•A model coupling fluid dynamics and electrochemistry of a VRFB is developed.•3D simulations are performed for 25 cm2 interdigitated and serpentine flow fields.•Serpentine flow field allows better ...performances with higher auxiliary consumption.•Interdigitated flow field shows reduced heterogeneity and reduced pressure drops.•Under-the-rib fluxes play a crucial role in determining performance and heterogeneity.
Homogeneous distribution of the electrolyte over the porous electrode is a critical issue hindering the commercialization of vanadium redox flow batteries, owing to increased overpotential at high current and limited power density of the system. Therefore, an understanding of the physical phenomena regulating mass transport of the electrolyte is crucial to improving system performance. The present work describes the development and experimental validation of a 3D computational fluid dynamic model of a vanadium redox flow battery in a half-cell configuration with an active area of 25 cm2. The model simulates the influence of a single serpentine and an interdigitated flow field. The adoption of the half-cell configuration allows the negative electrode to be considered as a pseudo-reference electrode with zero potential loss, leading to a reduction in computation time and the number of fitting parameters, which can be determined with reduced uncertainty. The developed model includes a traditional fluid dynamic analysis of the electrolyte in the flow field and in the porous electrode, coupled with the electrochemistry of the reactions involved. In both the experiments and the simulations, the single serpentine distributor exhibits better performance and higher pressure drops compared to those of the interdigitated geometry under all the investigated operating conditions. In the analysis of the local reaction rate, both distributors experienced increased reaction rates under the rib, induced by a by-pass flow between adjacent channels. The reaction rate shows a highly heterogeneous distribution in the serpentine geometry, while it is more uniform in the interdigitated configuration.
A CFD study is conducted in order to characterize the dynamic behavior of a Savonius vertical axis wind turbine. All simulations are executed using the open source code, OpenFOAM. Both ...two-dimensional and full three-dimensional cases have been investigated in order to provide a suitable tool for geometrical optimization of this rotor. Unsteady simulations are carried out at different tip speed ratio (TSR), varying angular speed of rotor at constant wind speed, using different one and two-equation URANS turbulence models and selecting the k−ω SST for the final analysis. The two-dimensional model was compared with experimental data available in literature and obtained from tests in wind tunnel. This simplified model shows an over-estimation of experimental data, reporting a maximum efficiency at TSR 1, 20% higher than experimental value. The results of 3D model are in good agreement with experiments with a peak of 0.202 at TSR 0.8 for a rotor with aspect ratio 1.1. The influence of the rotor height has been evaluated on flow dynamics of the turbine and its power coefficient.
•CFD study to characterise the dynamic behaviour of a Savonius vertical axis wind turbine.•URANS modeling approach with k-ω SST turbulence model in OpenFOAM code.•Analysis at different TSR and angular speed of rotor at constant wind speed.•Over-estimation of experimental data with 2D approach, good agreement with 3D approach.•Evaluation of influence of the rotor height on fluid dynamics and power coefficient.
This work focuses on Savonius turbine numerical modeling and mutual turbine interaction in a linear array farm. Two-dimensional Computational Fluid Dynamics modeling was carried out using the open ...source solver OpenFOAM. Results are compared with available experimental data and three-dimensional CFD modeling. The influence of main parameters, such as the distance between adjacent turbines, the wind incidence angle and the number of turbines is investigated and the linear array efficiency is defined. The obtained results show a performance increase as the distance between the turbines reduces, higher efficiency for small wind incidence angles, and a larger number of turbines.
•CFD study to characterise the interaction effect between multiple Savonius turbines.•URANS modeling approach with k-omega SST turbulence model in OpenFOAM code.•Analysis at different distance between rotors and the number of turbines.•Increase in performance with the reduction of the distance between rotors.•Influence of wind incident direction and number of turbines on the array performance.
Abstract
The fluid dynamics in large-diameter bubble columns can be described by an analytical relation between two global flow parameters, the drift flux and the gas holdup. This relation, named ...bubble column operating curve, builds on five flow regime transitions. In order to determine the variables influencing the flow regime transitions, a statistical approach was derived by coupling: (1) the ordinary least squares method (OLS) to determine the relationship between the variables, (2) the variance inflation factor (VIF) to check for multicollinearity issues, and (3) the least absolute shrinkage and selection operator (LASSO), to select suitable variables. It was found that the geometrical characteristics of the sparger strongly influence the flow regime transitions, and uniform aeration is essential for all the regimes to exist. Increasing the superficial liquid velocity in the counter-current mode destabilises the mono-dispersed and poly-dispersed homogeneous flow regimes. As for the aspect ratio, an increase in the column aspect ratio slightly destabilises the existing flow regimes. The statistical method identifies viscosity as the only significative variable concerning the liquid phase properties.
