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排序方式: 共有1616条查询结果,搜索用时 15 毫秒
71.
Fine-grained B4C-SiC/C composites were fabricated using a ball-milling dispersion process. The oxidation behaviors of both fine-grained B4C-SiC/C composites and coarse-grained B4C-SiC/C composites at temperatures of up to 1400 °C were analyzed by the differential thermal analysis technique, and the surface morphology of the composites after isothermal oxidation at 800, 1200 and 1400 °C was examined by scanning electron microscopy (SEM). The results indicated that fine-grained B4C-SiC/C composites had excellent oxidation resistance with self-healing properties at 1400 °C. A general model and mechanism for self-protection against oxidation of carbon materials were proposed. 相似文献
72.
《Advanced Powder Technology》2014,25(1):163-173
Mixing of powders and granular materials of different functions and/or properties is frequently encountered by engineers and scientists. Nevertheless, the guidelines for the selections of particle mixers are still not fully developed and predictions of the mixture quality after mixing operations are still not possible. These are largely due to the fact that the tools for particle mixing studies are far from well developed. In the last decades, advances in experimental and computational methods have brought lights to better particle mixer design and operation. This paper reviews the tools for the investigation of mixing in particulate systems. 相似文献
73.
Mixing characterisation of full-scale membrane bioreactors: CFD modelling with experimental validation 总被引:2,自引:0,他引:2
Membrane Bioreactors (MBRs) have been successfully used in aerobic biological wastewater treatment to solve the perennial problem of effective solids-liquid separation. The optimisation of MBRs requires knowledge of the membrane fouling, biokinetics and mixing. However, research has mainly concentrated on the fouling and biokinetics (Ng and Kim, 2007). Current methods of design for a desired flow regime within MBRs are largely based on assumptions (e.g. complete mixing of tanks) and empirical techniques (e.g. specific mixing energy). However, it is difficult to predict how sludge rheology and vessel design in full-scale installations affects hydrodynamics, hence overall performance. Computational Fluid Dynamics (CFD) provides a method for prediction of how vessel features and mixing energy usage affect the hydrodynamics. In this study, a CFD model was developed which accounts for aeration, sludge rheology and geometry (i.e. bioreactor and membrane module). This MBR CFD model was then applied to two full-scale MBRs and was successfully validated against experimental results. The effect of sludge settling and rheology was found to have a minimal impact on the bulk mixing (i.e. the residence time distribution). 相似文献
74.
A. Parvareh M. Rahimi M. Yarmohammadi A.A. Alsairafi 《International Communications in Heat and Mass Transfer》2009
This paper reports the effect of jet position on the acid dispersion in a neutralization process. Experiments were carried out in a continuous stirred reactor and the effect of jet nozzle position on non-reactive dye dispersion at seven layouts was studied. Consequently, the neutralization reaction mixing was carried out at the best and worst positions. The results reveal that the ways that flow pushes the acid inside the tank are quite different and the neutralization performance can significantly be affected by the jet position. The Computational Fluid Dynamics (CFD) modeling was carried out in order to analyze the experimental observations. 相似文献
75.
Personalized ventilation (PV) system in conjunction with total ventilation system can provide cleaner inhaled air for the user. Concerns still exist about whether the normally protecting PV device, on the other hand, facilitates the dispersion of infectious agents generated by its user. In this article, two types of PV systems with upward supplied fresh air, namely a chair‐based PV and one kind of desk‐mounted PV systems, when combined with mixing ventilation (MV) and displacement ventilation (DV) systems, are investigated using simulation method with regard to their impacts on co‐occupant's exposure to the exhaled droplet nuclei generated by the infected PV user. Simulation results of tracer gas and particles with aerodynamic diameter of 1, 5, and 10 μm from exhaled air show that, when only the infected person uses a PV, the different PV air supplying directions present very different impacts on the co‐occupant's intake under DV, while no apparent differences can be observed under MV. The findings demonstrate that better inhaled air quality can always be achieved under DV when the adopted PV system can deliver conditioned fresh air in the same direction with the mainly upward airflow patterns of DV. 相似文献
76.
In this work we derive the fundamental equations for conditional moment closure (CMC) modelling of individual phases set in a two-phase flow. The derivation is based on the instantaneous transport equations for the single phase that involve a level set/indicator function technique for accounting for interfaces. Special emphasis is put on spray combustion with the CMC equations formulated for the gas phase. The CMC equations are to be viewed as an adjunct to existing methods for the modelling of the dynamics of sprays: they provide a refinement of the modelling of chemical reactions in the gas phase. The resulting CMC equations differ significantly from those already in use in the literature. They contain, of course, unclosed terms that need to be modelled. Investigation of the unclosed terms associated with evaporation at the droplet surface is well beyond the capabilities of laboratory measurement or direct numerical simulation. It is proposed that modelling of these terms be based on the well-established ‘laws’ of similarity between heat and mass transfer: an example is detailed for one example of the general modelling of the spray dynamics. Other unclosed terms are important throughout the gas phase. Models used for these terms in single-phase flows are reviewed and it is proposed that any modifications needed for these models be investigated by DNS of suitable model problems having good resolution of the flow and mixing in the inter-droplet space. It is proposed that a spray analogue of the scalar mixing layer that has been widely studied in single-phase flows be used as the model problem for such DNS studies and also for LES and RANS modelling. 相似文献
77.
This paper presents an innovative concept for optimized air diffusion in buildings. The method uses passive control of air jet through lobed diffusers. An analysis is done experimentally at different scales for a lobed shaped geometry. A cross-shaped jet is characterized first through an isolated orifice and then at the scale of one perforated panel. An intermediary analysis of two coalescent and a row of cross-shaped jets is also proposed. All the results lead to the same conclusion. The lobed diffuser favors the self-induction compared to a reference conventional circular perforated diffuser. The air flow induced in the case of the lobed perforated panel is in average twice as the one of the circular perforated panel. Despite the consequent gain in air induction for the lobed perforated panel flow, the streamwise maximum velocities display comparable values in the far field which signifies comparable throws for the two flows. Consequently, the presented lobed perforated panel concept can be generalized to different type of diffusers to improve mixing ventilation in buildings. 相似文献
78.
Effect of different mixers on physicochemical properties and water status of extruded and laminated fresh pasta 总被引:2,自引:0,他引:2
Physicochemical properties and water status of fresh pasta (both extruded and laminated) produced with recently designed mixers (Premix® and Bakmix®) that induce a uniform hydration of the solids and allow the formation of a dough in 1–2 s were evaluated. 相似文献
79.
We have developed a new method to determine the degree of mixing for a given system. The method assumes knowledge of the locations of all or some studied particles both before and after mixing. The method is scalable and gives comparable results for systems with varying shapes and sizes of the mixing space. It can also be used to determine the mixing of only a part of the space studied. Due to the information needed, the method is best suited for simulations, but in some cases it might be possible to use it with real laboratory experiments. 相似文献
80.