303 research outputs found
Simulation of gas/solid flow behaviors and choking for a CFB riser: The EMMS/CFD approach
No full textThis paper presents a drag model based on the Energy-Minimization Multi-Scale (EMMS) approach. Compared to the empirical drag correlations, the incorporation of this EMMS-based drag model with the two-fluid model can well capture the meso-scale heterogeneous structure and improve the simulation results of the gas/solid flow behaviors for a CFB riser with Geldart-A particles. The EMMS model itself is also adapted to predict the choking phenomena for a CFB riser, and the comparisons are carried out among this calculation, the experimental measurements, the empirical correlation presented by Xu et al.(1) and the simulation results from the combination of the EMMS and CFD approaches
Multi-scale simulation of gas solid fluidization based on EMMS- DPM
No full textThis presentation will discuss some efforts to improve the speed and accuracy of discrete particle method from physical models to computational methods.
For physical model, the multiscale method is used. At global scale, the particles are distributed according to global distribution predicted by the Energy Minimization Multi-Scale (EMMS) model, so that the computation domain can be decomposed non-uniformly for load balance. At grid scale, to improve accuracy, the structure dependent drag coefficient based on the EMMS is used. At particle scale, the coarse grained method is used. The size and solids concentration of the coarse-grained particles (CGP) are determined by the cluster properties which can be predicted by the EMMS model. The coefficient of restitution is modified according to the kinetic theory of granular flows (KTGF). The method thus established in called EMMS-DPM(Lu, Xu et al. 2014).
As for computation, using system shared memory, the CFD computation on CPU is fully overlapped with particle computation on GPU. Also, the computation program is coupled with parallel visualization and control program, forming an online interactive simulation platform(Ge, Lu et al. 2015).
This method is verified by the simulation of two different CFB risers and several orders of speedup can be achieved. A methanol to orifin (MTO) process is simulated for more than 6800s. We also simulated a CFB with 30kg 0.082mm particles in 3D full loop. Furthermore, the interactive simulation platform can also be used for education and training purpose since it allows virtual experiment on computers.
REFERENCES
1.Ge, W., L. Lu, S. Liu, J. Xu, F. Chen and J. Li (2015). Multiscale Discrete Supercomputing - A Game Changer for Process Simulation? Chemical Engineering & Technology 38(4): 575-584.
2.Lu, L., J. Xu, W. Ge, Y. Yue, X. Liu and J. Li (2014). EMMS-based discrete particle method (EMMS–DPM) for simulation of gas–solid flows. Chemical Engineering Science 120(0): 67-87
Investigation of a GL-EMMS gradual drag model by comparative simulations of bubble columns
No full textThe mesoscale model for gas-liquid flow based on the energy minimization multi-scale method, which is denoted by the GL-EMMS model, demonstrates its capability of predicting the regime transition in bubble columns. Since the dominant mechanisms and stability conditions are important for this mesoscale model, it is desirable to reveal more details through the computational fluid dynamics (CFD) work. This work proposes a gradual drag correlation based on the GL-EMMS model, and then incorporates it into the Euler-Euler (E-E) and Euler-Lagrange (E-L) frameworks respectively. Cases with different gas distributors are simulated via the opensource platform of OpenFOAM. A simplified meshing treatment of the inlet boundary is adopted and has proven effective to reducing the computing load. The E-E simulation predicts the total gas holdup and the radial distribution of liquid velocity well, but obvious deviation is observed in the radial distribution of gas holdup, especially at lower superficial gas velocities for the single-orifice aeration. Nonetheless, this shortage can be overcome saliently by the E-L method. These verified simulations enable further possible iterative investigation between the GL-EMMS model and the CFD work, and also inspire some meaningful simulating strategy for bubble columns. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved
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.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000088378500028&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Chemistry, AnalyticalElectrochemistryInstruments & InstrumentationSCI(E)EICPCI-S(ISTP)
