A PBM-Based Procedure for the CFD Simulation of Gas–Liquid Mixing with Compact Inline Static Mixers in Pipelines

A compact static mixer for gas–liquid dispersion in pipelines is studied in this paper with a Reynolds averaged two fluid model approach. A procedure based on the lumped parameter solution of a population balance model is applied to obtain the bubble Sauter mean diameter needed to model the interphase forces. The gas distribution in the pipe is analyzed in two different operative conditions and the efficiency of the static mixer is assessed in terms of the gas homogeneity in the pipe section, with low coefficients of variations being obtained. A computational model to obtain the volumetric mass transfer coefficient, kLa, developed for partially segregated systems is applied finding kLa values comparable to those typically obtained with other static mixers. The proposed computational model allows us to locally analyze the oxygen transfer rate by observing the limitations due to gas accumulation behind the body of the static mixer, which leads to the local depletion of the driving force. Geometrical optimization of the static element is proposed, based on the analysis of gas–liquid fluid dynamics and of the interphase mass transfer phenomena

Hydrodynamics, power consumption and bubble size distribution in gas-liquid stirred tanks

In this work, we present the results collected in a gas-liquid stirred tank by a combination of experimental and computational methods, with the aim of presenting original data on the bubbles size distribution and contributing to the development of fully predictive methods for the design and the scale-up of chemical and biochemical gas-liquid reactors. Basic variables which affect mass transfer and consequently the performances of industrial aerobic fermentations are discussed, with special focus on the bubble size distribution, the gassed power consumption and the gas cavities. The current developments of Two Fluid and Population Balance models for obtaining fully predictive results on gas-liquid mixing in stirred tanks are discussed. The results confirm that the correct prediction of the bubble size in the impeller zone is a crucial prerequisite for obtaining reliable results of the hydrodynamics of aerated stirred tanks

Prediction of gas cavities size and structure and their effect on the power consumption in a gas-liquid stirred tank by means of a two-fluid RANS model

Aerated cavities behind the impeller blades in stirred tanks affect the power transferred to the liquid that in turns affects heat and mass transfer, thus the development of fully predictive simulation methods to detect the formation of cavities, their size and structures is of paramount importance for an effective simulation of aerated reactors and bioreactors. In this work, operating conditions corresponding to different cavity structures are investigated by means of a Reynolds averaged two-fluid model without adjustable parameters. Based on the comparison with previous experiments and correlations, the method proved to be reliable in the prediction of the transition between vortex-clinging and small '3-3′ cavities, cavity size and power drawn reduction. For the first time, small '3-3′ cavities with volume fractions close to unity are obtained with a steady approach. The power reduction mechanism is observed and a novel interpretation of the formation of the asymmetrical cavities is proposed

Liquid mixing time and gas distribution in aerated multiple-impeller stirred tanks

Gas-liquid fluid dynamics and mass transfer are crucial aspects of aerobic fermentation and robust methodologies for their determination in industrial bioreactors are expected to provide significant improvements in many production processes. In this work, a gas-liquid stirred tank of high aspect ratio, that replicates the geometry of typical industrial aerated fermenters, is investigated. In particular, the liquid phase homogenization dynamics and the gas phase spatial distribution are determined. The selected methodology is based on the analysis of the conductivity measurements obtained by Electrical Resistance Tomography. The gas-liquid flow regimes and the mixing time are identified at various gas flow rates and impeller speeds, thus covering different gas-liquid regimes. Data col lected with vertical and horizontal arrangements of the electrodes allow to obtain a tailed picture of the equipment working mode and to gain insight into the gas-liquid flow dynamics under optically inaccessible conditions. Quantitative evaluation of the bility of the collected data is attempted by comparing the results obtained with the tical and horizontal arrangements in the same locations

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

Application of large blade impellers to turbulent single-phase and two-phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three-dimensional velocity fields collected in a single-phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two-phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear-rate controlled and bulk-motion controlled processes

Numerical and Experimental Analysis of the Daughter Distribution in Liquid-Liquid Stirred Tanks

