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71.
A model of a downdraft gasifier has been developed based on chemical equilibrium in the pyro‐oxidation zone and finite rate kinetic‐controlled chemical reactions in the reduction zone. The char reactivity factor (CRF) in the reduction zone, representing the number of active sites on the char and its degree of burn out, has been optimized by comparing the model predictions against the experimental results from the literature. The model predictions agree well with the temperature distribution and exit gas composition obtained from the experiments at CRF=100. A detailed parametric study has been performed at different equivalence ratios (between 2 and 3.4) and moisture content (in the range of 0–40%) in the fuel to obtain the composition of the producer gas as well as its heating value. It is observed that the heating value of the producer gas increases with the increase in the equivalence ratio and decrease in the biomass moisture content. The effect of divergence angle of the reduction zone geometry (in the range of 30–150°) on the temperature and species concentration distributions in the gasifier has been studied. An optimum divergence angle, giving the best quality of the producer gas, has been identified for a particular height of the reduction zone. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Hongseok Choi Datta A. Xudong Cheng Xiaochun Li 《Journal of microelectromechanical systems》2006,15(2):322-329
Effective monitoring and diagnosis of manufacturing processes is of critical importance. If critical manufacturing process conditions are continuously monitored, problems can be detected and solved during the processing cycle. However, current technology still evidently lags behind practical needs. Microfabricated thin-film thermocouples and strain gauges are attractive for their small size and fast response. It is challenging to fabricate and embed these sensors into metallic components that are widely used in manufacturing. This paper investigates the fabrication, embedding, and characterization of metal embedded thin-film thermocouples and strain gauges. The materials (dielectric and metallic) constituting a complete microsensor were characterized and optimized. The results obtained from characterization and optimization of materials are presented and discussed. Thin-film thermocouples on stainless steel substrates (before and after embedding) were calibrated to elevated temperatures. The behavior of thin-film strain gauges was also studied. The metal embedded sensors demonstrated good accuracy, sensitivity, and linearity that matched the performance of commercial thermocouples and strain gauges well. The metal embedded microsensors are promising for in situ monitoring in hostile manufacturing environments. 相似文献
74.
Group theory considerations and properties of a continuous path are used to define a failure tree procedure for finding eigenvalues of the Schrödinger equation using stochastic methods. The procedure is used to calculate the lowest excited state eigenvalues of eigenfunctions possessing anti-symmetric nodal regions in configuration space using the Feynman-Kac path integral method. Within this method the solution of the imaginary time Schrödinger equation is approximated by random walk simulations on a discrete grid constrained only by symmetry considerations of the Hamiltonian. The required symmetry constraints on random walk simulations are associated with a given irreducible representation and are found by identifying the eigenvalues for the irreducible representation corresponding to symmetric or antisymmetric eigenfunctions for each group operator. The method provides exact eigenvalues of excited states in the limit of infinitesimal step size and infinite time. The numerical method is applied to compute the eigenvalues of the lowest excited states of the hydrogenic atom that transform as Γ2 and Γ4 irreducible representations. Numerical results are compared with exact analytical results. 相似文献
75.
Real-time active database systems (RTADBSs) have attracted a considerable amount of research attention in the past and a number of important applications have been identified for such systems, such as telecommunications network management, automated air traffic control, automated financial trading, process control and military command and control systems. In spite of the recognized importance of this area, very little research has been devoted to exploring the dynamics of transaction processing in RTADBSs. Concurrency control (CC) constitutes an integral part of any transaction processing strategy and, thus, deserves special attention. We study CC strategies in RTADBSs and postulate a number of CC algorithms. These algorithms exploit the special needs and features of RTADBSs and are shown to deliver substantially superior performance to conventional real-time CC algorithms 相似文献
76.
A. Datta S. Kal S. Basu M. Nayak A. K. Nath 《Journal of Materials Science: Materials in Electronics》1999,10(9):627-631
-FeSi2 is an important semiconducting silicide which is being studied extensively. In this paper, we report our results of the effect of laser and laser-thermal annealing on the properties of -FeSi2. 5N purity Fe was deposited on Si substrate and was subsequently irradiated by CW and pulsed laser separately followed by thermal annealing to reduce the laser induced damage. The samples were then characterized by sheet resistance, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical reflectance and absorption studies. Lastly, -FeSi2/n-Si heterojunctions were fabricated and the effect of laser treatment on the junction ideality factor was investigated. All these characterizations indicated the formation of good quality -FeSi2, particularly after pulsed laser followed by thermal treatment. 相似文献
77.
Ultrasonic measurements and scanning electron microscope studies are reported on a series of drawn samples of polypropylene. The ultrasonic measurements were performed over the frequency range 15 to 35 MHz and over a temperature range 283 to 343K. The scanning electron microscope observations confirmed the predictions from density data that the ‘void’ content initially increases on drawing and then decreases. The acoustic measurements on the samples with the highest draw ratios indicated that severe restriction of the motion of the polymer occurs when the fibrous structure is formed. 相似文献
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