The effect of mechanical stirring on horizontal convection

An important experimental result, as yet poorly understood, is that mechanical stirring can significantly enhance the strength of horizontal convection. A contentious issue is whether this necessarily implies that the mechanical stirring replaces the buoyancy forcing as the main source of energy driving the observed overturning circulation, as has been suggested for the Atlantic meridional overturning circulation (AMOC). In this paper, rigorous energetics considerations and idealized numerical experiments reveal that the rate at which the surface buoyancy forcing supplies energy to the fluid, as measured by the production rate of available potential energy G(APE), does not solely depend upon the buoyancy forcing, as is often implicitly assumed, but also upon the vertical stratification, such that the deeper the thermocline depth, the larger G(APE). This suggests that mechanical stirring enhances horizontal convection because it causes more energy to be extracted from the buoyancy forcing. It does so by enhancing turbulent mixing, which allows surface heating to reach greater depths, which increases the thermocline depth and hence G(APE). This paper therefore proposes a new hypothesis, namely that mechanically stirred horizontal convection and the AMOC are best described as mechanically controlled heat engines.

Effect of Fill Time on the Performance of Pilot-scale ASBR and AnSBBR Applied to Sanitary Wastewater Treatment

Many lab-scale studies have been carried out regarding the effect of feed strategy on the performance of anaerobic sequencing batch reactors (ASBR); however, more detailed pilot-scale studies should be performed to assess the real applicability of this type of operation. Therefore, the objective of this work was to assess the effect of feed strategy or fill time in a 1-m(3) mechanically stirred pilot-scale sequencing batch reactor, treating 0.65 m(3) sanitary wastewater in 8-h cycles at ambient temperature. Two reactor configurations were used: one containing granular biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam as inert support (denominated anaerobic sequencing batch biofilm reactor (AnSBBR)). The reactors were operated under five distinct feed strategies, namely: typical batch and fed-batch for 25%, 50%, 75%, and 100% of the cycle length. Stirring frequency in the ASBR was 40 rpm with two flat-blade turbine impellers and 80 rpm in the AnSBBR with two helix impellers. The results showed that both the ASBR and AnSBBR when operated under typical batch, fed-batch for 50% and 75% of the cycle length, presented improved organic matter removal efficiencies, without significant differences in performance, thus showing important operational flexibility. In addition, the reactors presented operation stability under all conditions.

Influence of organic shock loads in an ASBBR treating synthetic wastewater with different concentration levels

Safe application of the anaerobic sequencing biofilm batch reactor (ASBBR) still depends on deeper insight into its behavior when faced with common operational problems in wastewater treatments such as tolerance to abrupt variations in influent concentration, so called shock loads. To this end the current work shows the effect of organic shock loads on the performance of an ASBBR, with a useful volume of 5 L, containing 0.5-cm polyurethane cubes and operating at 30 degrees C with mechanical stirring of 500 rpm. In the assays 2 L of two types of synthetic wastewater were treated in 8-h cycles. Synthetic wastewater I was based on sucrose-amide-cellulose with concentration of 500 mg COD/L and synthetic wastewater II was based on volatile acids with concentration ranging from 500 to 2000 mg COD/L. Organic shock loads of 2-4 times the operation concentration were applied during one and two cycles. System efficiency was monitored before and after application of the perturbation. When operating with concentrations from 500 to 1000 mg COD/L and shock loads of 2-4 times the influent concentration during one or two cycles the system was able to regain stability after one cycle and the values of organic matter, total and intermediate volatile acids, bicarbonate alkalinity and pH were similar to those prior to the perturbations. At a concentration of 2000 mg COD/L the reactor appeared to be robust, regaining removal efficiencies similar to those prior to perturbation at shock loads twice the operation concentration lasting one cycle and stability was recovered after two cycles. However, for shock loads twice the operation concentration during two cycles and shock loads four times the operation concentration during one or two cycles filtered sample removal efficiency decreased to levels different from those prior to perturbation, on an average of 90-80%, approximately, yet the system managed to attain stability within two cycles after shock application. Therefore, this investigation envisions the potential of full scale application of this type of bioreactor which showed robustness to organic shock loads, despite discontinuous operation and the short times available for treating total wastewater volume. (c) 2007 Elsevier Ltd. All rights reserved.

