Dense Annulus Research Articles

Numerical investigation of gas thermal property in the gasification process of a spouted bed gasifier

Steam-biomass gasification in a three-dimensional lab-scale spouted bed gasifier is numerically simulated via the multiphase particle-in-cell approach. The spatial distribution of gas thermal properties (i.e., temperature, conductivity, specific heat capacity, density, and viscosity) together with the impact of operating parameters are comprehensively studied. The results show that distinct flow hydrodynamics in the three regions of the spouted bed gasifier lead to different spatial distributions of gas thermal properties. The gas thermal properties show significant transitions in the spout-annulus and fountain-annulus interfaces. Elevating the bed height decreases the gas temperature, density, and viscosity but increases the gas thermal conductivity and specific heat capacity. Among all operating parameters, the bed temperature exerts the most significant influence on the spatial distribution of gas thermal properties. Due to the existence of dead zone in the annulus region of the bed, bed height, biomass diameter, and steam to biomass ratio exert negligible influences on the gas thermal properties in the dense annulus region but noticeable impacts in the dilute fountain region. Based on the relationship between solid transportation and gas thermal property variations, the current work also provides a guideline for the optimization of spouted bed gasifiers, for example, the dead zone is recommended to be optimized by adjusting the inclination angle of the conical part to enhance the solid internal circulation and gasification performance.

Effects of cohesion on the flow patterns of granular materials in spouted beds

Two-dimensional spouted bed, capable to provide both dilute granular gas and dense granular solid flow patterns in one system, was selected as a prototypical system for studying granular materials. Effects of liquid cohesion on such kind of complex granular patterns were studied using particle image velocimetry. It is seen that the addition of liquid oils by a small fraction of 10(-3)-10(-2) causes a remarkable narrowing (about 15%) of the spout area. In the dense annulus, as the liquid fraction increases, the downward particle velocity gradually decreases and approaches a minimum where, at a microscopic grain scale, the liquid bridge reaches spherical regimes with a maximum capillarity. Viscous lubrication effect is observed at a much higher fraction but is really weak with respect to the capillary effect. In the dilute spout, in contrast to the dry grains, the wet grains have a lightly smaller acceleration in the initial 1/3 of the spout, but have a dramatically higher acceleration in the rest of the spout. We attribute the former to the additional work needed to overcome interparticle cohesion during particle entrainment at the spout-annulus interface. Then, using mass and momentum balances, the latter is explained by the relative higher drag force resulting from both higher gas velocities and higher voidages due to spout narrowing in the wet system. The experimental findings will provide useful data for the validation of discrete element simulation of cohesive granular-fluid flows.

Ultrastructure of the Spermatozoa of the Domestic Duck (Anas platyrhynchos sp.)

The ultrastructure of the spermatozoa of the domestic duck (Anas platyrhynchos sp.) was analysed by transmission and scanning electron microscopies and compared with the results obtained in preliminary studies involving other non-passerine birds. The spermatozoa were characterised by the presence of a short head, short midpiece and long principal piece. The head consisted of a reduced acrosome that contained moderately electron-dense homogenous material. The implantation fossa was observed between the base of the nucleus and the proximal centriole. The midpiece contained electron-dense material associated with the proximal centriole and nuclear membrane, and a long distal centriole surrounded throughout its length by 11-12 elliptical mitochondria. A dense annulus separating the midpiece from the principal piece was visible. Posterior to the annulus, the axoneme was formed surrounded by a dense fibrous sheath, representing the principal piece or flagellum, which was a long segment with a smooth surface and a smaller diameter than the midpiece. The spermatozoon of the domestic duck resembles that of other non-passerine birds, corresponding to a basic type of spermatozoon similar to that of reptiles, called sauropsid type.