Earth-abundant and non-toxic Kesterite-based Cu
2
ZnSnS
4
(CZTS) thin film solar cells are successfully fabricated on flexible Molybdenum (Mo) foil substrates by an electrodeposition-annealing route. ...A well-adherent, densely packed, homogeneous, compact, and mirror-like CZT precursor is initially produced through electrodeposition by using a rotating working electrode. Subsequently, the co-electrodeposited CuZnSn (CZT) precursor is sulfurized in quartz tube furnace at 550 °C for 2 h in N
2
atmosphere with the presence of elemental sulfur in order to form CZTS. Different characterization techniques like XRD, SEM, HR-TEM, Raman, and Photoluminescence demonstrate that almost phase-pure CZTS formed after sulfurization. A flexible Al/Al-ZnO/i-ZnO/CdS/CZTS/Mo foil solar cell is produced, where CdS is deposited by chemical bath deposition and transparent conducting oxide (TCO) is deposited by DC sputtering. The CZTS solar device shows a 0.55% power conversion efficiency on flexible Mo foil substrate and it constitutes the first prototype of this kind of solar cell produced by electrodeposition-annealing route without any surface modification of the Mo substrate.
Graphic abstract
Novel iron(II) Schiff base type complexes of Fe(4-benzyl-2-hydroxy-propiophenone)
2
(o-phenylenediamine), Fe(ninhydrin)
2
(ethylenediamine), Fe(ninhydrin)
2
(1,2-propylenediamine), ...Fe(2,4,6-trihydroxy-benzyl-4-methoxyphenyl-ketone)
2
(ethylenediamine) and Fe(ninhydrin)
2
(1,3-propylenediamine) have been prepared by reaction of the components dissolved in ethanol at refluxing temperature in inert atmosphere, and were characterized by mass spectrometry (MS), infrared spectrometry (IR), thermal analysis, atomic force microscopy (AFM),
57
Fe Mössbauer spectroscopy, cyclic voltammetry and biological activity tests. Mössbauer spectroscopy revealed the dominant occurrence of high spin Fe
II
besides minor or no low spin Fe
II
in the complexes, and minor Fe
III
impurity phase. The cyclic voltammograms indicated peaks due to redox processes in certain complexes. In these cases the occurrence of low spin Fe
II
was also observed. Low biological activity was experienced for some compounds. The thermal decomposition process of all complexes was performed by TG–DTG–DTA analysis in air atmosphere aiming to understand the mechanism of the mass change with increasing temperature. The importance of the current research is to find correlation between the Fe spin states, redox processes and biological activity.
In this study we analyzed body composition in relation to cognitive and functional status, in a cross-sectional sample of patients with Alzheimer's disease (AD).
Seventy individuals (27 men, ...78.1±6.5years; 43 women, 80.4±5.6years) with mild–moderate stages of AD (clinical dementia ratings 1 and 2) were selected from the Alzheimer Center, SS. Trinità Hospital, ASL 8 of Cagliari (Italy). Cognitive and psycho-functional status was evaluated using mini-mental state examination (MMSE), activities of daily living (ADL) scale, and geriatric depression scale (GDS). Mini-nutritional assessment (MNA) was applied. Anthropometric measurements were taken and body mass index (BMI) was calculated. Body composition was assessed by means of specific bioelectrical impedance vector analysis (BIVA), using the references for the elderly. In comparison with the reference group, patients with AD showed similar BMI and MNA, but peculiar bioelectrical characteristics: lower phase angles and longer vectors (p<0.05). According to specific BIVA, this bioelectrical pattern is indicative of a reduction of lean tissue mass and an increase of percent fat mass (FM%). A more accentuated lean mass reduction (p < 0.05) was observed in women with worse cognitive status and a FM% increase (p < 0.01) in women with worse functional status.
In conclusion, patients with AD had lower lean tissue mass and higher percent fat mass than healthy elderly individuals. In women, this pattern was associated with cognitive and functional decline, as indicated by MMSE and ADL values. Specific BIVA showed to be a suitable technique in the elderly, that could enhance BMI and MNA information in the evaluation of nutritional status.
