Effect of air flowrate on particle velocity profile in a circulating fluidized bed

The research was conducted in a cold flow circulating fluidized bed (CFB). The diameter and height of riser are 5 and 200 cm, respectively. The objective is to study effect of gas velocity on hydrodynamic of glass beads having mean diameter of 547 micron and density of 2,400 kg/m³. The measurement of particle velocity profile was achieved by using a high-speed camera and an image processing software. A probe of 0.5 cm in diameter was inserted into the riser at the height of 110 cm from gas distributor and was set at 3 positions along the radius of the riser; 0, 0.6, and 1.8 cm from center. Transport velocity (U _tr ), core-annulus velocity (V _CA ) and minimum pneumatic velocity (V _mp ) were employed in determining solid flow pattern in the riser. It was observed that the flow regimes changed from fast fluidization to core-annulus and to homogeneous dilute bed when the gas velocities increased from 7, 8 and 9 m/s, respectively. The results from high-speed camera showed that glass beads velocity existed a maximum value at the center of the riser and gradually decreased toward the wall for all three gas velocities. It was also found that most of solid traveled upward in the core of the riser, however, solid traveled downward was identified at the wall layer.     

Explosive dissemination and flow of nanoparticles

Flow properties of 10 nm silica particles were determined in a two-story circulating fluidized bed riser. The pressure drop has a minimum at a velocity of 0.3 m/s. Particle concentrations were measured with a gamma ray densitometer. The solid fluxes were measured with a suction probe. From these measurements the nanoparticle viscosity was estimated. The measured viscosity is close to an estimate obtained from kinetic theory, assuming Brownian motion of nanoparticles. The viscosity and the previously measured solid stress modulus were used in a multiphase CFD code to study the behavior of explosive dissemination of mixtures of nanoparticles and micron size particles.The dissemination process was divided into two steps: early-time hydrodynamics and dissemination into an atmosphere. In the early-time hydrodynamic step the particles were accelerated by means of a high pressure and high temperature gas from a plastic explosive. When the device containing the particles broke, the early-time hydrodynamic velocities, concentrations, pressure and temperatures were used as the initial conditions for the dissemination step. This study shows how to use CFD to design a dissemination device that will prevent the overheating of a mixture of particles to be disseminated. The computed phenomena were similar to the experimental observations. The nanoparticles formed a cloud with a vortex ring structure for dissemination of small micron size particles and nanoparticles. For the dissemination of 100 μm aluminum and 10 nm silica particles, there was no vortex ring structure. As expected, the larger particles settled on the ground. The computed ground concentrations can be used to compare the model with observations, such as the covering of ground by dust after volcanic eruptions.     

Role of silk fibroin and rice starch on some physical properties of hydroxyapatite‐based composites

The role of organic blends of silk fibroin (SF) and rice starch (RS) in bone composites based on inorganic hydroxyapatite (HA) is studied. The physical property of HA‐based composites prepared by using the sol–gel method from Ca(OH)₂ and H₃PO₄ in ethanol and water solvent (4 : 1 volume ratio) could be improved by adding SF and RS (1 : 2 weight ratio) to HA (7 : 3 weight ratio). The Fourier transform infrared spectrometer spectrum shows that the SF and RS organic phases are blended homogeneously into the HA crystal structure. Addition of SF increases the pore size and surface area of the composites, as measured by Brunauer–Emmett–Teller method, but their pore volume is slightly decreased. The values of lattice parameters, crystallinity, and crystallite size, as determined from the field‐emission scanning electron microscope, transmission electron microscope, and X‐ray diffractometer results, increase after adding RS. The results are agreeable with the increase of their compressive strength and Young's modulus. Thus, the improved physical property of the prepared HA–SF/RS composites is better suited as bone‐filling material than the standard HA or HA‐based composites with either SF or RS only. Therefore, due to its low cost, biocompatibility, and nontoxicity, this innovative solution could be worth taken under consideration by the restorative dental and orthopedic implants industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42722.