Intravitreal Injection of AAV2 Transduces Macaque Inner Retina

Adeno-associated virus serotype 2 (AAV2) has been shown to be effective in transducing inner retinal neurons after intravitreal injection in several species. However, results in nonprimates may not be predictive of transduction in the human inner retina, because of differences in eye size and the specialized morphology of the high-acuity human fovea. This was a study of inner retina transduction in the macaque, a primate with ocular characteristics most similar to that of humans. In vivo imaging and histology were used to examine GFP expression in the macaque inner retina after intravitreal injection of AAV vectors containing five distinct promoters. AAV2 produced pronounced GFP expression in inner retinal cells of the fovea, no expression in the central retina beyond the fovea, and variable expression in the peripheral retina. AAV2 vector incorporating the neuronal promoter human connexin 36 (hCx36) transduced ganglion cells within a dense annulus around the fovea center, whereas AAV2 containing the ubiquitous promoter hybrid cytomegalovirus (CMV) enhancer/chicken-β-actin (CBA) transduced both Müller and ganglion cells in a dense circular disc centered on the fovea. With three shorter promoters--human synapsin (hSYN) and the shortened CBA and hCx36 promoters (smCBA and hCx36sh)--AAV2 produced visible transduction, as seen in fundus images, only when the retina was altered by ganglion cell loss or enzymatic vitreolysis. The results in the macaque suggest that intravitreal injection of AAV2 would produce high levels of gene expression at the human fovea, important in retinal gene therapy, but not in the central retina beyond the fovea.

Euspermatozoa and paraspermatozoa in the volutid gastropod Odontocymbiola magellanica, Patagonia, Argentina, Southwestern Atlantic Ocean

Giménez J. 2010. Euspermatozoa and paraspermatozoa in the volutid gastropod Odontocymbiola magellanica, Patagonia, Argentina, Southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92: 355–362. The ultrastructure of mature spermatozoa and paraspermatozoa of Odontocymbiola magellanica is investigated. Euspermatozoa consist of: (1) a tall, conical acrosomal vesicle (with a short basal invagination, constricted anteriorly); (2) a rod-shaped, solid and highly electron-dense nucleus; (3) an elongate midpiece consisting of the axoneme sheathed by helical mitochondrial elements each exhibiting a dense U-shaped outer layer; (4) an elongate glycogen piece; (5) a dense annulus at the junction of the midpiece and glycogen piece; and (6) a short free-tail region. Paraspermatozoa of O. magellanica are vermiform and dimorphic. First type contain approximately 14–17 axonemes (arranged peripherally and interspersed with microtubules) and numerous oblong dense vesicles, numerous less dense (round) vesicles, and scattered mitochondria; the second type contains 38–45 axonemes peripherally arranged and closer to the core region of the cell and occasional mitochondria. Most of the euspermatozoal features of O. magellanica are also observed in many neotaenioglossans and neogastropods. However, the U-shaped outer layer of each mitochondrial element has only been previously reported in the Volutidae subfamily Zidoniinae. It is now reported here in the subfamily Odontocimbiolinae and may prove to be a diagnostic feature of the Volutidae family.

Ultrastructure of euspermatozoa and paraspermatozoa in the marine gastropod Adelomelon beckii (Caenogastropoda, Volutidae)

The sperm morphology of Adelomelon beckii is described by optical and transmission electron microscopy. Both euspermatozoa and paraspermatozoa were found in the specimens studied. Euspermatozoa are filiform and have an elongate nucleus capped by an acrosome. A small basal plate lies between the base of the acrosome and the nucleus. The mid-piece consists of U-shaped mitochondria wrapped helically around the central axoneme. A dense annulus at the junction of the mid-piece and glycogen piece is found, ending in a short end-piece, composed of the axoneme surrounded by a plasma membrane. Two types of paraspermatozoa are found, both vermiform but differing internally with respect to the disposition and number of axonemes, as well as to the types of secretory vesicles. We suggest the use of paraspermatozoa as a systematic character to reveal phylogenetic relationships in this family.

Gas-solids flow behavior with a gas velocity close to zero

In a 9.3 m high and 0.10 m i.d. gas-solids downflow fluidized bed (downer), the radial and axial distributions of the local solids holdups and particle velocities along the downer column were measured with the superficial gas velocity set to zero. A unique gas-solids flow structure was found in the downer system with zero gas velocity, which is completely different from that under conditions with higher gas velocities, in terms of its radial and axial flow structures as well as its micro flow structure. The gas-solids flow pattern under zero gas velocity conditions, together with that under low gas velocity conditions, can be considered as a special regime which differs from that under higher gas velocity conditions. According to the hydrodynamic properties of the two regimes, they can be named the “dense annulus” regime for the flow pattern under zero or low gas velocity conditions and the “dense core” regime for that under higher gas velocity conditions.