Three-dimensional modelling on the hydrodynamics of a circulating fluidised bed
No full textThe rapid depletion of oil and the environmentalimpact of combustion has motivated the search for cleancombustion technologies. Fluidised bed combustion (FBC)technology works by suspending a fuel over a fast air inletwhilst sustaining the required temperatures. Using biomassor a mixture of coal/biomass as the fuel, FBC provides alow-carbon combustion technology whilst operating at lowtemperatures. Understanding the hydrodynamic processes influidised beds is essential as the flow behaviours causing heatdistributions and mixing determine the combustion processes.The inlet velocities and different particle sizes influence theflow behaviour significantly, particularly on the transitionfrom bubbling to fast fluidising regimes. Computationalmodelling has shown great advancement in its predictive capabilityand reliability over recent years. Whilst 3D modellingis preferred over 2D modelling, the majority of studies use2D models for multiphase models due to computational costconsideration. In this paper, two-fluid modelling (TFM) isused to model a 3D circulating fluidised bed (CFB) initiallyfocussing on fluid catalytic cracker (FCC) particles. Thetransition from bubbling to fast fluidisation over a rangeof velocities is explored, whilst the effects on the bubblediameter, particle distributions and bed expansion for differentparticle properties including particle sizes are compared. Dragmodels are also compared to study the effects of particleclustering at the meso-scale
Risks of Offline Verify PIN on Contactless Cards
No full textContactless card payments are being introduced around the world al- lowing customers to use a card to pay for small purchases by simply placing the card onto the Point of Sale terminal. Contactless transactions do not require veri- fication of the cardholder’s PIN. However our research has found the redundant verify PIN functionality is present on the most commonly issued contactless credit and debit cards currently in circulation in the UK. This paper presents a plausible attack scenario which exploits contactless verify PIN to give unlimited attempts to guess the cardholder’s PIN without their knowledge. It also gives experimental data to demonstrate the practical viability of the attack as well as references to support our argument that contactless verify PIN is redundant functionality which compromises the security of payment cards and the cardholder
离散颗粒法的EMMS曳力模型及其应用
No full text气固流化床在过程工业中有着极其广泛的应用，其内部的两相流场是典型的非平衡、非均匀系统，存在以颗粒团聚为代表的介尺度结构，这给气固流化床的模拟带来了很大的难度。在气固两相流系统中，曳力对于流场的演变起着至关重要的作用，因此建立能够描述介尺度结构的非均匀曳力模型是解决问题的关键。以往的非均匀曳力模型多基于双流体模型发展而来，面向离散化方法的非均匀曳力模型还少有报道。本文在能量最小多尺度（EMMS）理论框架下对面向离散方法的非均匀曳力模型（EMMS/DP）进行了相关研究，并利用EMMS/DP曳力模型对多个气固流化床提升管进行模拟。最终应用该方法对航天气化炉冷模装置中的气固两相流动行为进行了模拟预测。本文各个章节的研究内容如下：第一章综述了气固流态化系统的发展过程，介绍了当前比较流行的三种数值模拟方法，并且对非均匀曳力模型的发展过程作了简要的介绍，提出了发展离散化非均匀曳力模型的必要性。第二章介绍了本文使用的颗粒轨道模型中一种粗粒化的数值模拟方法——MP-PIC方法，利用该方法模拟了两个提升管算例，模拟结果与实验值吻合很好，并对该方法的两个重要参数：网格分辨率和粗粒化参数进行了相关分析。第三章对EMMS/DP曳力模型进行了改进和发展。改进了该模型颗粒参数的生成方式并将非均匀因子与固相浓度和滑移速度进行关联以考虑介尺度结构的动态效应的影响。本章还对该曳力模型进行了发展，引入了操作条件对介尺度结构的影响，使其能够适应多种工况。最后利用改进后的曳力模型与MP-PIC方法耦合对不同气固流化床提升管、不同操作条件进行了模拟验证，模拟结果与实验值吻合很好。第四章利用改进后的曳力模型对工业航天炉实验装置进行了模拟，模拟结果可以捕捉到颗粒团聚、颗粒返混等现象，对流场整体的再现与实验现象吻合。 第五章对本文进行了总结并对以后工作提出了建议。 ;Gas-solid fluidized bed is widely used in the process industry. The flow field inside gas-solid fluidized bed is a typical non-equilibrium and inhomogeneous system, where there exists mesoscale structures e.g. particle clusters. Those make it difficult to the simulation of gas-solid fluidized bed. In gas-solid two-phase flow systems, the drag force plays an important role in the evolution of the flow field. Therefore, it is necessary to establish an inhomogeneous drag model which can describe the mesoscale structure. Most of the inhomogeneous drag models were developed based on the two-fluid model, while there is seldom report about the inhomogeneous drag model for discrete particle method. In this study, we investigate the discrete-based inhomogeneous drag model (EMMS/DP) in the framework of the energy minimization multi-scale (EMMS) theory and simulate several gas-solid fluidized bed risers with the EMMS/DP drag model. Finally, this method has been used in the prediction of gas-solid flow behavior in cold-state HT-L gasifier. The content of each chapter of this dissertation is as follows:Chapter 1 summarizes the development of the gas-solid fluidization system. Three