CFD modelling for a TiO2-coated glass-bead photoreactor irradiated by optical fibres: Photocatalytic degradation of oxalic acid

Computational fluid dynamics coupled with the radiant transport equation was used to simulate oxalic acid photodegradation in a TiO₂-coated glass-bead photoreactor irradiated by end-emitting optical fibre (EEOF) or side-emitting optical fibre (SEOF) bundles. Light irradiance distributions in the photoreactor were modelled for specular, partially specular and diffusive reactor wall reflectivities with specularly reflective reactor walls best representing the experimental data. The light irradiance distribution for the SEOF bundle was found to be more uniform along the fibre length than for the EEOF bundle. Under the experimental radiant power input (108 mW) the EEOF and SEOF bundles exhibited similar oxalic acid photodegradation rates. However, the developed model demonstrated that at incident radiant power more than ten times greater than the experimental power used, a uniform light distribution gave faster oxalic acid photodegradation with the relative improvement of the SEOF bundle over the EEOF bundle increasing with increasing radiant power. This was attributed to increased electron-hole recombination in photocatalytic surfaces close to the EEOF tip, induced by the increased light irradiance in this region. The model also demonstrated a constant light irradiance profile along the length of a SEOF bundle giving an improved photocatalytic performance when compared to linear or exponentially decaying light profiles.     

Sucrose-nitrate auto combustion synthesis of Ce0.85Ln0.10Sr0.05O2-δ (Ln = La and Gd) electrolytes for solid oxide fuel cells

Nanocrystalline powders of co-doped ceria oxides Ce_0.85La_0.10Sr_0.05O_2-δ (CLSO) and Ce_0.85Gda_0.10Sr_0.05O_2-δ (CGSO) have been synthesized by auto combustion method at 100°C using sucrose as fuel. Thermal analysis (TGA/DSC) of as-prepared powders indicated calcination above 400°C to remove organic residue. The average grain size of the pellets sintered at 1200°C for 4 hours is 436 and 683 nm for CLSO and CGSO, respectively. The electrical conductivity of the sintered samples was determined by impedance measurements in the temperature range 300°C to 600°C and the frequency range 20 Hz to 2 MHz. At 600°C, the total electrical conductivity (σ_t) of CGSO is 6.78 × 10⁻³ S cm⁻¹, 2.5 times higher than 2.72 × 10⁻³ S cm⁻¹ of CLSO. Further, it is found that the value of grain boundaries blocking factor (α_gb) of CGSO is 0.47 which is 30% lesser than 0.68 of CLSO at 600°C. The higher value of electrical conductivity of CGSO as compared to CLSO is attributed to the lesser blocking effect of grain boundaries, smaller lattice distortion and denser microstructure of CGSO as compared to CLSO. The electrical conductivity of synthesized samples has been compared with the electrical conductivity of similar compositions of co-doped CeO₂ oxides. Our study indicated that the sintering temperature, and hence, the morphology of sintered samples has a significant role in determining the electrical conductivity. The presence of oxygen vacancies in the synthesized samples is experimentally supported by using UV-visible spectroscopy, Raman spectroscopy, and thermal analysis techniques.     

Dynamic tank in series modeling of direct internal reforming SOFC

A dynamic tank in series reactor model of a direct internally reforming solid oxide fuel cell is presented and validated using experimental data as well as a computational fluid dynamics (CFD) model for the spatial profiles. The effect of the flow distribution pattern at the inlet manifold on the cell performance is studied with this model. The tank in series reactor model provides a reasonable understanding of the spatio‐temporal distribution of the key parameters at a much lesser computational cost when compared to CFD methods. The predicted V–I curves agree well with the experimental data at different inlet flows and temperatures, with a difference of less than ±1.5%. In addition, comparison of the steady‐state results with two‐dimensional contours from a CFD model demonstrates the success of the adopted approach of adjusting the flow distribution pattern at the inlet boundaries of different continuous stirred tank reactor compartments. The spatial variation of the temperature of the PEN structure is captured along with the distributions of the current density and the anode activation over‐potential that strongly related to the temperature as well as the species molar fractions. It is found that, under the influence of the flow distribution pattern and reaction rates, the dynamic responses to step changes in voltage (from 0.819 to 0.84 V), fuel flow (15%) and temperature changes (30 °C), on anode side and on cathode side, highly depend on the spatial locations in the cell. In general, the inlet points attain steady state rapidly compared to other regions. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation of column studies using Cynodon dactylon plant‐mediated amino‐grouped silica‐layered magnetic nanoadsorbent to remove noxious hexavalent chromium metal ions

