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961.
The effects of short carbon fibers on static and dynamic properties of thermoplastic elastomeric blends of natural rubber (NR) and high density polyethylene (HDPE) have been studied. Both mechanical and dynamic properties are dependent on fiber concentration. The fiber aspect ratio ranges from 20 to 30. Adhesion between fiber and matrix is evident from the SEM photomicrographs of the failed composites and from variation of relative damping properties. Fiber orientation occurring during processing causes anisotropy in the physical properties. In composites with longitudinally oriented fibers, tensile failure occurs by both fiber pullout and breakage, while in composites with transversely oriented fibers, matrix failure dominates. The incorporation of fibers into the matrix lowers the tan δmax value, but no change in glass transition temperature is observed. 相似文献
962.
963.
K. Haenen M. Nesldek L. De Schepper R. Kravets M. Van
ek S. Koizumi 《Diamond and Related Materials》2004,13(11-12):2041
The application of very sensitive photocurrent-based spectroscopic techniques have led to the detection of new levels for the electronic structure of the phosphorous donor in n-type CVD diamond. By combining quasi-steady-state photocurrent measurements (PC), photothermal ionisation spectroscopy (PTIS) and the highly sensitive Fourier transform photocurrent spectroscopy (FTPS) technique at different temperatures, ranging from liquid nitrogen temperature to 170 K, the resulting spectra point to a richer structure than assumed up to now. This is the consequence of the improved sample quality over the last years, opening up to a much larger attainable doping window. By using doping levels, ranging from 1019 cm−3 down to 1016 cm−3 on 111 -oriented Ib HPHT substrates, still giving rise to measurable n-type conductivity, spectra showed less line broadening and more fine structure. Finally, the results will be compared with spectra measured on active P-doped polycrystalline n-type films. 相似文献
964.
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. 相似文献
965.
966.
967.
Baoqing Deng Shanshan Kong Chang Nyung Kim 《Korean Journal of Chemical Engineering》2007,24(4):577-582
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. 相似文献
968.
Kronkanok Hongthong Kejvalee Pruksathorn Pornpote Piumsomboon Paiboon Sripakagorn 《Korean Journal of Chemical Engineering》2007,24(4):612-617
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. 相似文献
969.
Delba N.C. Melo Eduardo C. Vasco De Toledo Marcela M. Santos Salah D.M. Hasan Maria Regina Wolf Maciel Rubens Maciel Filho 《Computers & Chemical Engineering》2005,29(11-12):2485
In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO2. 相似文献
970.
We state and analyse one-shot methods in function space for the optimal control of nonlinear partial differential equations (PDEs) that can be formulated in terms of a fixed-point operator. A general convergence theorem is proved by generalizing the previously obtained results in finite dimensions. As application examples we consider two nonlinear elliptic model problems: the stationary solid fuel ignition model and the stationary viscous Burgers equation. For these problems we present a more detailed convergence analysis of the method. The resulting algorithms are computationally implemented in combination with an adaptive mesh refinement strategy, which leads to an improvement in the performance of the one-shot approach. 相似文献