currently popular numerical simulation methods are introduced in this chapter, and the development process of heterogeneous drag model is made a brief introduction. Finally, we propose the necessity of developing the inhomogeneous drag model for discrete particle method.In chapter 2, we introduce the MP-PIC method which is a coarse grained numerical simulation method belonging to the particle tracking model used in this dissertation. Two risers are simulated by this method and the simulation results are in good agreement with the experimental measurements. Two important parameters of this method: grid resolution and coarse graining parameters were discussed in this chapter.In chapter 3, the EMMS drag model for discrete particle method (EMMS/DP) was improved and developed. This study improves the generating method of particles information and correlates the heterogeneity index (HD) with solid concentration and slip velocity to account for the dynamic effects of meso-scale structure. Further we developed this drag model by introducing the influence of operating conditions on the mesoscale structure so that it can adapt to a variety of operating conditions. Then, different gas-solid fluidized bed risers and different operating conditions were simulated with the improved drag model. The simulation results agreed well with the experimental work.In chapter 4, the experimental device of HT-L gasifier was simulated by using the improved drag model. The simulation results can capture the phenomena of particle agglomeration and backmixing. The overall reproduction of the flow field is consistent with the experimental measurement. In chapter 5, we summarize this dissertation and provide suggestions for future work. </p
EMMS: Increasing Hope and Transforming Lives Through Improved Access to Electrical Power
No full textDeveloping countries often face a challenge involving energy conservation. Energy Monitoring and Management Systems (EMMS) was tasked to make an energy meter in order to provide a practical way of controlling energy consumption and create a tool for teaching energy conservation. This meter should be able to measure energy usage over a period of time and prevent further energy usage after a specified amount has been consumed. In this poster, the team will explain what they have been doing in recent semesters to work towards their goal of testing and preparing this meter for implementation in Zimbabwe this summer, as well as how they have been improving the user experience through website implementation.
Funding for this work provided by The Collaboratory for Strategic Partnerships and Applied Research.https://mosaic.messiah.edu/engr2022/1005/thumbnail.jp
Cost-effectiveness analysis of a hospital electronic medication management system
No full textOBJECTIVE: To conduct a cost-effectiveness analysis of a hospital electronic medication management system (eMMS). METHODS: We compared costs and benefits of paper-based prescribing with a commercial eMMS (CSC MedChart) on one cardiology ward in a major 326-bed teaching hospital, assuming a 15-year time horizon and a health system perspective. The eMMS implementation and operating costs were obtained from the study site. We used data on eMMS effectiveness in reducing potential adverse drug events (ADEs), and potential ADEs intercepted, based on review of 1 202 patient charts before (n = 801) and after (n = 401) eMMS. These were combined with published estimates of actual ADEs and their costs. RESULTS: The rate of potential ADEs following eMMS fell from 0.17 per admission to 0.05; a reduction of 71%. The annualized eMMS implementation, maintenance, and operating costs for the cardiology ward were A55 296). The estimated reduction in ADEs post eMMS was approximately 80 actual ADEs per year. The reduced costs associated with these ADEs were more than sufficient to offset the costs of the eMMS. Estimated savings resulting from eMMS implementation were A56-59) per admission (A102 000 per annum for this ward). Sensitivity analyses demonstrated results were robust when both eMMS effectiveness and costs of actual ADEs were varied substantially. CONCLUSION: The eMMS within this setting was more effective and less expensive than paper-based prescribing. Comparison with the few previous full economic evaluations available suggests a marked improvement in the cost-effectiveness of eMMS, largely driven by increased effectiveness of contemporary eMMs in reducing medication errors
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