Ultrasound enhances lipase-catalyzed synthesis of poly (ethylene glutarate)

The present work explores the best conditions for the enzymatic synthesis of poly (ethylene glutarate) for the first time. The start-up materials are the liquids; diethyl glutarate and ethylene glycol diacetate, without the need of addition of extra solvent. The reactions are catalyzed by lipase B from Candida antarctica immobilized on glycidyl methacrylate-ter-divinylbenzene-ter-ethylene glycol dimethacrylate at 40 °C during 18 h in water bath with mechanical stirring or 1 h in ultrasonic bath followed by 6 h in vacuum in both the cases for evaporation of ethyl acetate. The application of ultrasound significantly intensified the polyesterification reaction with reduction of the processing time from 24 to 7 h. The same degree of polymerization was obtained for the same enzyme loading in less time of reaction when using the ultrasound treatment. The degree of polymerization for long-term polyesterification was improved approximately 8-fold due to the presence of sonication during the reaction. The highest degree of polymerization achieved was 31, with a monomer conversion of 96.77%. The ultrasound treatment demonstrated to be an effective green approach to intensify the polyesterification reaction with enhanced initial kinetics and high degree of polymerization.

Formulation and characterization of poloxamer 407®: thermoreversible gel containing polymeric microparticles and hyaluronic acid

The influence of the composition and preparation method on the sol-gel transition temperature (Tsol-gel) and rheological response of poloxamer-based formulations was determined. Manual and more complex mechanical stirring were found to provide similar results. In addition, a linear dependence of Tsol-gel on the poloxamer content was observed in the range of concentrations analyzed, and a Poloxamer 407® concentration of 18% was selected. The addition of hyaluronic acid did not lead to significant changes in the Tsol-gel values. In contrast, the addition of microparticles caused a reduction in Tsol-gel without a significant reduction in gel strength, and pseudoplastic characteristics were observed, indicating that a thermoreversible gel was obtained with a rheology suitable for application in the treatment of burn wounds.

DISPOSITIVO PARA EXTRAÇÃO LÍQUIDO-LÍQUIDO EM SISTEMAS DE ANÁLISES EM FLUXO

AbstractA device comprising a lab-made chamber with mechanical stirring and computer-controlled solenoid valves is proposed for the mechanization of liquid-liquid extractions. The performance was demonstrated by the extraction of ethanol from biodiesel as a model of the extraction of analytes from organic immiscible samples to an aqueous medium. The volumes of the sample and extractant were precisely defined by the flow-rates and switching times of the valves, while the mechanic stirring increased interaction between the phases. Stirring was stopped for phase separation, and a precise time-control also allowed a successful phase separation (i.e., the absence of the organic phase in the aqueous extract). In the model system, a linear response between the analytical response and the number of extractions was observed, indicating the potential for analyte preconcentration in the extract. The efficiency and reproducibility of the extractions were demonstrated by recoveries of ethanol spiked to biodiesel samples within 96% and 100% with coefficients of variation lower than 3.0%.

Methylene blue adsorption onto modified lignin from sugar cane bagasse

The adsorption kinetics and equilibrium of methylene blue (MB) onto reticulated formic lignin (RFL) from sugar cane bagasse was studied. The adsorption process is pH, temperature and ionic strength (µ) dependent and obeys the Langmuir model. Conditions for higher adsorption rate and capacity were determined. The faster adsorption (12 hours) and higher adsorption capacity (34.20 mg.g-1) were observed at pH = 5.8 (acetic acid-sodium acetate aqueous buffer), 50 ºC and 0.1 ionic strength. Under temperature (50 ºC) control and occasional mechanical stirring it took from 1 to 10 days to reach the equilibrium.

On the energetics of stratified turbulent mixing, irreversible thermodynamics, Boussinesq models and the ocean heat engine controversy

