Characteristic modes and flow structure of non-premixed flame in humid-air combustion

An experimental study has been performed in order to determine the effect of humidity on the flow field and the flame stability limit in turbulent non-premixed flame. Two-dimensional Particle Image Velocimetry (PIV) measurements were made to quantify the velocity field, with and without steam injected. The results indicate the addition of steam decreases the recirculation flow and reduces the distance between the forward and aft stagnation points. The detailed stabilization regimes show that the critical fuel-to-air velocity ratios of the central fuel penetration in the humid air case are 16% to 22% lower, and the partially quenching limits are at least 25% lower. The decreased penetration limit is due to a reduction in momentum of the humid air. An analysis of flamelet concepts reveals that increased chemical reaction time leads to lower partially quenching limits in the humid air combustion.     

Preparation and Characterization of Mordenite Thin Films via Pulsed Laser Deposition

Zeolite thin films are interesting for their potential application in membrane based separations, catalysis, and molecular sensing. Mordenite is a one-dimensional channel type zeolite that has been used in alcohol/water separations. Pulsed-laser deposition has been used to prepare partially oriented, crystalline mordenite thin films on stainless steel foil, and frits as well as carbon fibers and DAM-1 particles. Preliminary results for pervaporation of isopropanol/H₂O mixtures using mordenite membranes indicate separation factors of 133 and 459 at room temperature and 76°C, respectively.     

Modeling of photocatalytic oxidation of VOCs in a packed bed reactor under continuous and discontinuous illuminations

In this paper, a mathematical model is presented to describe the photocatalytic degradation of VOCs in a packed bed reactor. Here, the adsorption of VOCs on the wall of the reactor is taken into account and the diffusion of VOCs in the axial direction is neglected. First-order kinetics is used to describe the photocatalytic oxidation of VOCs. The analytical solution of the present model is obtained by traveling wave method. The solution shows that the reactor performance is totally dependent on the inlet concentration of VOCs when the time is large enough. The present model is validated through the experimental result of the photocatalytic oxidation of trichloroethylene in a packed bed and the predicted results accord well with the experimental data. The influence of flow rate and inlet concentration on the performance of the reactor is discussed in detail. High flow rate offers high reaction rate and low conversion efficiency. The different inlet conditions and different reaction patterns are also investigated. The model would be useful to estimate the rate constant and help to the design of the reactor.     

Miscibility studies of polymer blends by viscometry methods

The intrinsic viscosities of blends of poly(vinyl chloride)/poly(ethylene-co-vinyl acetate) (PVC/EVA), poly(vinyl chloride)/poly(styrene-co-acrylonitrile) (PVC/SAN), and poly(ethylene-co-vinyl acetate)/poly(styrene-co-acrylonitrile) (EVA/SAN) have been studied in cyclohexanone as a function of blend composition. In order to predict the compatibility of polymer pairs in solution, the interaction parameter term, Δb, obtained from the modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight average intrinsic viscosities of the two polymer solutions taken separately are used. © 1994 John Wiley & Sons, Inc.     

Improvement of cyclodextrin glucanotransferase as an antistaling enzyme by error-prone PCR

In an effort to improve the properties of cyclodextrin glucanotransferase (CGTase) as an antistaling enzyme, error-prone PCR was used to introduce random mutations into a CGTase cloned from alkalophilic Bacillus sp. I-5 (CGTase I-5). A mutant CGTase[3-18] with the three mutations M234T, F259I and V591A was selected by agar plate assay. Sequence alignment of various CGTases indicated that M234 and F259 are located in the vicinity of the catalytic sites of the enzyme and V591 in the starch binding domain E. The cyclization activity of CGTase[3-18] was dramatically decreased by 10-fold, while the hydrolyzing activity was increased by up to 15-fold. These mutations near subsite +1 (M234T) and at subsite +2 (F259I) are likely to alter the enzyme activity in a concerted manner, promoting hydrolysis of substrate while retarding cyclization. The addition of CGTase[3-18] reduced the retrogradation rate of bread by as much as did the commercial antistaling enzyme Novamyl during 7-day storage at 4 degrees C. No cyclodextrin (CD) was detected in bread treated with CGTase[3-18], whereas 21 mg of CD per 10 g of bread was produced in bread treated with wild-type CGTase.     

