Charged Particle Trajectory Statistics and Deposition in a Turbulent Channel Flow

The statistical properties of charged particles and their wall deposition in a turbulent channel flow in the presence of an electrostatic field is studied in this paper. For a dilute concentration, the influence of small particles on the fluid motion is neglected. The instantaneous velocity field is generated by a direct numerical simulation of the Navier-Stokes equation via a pseudospectral method. The case in which each particle carries a single unit of charge and the case in which the particles have a saturation charge distribution are analyzed. Ensembles of 8192 particle trajectories are used for evaluating various statistics. Effects of size and electric field intensity on particle trajectory statistics and wall deposition rate are studied. RMS particle velocities and particle concentrations at different distances from the wall are evaluated and discussed. The results for deposition rates are compared with those obtained from empirical equations.     

Transport and Deposition of Angular Fibers in Turbulent Channel Flows

Transport and deposition of angular fibrous particles in turbulent channel flows were studied. The instantaneous fluid velocity field was generated by the direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudo-spectral method. An angular fibers was assumed to consist of two elongated ellipsoids attached at their tips. For a dilute suspension of fibers, a one-way coupling assumption was used in that the flow carries the fibers, but the coupling effect of the fiber on the flow was neglected. The particle equations of motion used included the hydrodynamic forces and torques, the shear-induced lift and the gravitational forces. The hydrodynamic interactions of the high aspect ratio linkage were assumed to be negligibly small. Euler's four parameters (quaternions) were used for describing the time evolution of fiber orientations. Ensembles of fiber trajectories and orientations in turbulent channel flows were generated and statistically analyzed. The results were compared with those for spherical particles and straight fibers and their differences were discussed. Effects of fiber size, aspect ratio, fiber angle, turbulence near wall eddies, and various forces were studied. The DNS predictions were compared with experimental data for straight fibers and a proposed empirical equation model.     

Efficient Degradation of a Biorecalcitrant Pollutant from Wastewater Using a Fluidized Catalyst-Bed Reactor

This study investigated the treatment of an azo dye, as a biorecalcitrant model, from industrial wastewater by using Cu/Mg/Al-chitosan in a fluidized catalyst-bed reactor. A number of variables were used to study the impact they had on the oxidation process involving azo dye. The maximum degradation of the azo dye was achieved at 7 g Cu/Mg/Al-chitosan. The chloride and sulfate ions had a synergistic effect on azo dye removal. The oxidation of the azo dye under the selected conditions was of pseudo-first-order. Textile wastewater could effectively be treated using a low concentration of about 7 g of Cu/Mg/Al-chitosan in a short hydraulic retention time of 10 min. The use of Cu/Mg/Al-chitosan demonstrated a promising method to eliminate the azo dye from the wastewater.     

Direct Numerical Simulation of Curly Fibers in Turbulent Channel Flow

Wall deposition of rigid-link fibrous aerosols in a turbulent channel flow is studied. The instantaneous turbulent velocity vector field is generated by the direct numerical simulation of the Navier-Stokes equation with the aid of a pseudospectral code. It is assumed that the fiber is composed of five rigidly attached ellipsoidal links. The dynamic behavior of these elongated and irregular shaped particles is markedly different from the spherical ones. The hydrodynamic forces and torques acting on the fiber are evaluated and the equations governing the translational and rotational motions of the fiber are analyzed. Euler's four parameters are used, and motions of fibrous particles in the turbulent channel flow field are studied. Ensembles of 8000 fiber trajectories are generated and are used for evaluating various statistics. Root mean-square fiber velocities and fiber concentrations at different distances from the wall are evaluated and discussed. Empirical models for the deposition rate of curly fibers are also developed. The model predictions are compared with the simulation data and good agreement is observed.     