Magnetic nanoparticles are desirable adsorbents because of their unique superparamagnetic nature with the enhanced binding specificity and surface material interaction. The above unique features attract researchers to use it for wider applications. Herein, the study focuses on the amino‐induced silica‐layered magnetic nanoparticles amalgamated with plant‐extracted products of Cynodon dactylon in order to turn them into a potent adsorbing material in a continuous column set up for the elimination of noxiously distributed Cr(VI) ionsin the effluents. The selected plant‐mediated magnetite nanoadsorbent, which was used in the fixed column studies, is optimised with the attributes of inlet concentration, adsorbent bed depth, and flow rate. Thomas, Yoon‐Nelson and bed depth model showed the best experimental fit. Breakthrough adsorption time was reported for the various inlet concentrations of 100, 200 and 300 mg/L, adsorbent bed depths 2, 3 and 4 cm and volumetric flow rates of 4, 5 and 6 mL/min. The breakthrough point evaluated for the optimised attribute of inlet concentration of 100 mg/L, packed adsorbent depth 4 cm and flow rate 4 mL/min was 1400 min and the maximum removal efficiency was 60.6%. A better insight of the adsorption of metal ions for large‐scale industrial effluents is provided.     

Experimental and parametric studies of Nd:YAG laser drilling on austenitic stainless steel

To ensure overall quality of a precision large-scale component, a tool condition monitoring (TCM) technique for multi-step form milling is presented. The form milling of fir tree slots for a steam turbine rotor is an appropriate example that requires a fine surface finish and high dimensional accuracy. Therefore, we propose a novel TCM system based on a multi-sensor fusion strategy which utilises the combination of spindle motor current and acoustic emission (AE) as well as adaptive thresholding for multiple manufacturing steps (roughing, semi-finishing and finishing). To investigate the tool deterioration process, tool longevity tests using a test piece are carried out for each step. With the aid of qualitative inspection, it is found that AE signals provide comprehensive tool state information regarding tool flank wear, crack propagation and severe adhesive wear. In addition, by intentionally adding a bundle of chips to the surface, bursts of AE of large amplitudes occur in finishing, which provides the possibility of discovering anomalous events related to surface quality. By careful consideration of such characteristics, provisional alert levels are determined using a two-dimensional diagram with respect to both sensors. The strategy is verified throughout the actual manufacturing processes of the rotors. The proposed TCM system shows not only an excellent ability to prevent catastrophic tool failure and surface irregularities in form milling but also acceptable expendability for various groove specifications.     

Photosynthetic Bioelectronic Sensors for Touch Perception,UV‐Detection,and Nanopower Generation: Toward Self‐Powered E‐Skins

Energy self‐sufficiency is an inspirational design feature of biological systems that fulfills sensory functions. Plants such as the “touch‐me‐not” and “Venus flytrap” not only sustain life by photosynthesis, but also execute specialized sensory responses to touch. Photosynthesis enables these organisms to sustainably harvest and expend energy, powering their sensory abilities. Photosynthesis therefore provides a promising model for self‐powered sensory devices like electronic skins (e‐skins). While the natural sensory abilities of human skin have been emulated in man‐made materials for advanced prosthetics and soft‐robotics, no previous e‐skin has incorporated phototransduction and photosensory functions that could extend the sensory abilities of human skin. A proof‐of‐concept bioelectronic device integrated with natural photosynthetic pigment‐proteins is presented that shows the ability to sense not only touch stimuli (down to 3000 Pa), but also low‐intensity ultraviolet radiation (down to 0.01 mW cm^‐2) and generate an electrical power of ≈260 nW cm^‐2. The scalability of this device is demonstrated through the fabrication of flexible, multipixel, bioelectronic sensors capable of touch registration and tracking. The polysensory abilities, energy self‐sufficiency, and additional nanopower generation exhibited by this bioelectronic system make it particularly promising for applications like smart e‐skins and wearable sensors, where the photogenerated power can enable remote data transmission.     

