170,103 research outputs found
Generalized Boltzmann kinetic theory for EMMS-based two-fluid model
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It has long been recognized that the solid particles in circulating fluidized bed risers are distributed heterogeneously in the form of clusters. In response to this fundamental phenomenon, an EMMS-based two-fluid model has been developed recently from the viewpoint of continuum mechanics, however, its microscopic foundation remains unknown. In this study, the statistical mechanics foundation of EMMS-based two-fluid model was presented using generalized Boltzmann kinetic theory. With respect to the gas phase, a new method was developed by considering the fluctuations at different scales simultaneously, with which we can for the first time derive the correct governing equations of gas phase via kinetic theory, in the sense that both the molecular stress and the Reynolds (or pseudo-Reynolds) stress can be obtained simultaneously, whereas all previous kinetic theory analyses failed to predict the appearance of Reynolds (or pseudo-Reynolds) stress in the momentum conservation equation of gas phase due to the assumption of uniform structure, although it is physically always existent no matter how small the Reynolds number is. In case of particle phase, the generalized Boltzmann equation considering the spatio-temporal variation of the volume, density and velocity of clusters was firstly derived, a set of macroscopic transport equations was then derived in different phase spaces. It was shown that the governing equations of dense phase in the EMMS-based two-fluid model derived from continuum mechanics viewpoint corresponds to the macroscopic transport equations at (r, t) space. Therefore, present study launches a solid microscopic foundation of EMMS-based two-fluid model. Finally, CFD simulations have been carried out to validate EMMS-based two-fluid model and to study the effect of gas phase pseudo-turbulence. (C) 2016 Elsevier Ltd. All rights reserved.</p
A simplified two-fluid model coupled with EMMS drag for gas-solid flows
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A simplified two-fluid model (STFM) combined with energy-minimization multi-scale (EMMS) drag was proposed for accurate and fast simulation of gas-solid flows. In the proposed approach, the solid phase viscosity is neglected, the solid phase pressure is calculated with an empirical formulation, and the interphase momentum transfer is modeled with EMMS drag, which takes the effects of meso-scale structures into consideration. Three typical fluidization cases, namely, a 2D circulating fluidized bed, a 3D lab-scale bubbling fluidized bed, and a 3D lab-scale full-loop circulating fluidized bed, were successfully simulated with this approach. The numerical results are compared with those of full two-fluid model (FTFM, i.e., the two-fluid model using the kinetic theory for granular flow to close solid phase stress term), as well as experimental data. Predictions of STFM coupled with EMMS drag are comparable with those of FTFM coupled with EMMS drag, and both agree well with experimental data. However, computational cost of STFM is significantly reduced compared with that of FTFM. It is suggested that drag model has a dominant effect on gas-solid simulation, and the effect of solid phase stress term seems to play a minor role, demonstrating the feasibility and practicality of STFM with EMMS drag for describing the hydrodynamics of heterogeneous gas-solid flows. (C) 2016 Elsevier B.V. All rights reserved.</p
Electro-mass olfactory multi-sensor (EMMS)
No full textFor an olfactory sensor or electronic nose, the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e(+)/m. We tried to imitate this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is quartz crystal microbalance (QCM) for detecting the change in mass, the other is interdigital electrode (IE) for detecting the change in conduction, as an electro-mass multi-sensor (EMMS). in this paper, the principle and the feasibility of this method are discussed. The preliminary results on the recognition of alcohol by EMMS coated with lipids are presented. Meanwhile, the multi-sensor can also be used as an instrument for research on some physico-chemistry problems. The change in conduction of coated membrane caused by one absorbed molecule is reported. It is found that when a QCM is coated with membrane, it still obeys the relationship Delta F (frequency change of QCM) = K Delta m (mass change of absorbed substance) and the proportional coefficient, K, depends not only on quartz properties but also on membrane characteristics as well. (C) 2000 Elsevier Science S.A. All rights reserved
Application of an EMMS Model for Bubbly Fluidized Bed
No full textIn computational fluid dynamics (CFD) of fluidization processes, the modeling of drag between fluid and particles has a direct effect on the results. The EMMS (Energy Minimization Multi-Scale) models are based on the micro-scale of individual particles and the macro scale of equipment to model the meso-scale phenomena related to particle clustering, which directly affect the drag between fluid and particles. The EMMS/bubbling model was introduced as a change from the classic EMMS model to specific bubbling fluid bed conditions. The present work aims to apply the EMMS/bubbling model in the CFD of Geldart-D particles fluidized by air. The results were compared with results from the literature. It was observed that, for particles of Geldart groups A and B, the results using the EMMS/bubbling model agreed well with the literature. The CFD results for Geldart-D particles showed good agreement with the literature results for this method using coarse grids.</jats:p