Effect of the geometry and pattern of the flow channel on the performance of polymer electrolyte membrane fuel cell

This research focuses on the effect of the geometry and patterns of the gas flow channel on the PEM fuel cell performance. Simulation was conducted and the results were verified by experiments. Three-dimensional, single phase, compressible and isothermal models of 5 cm² electrodes, anode and cathode, were developed and studied by utilizing a commercial Computational Fluid Dynamics (CFD) software, FLUENT 4.5. Two types of gas flow channel were investigated: conventional and interdigitated. The results showed that the flow channel pattern does not have a significant effect on the anode cell performance, whereas it has a strong effect/influence on the cathode cell performance. The interdigitated design provides a higher limiting current density and cell performance than the conventional design on the cathode side. Moreover, the cell performance does not depend on the inlet and outlet channel widths. On the contrary, for the interdigitated design, it was influenced by the shoulder width. Finally, experiments were conducted to validate the simulation results.     

Reaction rate and MWD changes in crosslinking of PVC,with dithioltriazine

The reaction rate of crosslinking of PVC with dithioltriazine has been studied by following gel formation and changes in the molecular weight distribution (MWD). Compounding was performed on a roll mill at 145°C and crosslinking by heat treatment at 180 or 90°C. In this system crosslinking is executed by the thiolate anion, formed in situ by reaction with MgO. We have studied the catalyzing effect of several polyols in order to achieve a more efficient reaction. Most likely, these catalysts work by chelating the Mg²⁺ ions, thus increasing the nucleophilic character of the thiolate. With the most efficient ones, ditrimethylolpropane and HO(CH₂CH₂)_6-7H, complete crosslinking can be obtained in 3 min at 180°C, i.e., at processing temperatures. We also followed the changes in the MWD before gelation at a considerably lower temperature, 145°C, and found an extensive molecular enlargement even after 5-10 min. Most surprisingly, μM_n increased up to 100% without formation of insoluble material. By ¹H-NMR measurements on low molecular weight extracts, we have shown this to be due to a fast and selective reaction with allylic chlorine in the unsaturated end groups, ～ CH₂? CH?CH? CH₂Cl, formed in the mechanism of chain transfer to monomer. Due to this reaction, formulations with too high reactivity may crosslink during processing, which calls for a careful balancing of the reactivity for each processing case.     

An experimental study of plasticating in a reciprocating-screw injection molding machine

Experimental studies were performed with low density polyethylene, acrylonitrile-butadiene-styrene polymers and on polyvinyl chloride to elucidate the nature of the plasticating process in a reciprocating-screw injection molding machine. Melting data, obtained by use of the “cooling experiment,” and plastic temperature data reveal that the screw recharge process is a transient plasticating extrusion process which gradually approaches the equilibrium extrusion behavior as the screw rotates. If the screw rotation time is a high percentage of the total cycle time, the plasticating behavior is very similar to steady-state extrusion behavior, but if the screw rotation time is a small percentage of the total cycle time, the plasticating behavior is significantly different. Furthermore, better plasticating is obtained by use of a low RPM and high percentage rotation time than by a high RPM and low percentage rotation time.     

Selectivity of Supercritical CO<Subscript>2 </Subscript>in the Fractionation of Hake Liver Oil Ethyl Esters

The solubility of different ethyl esters derivatized from hake liver oil in supercritical carbon dioxide was studied. A selectivity factor was used to determine optimal conditions to fractionate the ethyl ester mixture. A strong influence of solvent pressure and temperature was observed within 8.63–18.04 MPa and 40–70 °C. The lowest total solubility of the ethyl ester mixture was obtained when using supercritical carbon dioxide at the lowest density (the lowest pressure and the highest temperatures value tested). The highest discrimination against long-chain polyunsaturated fatty acids (e.g. EPA and DHA) was also obtained at these above conditions. Conversely, higher solubility and lower selectivity were obtained when solvent density increased. Considering this inverse correlation between selectivity and solubility, a single-step batch-fractionation process was designed to increase the 22:6 ethyl ester content from an initial value of 17.5% in the starting material to 55% in the final extract.     

Comparison of YAG: Eu phosphors synthesized by supercritical water in batch and continuous reactors

Luminescent yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) nanoparticles doped with Eu (10 at%) were synthesized in batch-type and continuous-type supercritical water (SCW) reactors. In the case of the continuous-type SCW method, the particles of YAG: Eu phosphors were much smaller and demonstrated a uniform spherical-like shape. Inversely, in the case of the batch-type SCW method, a needle-like or elliptical-like shape was formed because a finite amount of time was required to reach SCW conditions from ambient conditions. However, the emission intensity of YAG: Eu phosphors synthesized by using the batch-type SCW method was stronger. Therefore, it is concluded that the continuous-type SCW method is superior to the batch-type SCW method from the viewpoint of the particle size and shape, but the luminescence property of phosphors in the continuous-type SCW method needs to be improved. In addition, a calcination process slightly improved the luminescence intensities of YAG: Eu phosphors generated by using either the batch-type or continuous-type SCW methods.