Focus-engineered coherent anti-Stokes Raman scattering microscopy: a numerical investigation

The coherent anti-Stokes Raman scattering (CARS) signal is calculated as a function of focal-field distributions with engineered phase jumps. We show that the focal fields in CARS microscopy can be shaped such that the signal from the bulk is suppressed in the forward detection mode. We present the field distributions that display enhanced sensitivity to vibrationally resonant object interfaces in the lateral dimension. The use of focus-engineered CARS provides a simple means to detect chemical edges against the strong background signals from the bulk.     

Growth and characterizations of dual ion beam sputtered CIGS thin films for photovoltaic applications

The growth of CIGS thin films on soda-lime glass substrates at different substrate temperatures by dual ion beam sputtering system in a single-step route from a single quaternary sputtering target with the composition of Cu (In_0.70 Ga_0.30) Se₂ was reported. The effects of the substrate temperature on structural, optical, morphological and electrical properties of CIGS films were investigated. Stoichiometry of one such film was investigated by X-ray photoelectron spectroscopy. All CIGS films had demonstrated a strong (112) orientation located at 2θ ~26.70^o, which indicated the chalcopyrite structure of films. The value of full-width at half-maximum of (112) peak was reduced from 0.58° to 0.19° and crystallite size was enlarged from 14.98 to 43.05 nm as growth temperature was increased from 100 to 400 °C. However, atomic force microscope results showed a smooth and uniform surface at lower growth temperature and the surface roughness was observed to increase with increasing growth temperature. Hall measurements exhibited the minimum film resistivity of 0.09 Ω cm with a hole concentration of 2.42 × 10¹⁸ cm^?3 and mobility of 28.60 cm² V^?1 s^?1 for CIGS film grown at 100 °C. Film absorption coefficient was found to enhance nominally from 1 × 10⁵ to 2.3 × 10⁵ cm^?1 with increasing growth temperature from 100 to 400 °C.     

Integration of Cynodon dactylon and Muraya koenigii plant extracts in amino‐functionalised silica‐coated magnetic nanoparticle as an effective sorbent for the removal of chromium(VI) metal pollutants

Immobilised magnetic nanoparticles are extensively used owing to their superparamagnetic nature, surface interaction, and binding specificity with the appropriate portentous substances. The present research focuses on the development of a portentous, robust carrier, which integrates the silica‐coated amino‐functionalised magnetic nanoparticle (AF‐MnP) with the plant extracts of Cynodon dactylon (L1) and Muraya koenigii (L2) for the stable and enhanced removal of hazardous hexavalent chromium pollutant in the wastewater. Vibrating sample magnetometer (M _s – 45 emu/g) determines the superparamagnetic properties; Fourier‐transform infrared spectroscopy determines the presence of functional groups such as NH₂, Si–O–Si, C=C; high‐resolution transmission electron microscopy, field emission scanning electron microscope and energy‐dispersive X‐ray spectroscopy determine the size of the green adsorbents in the range of 20 nm and the presence of elements such as Fe, N, and Si determines the efficacy of the synthesised silica‐coated AF‐MnP. The AF‐MnP‐L1 shows the maximum adsorption capacity of 34.7 mg/g of sorbent calculated from the Langmuir isotherm model and the process follows pseudo‐second‐order kinetics. After treatment, the adsorbents can be easily separated from the solution in the presence of an external magnetic field and are reused for nine cycles after acid treatment with the minimal loss of adsorption efficiency.     

Slag eye formation in single and dual bottom purged industrial steelmaking ladles

ABSTRACT

Argon gas is often injected from the bottom of the ladle during steel refining operations. The injected gas interacts with the liquid (metal and slag) bath and enhances the momentum, heat, and mass transfer rate in the melt. However, during these gas–liquid interactions, an opening of the slag layer called slag eye is formed, which exposes the molten metal surface to the atmosphere, which is generally undesirable. In the current work, a transient, three-dimensional mathematical model is used to study the turbulent gas–liquid interactions in single as well as dual bottom blown industrial steelmaking ladles. A Coupled Level Set Volume of Fluid (CLSVOF) model is used for tracking the steel-argon, steel-slag, and argon-slag interfaces, from which the slag-eye area has been predicted. It is found that the inlet gas purging rate, melt height, slag layer thickness, angular and radial positions of the gas inlets affect the slag opening area. Non-dimensional empirical correlations are proposed to predict the slag opening area in both single as well as dual purged ladles, using non-linear regression analysis.