The importance of vegetative seedling traits in distinguishing herbaceous legumes of differing impact in temperate natural ecosystems
No full textJason Emms, John G. Virtue, Christopher Preston and William D. Bellottihttp://www.weedinfo.com.au/bk_15awc.htm
Extending EMMS-based models to CFB boiler applications
No full textRecently, EMMS-based models are being widely applied in simulations of high-throughput circulating fluidized beds (CFBs) with fine particles. Its use for low flux systems, such as CFB boiler (CFBB), still remains unexplored. In this work, it has been found that the original definition of cluster diameter in EMMS model is unsuitable for simulations of the CFB boiler with low solids flux. To remedy this, we propose a new model of cluster diameter. The EMMS-based drag model (EMMS/matrix model) with this revised cluster definition is validated through the computational fluid dynamics (CFD) simulation of a CFB boiler. (c) 2012 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved
Energy Monitoring & Management System (EMMS)
No full textThe Energy Monitoring and Management System (EMMS) is developing an electrical power meter to help make electricity more available in energy impoverished regions of the world. The meter fills a unique niche for energy tracking and regulation within micro-grid systems. The EMMS project has partners in Burkina Faso and Zimbabwe: Open Door Development (ODD), the Institut Missiologique du Sahel (IMS), and the Theological College of Zimbabwe (TCZ). Ties are also maintained on a regular basis with IEEE Smart Village for potential future widespread system implementation.
Recent work on the EMMS meter has been focused on resolving the last few remaining bugs, establishing a robust communication system, and developing a centralized server-based interface which aids with meter configuration and administration. The team has also begun several future developments which include datalogging and remote access features.https://mosaic.messiah.edu/engr2021/1004/thumbnail.jp
A bubble-based EMMS model for gas-solid bubbling fluidization
No full textAn EMMS/bubbling model for gas-solid bubbling fluidized bed was proposed based on the energy-minimization multi-scale (EMMS) method (Li and Kwauk, 1994). In this new model, the meso-scale structure was characterized with bubbles in place of clusters of the original EMMS method. Accordingly, the bubbling fluidized bed was resolved into the suspending and the energy-dissipation sub-systems over three sub-phases, i.e., the emulsion phase, the bubble phase and their inter-phase in-between. A stability condition of minimization of the energy consumption for suspending particles (N(5)-> min) was proposed, to close the hydrodynamic equations on these sub-phases. This bubble-based EMMS model has been validated and found in agreement with experimental data available in literature. Further, the unsteady-state version of the model was used to calculate the drag coefficient for two-fluid model (TFM). It was found that TFM simulation with EMMS/bubbling drag coefficient allows using coarser grid than that with homogeneous drag coefficient, resulting in both good predictability and scalability. (C) 2011 Elsevier Ltd. All rights reserved
EMMS-based Eulerian simulation on the hydrodynamics of a bubbling fluidized bed with FCC particles
No full textAlthough great progress has been made in modeling the bubbling fluidization of Geldart B and D particles using standard Eulerian approach, recent studies have shown that suitable sub-grid scale models should be introduced to improve the simulation on the hydrodynamics of Geldart A particles. In this study, the flow structures inside a bubbling fluidized bed of KC particles are simulated in an Eulerian approach employing the energy minimization multi-scale (EMMS) model (Chemical Engineering Science, 2008. 63: 1553-1571) as the sub-grid scale model for effective inter-phase drag force, using an implicit cluster diameter expression. It was shown that the experimentally found axial and radial solid concentration profiles and radial particle velocity profiles can be well reproduced. (C) 2009 Elsevier B.V. All rights reserved
Bubble-based EMMS/DP drag model for MP-PIC simulation
No full textTo account for the sub-grid heterogeneity of bubbling gas-solid flows in the multi-phase particle-in-cell (MP-PIC) method, a bubble-based EMMS/DP drag model is proposed in this work by taking into account the particle/parcel position information. The local, inter-parcel porosity is calculated by using the method of smoothed particle hydrodynamics (SPH), while the intra-parcel porosity is closed by using the Energy Minimization Multi-scale (EMMS) model. The local velocities of gas phase and different solid parcels are determined by using the constraint of pressure drop balance between phases as in the EMMS/bubbling model. The drag force acting on each parcel is then determined with the sub-grid information of velocities and porosities. Two cases of bubbling fluidized bed are simulated to validate this drag model. And the results show good agreement with experimental data. (C) 2020 Elsevier B.V. All rights reserved
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