Distribution of large biomass particles in a sand‐biomass fluidized bed: Experiments and modeling

The axial distribution of large biomass particles in bubbling fluidized beds comprised of sand and biomass is investigated in this study. The global and local pressure drop profiles are analyzed in mixtures fluidized at superficial gas velocities ranging from 0.2 to 1 m/s. In addition, the radioactive particle tracking technique is used to track the trajectory of a tracer mimicking the behavior of biomass particles in systems consisting of 2, 8, and 16% of biomass mass ratio. The effects of superficial gas velocity and the mixture composition on the mixing/segregation of the bed components are explored by analyzing the circulatory motion of the active tracer. Contrary to low fluidization velocity (U = 0.36 m/s), biomass circulation and distribution are enhanced at U = 0.64 m/s with increasing the load of biomass particles. The axial profile of volume fraction of biomass along the bed is modeled on the basis of the experimental findings. © 2014 American Institute of Chemical Engineers AIChE J, 60: 869–880, 2014     

Synthesis of Na-A and faujasitic zeolites from high silicon fly ash

High silicon fly ash (HSFA) utilized as a source of silicon in synthesizing of Na-A, -X and -Y zeolites through alkali fusion followed by hydrothermal treatment at 100 °C for 12 h. Various types of zeolites with different degrees of purity were prepared by changing Si/Al ratio of the reaction mixture from 1.6 to 3.0. In addition, exact boundaries of this ratio for synthesis of each zeolite type were determined. Furthermore, the effect of NaOH amount utilized in alkaline fusion step on crystalinity of samples investigated. The synthesized zeolites were characterized using various techniques including; XRD, TGA, FTIR, SEM and BET. The ion-exchange behaviors of zeolitic samples tested with Co²⁺. The obtained Na-X zeolite was crystaline, had a very high cation-exchange capability of 4.9 mequiv. g⁻¹ and possessed relatively high specific surface area of about 434 m² g⁻¹.     

Bubble rupture in a vibrated liquid under microgravity

The response of an air bubble surrounded by a liquid in a sealed cell submitted to vibrations was investigated experimentally under microgravity conditions and compared to experiments under normal gravity conditions. As in normal gravity [1], it was observed that the bubble split into smaller parts when the acceleration of the vibrations reached a threshold. This threshold in microgravity is substantially smaller than that in normal gravity. Experimental results are presented in terms of an acceleration based Bond number which has been found to characterize the bubble behaviour in the laboratory experiments [1].     

Ni-TiO2 nanocomposite coating with high resistance to corrosion and wear

Ni-TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO₂ nanoparticles to be codeposited. The influences of the TiO₂ nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were investigated. The composition of coatings was studied by using energy dispersive X-ray system (EDX). The wear behavior of the pure Ni and Ni-TiO₂ nanocomposite coatings were evaluated by a pin-on-disc tribometer. The corrosion performance of coatings in 0.5 M NaCl, 1 M NaOH and 1 M HNO₃ as corrosive solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods (EIS). The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO₂ nanoparticle content in the coating. With increasing of TiO₂ nanoparticle content in the coating, the polarization resistance increases, the corrosion current decreases and the corrosion potential shifts to more positive values.     

Structure,stability and permeation properties of NaA zeolite membranes for H2O/H2 and CH3OH/H2 separations

NaA zeolite membranes were synthesised in the secondary growth hydrothermal method based on the seeding of the inner surface of a ceramic α-alumina tube. The impacts of crystallisation time and zeolite precursor concentration (in H₂O) were investigated. The structure and stability of the prepared NaA zeolite membranes were also investigated with operating temperatures, times and pressures. The results indicate that the optimal synthesis gel molar composition was 3Na₂O: 2SiO₂: Al₂O₃: 200H₂O. This led to cubic-shaped NaA zeolite which showed good stability. The optimal NaA zeolite membrane had H₂O and CH₃OH fluxes of 2.77 and 0.19 kg/m²h, with H₂O/H₂ and CH₃OH/H₂ separation factors of ∞ and 0.09 at a temperature of 30 °C. The NaA zeolite membrane had high thermal stability, but poor separation performance at high temperature (240 °C). The results suggested that the H₂ permeation flux is significantly influenced by preferential adsorption of vapour in the NaA zeolite membrane.     