In this paper, the available potential energy (APE) framework of Winters et al. (J. Fluid Mech., vol. 289, 1995, p. 115) is extended to the fully compressible Navier– Stokes equations, with the aims of clarifying (i) the nature of the energy conversions taking place in turbulent thermally stratified fluids; and (ii) the role of surface buoyancy fluxes in the Munk & Wunsch (Deep-Sea Res., vol. 45, 1998, p. 1977) constraint on the mechanical energy sources of stirring required to maintain diapycnal mixing in the oceans. The new framework reveals that the observed turbulent rate of increase in the background gravitational potential energy GPEr , commonly thought to occur at the expense of the diffusively dissipated APE, actually occurs at the expense of internal energy, as in the laminar case. The APE dissipated by molecular diffusion, on the other hand, is found to be converted into internal energy (IE), similar to the viscously dissipated kinetic energy KE. Turbulent stirring, therefore, does not introduce a new APE/GPEr mechanical-to-mechanical energy conversion, but simply enhances the existing IE/GPEr conversion rate, in addition to enhancing the viscous dissipation and the entropy production rates. This, in turn, implies that molecular diffusion contributes to the dissipation of the available mechanical energy ME =APE +KE, along with viscous dissipation. This result has important implications for the interpretation of the concepts of mixing efficiency γmixing and flux Richardson number Rf , for which new physically based definitions are proposed and contrasted with previous definitions. The new framework allows for a more rigorous and general re-derivation from the first principles of Munk & Wunsch (1998, hereafter MW98)’s constraint, also valid for a non-Boussinesq ocean: G(KE) ≈ 1 − ξ Rf ξ Rf Wr, forcing = 1 + (1 − ξ )γmixing ξ γmixing Wr, forcing , where G(KE) is the work rate done by the mechanical forcing, Wr, forcing is the rate of loss of GPEr due to high-latitude cooling and ξ is a nonlinearity parameter such that ξ =1 for a linear equation of state (as considered by MW98), but ξ <1 otherwise. The most important result is that G(APE), the work rate done by the surface buoyancy fluxes, must be numerically as large as Wr, forcing and, therefore, as important as the mechanical forcing in stirring and driving the oceans. As a consequence, the overall mixing efficiency of the oceans is likely to be larger than the value γmixing =0.2 presently used, thereby possibly eliminating the apparent shortfall in mechanical stirring energy that results from using γmixing =0.2 in the above formula.

Desgaste corrosivo-cavitativo-erosivo de um aço-carbono em meio aquoso com frações de sal (NaCl), CO2 e particulados sólidos (SiO2)

A batch of eighty-four coupons of low carbon steel were investigated at laboratory conditions under a corrosive, cavitative-corrosive (CO2) and corrosive-erosive (SiO2 + CO2) in an aqueous salt solution and two levels of temperature. The following measurements were made on Vickers (HV0,05, HV0,10, HV0,20) Microhardness tests at three levels of subsurface layer. A turbulent flow collided on the cylindrical sample, with and without mechanical stirring and gas bubbling, with and without fluid contamination by solid particles of SiO2, at two temperatures. Surface Roughness and Waviness, under two conditions "as received, after machining" and "after worn out", as well as gravimetric and electrochemical parameter were measured on the two opposite generatrices of each cylindrical sample, on the flow upstream (0°) and downstream (180°) by Profilometry, Mass Variation and Linear Polarization Resistance (LPR). The results of the Microhardness and Surface Texture of all coupons were subjected to statistical comparison, using the software Statgraphics® Centurion XVI, 95% statistical certainty, and significant differences were observed in some arrays of measurements. The corrosive wear rate measured by LPR and mass variation shown to be sensitive to the presence of bubbles and hydrodynamic fluctuations inside the cell, considering the temperature and contamination of corrosive fluid by solid particles. The main results of visual inspection relative to some topologies of the surface damages involving different mechanisms that were seen to give explanation for some fluctuations in wear rates of the steel experimentally investigated

Remoção de óleo da água de produção por flotação em coluna utilizando tensoativos de origem vegetal

In the petroleum industry, water is always present in the reservoir formation together with petroleum and natural gas and this fact provokes the production of water with petroleum, resulting in a great environmental impact. Several methods can be applied for treatment of oily waters, such as: gravitational vases, granulated media filtration systems, flotation process, centrifugation process and the use of hydrocyclones, which can also be used in a combined way. However, the flotation process has showed a great efficiency as compared with other methods, because these methods do not remove great part of the emulsified oil. In this work was investigated the use of surfactants derived from vegetable oils, OSS and OGS, as collectors, using the flotation process in a glass column with a porous plate filter in its base for the input of the gaseous steam. For this purpose, oil/water emulsions were prepared using mechanical stirring, with concentrations around 300 ppm. The air flow rate was set at 700 cm3/min and the porous plate filter used for the generation of the air bubbles has pore size varying from 16 to 40 Pm. The column operated at constant volume (1500mL). A new methodology has been developed to collect the samples, where, instead of collecting the water phase, it was collected the oil phase removed by the process in the top of the flotation column. It has been observed that it is necessary to find an optimum surfactant concentration to achieve enhanced removal efficiency. Being for OSS 1.275 mmol/L and for OGS 0.840 mmol/L, with removal efficiencies of 93% and 99%, respectively, using synthetic solutions. For the produced water, the removal in these concentrations was 75% for OSS and 65% for OGS. It is possible to remove oil from water in a flotation process using surfactants of high HLB, fact that is against the own definition of HLB (Hydrophile-Lipophile Balance). The interfacial tension is an important factor in the oil removal process using a flotation process, because it has direct interference in the coalescence of the oil drops. The spreading of the oil of the air bubble should be considered in the process, and for the optimum surfactant concentrations it reached a maximum value. The removal kinetics for the flotation process using surfactants in the optimum concentration has been adjusted according to a first order model, for synthetic water as for the produced water.

