Advanced PIV/LIF and shadowgraphy system to visualize flow structure in two-phase bubbly flows

Particle image velocimetry (PIV) is a promising technique to measure dispersed phase size, dispersed phase hold-up and velocity of both the phases. The current work reports measurement of the shape, size, velocity and acceleration of bubbles using shadowgraphy, and liquid velocity measurement obtained using PIV/LIF with fluorescent tracer particles. Measurements were performed in a narrow rectangular column at moderate gas hold-up (～5%) with wide variation of bubble sizes (0.1–15 mm). The liquid velocity field was subjected to 2D discrete wavelet transform (DWT) to visualize the flow structures in the bubbly flow. Further, the slip velocity of individual bubbles was obtained from the DWT filtered liquid velocity field. The results are compared with the slip velocity correlations reported in literature for single bubbles rising in quiescent water. The comparison shows the difference in slip velocity of single bubbles and bubbles rising in swarm. The scale wise decomposition obtained from DWT was also used to quantify the liquid velocity field in terms of wavenumber spectrum. The velocity and acceleration measurements are demonstrated on a single spherical cap bubble rising in quiescent water. The measurements show the potential of the 2D acceleration measurement to facilitate the estimation of unsteady drag on bubbles.     

Chemical deposition of CuInSe2 thin films by photoelectrochemical applications

Copper indium diselenide films have been synthesized by chemical bath deposition method. The configuration of fabricated cell is n-CuInSe₂|NaOH (1 M) + S (1 M) + Na₂S (1 M)|C_(graphite). The photoelectrochemical cell characterization of the films is carried out by studying current-voltage characteristics in dark, capacitance-voltage in dark, barrier height measurements, power output, photoresponse and spectral response. The study shows that CuInSe₂ thin films are n-type conductivity. The junction ideality factor is found to be 3.81. The flat band potential is found to be 0.763 V. The barrier height value is found to be 0.232 eV. The study of power output characteristic shows open circuit voltage, short circuit current, fill factor and efficiency are found to be 310 mV, 20 μA, 42.12% and 0.82%, respectively. Photoresponse shows lighted ideality factor which is 2.92. Spectral response shows the maximum current observed at 650 nm.     

Modeling of fluid–structure interactions with the space–time finite elements: contact problems

Fluid–structure interaction computations based on interface-tracking (moving-mesh) techniques are often hindered if the structural surfaces come in contact with each other. As the distance between two structural surfaces tends to zero, the fluid mesh in between distorts severely and eventually becomes invalid. Our objective is to develop a technique for modeling problems where the contacting structural surfaces would otherwise inhibit flow modeling or even fluid-mesh update. In this paper, we present our contact tracking technique that detects impending contact and maintains a minimum distance between the contacting structural surfaces. Our Surface-Edge-Node Contact Tracking (SENCT) technique conducts a topologically hierarchical search to detect contact between each node and the elements (“surfaces”), edges and other nodes. To keep the contacting surfaces apart by a small distance, we apply to the contacted nodes penalty forces in SENCT-Force (SENCT-F) and displacement restrictions in SENCT-Displacement (SENCT-D). By keeping a minimum distance between the contacting surfaces, we are able to update the fluid mesh in between and model the flow accurately.     

Swelling behavior of hyaluronic acid gels

Hyaluronic acid is a naturally occurring mucopolysaccharide. It is an important component of the intercellular matrix. It controls the permeability of tissues by means of the highly entangled network which can be formed because of its high molecular weight. To be able to use hyaluronic acid for several biomedical applications it is necessary to have an understanding of its swelling properties. Equilibrium swelling properties of hyaluronic acid gels were investigated by varying the temperature, pH, ionic strength, and composition of the surrounding solution. Swelling was found to depend on pH and ionic strength and to be reversible. The gel was highly swollen at high pH, but it shrank continuously as the pH was lowered to 10% of its maximum volume. The gel was comparatively insensitive to temperature. Drying affected the swelling capacity of the gel significantly. Gel swelling was also affected by a high concentration of acetone or propyl alcohol in the aqueous swelling solutions.     

Release of volatiles from the pyrolysis of a Victorian lignite at elevated pressures

A Loy Yang lignite sample was pyrolysed in a wire-mesh reactor at pressures from 1 to 61 bar. The char yield did not show considerable sensitivity to changes in pressure or heating rate and was mainly a function of temperature. However, the tar yield was sensitive to changes in pressure, holding time and heating rate. The tar yield at 1000 K s⁻¹ showed a minimum at around 6-11 bar. The tar yield at 1 K s⁻¹ increased slightly with increasing pressure from 1 to 20 bar. The UV-fluorescence spectroscopy of the tar samples indicated that the release of larger (three or more fused rings) aromatic ring systems was also greatly affected by increases in pressure. It is believed that increases in pressure have slowed down the bulk diffusion within meso- and macro-pores in the pyrolysing lignite/char particles. During the extended stay within the char particle, volatile precursors were thermally cracked to form mainly gaseous species as well as very small amounts of char. At very high pressures where the diffusion was very slow, the formation of light gases caused the pressure to build up within the particles, inducing the forced flow of volatile precursors out of the particles and leading to increased tar yield.     

Legume‐based fermented foods: Their preparation and nutritional quality

Legume‐based fermented foods are very popular in the Southeast Asia, the Near East, and parts of Africa. They form an appreciable part of daily diet of people as a main source of protein, calories, and certain vitamins. Preparation of legume‐based fermented foods has remained to some extent an art, and their nutritional quality has been of interest to both professionals and layman. The fermentation process helps not only in improving the organoleptic quality of legumes but also enhances nutritional quality. This review examines the production of various legume‐based fermented foods and critically assesses their nutritional quality.     