Inter-particle heat transfer in a riser of gas-solid turbulent flows

Effects of the particle-particle heat transfer in a gas-solid turbulent flow in a riser were evaluated. An Eulerian/Lagrangian four-way interaction formulation including the particle collisions in conjunction with the k − τ and the k_θ − τ_θ model equations were used in the numerical simulation. Inter-particles and particle-wall interactions were accounted for with an inelastic collision model, where the restitution coefficient was evaluated for each collision. The special case when the flow initially contains two groups of hot and cold particles was treated in details. Particular attention was given to the nature of heat transfer to particles due to inter-particle interactions. The results showed that the effect of particle-particle heat transfer was more significant for smaller sizes, lower flow Reynolds numbers, and for higher loading ratios. Solid thermal properties, however, did not have a noticeable effect on the inter-particle heat transfer. The simulation results indicates that although the heat transferred to each group of hot and cold particles was significant, the mean values of gas and particle temperatures and suspension heat transfer was insensitive to the inter-particle heat transfer.     

Prediction of restrained shrinkage based on restraint factors in patching repair mortar

Shrinkage of repair material, especially in patching repairs, is the major factor inducing cracking in concrete repairs. Induced cracks in repair materials are due to restrained shrinkage. Although in usual practice, the free shrinkage of the repair mortar is measured, in reality, cracking is not due to free shrinkage. It is well known that cracking is due to restrained shrinkage. It is very hard to measure the restrained shrinkage; therefore, to overcome this problem a restraint factor (R) is used to modify the free shrinkage and come up with the restrained shrinkage. The restraint factor is influenced by the surface and boundary condition.In this study, the restraint factor for patching repair with different boundary conditions (with eaves and without eaves) and surface condition (rough and smooth) of the substrate concrete is investigated.The results show that the restraint factor R lies between 0.1 and 0.94; with an increase of restraint, the restraint factor is increased. In situations with a high level of restraint (eaves at the perimeter and a rough surface of substrate), the average R is 0.83. while with a low level of restraint (without eaves at the perimeter and a smooth surface of the substrate), the average R is 0.22.     

Influence of Interesterification of a Stearic Acid-Rich Spreadable Fat on Acute Metabolic Risk Factors

Chemical and enzymatic interesterification are used to create spreadable fats. However, a comparison between the two processes in terms of their acute metabolic effects has not yet been investigated. A randomised crossover study in obese (plasma TAG > 1.69 mmol/L, and BMI > 30 (BMI = kg/m²) or waist circumference > 102 cm, n = 11, age = 59.3 ± 1.8 years) and non-obese (plasma triacylglycerol (TAG) < 1.69 mmol/L, and BMI < 30  or waist circumference < 102 cm, n = 10, age = 55.8 ± 2.2 years) men was undertaken to compare the effects of chemical versus enzymatic interesterification on postprandial risk factors for type 2 diabetes (T2D) and cardiovascular disease (CVD). TAG, cholesterol, glucose, insulin and free fatty acid concentrations were measured for 6 h following consumption of 1 g fat/kg body mass of non-interesterified (NIE), chemically interesterified (CIE), enzymatically interesterified (EIE) stearic acid-rich fat spread or no fat, each with 50 g available carbohydrate from white bread. Interesterification did not affect postprandial glucose, insulin, free fatty acids or cholesterol (P > 0.05). Following ingestion of NIE, increases in serum oleic acid were observed, whereas both oleic and stearic acids were increased with CIE and EIE (P < 0.05). While postprandial TAG concentrations in non-obese subjects were not affected by fat treatment (P > 0.05), obese subjects had an 85% increase in TAGs with CIE versus NIE (P < 0.05). The differences in TAG response between non-obese and obese subjects suggest that interesterification may affect healthy individuals differently compared to those already at risk for T2D and/or CVD.     

Synthesis of Y(Al,Cr)O3 red pigments by co-precipitation method and their interactions with glazes

New red pigment based on the system YAl_1−yCr_yO₃ (y = 0.01–0.1) was synthesized by co-precipitation method. The precipitant was attained by mixing solutions of yttrium, aluminum and chromium nitrates, respectively, and addition of ammonia as the precipitator. The effects of chromium as dopant and glaze composition on the color shade of resulting pigments were studied. EDX analysis of the prepared pigment particles, which was embedded in glaze, showed the occurrence of reactions between some glaze constituents and pigment particles. Accordingly, a glaze which was enriched in Al₂O₃ and poor in ZnO was more suitable in point of achieving a reddish shade. The resulting pigments were characterized by using X-ray diffraction (XRD), SEM and UV–vis spectrophotometer.