Redução de crômio hexavalente por substâncias húmicas aquáticas imobilizadas em aminopropil sílica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Highly swollen liquid crystals as new reactors for the synthesis of nanomaterials

Synthesis and self-assembly of nanomaterials can be controlled by the properties of soft matter. on one hand, dedicated nanoreactors such as reverse microemulsions or miniemulsions can be designed. on the other hand, direct shape control can be provided by the topology of liquid crystals that confine the reacting medium within a specific geometry. In the first case, the preparation of micro- or miniemulsions generally requires energetic mechanical stirring. The second approach uses thermodynamically stable systems, but it remains usually limited to binary (water + surfactant) systems. We report the preparation of different families of materials in highly ordered quaternary mediums that exhibit a liquid crystal structure with a high cell parameter. They were prepared with the proper ratios of salted water, nonpolar solvent, surfactant. and cosurfactants that form spontaneously swollen hexagonal phases. These swollen liquid crystals can be prepared from all classes of surfactants (cationic, anionic, and nonionic). They contain a regular network of parallel cylinders, whose diameters can be swollen with a nonpolar solvent, that are regularly spaced in a continuous aqueous salt solution. We demonstrate in the present report that both aqueous and organic phases can be used as nanoreactors for the preparation of materials. This property is illustrated by various examples such as the synthesis of platinum nanorods prepared in the aqueous phase or zirconia needles or the photo- or gamma-ray-induced polymerization of polydiacetylene in the organic phase. In all cases, materials can be easily extracted and their final shapes are directed by the structure-directing effect imposed by the liquid crystal.

Incorporação da apatita na superfície da liga Ti30ta empregando tratamento alcalino associado à eletrofiação de fibras de PCL

Pós-graduação em Engenharia Mecânica - FEG

Liquid crystalline cellulose derivatives for mirrorless lasing

In this thesis cholesteric films made of liquid crystalline cellulose derivatives with improved optical properties were prepared. The choice of the solvent, hydrogen bond influencing additives, the synthetic realization of a very high degree of substitution on the cellulosic polymer and the use of mechanical stirring at the upper concentration limit of the liquid crystalline range were the basis for an improved alignment of the applied cellulose tricarbamates. In combination with a tuned substrate treatment and film preparation method, cholesteric films were obtained, with optical properties that were theoretically predicted and only known from low molecular weight liquid crystals so far. Subsequent polymerization allowed a permanent fixing of the alignment and the fabrication of free standing and insensitive films.rnThe incorporation of inorganic nanorods into the cholesteric host material was mediated with tailored block copolymers, available via controlled radical polymerization methods. In addition to the shape match between the rodlike mesogens of the host and the nanorods it was possible to increase the miscibility of both materials. Nevertheless, the size of the nanorods, in comparison to the mesogens, in these densely packed liquid crystalline phases as well as their long equilibration times were the reasons for phase separation. Nanorods are, in principle, valuable substitutes for organics, but their utilization in cellulosic CLC was not to be combined with a high quality alignment of the cholesteric structure.rnA swelling process of polymerized films in a dye solution or dissolving dyes in non-polymerized CLC was used for incorporation of the organic chromophores. With the first method the CLC could be aligned and polymerized without any disturbance due to dye molecules. The optical properties of dye and CLC were matched, with regard to mirrorless lasing devices. The dye was optically excited and laser emission supported by the cholesteric cavity was obtained. The polarization and wavelength of the emitted radiation as well as its bandwidth, the obtained interference pattern and threshold behavior of the emission proofed the feedback mechanism that was not believed to be realizable in liquid crystalline polymers. rnUtilization of a microfluidic co-flow injection device enabled us to transfer the properties of cellulosic CLC from the planar film shape to spherical micrometer sized particles. The pure material yielded particles with distorted mesogen alignment similar to films prepared by capillary flow. Dilution of the CLC with a solvent that migrated into the carrier phase during particle preparation provided the basis for particles with well ordered areas. rnAlthough cellulose derivatives were known for their liquid crystalline behavior for decades and synthesized in mass production, their application as feedback material was affected by bad optical properties. In comparison to low molar mass compounds, the low degree of order in the CLC phase was the cause. With the improved material, defined lasing emission was shown and characterized. Derivatives of cellulose are desirable materials, because, as a renewable resource, they are available in large amounts for a low price and need only simple derivatization reactions. The fabrication of CLC films with tunable lasing emission, for which this thesis can provide a starting point, is in good agreement with today's requirements of modern technology and its miniaturization.rn

