•Development of a simplified population balance model to predict Sauter diameter.•Identification of the best kernels over 60 possible combinations.•Flows in a bubble column and a stirred tank are ...considered, leading to two different sets of PBM kernels.•Kernels suitable to both flows are also reported.
A simplified population balance model has been developed to predict the Sauter mean diameter, and to optimize any breakage and coalescence kernel. Firstly, the shortcut model is detailed, and the simplifying assumptions are argued. Then the model is applied in a comparison of 60 combinations of a selection of classical breakage, collision frequency and coalescence efficiency kernels. The models are fitted and then compared with an experimental dataset measured in two different technologies of interest for biotechnology: bubble columns (Gemello et al., 2018), and stirred tanks (Cappello et al., 2020). The best kernels are identified for each flow configuration separately, and some kernels are identified as giving acceptable predictions simultaneously of both flows (average error on bubble size less than 20%).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract Introduction: Inferior vena cava agenesis is one of the most uncommon anomalies of this vessel, with an estimated prevalence of 0.0005-1% in the general population. However, around 5% of the ...patients younger than 30 years with a diagnosis of deep vein thrombosis have this anomaly. Methods and material: Report of two clinical cases of inferior vena cava agenesis with different clinical presentations. Clinical case 1: A 40-year-old man was admitted with a 3 days history of unilateral lower limb swelling and pain, gradually progressing to the inability to walk. On physical examination he had swelling, bruising and tenderness involving leg and thigh and prominent engorged superficial abdominal collateral veins. Venous Doppler Ultrasound showed left deep venous thrombosis extending from popliteal vein to common iliac vein. A computed tomography angiogram showed agenesis of the infrarenal vena cava and patent renal veins draining in to the azygous system and hemiazygous systems. The patient as discharged with rivaroxaban and compression stockings. At 2 months follow up he was asymptomatic and still anticoagulated. Clinical case 2: A 35 year- old woman, with a previous history of recurrent lower limb varicose veins surgery and left internal malleolar ulcer at 30 years presented at medical department 3 years later with complains of ulcer recurrence. A computed tomography angiogram revealed an absent infrahepatic vena cava, prominently dilated azygos and hemiazygos veins with enlarged retroperitoneal collaterals. The patient initiated dressing care with oxide zinc and oral rivaroxaban. Discussion/conclusion: The majority of cases remain asymptomatic. However, when symptomatic, the majority present as proximal DVT involving the iliac and femoral veins. CT or MRI should be the imagiological methods used to diagnose this anomaly. No clear consensus has been reached on therapeutic strategy, other than long-term anticoagulation and elastic stockings.
Abstract Introduction: Traumatic popliteal artery injury is a rare clinical entity, but it is the most common cause of amputation in injured extremities. The aim of this study was to report the ...incidence of popliteal artery injury after knee trauma and report therapeutic management and results. Methods and material: ICD-10/ ICD-9 codes (S85.0/904.41; S83.1/836.5; S83.4; S83.5; S72,4/821.2; S82,1/823.0) were used to identify patients admitted with popliteal artery injury and/or knee trauma at our tertiary center from 1/1/2010 to 31/5/2021. A statistical analysis was realized using the SPSS program version27. Results: At our center from 1/1/2010 to 31/5/2021 535 patients were admitted due to knee trauma (28 with knee dislocation and 507 with fracture close to the knee) and 9 patients with popliteal artery injury (seven males, median age 39.0 years) The mechanism of PAI was motorcycle (4) or bicycle (1) or work (1) accidents (4); one fall, one running over and one iatrogenic injury. The incidence of PAI after knee trauma was 1.5%, after knee dislocation 17.9% and 0.8% after fracture close to the knee. Regarding associated injuries, four patients had severe soft tissue damage, two had venous injuries and two had nerve disruptions. The median ischemic time was 6.0 hours and mean vascular surgical time was 2.4 hours. Regarding vascular treatment, eight patients were submitted to bypass surgery and one was treated conservatively. Therapeutic fasciotomies were performed in three patients. No primary amputations were performed. A secondary major amputation was performed in one patient. The mean hospital length of stay was 24.9 days and mortality was 0%. Three patients returned to their normal activity level and six were limited in their daily activity. Discussion/Conclusion: The risk of PAI after knee dislocation is higher than after knee fracture (17,9% vs 0.8% in our study, and 3,4-8,2% vs 0,2 % in Swedish registration), so orthopedic surgeons must be aware of that increased risk, to avoid missing this diagnosis. The amputation rate in our serie was lesser than the Swedish registration and the United States National Trauma Data Bank (11% vs 28% and 14,5%, respectively). However, it´s still a high rate considering that it mostly affects a young and active population and only 33.3% patients return to a normal life. A multidisciplinary approach is essential to decrease ischemia time and to promote a holistic treatment.