•Patients with AD showed normal BMI but peculiar bioelectrical characteristics.•Bioelectrical peculiarities were: low phase angles and long specific vectors.•This pattern is indicative of decreased lean tissue mass and increased FM%.•This pattern was associated with cognitive and functional decline.•Specific BIVA represents a useful technique for assessing body composition in AD.
Objectives
Analysis of variations of nutritional status in relation to psycho-functional conditions in elderly patients with mild to moderate Alzheimer’s disease (AD) by means of bioelectrical ...impedance vector analysis (BIVA).
Design
Cross-sectional study. Setting: Alzheimer Center, SS. Trinità Hospital, Cagliari (Italy).
Participants
83 free-living patients (29 men, 54 women) with mild-moderate Alzheimer’s disease, aged 66 to 96 years, and 91 age-matched controls (37 men and 54 women).
Measurements
Nutritional status was evaluated by anthropometry (weight, height, waist and upper arm circumferences, triceps skinfold; body mass index, BMI; arm muscle area, AMA); Mini Nutritional Assessment, MNA®; bioelectrical impedance vector analysis, BIVA. Psycho-functional status was assessed by the Mini Mental State Examination (MMSE), Geriatric Depression Scale (GDS), Activities of Daily Living (ADL), and Instrumental Activities of Daily Living (IADL).
Results
Compared to the control groups, patients with Alzheimer’s disease had a worse psycho-functional and nutritional status. BIVA detected lower body cell mass in Alzheimer’s patients with respect to controls (men: T
2
= 23.4; women: T
2
=27.3; p<0.01), as well as in the female patients with lower levels of IADL and MMSE (respectively, T
2
= 8.0; T
2
=7.4; p<0.05). In patients with AD, a worse psycho-functional status was associated with obesity.
Conclusion
The psycho-functional decline of patients with AD is related to body composition variations, with a relative increase of fat mass with respect to the muscle component. The BIVA technique distinguished patients from controls and patients with different levels of cognitive decline. Therefore, it is a suitable tool for the screening and monitoring of nutritional status in Alzheimer’s disease.
The deposition of undoped, aluminum and/or holmium doped and co-doped zinc oxide thin films on different substrates was achieved using a very simple and versatile aqueous solution method. The effect ...of the precursor solution concentration on the morphological and structural characteristics, as well as on the optical properties of the undoped ZnO thin films was also investigated. The AFM investigations have revealed that the morphology of the films is smooth and homogeneous. The room-temperature photoluminescence (PL) and the optical absorption (UV–vis) properties of the as-obtained undoped and doped ZnO thin films were investigated, as well. A strong UV emission (380nm) was recorded for the undoped, aluminum and holmium doped and co-doped ZnO thin films. The band gap value obtained for the doped ZnO thin films is ranging between 3.01eV and 3.56eV, depending on the nature and the concentration of the dopant.
Objectives
This paper evaluates the nutritional status in patients with mild-moderate and severe Alzheimer’s disease (AD) by bioelectrical impedance vector analysis (BIVA).
Design
Cross-sectional ...study. Setting: Alzheimer Center, SS. Trinità Hospital, Cagliari, and “Monsignor Angioni” Nursing Home, Quartu Sant’Elena (Cagliari, Italy).
Participants
83 free-living patients with mild-moderate Alzheimer’s disease (29 men, 54 women), 9 institutionalized women in the severe stage; 468 age-matched controls (202 men, 266 women).
Measurements
Mini Nutritional Assessment (MNA), anthropometric (height, weight, BMI), bioelectrical (R, Xc) and biochemical variables (serum albumin) were assessed.
Results
Bioelectrical characteristics were significantly different in the patients with mild-moderate AD with respect to controls, indicating low body cell mass (men, T
2
= 12.8; women, T
2
=34.9; p<0.01). Women with severe AD showed low body cell mass and dehydration with respect to patients with mild-moderate AD (T
2
=17.1; p<0.01). The phase angle, R/H and Z/H were significantly correlated (p<0.05) with MNA (phase: r = 0.31; R/H: r =−0.37; Z/H: r =−0.37) and albumin (phase: r=0.47; R/H: r=−0.36; Z/H: r=−0.36).
Conclusion
Alzheimer’s disease is characterized by a tendency to malnutrition, present even in the mild-moderate stages, and a tendency to dehydration that appears in the severe stage. The BIVA technique is a promising tool for the screening and monitoring of nutrition and hydration status in Alzheimer’s disease.
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