Produção de biohidrogênio a partir de soro de leite em AnSBBR com recirculação da fase líquida

O presente estudo investigou a aplicação de dois tipos de AnSBBR (reatores anaeróbio com biofilme e operados em batelada e batelada alimentada sequenciais: com recirculação da fase líquida e com agitação) para produção de biohidrogênio tratando água residuária sintética (a base de soro de leite e lactose, respectivamente). O AnSBBR com recirculação da fase líquida, que foi o estudo principal do presente trabalho, apresentou problemas na produção de hidrogênio utilizando soro de leite como substrato. Algumas alternativas, como adaptação da biomassa com substratos puros de degradação mais fácil, controle do pH em valores muito baixos e diferentes formas de inoculação foram testadas, entretanto, sem obtenção de sucesso. A solução do problema foi obtida ao refrigerar o meio de alimentação a 4ºC para evitar a fermentação no frasco de armazenamento, retirar a ureia e a suplementação de nutrientes, e realizar lavagens periódicas do material suporte para retirada de parte da biomassa. Dessa forma eliminaram-se indícios de produção de H2S por possível ação de bactérias redutoras de sulfato (BRS) e atingiu-se uma produção estável de hidrogênio sem, entretanto, eliminar completamento o metano, que foi produzido em baixas concentrações. Depois de atingida a estabilidade, investigou-se a influência da concentração afluente de substrato, do tempo de enchimento e da temperatura na produção de biohidrogênio no AnSBBR com recirculação da fase líquida tratando soro de leite. O estudo da concentração afluente apresentou um ponto ótimo para a concentração de 5400 mgDQO.L-1, atingindo valores de 0,80 mol H2.mol-1 lactose e de 660 mL H2.L-1.d-1. O estudo do tempo de enchimento apresentou resultados similares para as condições analisadas. Com relação à temperatura, os melhores resultados foram obtidos com a temperatura mais baixa testada de 15ºC (1,12 mol H2.mol lactose-1 e 1080 mL H2.L-1.d-1), sendo que na temperatura mais alta testada (45°C) não ocorreu produção de hidrogênio. Para o AnSBBR com agitação mecânica, que foi um estudado complementar realizado pelo fato da lactose ser o principal complemento do soro de leite, o desempenho do biorreator foi avaliado de acordo com influência conjunta do tempo de ciclo (tC – 2, 3 e 4 h), da concentração afluente (CSTA – 3600-5400 mgDQO.L-1) e da carga orgânica volumétrica aplicada (COAV – 9,3, 12,3, 13,9, 18,5 e 27,8 mgDQO.L-1.d-1). Foram obtidos excelentes resultados: consumos de carboidratos (lactose), com valores médios sempre acima de 90% e uma produção estável de biohidrogênio em todas as condições estudadas, com metano em baixas concentrações apenas na condição de maior COAV. A diminuição do tC apresentou tendência clara de melhora sobre o RMCRC,n (rendimento molar entre hidrogênio produzido e carboidrato removido) apenas para as condições com menor concentração CSTA, havendo uma relação direta entre CSTA, e RMCRC,n em todos os valores de tC, exceto para o tempo de ciclo de 3 h, exatamente onde ocorreu produção de metano. O melhor valor de RMCRC,n obtido na operação com lactose (1,65 mol H2.mol Carboidrato-1) foi superior aos obtidos em outros trabalhos utilizando a mesma configuração de reator e sacarose como substrato. As análises filogenéticas mostraram que a maioria dos clones analisados foi semelhante à Clostridium. Além destes, clones filogeneticamente semelhantes com a Família Lactobacilaceae, especificamente Lactobacillus rhamnosus foram observados em menor porcentagem no reator, assim como clones com sequências semelhantes a Acetobacter indonesiensis.