Spontaneous structures in three-dimensional bubbling gas-fluidized bed by parallel DEM-CFD coupling simulation

Flow structures induced by bubbles formed in three-dimensional shallow rectangular gas-fluidized beds are investigated by the DEM-CFD coupling simulation. A numerical code is parallelized and more than 4.5million particles are tracked in the maximum by using 16 CPUs. To investigate the domain-size dependency, the cross-sectional area of beds is enlarged by the factors up to 8² and the results are compared. Under the ideal uniform inflow condition, multiple bubbles are spontaneously formed in large cross-section cases. The dependency of bubble size on the cross-section size is not so clear under the same bed height condition. Clear circulation patterns are observed in the time-averaged data. Down-flows of particles exist in low void fraction portions selectively with particle up-flows dominating in the high void fraction regions. Three-dimensional visualization of bubble shape is also conducted. Bubbles that have complex structures such as worm-like one exist in addition to the conventional spherical cap.     

Investigation of recycled gypsum in conjunction with waste plastic trays for ground improvement

During the three stages of production, construction and demolition, approximately 15 million tons of gypsum waste plasterboard is generated annually in the world. It is considered a serious problem due to scarcity of land-filling space, increasing the cost of disposal and increasing environmental regulations. Investigations of using recycled gypsum “bassanite” which is derived from gypsum waste plasterboard and waste plastic trays for ground improvement were studied. Recycled gypsum was used as a stabilizing agent to improve the compressive strength while the waste plastic trays were used to improve the tensile strength. Recycled gypsum content, curing time and frost heave property throughout capillary rise test were investigated to determine the behavior of treated soil with recycled gypsum. In addition, size, content and aspect ratio of strips of waste plastic trays were investigated. Test results showed that increasing recycled gypsum content has a more significant effect on compressive strength compared to the tensile strength. The effect of curing time on the strength of treated soil samples with recycled gypsum is much pronounced in the early curing days compared to later ages. Adding strips of waste plastic trays to samples treated with recycled gypsum enhanced both splitting tensile and compressive strengths as well increased the value of secant modulus. Capillary rise rate was reduced with the increase of recycled gypsum content, which helps to reduce the formation of ice lenses; hence the susceptibility of treated soil against frost heave is increased. The size and content of strips of waste plastic trays have significant effect on the potential of capillary rise and the enhancement of strength and stiffness of tested soil.     

Adsorption Effects on the Rheological Properties of Aqueous Alumina Suspensions with Polyelectrolyte

The influence of adsorption coverage and free polymer on the rheological properties of aqueous alumina suspensions with polyelectrolyte was studied. The flow curves of the suspensions followed the Casson model very well in the observed range of shear rate. The Casson yield value, τ_c, was used to evaluate the stability. The coverage exerted a profound influence on the rheological properties by affecting the interaction between particles. The zeta potential increased and the value of τ_c decreased as the coverage increased. The free polymer could cause weak flocculation as its concentration was increased to a certain level. The opposite effects of the adsorbed polymer and free polymer on stability resulted in the presence of optimum coverage for stabilization. The concentration of free polymer increased rapidly as the adsorption coverage approached the saturation limit, and then the free polymer started to dominate the stability. Stabilization could be achieved at a condition of unsaturated adsorption and was related to the non-high-affinity adsorption at alkaline pH (9.2). The impact of adsorption affinity on stability was discussed.     

Phase relations in an Fe-Cr-S system at temperatures of 1073 and 1173 K in the sulfur pressure range from 100 to 10−5 Pa

Phase relations and stability fields in the Fe-Cr-S system were investigated at 1073 and 1173 K in the sulfur pressure range 10⁰–10^–5 Pa. The sulfides, produced by the sulfidation-annealing process of Fe-Cr alloys followed by rapid quenching, were characterized using X-ray diffraction powder analysis at room temperature. The Cr₃S₄ in the Cr-S system extends beyond the FeCr₂S₄ stoichiometry in the Fe-Cr-S ternary system at intermediate sulfur pressures. The spinel-monoclinic transition of the FeCr₂S₄ was observed at sulfur pressures of 10^–3–10^–3.5Pa at 1073 K and at 10⁰–10^–0.5 Pa at 1173 K. The free energy change for formation of the spinel, FeCr₂S₄, from a monoclinic (Cr, Fe)₃S_4–y, hexagonal (Fe, Cr)_1–xS, and sulfur vapor is given by the relation G = –1523 + 1.09 T (kJ/mol). The phase-transition mechanism of FeCr₂S₄ is discussed on the basis of an enhancement of the cation coordination numbers from 4-6-6 for the spinel to 6-6-6 for the monoclinic, when the sulfur partial pressure decreases.Emeritus Professor.     

Effect of electron beam radiation on the performance of biodegradable Bionolle-jute composite

To study the radiation effect on the physical, thermal, mechanical and degradable properties of biodegradable polymer Bionolle (chemosynthetic polyester poly(1,4-butylene succinate)), Bionolle films prepared by compression molding process and were irradiated with electron beam (EB) radiation of different doses. Gel content was found to increase with increase of radiation dose. Tensile strength of Bionolle was enhanced when Bionolle film was exposed under 20 kGy radiation. The loss of tensile strength of both unirradiated and irradiated Bionolle is 70% and 8% due to thermal aging at 70°C for 30 days. Both irradiated and unirradiated films of Bionolle were subjected to different degradation test in compost (soil burial), enzyme and storage degradation both in outdoor and indoors conditions. The loss of weight due to soil (compost) degradation test decreased with increase of radiation dose. The loss of weights of irradiated samples were found to be very less within the first three months of compost degradation. After 120 days, tensile strength of the Bionolle films irradiated at 20 kGy and 100 kGy were 68 MPa and 40 MPa, respectively, compared to the value (30 MPa) of the unirradiated Bionolle samples. Loss of tensile strength of irradiated Bionolle due to storage degradation like in roof, ground and indoors was minimum compared to unirradiated Bionolle. The weight loss due to enzymatic degradation was found to be decreased with increase of radiation dose. The tensile strength of jute reinforced Bionolle composites (23 wt.-% jute content) irradiated at 20 kGy was found to be higher (22%) than that of an unirradiated composite.     

Hydrogel coating of RVNRL film by electron‐beam irradiation

The tackiness properties of radiation‐vulcanized natural rubber latex (RVNRL) film surfaces coated by various monomers were investigated in order to define the suitable hydrogels which reduce the tackiness of the film. In this context, different types of monomers, namely, N‐vinyl‐2‐pyrrolidone (NVP), N,N‐dimethylaminoethylamide (DMAEA), acrylic acid (AAc), n‐butyl acrylate (n‐BA), and 2‐hydroxyethyl methacrylate (HEMA) as well as the monomer mixtures were tried with varying degrees of success. Coating the RVNRL film with 80% HEMA/20% n‐BA by irradiation at 80 kGy using a low‐energy electron beam gave a remarkable reduction in the surface tackiness of the RVNRL film. Several other attempts were made such as priming the RVNRL film with acid and aluminum sulfate prior to coating, mixing the aluminum sulfate into the monomer mixtures, and dipping the partially wet RVNRL film into the monomer to enhance the wettability of the monomers with the film. The photomicrographs taken illustrate that the decrease in tackiness with the coating is due to the increase of the surface roughness at an 80‐kGy irradiation dose. The studies also revealed that the reduction in the contact angle and the increase in water absorption of the RVNRL film after irradiation are due to the formation of the hydrogel layer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1421–1428, 1999