NUMERICAL SIMULATION OF GAS FLOW AND MIXING IN A MICROCHANNEL USING THE DIRECT SIMULATION MONTE CARLO METHOD

The direct simulation Monte Carlo (DSMC) method was employed to investigate gas flow and mixing in a microchannel at near-atmospheric pressure conditions. Simulations for pressure-driven flows were first carried out for a single-component gas flow in a microchannel. Mixing of two parallel gas streams (H 2 and O 2 ), separated by a splitter plate and then entering a microchannel, was considered. The effects of the inlet velocities, the inlet-outlet pressure difference, and the pressure ratio of the incoming streams (H 2 and O 2 ) on the mixing behavior were considered. The effect of the "accommodation coefficient" of the solid wall of the microchannel on the mixing behavior was also examined. The simulation results indicate that mixing decreases with the increase of inlet-outlet pressure difference. When the two streams enter the microchannel with different inlet pressures, mixing is found to decrease with the increase of the pressure ratio. The mixing process is found to be much slower for nearly specularly reflected walls compared to the mixing in a microchannel with completely diffuse walls.     

Boundary Layer Development on a Concave Surface： Flow Visualization and Hot Wire Velocity Measurements

Gortler vortices are key issues in the design of gas turbine blades. The present study deals with flow visualization over concave surface for gas turbine applications. The aim is to comprehend qualitatively the flow trends, particularly the Gortler vortices formation and development. Gortler vortices have the shape of mushroom-like vortices regularly spaced at 25 mm. These vortices grow and increase in strength more rapidly along the surface in the case of the same grid of turbulence applied to the measuring section. The curvature radius of the studied blade is 0.5 m and the stream turbulence intensity level is 2.6%. The velocity field is measured by hot wire anemometer in the streamwise direction. The velocity profile is found to be highly distorted by the momentum transfer associated with Gortler vortices. The results are compared to Blasius flow and to literature data for a blade with curvature radius equal to 2 m.     

Halal and kosher slaughter methods and meat quality: A review

There are many slaughter procedures that religions and cultures use around the world. The two that are commercially relevant are the halal and kosher methods practiced by Muslims and Jews respectively. The global trade in red meat and poultry produced using these two methods is substantial, thus the importance of the quality of the meat produced using the methods. Halal and kosher slaughter per se should not affect meat quality more than their industrial equivalents, however, some of their associated pre- and post-slaughter processes do. For instance, the slow decline in blood pressure following a halal pre-slaughter head-only stun and neck cut causes blood splash (ecchymosis) in a range of muscles and organs of slaughtered livestock. Other quality concerns include bruising, hemorrhages, skin discoloration and broken bones particularly in poultry. In addition to these conventional quality issues, the “spiritual quality” of the meat can also be affected when the halal and kosher religious requirements are not fully met during the slaughter process. The nature, causes, importance and mitigations of these and other quality issues related to halal and kosher slaughtering and meat production using these methods are the subjects of this review.     

Removal of basic blue 41 from aqueous solution by carboxymethylated Posidonia oceanica

The aim of this work is to improve the retention capacity already noticed for the raw Posidonia towards basic dyes and notably for basic blue 41 (BB41). To improve the fixation rate of these cationic entities, we have undertaken the introduction of carboxymethylate groups on the raw Posidonia. Thus, we have obtained materials with various carboxymethylate groups contents (from 10 to 30%). We have then studied the fixation capacities of BB41 on the different materials. We have noticed that the retention capacity of modified Posidonia was improved compared to the raw one. We have studied the effect of different parameters influencing the fixation capacities such as initial dye concentration, support dose, contact time, pH, carboxymethylate groups content, and temperature. This phenomenon of retention is compared to classic models of Langmuir and Freundlich. Some thermodynamic parameters such as free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) changes have been studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1215–1225, 2007     

Thermal fatigue analysis of solar panel structure for micro-satellite applications

Thermal fatigue analysis based on 2D finite difference and 3D finite element methods is carried out to study the performance of solar panel structure during micro-satellite life time. Solar panel primary structure consists of honeycomb structure and composite laminates. The 2D finite difference (I-DEAS) model yields predictions of the temperature profile during one orbit. Then, 3D finite element analysis (ANSYS) is applied to predict thermal fatigue damage of solar panel structure. Meshing the whole structure with 2D multi-layer shell elements with sandwich option is not efficient, as it misses thermal response of the honeycomb structure. So we applied a mixed approach between 3D solid and 2D shell elements to model the solar panel structure without the sandwich option.     

The impact of the overexpression of human UDP-galactose transporter gene hUGT1 in tobacco plants

When the human UDP-galactose transporter 1 gene (hUGT1) was introduced into tobacco plants, the plants displayed enhanced growth during cultivation, and axillary shoots had an altered determinate growth habit, elongating beyond the primary shoots and having a sympodial growth pattern similar to that observed in tomatoes at a late cultivation stage. The architecture and properties of tissues in hUGT1-transgenic plants were also altered. The leaves had an increase in thickness, due to an increased amount of spongy tissue, and a higher content of chlorophyll a and b; the stems had an increased number of xylem vessels and accumulated lignin and arabinogalactan proteins (AGPs). Some of these characteristics resembled a gibberellin (GA)-responsive phenotype, suggesting involvement of GA. RT-PCR-based analysis of genes involved in GA biosynthesis suggested that the GA biosynthetic pathway was not activated. However, an increase in the proportion of galactose in polysaccharide side chains of AGPs was detected. These results suggested that because of higher UDP-galactose transport from the cytosol to the Golgi apparatus, galactose incorporation into polysaccharide side chains of AGP is involved in the gibberellin response, resulting in morphological and architectural changes.     

Modulus prediction of a cross-ply fiber reinforced fabric composite with voids

Voids or bubbles in polymer composites have a detrimental effect on the properties of the material. Such voids are found in PMR 15/graphite fiber (fabric type) composites. The matrix, PMR 15, is formed in-situ during the molding process and undergoes two major stages of reactions, viz., imidization and crosslinking. Volatiles are formed as by-products of these reactions and may remain trapped in the matrix to form voids or bubbles. Photomicrographs of composite cross sections suggested the classification of voids as two different phases in two different directions, each aligned with the fibers, resulting in a five phase model. The composites were tested in three-point bending tests to obtain the flexural modulus. By combining Weng's inclusion approach (1) and Ishikawa and Chou's crimp method (2), an analytical model has been developed to predict the elastic moduli of such a multiphase composite material. Thus, the voids have been treated as inclusions in an enclosing matrix, which in turn is reinforced by woven fibers in two directions. The stiffness behavior obtained analytically was within 10% of the experimental values.     

Study of the miscibility of poly(ethyl methacrylate-co-4-vinylpyridine)/poly(styrene-co-cinnamic acid) blends

Summary The miscibility of a series of poly(ethyl methacrylate-co-4-vinylpyridine) with poly(styrene-co-cinnamic acid), is investigated by differential scanning calorimetry. The results show that each blend is miscible as ascertained by a single composition dependent glass transition temperature. The Tg's of the blends exhibit positive deviations from the weight average Tg's of the blend components. The thermograms data exploited according to the Kwei and Schneider approaches suggest the occurrence of strong specific intermolecular attractive interactions within the binary systems. The strength of these interactions, as estimated from the Kwei q-values, increases with the proton donor and proton acceptor contents in the copolymers. Received: 23 January 1999/Revised version: 29 April 1999/Accepted: 1 June 1999