The drop size distributions (DSDs) of a dilute immiscible liquid-liquid mixture were measured in a fully turbulent stirred tank operating at different impeller speeds. The results were used to infer the best daughter distribution function (DDF) leading to the best reproduction of the shape of the DSD. Bell-shaped, U-shaped, M-shaped, and uniform statistical DDFs were studied, producing from two to four daughters from each breakup event. A simplified approach from the literature was adopted to solve the population balance equation that considers the spectrum of the turbulence inside the tank obtained from computational fluid dynamics simulations. The U-shaped distribution producing four fragments better reproduces the shape of the experimental DSD in the studied system

Avaliação da capacidade imunoestimulante e da estabilidade de um probiótico empregado em rações de cães

The time of viability of a thermostableprobiótica (TR) in extruded and mealy formulationsfor dog food and their imunoestimulant effects indogs were evaluated. A commercial, lyophilized,thermostable and encapsulated probiotic,composed of Bacillus cereus (ATCC 9634) 4,0 xl08 UFC/g; Bacillus subtilis (ATCC 3131) 4,0 x l08UFC/g, was incorporated in an extruded and in amealy commercial dog food. In one experiment,quantitative and qualitative survival ratios of bacteriawere evaluated at 3, 6, 9 and 12 months of storage.In other, 10 dogs (males and females) with weightvarying from 10 to 30 kg, without defined breeds,were divided in two groups of five animals each.All animals without serological titre anti-leptospiraswere vaccinated against the serovares canicolaand icterohaemorrhagiae in the beginning of theexperiment and maintained in individual facilities for60 days. The animals of group I received extrudedration with Probiotic TR and the animals of group IIreceived the same extruded ration without ProbioticTR (controls). The antibodies’ titres againstserovares canicola and icterohaemorrhagiaewere determined before vaccination, and at 15o,30o and 60o day after, using microscopic serumagglutinationreaction with live antigens. Accordingto the results of total count of spores in extrudedand mealy rations, the probiotic TR was stable for asuperior period than 12 months. The stimulation ofthe immune response was verified by elevation ofserological titres from group I animals at 15o., 30o.and 60o. day after vaccination while the control dogsshowed lower and unstable responses.Foi avaliado um probiótico termo-resistente,liofilizado e encapsulado, composto de Bacilluscereus (ATCC 9634) 4,0 x l08 UFC/g e Bacillus subtilis(CCT 3131) 4,0 x l08 UFC/g, incorporado emuma ração comercial para cães com o objetivo deavaliar sua viabilidade durante o período de umano, e o seu efeito imunoestimulante quando fornecidoàs dietas. No primeiro experimento, foi avaliadaa sobrevivência das bactérias quantitativamentee qualitativamente depois de 3, 6, 9, 12 meses deestocagem. No segundo ensaio, foram utilizados 10cães (machos e fêmeas) com peso variando de 10a 30 kg, sem raças definidas, divididos em dois gruposde cinco animais cada. Todos os animais semtítulo sorológico anti-leptospira, foram vacinadoscontra os sorovares canicola e icterohaemorrhagiaeno início do experimento e mantidos em canis individuaisdurante 60 dias. Os animais do grupo Ireceberam ração extrusada acrescida de ProbióticoTR e, os animais do grupo II receberam a mesmaração extrusada sem o Probiótico TR, sendo mantidoscomo controles. Os títulos de anticorpos contraos sorovares canicola e icterohaemorrhagiae foramdeterminados antes da vacinação, no 15o, 30o e 60odia após, utilizando a reação de soro-aglutinaçãomicroscópica com antígenos vivos. Pelos resultadosda contagem total de esporos nas rações extrusadae farelada, o probiótico TR é notadamente estávelpor período superior a 12 meses. O estímuloda resposta imune foi verificado pela elevação dostítulos dos animais do grupo I no 15o, 30o e 60o diaapós a vacinação. Este fato é atribuído à ingestãodo probiótico TR, uma vez que entre os animais quenão receberam ração com probiótico TR (grupo II), a resposta imune foi menor e instável

