castor bean, which grows in regions with low rainfall, as the semi - arid northeastern region. This work aimed to study the effect of stirring and mixing in the production of biodiesel from castor oil via transesterification and methyl alkaline catalysis process. Stirring rate, molar ratio oil / alcohol, the impeller type, the reaction time, the temperature, presence or absence of baffles and catalyst type. Therefore, a fractional factorial design 27-2, having as variables was used. We initially determined the physicochemical properties of castor oil. The experiment was performed in duplicate...

Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation

Murphy, Ryan P.; Kelley, Elizabeth G.; Rogers, Simon A.; Sullivan, Millicent O.; Epps, Thomas H. III
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
35.99%
Publisher's PDF; Chain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene-b-ethylene oxide) or pure poly(butadiene-b-ethylene oxide-d4) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air–water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies.; University of Delaware. Department of Chemical and Biomolecular Engineering.

Mixing and mass transfer characteristics of an unbaffled aerated agitation vessel with unsteadily forward-reverse rotating multiple impellers

Yoshida,M.; Akiho,M.; Nonaka,K.; Yamagiwa,K.; Ohkawa,A.; Tezura,S.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 EN
Relevância na Pesquisa
36.05%
Mixing and mass transfer characteristics of an unbaffled aerated agitation vessel with a liquid height-to-diameter ratio of 2 having unsteadily forward-reverse rotating multiple impellers, a cross type of impellers with four delta blades (CDs), were experimentally studied for air-water system in comparison with those of a baffled vessel having steadily unidirectionally rotating disk turbine impellers with six flat blades (DTs). For the forward-reverse rotating CD vessel, the contribution of sparged gas to enhancement in liquid phase mixing was observed in the entire range of gas sparging rate including its lower range. Agitating by the forward-reverse rotating CDs functioned effectively to enhance gas-liquid mass transfer not only in the lower range of gas sparging rate but also in its higher range. The features in operating the forward-reverse rotating multiple CD vessel were discussed in terms of the differences in the mixing time and volumetric mass transfer coefficient due to changes in the power input.

Mixing characteristics of liquid phase in an unbaffled vessel agitated by unsteadily forward-reverse rotating multiple impellers

Yoshida,Masanori; Taguchi,Yoji; Yamagiwa,Kazuaki; Ohkawa,Akira; Abe,Masahiko; Tezura,Shuichi; Shimazaki,Masuo
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2004 EN
Relevância na Pesquisa
36.06%
Mixing characteristics of liquid phase in an unbaffled vessel containing water with a liquid height-to-diameter ratio of 2 agitated by unsteadily forward-reverse rotating multiple impellers, a cross type of impellers with four delta blades (CDs), were experimentally studied in comparison with that in a baffled vessel agitated by steadily unidirectionally rotating disk turbine impellers with six flat blades (DTs). For the forward-reverse as well as unidirectional modes of operation, the mixing time in multiple impeller system was larger than that in single impeller system with a liquid height-to-diameter ratio of 1. The ratio of mixing time in multiple impeller system to that in single impeller system was small for the forward-reverse agitation mode compared with that for the unidirectional agitation mode. The result was discussed in relation to the difference in bulk flow pattern between the unbaffled vessel with forward-reverse rotating CDs and the baffled vessel with unidirectionally rotating DTs.

Mixing system design for the Tati Activox® autoclave

Nicolle,M.; Nel,G.; Plikas,T.; Shah,U.; Zunti,L.; Bellino,M.; Pieterse,H.J.H.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 EN
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The Tati Activox® Project will be the first full-scale implementation of the patented Activox® process (The Tati Activox® project was deferred in 2008. Please refer to the Norilsk Nickel press issue on the topic for more info). The process was developed by Norilsk Process Technology and has been tested on Tati mine sulphide concentrates in laboratory, pilot and demonstration plant scales and demonstrated its viability. There are inherent risks to the final scale-up of the process from the demo plant and one of them will be investigated in this paper. Compartment 1 is designed to leach approximately 77% of the total nickel leached. For this reason agitation requirements in the first compartment of the autoclave are reviewed. An attempt is made to minimize the process and mechanical risks associated in achieving oxygen mass transfer into the slurry solution. The agitator powers for oxygen mass transfer are calculated using empirical correlations and compared to demonstration plant testwork. The resulting gassed power per unit volume (P/V) is higher than most commercial autoclaves and raises uncertainty on the viability of using such high unit power inputs. Additionally, there is concern about the ability of the autoclave shell to withstand and support the higher loading of large agitators. An alternative solution to designing for the increased P/V is assessed in which the number of compartments within the autoclave is reduced from 5 to 4 by removing the compartment wall separating compartments 1 and 2. This results in an enlarged first compartment containing 3 agitators instead of 2. Therefore the compartment 1 oxygen demand is supplied through 3 agitators...