A novel method for isokinetic measurement of particle flux within the riser of a circulating fluidized bed

Previous workers have shown that the net particle flux within the riser of a circulating fluidized bed (CFB) may be measured by a simple technique with a suction probe facing upwards and then downwards. However, this technique does not give accurate measurements of the upward and downward particle fluxes independently. A probe similar to that of previous workers is used here to measure the flux of the upflow. However, the flux of the downflow is measured with a probe through which no external air flow is imposed. The method presented here uses an 8-mm tubular probe, penetrating the riser wall and rising at a sharp angle. The probe is constructed of sections of steel tube and 400 mesh screen. Particles fall into the probe and then into a sealed reservoir for subsequent analysis. The gas flow in the riser passes through the screen sections of the tube, so that the gas flow at the tip of the probe is virtually undisturbed by the presence of the probe. The method is verified in a CFB riser of diameter 115 mm, fluidizing sand of average size 209 μm, with a solids circulation rate in the range of 10–30 (m 2s) and air velocity in the range of 3.4–5.4 m/s, corresponding to a nominal solids concentration (based on pressure-drop measurements) of 0.5–2.5%. The technique presented here allows for accurate and independent measurements of both the upward flux and the downward flux, and thus represents an improvement on previous methods. Previous workers have specified that a critical surface where the time-averaged net flux is zero demarcates the dilute core from the dense annulus. However, the total particle flux, defined as the sum of the upward and downward fluxes, is proportional to the time-averaged local particle concentration, and so is indicative of physical phenomena in the riser. Trends for the total flux are presented.

On-Farm Drying of Large Round Bales

In response to the interest expressed by farmers in drying large round bales of hay over ductwork using ambient air, a system capable of drying 84 soft-center bales at a time was designed and built. Each bale was capped with 6 mil polyethylene film to provide protection from rain and to minimize channeling of air through the bale’s soft center. Thermocouples placed in various locations in bales showed that the air flow was sufficient to maintain bale temperatures very close to ambient. Core samples showed satisfactory drying occurring in the dense annulus of the bales. Final moisture content of the bales ranged from 14%-18% (wb). This study shows that it is both technically and economically feasible to dry large round bales of good quality hay using ambient air and the drier system described here.

Flow characterization in high-velocity fluidized beds using pressure fluctuations

Fast fluidization flow characteristics were studied using instantaneous pressure signals in a fast fluidization unit with 0.152 m i.d. and 8.4 m height using a Zeolite FCC catalyst. The data confirmed that a fast fluidized bed can usually be divided into two main regions, a dense region at the bottom and a dilute region at the top. Within both regions the mean void fractions are essentially constant along the height. The void fraction in the dense region appears to be independent of the solid circulation rate and varies only slightly with the superficial gas velocity. Upward moving instabilities were detected within the dense region of the bed with a fairly constant wave speed over a wide range of flow parameters. These have similarity to phenomena in slugging fluidized beds. The results suggest that the solids in the dense region of a high-velocity fluidized bed are present in three different forms—relatively stagnant in a dense annulus region, very dilute in a core region, and in the form of waves rolling upward between the core and dense annulus.

Morphology of microtubules in rabbit platelets.

The morphology of the microtubular wall in rabbit platelets fixed in glutaraldehyde and osmic acid solution and stained with uranyl acetate, or lead hydroxide, or doubly stained, is variable. In cross section, the wall may appear as a uniformly dense annulus, an annulus containing nodular densities about 35 A in diameter or as a series of contiguous subunits with a circular cross sectional profile about 70 A wide. The authors relate the varying morphology to the intensity of staining and equate the nodular and circular subunits. Rotational analysis suggests that there are 12 ± 2 subunits in the microtubular wall.