Effects of processing and storage on walnut (Juglans regia L) tannins

Walnut tannins were maximally extracted with absolute methanol and an extraction time of 60 min. Storage (21 days at 25 °C) significantly reduced (20–40% reduction) the assayable tannin content in walnuts. The ranges of tannin content in freshly cracked inshell and shelled walnuts were respectively 372–1095 and 363–667 mg catechin equivalent per 100 g dry weight. The assayable tannin content in inshell and shelled walnuts was 10–20% higher when the particle size was reduced from 2‐ to 8‐mesh. Using 0.5 as compared to 2% (w/v) vanillin as colour development reagent yielded 15–20% higher assayable tannin contents. The assay colour development reached a maximum after 20 min of incubation at 25 °C. Roasting (204 °C for 5 min) caused a small (14%) but significant reduction in assayable tannins. Soaking in aqueous alkali solutions was more effective (44–100% reduction) than soaking in aqueous acid solutions (6–76% reduction) in decreasing the assayable tannin content in walnuts. Microwave heating in distilled deionised water resulted in 93–98% reduction in walnut assayable tannins. Blanching at 100 °C for 2 min was as effective as alkali soaking in significantly reducing the amount of extractable walnut tannins (98% reduction). The tannin content in blanched walnuts was positively related to astringency scores (r = 0.92). © 2001 Society of Chemical Industry     

Structural, dielectric and multiferroic properties of Er and La substituted BiFeO3 ceramics

Erbium (Er) and lanthanum (La) substituted BiFeO₃ (BFO) ceramics have been prepared through conventional solid solution route. X-ray diffraction data indicated a gradual phase transition from rhombohedral to monoclinic structure in Bi_0·9?x La_0·1Er _x FeO₃ (x = 0·05, 0·07 and 0·1) (BLEFO _{x = 0·05, 0·07, 0·1}) ceramics. Differential thermal analysis (DTA) measurements of BFO samples showed a ferroelectric transition at 835°C, whereas it is shifted to 792°C for BLEFO _{x = 0·1}. The Raman spectra of BLEFO _{x = 0·05, 0·07, 0·1} samples showed the shift of Raman modes to higher wavenumbers and suppression of A₁ modes indicating decrease in ferroelectricity. The Raman spectra also indicated the structural transformation due to Er and La substitution in BFO. On subsequent erbium doping, the intrinsic dielectric constant is found to decrease from 68 (for pure BFO) to 52 for BLEFO _{x = 0·05} to 43 for BLEFO _{x = 0·07} but increased to 89 for BLEFO _{x = 0·1} when compared to pure BFO. The increase in Er content resulted in the increase in spontaneous magnetization (0·1178 emu/g at 8T for BLEFO _{x = 0·1}) due to collapse of spin cycloid structure. Ferroelectric remnant polarization of BLEFO _{x = 0·05} and BLEFO _{x = 0·07} decreases when compared to pure BFO while small remnant polarization (close to paraelectric behaviour) is evident for BLEFO _{x = 0·1}.     

Electrical resistance tomography-assisted analysis of dispersed phase hold-up in a gas-inducing mechanically stirred vessel

Tomographic analysis of the hydrodynamic attributes of the gas–liquid–solid mixing in a 1-l capacity stirred-tank equipped with a 4-blade gas-entrainment impeller has been used to obtain the dispersed phase hold-up distribution as a function of stirring speed (impeller Reynolds Number, Re_I) and solid particle loading. Although the liquid phase stirring was turbulent, both gas and solid flows went through different hydrodynamic regimes and experienced radial hold-up gradient over the range of impeller speed employed. Global solid phase hold-up profile exhibited a sigmoid-shape with respect to the impeller Reynolds number indicative of three solid suspension regimes across the stirring range (1.0≤Re_I≤6.25×10⁴) investigated. The solid phase hold-up distribution was adequately captured by, ε_s=ε_s,max[1−exp(−τ_sppRe_I)]^γ with ε_s,max and γ dependent on solid loading. An analogous expression was also obtained for the radial solid phase hold-up distribution and has enabled the proposition of a criterion for existence of radial transport gradient in gas-induced stirred tanks (GIST). Additionally, correlations for estimating the mixing time and power number for gas-induced mechanical agitators also gave good agreement with the empirical data.     

Behavior of dual ion beam sputtered MgZnO thin films for different oxygen partial pressure

Mg-doped ZnO (MgZnO) films were grown on p-Si (001) substrates by dual ion beam sputtering deposition system at a constant growth temperature of 600 °C for different oxygen partial pressure. The impact of oxygen partial pressure on the structural, electrical, elemental and morphological properties was thoroughly investigated. X-ray diffraction (XRD) spectra revealed that the deposited MgZnO films were polycrystalline in nature with preferred (002) crystal orientation. The peak of MgZnO (101) plane was reduced significantly as oxygen partial pressure was increased and disappeared completely at 80 and 100 % O₂. The maximum electron concentration was evaluated to be 5.79 × 10¹⁸ cm^?3 with resistivity of 0.116 Ω cm and electron mobility of 9.306 cm²/V s at room temperature, for MgZnO film grown with 20 % O₂. Raman spectra shows a broad peak at 434 cm^?1 corresponded to E ₂ ^high phonons mode of MgZnO wurtzite structure. The peak at 560 cm^?1 corresponded to the E₁ (LO) mode and was associated with oxygen deficiency in MgZnO films. Raman intensity at 560 cm^?1 reduced, on increasing oxygen partial pressure. A correlation between structural, electrical, elemental and morphological properties with oxygen partial pressure was also established.