The mechanisms and energetics of condensation reactions between carboxyl or hydroxyl groups of oxidized carbon nanotubes and silanol groups of a silica aerogel were unveiled in several catalytic ...conditions via density functional theory calculations. The silanol–carboxyl condensation follows one-step SN2@Si mechanisms, which involve a simultaneous nucleophilic attack by an O atom of the carboxyl group on the Si atom and transfer of a proton to a leaving silanol group, via a pentacoordinated-Si transition state. AAC2 nucleophilic acyl substitution routes are very unlikely given the rather high activation free energies predicted. Different possible protonation sites and proton transfer pathways were explored for the cationic SN2@Si mechanism. The silanol-hydroxyl reaction occurs via a single-step SN2@Si mechanism in neutral media and via a two-step mechanism in basic conditions. In both cases, the nucleophilic hydroxyl O atom attacks the Si atom and an H is transferred to a silanol group that leaves as water. The condensation reactions in neutral media (no catalyst) have high activation free energies and thus require high temperatures, with the silanol–carboxyl reaction being more favoured under these conditions. One-pot synthesis of silica aerogel-CNT composites in strongly acidic media promotes the condensation between the silanol and carboxyl moieties, although the process is a chemical equilibrium. This reaction becomes unfeasible in basic conditions, which preferentially catalyze silanol–hydroxyl reactions.
•Key features of organic–inorganic chemistry in silica aerogel-carbon nanotube composites unveiled.•▪ /COOH and ▪ / ▪ reactions investigated, for the first time, by quantum mechanics.•These reactions follow one or two-step SN2@Si mechanisms, rather than AAC2.•▪ /COOH condensation preferentially occurs in acidic media, and is an equilibrium.•Basic conditions favour ▪ / ▪ reactions while prohibiting ▪ /COOH condensation.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Two types of ORMOSIL-based composite systems have been studied by all-atom molecular dynamics simulations: (i) tetramethylorthosilicate (TMOS) and vinyltrimethoxysilane (VMTS) with ...polydimethylsiloxane (PDMS); and (ii) tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) or TEOS/(3-glycidyloxypropyl)trimethoxysilane (GLYMO) with the polyimides/polyamic acids of 3,3’,4,4’-biphenyltetracarboxylic dianydride – 4,4’-oxydianiline (BPDA-ODA) and pyromellitic dianhydride – 3,5-diaminobenzoic acid (PMDA-DBA). For systems (i) it was concluded that an increase in the %mol of PDMS leads to the formation of smaller aggregates of silica primary particles, which is explained by the reduction in the number of silica–silica H-bonds in favor of silica-PDMS H-bonds; both electrostatic and van der Waals interactions contribute significantly for the overall attractive forces between the two phases. In the case of systems (ii), the silica hydroxyl and amine groups form H-bonds with anhydride, carbonyl, carboxyl and terminal amine groups in the polyimides/polyamic acids, whereas for the TEOS/GLYMO the most prevalent H-bonds are those developed between hydroxyl silica groups and carboxyl or terminal amine groups of the polymer chains; in the latter composite systems, van der Waals forces play a more significant role in the adhesion between silica particles and the polymer.
