The sensitivity of filtered Two Fluid Models to the underlying resolved simulation setup

Eulerian-Eulerian modelling based on the Kinetic Theory of Granular Flow has proven to be a promising tool for investigating the hydrodynamic and reactive behaviour inside fluidized beds. The primary limitation of this approach is the very fine grid size necessary to fully resolve the transient solid structures that are typical of fluidized bed reactors. It therefore remains impractical to simulate industrial scale fluidized bed reactors using resolved Two Fluid Model (TFM) simulations. For this reason, there is currently widespread interest in developing sub-grid (filtered) models that allow accurate simulations at coarser grids by correcting for the effects of unresolved solid structures. However, little attention has been paid to the importance of the choice of the underlying TFM closures during the derivation of the filtered models. This paper follows a similar approach to an establish filtered TFM (1) to derive sub-grid closures for the interphase momentum exchange , solids viscosity and solids pressure in 2D periodic simulations. These corrections are obtained for different particle-particle restitution coefficients, frictional pressure models and drag models as a function of the particle phase volume fraction and the filter size. This reveals at which values of the markers the individual resolved TFM model choices have significant effects on the final expressions derived for filtered TFMs. Based on these findings suggestions are made regarding the derivation of new filtered TFMs and the use of the existing models. 1. Y. Igci and S. Sundaresan. Constitutive Models for Filtered Two-Fluid Models of Fluidized Gas–Particle Flows. Ind. Eng. Chem. Res., 50: 13190-13201, 2013

Evaluation of the minimum fluidization velocity at elevated temperature and pressure through experiments and modelling

The minimum fluidization velocity is an important measure used in the design and scale-up of fluidized beds. Due to its importance, a large number of experiments over a wide range of operating conditions have focused on this property. Despite this attention, the amount of data where the combined effect of elevated temperature and pressure on the minimum fluidization velocity was investigated is still limited. In this study the minimum fluidization velocity is determined experimentally in a lab-scale fluidized bed reactor designed for use at elevated temperature and pressure. A central composite design (CCD) is used to design experiments where different operating parameters are varied over a wide range. This includes different particle sizes, pressures up to 5bar and temperatures up to 550°C. The collected data provides the basis for existing correlations, such as that given by Bi and Grace (1), to be evaluated at elevated temperature and pressure and allows for detecting any systematic deviations from the experimental data. In addition to the experiments, the minimum fluidization velocity and the voidage at minimum fluidization is calculated numerically over the CCD using computational. Several different drag models are evaluated, allowing their relative performances to be assessed and any weaknesses to be identified. Recommendations are made for drag model selection in pressurized fluidized bed reactors. 1. H.T. Bi and J.R. Grace. Flow regime diagrams for gas-solid fluidization and upward transport. Int. J. Multiphase Flow, 21: 1229-1236, 1995. Please click Additional Files below to see the full abstract

Industrial DevOps

The visions and ideas of Industry 4.0 require a profound interconnection of machines, plants, and IT systems in industrial production environments. This significantly increases the importance of software, which is coincidentally one of the main obstacles to the introduction of Industry 4.0. Lack of experience and knowledge, high investment and maintenance costs, as well as uncertainty about future developments cause many small and medium-sized enterprises hesitating to adopt Industry 4.0 solutions. We propose Industrial DevOps as an approach to introduce methods and culture of DevOps into industrial production environments. The fundamental concept of this approach is a continuous process of operation, observation, and development of the entire production environment. This way, all stakeholders, systems, and data can thus be integrated via incremental steps and adjustments can be made quickly. Furthermore, we present the Titan software platform accompanied by a role model for integrating production environments with Industrial DevOps. In two initial industrial application scenarios, we address the challenges of energy management and predictive maintenance with the methods, organizational structures, and tools of Industrial DevOps.Comment: 10 page

Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe

The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of gamma-ray flux attenuation by the EBL. We place upper limits on the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. (2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A. Reimer, L.C. Reye

Empfehlung zur Weiterentwicklung des Berliner Energie- und Klimaschutzprogramms 2030

EMPFEHLUNG ZUR WEITERENTWICKLUNG DES BERLINER ENERGIE- UND KLIMASCHUTZPROGRAMMS 2030 Empfehlung zur Weiterentwicklung des Berliner Energie- und Klimaschutzprogramms 2030 / Alt-Harnack, Claudia (Rights reserved) ( -

Verification of filtered two fluid models for reactive gas‐solid flows

CFD simulations of fluidized bed reactors are generally limited to the laboratory scale because of the fine grid sizes that are required to resolve complex particle clustering phenomena. The filtered Two Fluid Model (fTFM) approach has recently emerged as a promising method for allowing reasonable predictions of largescale fluidized beds. This paper presents a verification study of new two-marker fTFM closures. In general, the fTFMs matched well to the resolved simulations. It was shown that the two-marker models significantly increased the predicted degree of phase segregation (resolved in coarse grid simulations), and hence have superior capabilities compared to simpler one-marker models. Also, the two-marker model predicted a more dynamic transient flow behaviour. However, further work is recommended to extend the present study over a wider range of flow conditionsThe authors would like to express their gratitude for the financial support from the European Commission under the NanoSim grant (project number: 604656), as well as for the computational resources provided at NTNU by UNINETT Sigma2 AS, https://www.sigma2.no.publishedVersio