Il trattamento delle fratture del terzo prossimale di omero mediante chiodo endomidollare "Polarus"

Proximal humeral fractures are complex lesions with difficult management problems and so they are a professional struggles for orthopaedic surgeons. In literature a lot of techniques of treatment are proposed for these kind of fractures. In our study we have reviewed 30 patients with a proximal humeral fracture (Neer 2-3) with a mean age of 75 years, treated in our clinic with Polarus nail, with a mean follow-up of 7 years.We obtained 73,3% of good and excellent results, in line with literature results. The complications involved 6 patients (20%) of our study, in particular 3 cases of proximal screw pull-out, 1 case of deep infection and 2 cases of acromioclavicula impingement. The aim of our study is a review of our cases, comparing them with the literature, analysing these kind of complex fractures and the type of treatments

Tibial plateau fractures: compared outcomes between ARIF and ORIF.

The purpose of this study is to compare arthroscopic assisted reduction internal fixation (ARIF) treatment with open reduction internal fixation (ORIF) treatment in patients with tibial plateau fractures. We studied 100 patients with tibial plateau fractures (54 men and 46 women) examined by X-rays and CT scans, divided into 2 groups. Group A with associated meniscus tear was treated by ARIF technique, while in group B ORIF technique was used. The follow-up period ranged from 12 to 116 months. The patients were evaluated both clinically and radiologically according to the Rasmussen and HSS (The Hospital for Special Surgery knee-rating) scores. In group A, the average Rasmussen clinical score is 27.62 \ub1 2.60 (range, 19\u201330), while in group B is 26.81 \ub1 2.65 (range, 21\u201330). HSS score in group A was 76.36 \ub1 14.19 (range, 38\u201391) as the average clinical result, while in group B was 73.12 \ub1 14.55 (range, 45\u201391). According to Rasmussen radiological results, the average score for group A was 16.56 \ub1 2.66 (range, 8\u201318), while in group B was 15.88 \ub1 2.71 (range, 10\u201318). Sixty-nine of 100 patients in our study had associated intra-articular lesions. We had 5 early complications and 36 late complications. The study suggests that there are no differences between ARIF and ORIF treatment in Schatzker type I fractures. ARIF technique may increase the clinical outcome in Schatzker type II\u2013III\u2013IV fractures. In Schatzker type V and VI fractures, ARIF and ORIF techniques have both poor medium- and long-term results but ARIF treatment, when indicated, is the best choice for the lower rate of infections

Efficient low-loaded ternary Pd-In2O3-Al2O3 catalysts for methanol production

Pd-In2O3 catalysts are among the most promising alternatives to Cu-ZnO-Al2O3 for synthesis of CH3OH from CO2. However, the intrinsic activity and stability of In2O3 per unit mass should be increased to reduce the content of this scarcely available element and to enhance the catalyst lifetime. Herein, we propose and demonstrate a strategy for obtaining highly dispersed Pd and In2O3 nanoparticles onto an Al2O3 matrix by a one-step coprecipitation followed by calcination and activation. The activity of this catalyst is comparable with that of a Pd-In2O3 catalyst (0.52 vs 0.55 gMeOH h−1 gcat-1 at 300 °C, 30 bar, 40,800 mL h−1 gcat-1) but the In2O3 loading decreases from 98 to 12 wt% while improving the long-term stability by threefold at 30 bar. In the new Pd-In2O3-Al2O3 system, the intrinsic activity of In2O3 is highly increased both in terms of STY normalized to In specific surface area and In2O3 mass (4.32 vs 0.56 g gMeOH h−1 gIn2O3-1 of a Pd- In2O3 catalyst operating at 300 °C, 30 bar, 40,800 mL h−1 gcat-1).The combination of ex situ and in situ catalyst characterizations during reduction provides insights into the interaction between Pd and In and with the support. The enhanced activity is likely related to the close proximity of Pd and In2O3, wherein the H2 splitting activity of Pd promotes, in combination with CO2 activation over highly dispersed In2O3 particles, facile formation of CH3OH