Display omitted
•Molecular simulations of composite systems of organically modified silica aerogels with polydimethylsiloxane and polyimides.•Aggregation of silica particles highly correlated with the number of hydroxyl–hydroxyl H-bonds.•Increase in % mol of polydimethylsiloxane leads to rearrangement of H-bonds and to smaller aggregates.•Significant contributions of electrostatic and van der Waals forces for silica–polymer interactions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Bubble Sauter diameter, gas holdup and axial liquid velocity measurements are performed.•0.15 m, 0.4 m, 1 m and 3 m diameter bubble columns are investigated.•A wide experimental database is ...furnished to assist further model developments.•Void fraction and liquid velocities profiles happen to be self-similar in the heterogeneous regime.•The entrained liquid flow rate, proportional to D3/2, is only set by the column diameter.
The development of CFD models coupled with Population Balance is a very promising topic concerning multiphase reactors. In the case of bubbly flows and bubble columns, a serious lack of local hydrodynamic characterizations still harms development and validation of relevant models. To fill partially this gap, a new bubble size measurement technique, previously introduced by Maximiano Raimundo et al. (2016), has been applied on a very wide range of bubble column diameters (from 0.15 m to 3 m) and superficial gas velocities (from 0.06 m/s to 0.35 m/s). Size measurements have been coupled with others concerning gas holdup and axial liquid velocity, in order to provide an experimental database allowing to clarify the scale-up rules and to assist future modelling works. Average bubble sizes have been measured as globally similar at every scale. Measured holdup and average liquid velocity confirm already reported behaviours at lower column diameters. Liquid velocity fluctuations also follow self-similar radial profiles and are proportional to the average liquid velocity at the centre of the column leading to a strong turbulence intensity. The fact that the quantity (gD)1/2 appears as a natural velocity scale and the presence of strong gas-holdup gradients underline the similarity between bubble columns operated heterogeneous regime and free thermal convection in pipes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Molecular simulation has become an integral and invaluable part of Chemical Product Engineering, as it provides fundamental and indispensable insights for a rational product design. Silica aerogels ...are materials with exceptional properties and correspondingly broad applications whose study has benefited from this new paradigm. The complex physical/chemical phenomena involved in their synthesis are hard to explain with experimental data alone. This document reviews relevant atomistic studies regarding silica aerogels, highlighting their contributions to the understanding of the microscopic phenomena inherent to the sol–gel process. Quantum mechanics calculations have provided a framework for investigating the mechanisms, energetics, and products of silica precursor hydrolysis and condensation reactions. Classical molecular dynamics simulations have proven to be suitable for modeling the nanoscale porous network structure of the aerogels, allowing the reliable estimation of structural, mechanical, thermal, and surface properties. Coarse graining models have allowed the extension of these studies to the mesoscale.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Display omitted
•Primary particles of silica aerogels have been studied by DFT calculations.•Energetic analysis revealed the species most favoured thermodynamically.•Experimental and theoretical IR ...and 29Si-NMR data were analysed.•The most representative silica clusters were identified for each material.
The primary particles of silica aerogels resulting from three different mixtures of precursors – 50% tetramethylorthosilicate (TMOS)/50% vinyltrimethoxysilane (VMTS); 50% tetraethylorthosilicate (TEOS)/50% aminopropyltriethoxysilane and 50% TEOS/50% glycidylpropoxi – as well as aerogels of pure TMOS and VTMS, have been studied by quantum mechanics density functional theory calculations (DFT), at the B3LYP/6-311+G(d,p) level of theory). Thermo-chemical calculations have indicated that cage structures are the most favored for all materials, followed by other species (linear and cyclic) with high degrees of condensation. A vibration mode analysis based on a numerical model fitted to experimental infrared spectra, has allowed the identification of the most representative silica clusters for all the materials studied. The resulting theoretical spectra were close to their experimental counterparts. Analysis of calculated and experimental 29Si-NMR spectral data generally corroborated the derived model.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