A study on the anticorrosion performance of the epoxy-polyamide nanocomposites containing ZnO nanoparticles

Epoxy nanocomposites were prepared using different loadings (2, 3.5, 5 and 6.5 wt%) of ZnO nanoparticles. Nanocomposites were applied on steel substrates. Samples were immersed in 3.5 wt% NaCl solution for 1344 h. Corrosion resistance of the coatings was studied by an electrochemical impedance spectroscopy (EIS). The effects of addition of nanoparticles on the mechanical properties of the epoxy coating were studied by a dynamic mechanical thermal analysis (DMTA). Curing behavior of the coatings containing nanoparticles was studied by a differential scanning calorimeter (DSC). Atomic force microscope (AFM) was utilized to investigate the surface topography and surface morphology of the coatings. Coating resistance against hydrolytic degradation was studied by FTIR (Fourier Transform Infrared).Results showed that addition of low loadings of nanoparticles can increase T_g of the composite. Decrease in T_g and cross-linking density of the coating were observed at high loadings of nanoparticles. It was found that nanoparticles can influence the curing behavior of the epoxy coating. Nanoparticles improved the corrosion resistance of the epoxy coating. Increase in coating resistance against hydrolytic degradation was obtained using nanoparticles.     

The effect of MIO pigments on corrosion resistance and adhesion of synthetic rubber-based primer

In this research, the corrosion resistance and adhesion property of a synthetic rubber-based primer reinforced with different ratios of micaceous iron oxide (MIO) pigments were studied. Coatings were applied on carbon steel panels and also on steel pipes of 219.1 mm outer diameter. Scanning electron microscopy (SEM) was used to investigate the dispersion of MIO particles in the rubbery matrix. The anticorrosion performance of the coatings was studied, using electrochemical impedance spectroscopy (EIS) and salt spray tests. In addition, the adhesion of primers to carbon steel substrates was evaluated by pull-off test. In order to investigate the effect of MIO particles on the flexibility of the pigmented primers, a cupping test was conducted. The adhesion of cold-applied tape to the formulated primers was assessed by peel adhesion test using hanging mass method. The results indicated that adding 5, 10, and 15 wt% of MIO pigments into the primer improved corrosion resistance of the coatings. An increase in the MIO loading up to 10 wt%, improved the adhesion of the primer to both steel substrate and cold-applied tape.     

1-D coupled non-equilibrium sediment transport modeling for unsteady flows in the discontinuous Galerkin framework

A high-resolution,1-D numerical model has been developed in the discontinuous Galerkin framework to simulate 1-D flow behavior,sediment transport,and morphological evaluation under unsteady flow conditions.The flow and sediment concentration variables are computed based on the one-dimensional shallow water flow equations,while empirical equations are used for entrainment and deposition processes.The sediment transport model includes the bed load and suspended load components.New formulations for Harten-Lax-van Leer(HLL) and Harten-Lax-van Contact(HLLC) are presented for shallow water flow equations that include the bed load and suspended load fluxes.The computational results for the flow and morphological changes after two dam break events are compared with the physical model tests.Results show that the modified HLL and HLLC formulations are robust and can accurately predict morphological changes in highly unsteady flows.     

A new efficient shear deformation theory for FG plates with in-plane and through-thickness stiffness variations using isogeometric approach

In this paper, a new efficient hyperbolic shear deformation theory is presented for the static, free vibration, and buckling analysis of functionally graded plates by using the isogeometric analysis (IGA) approach. The IGA approach can easily formulate C¹ continuous elements by the use of Non-Uniform Rational B-Spline (NURBS) functions. Higher-order shear deformation theory satisfies free shear stress conditions on the top and bottom surfaces of plate and so a shear correction factor is not needed. Equations are derived based on physical neutral surface position. FG plates with in-plane and through-thickness stiffness variations are studied and the obtained results are compared with each other. The results of the present hyperbolic model compared with those of other hyperbolic models, show the efficiency of the present model. Furthermore, the results show that the direction of material gradient and type of gradient have significant effects on the behavior of FG plates, especially in buckling analysis.     

Synthesis and preliminary gas permeation studies of a tubular NaA zeolite membrane (NZM)

Different from traditional seeded method, NaA zeolite membranes (NZMs) were prepared by in situ synthesis onto the inner side of porous α-alumina tubular supports in a hydrothermal synthesis reactor. The influences of pretreatment of porous tubular support, temperature, time, and synthetic cycle for the synthesis of the zeolite membranes were investigated. The operating conditions were optimized. Characterization of the membranes by scanning electron microscopy and X-ray diffraction showed that the crystalline materials on the inner surface of the porous α-alumina tubes were NaA-type zeolite. Single- and binary-gas permeation tests were conducted. Single-component permeabilities of hydrogen and nitrogen through the NZM changed slightly when the transmembrane pressure difference varied from 80 to 420?kPa. Its selectivity for H₂ relative to N₂ was about 5.3, which was greater than that of the Knudsen diffusion. The separation factors of binary gases H₂/N₂ and H₂/CO₂ at 473?K were 3.9 and 5.7, respectively, again exceeding the Knudsen diffusion level. The separation of binary gases suggests that the NaA-type zeolite membranes on α-alumina substrate were defect free and able to provide molecular sieving. The results demonstrate that the unseeded synthetic method presented in this work is successful and reliable.