From micro-scale to technical dimension—Challenges in the simulation of dense gas-particle flows--颗粒学报PARTICUOLOGY

Werther, J., Hartge, E.-U., Li, J., & Ge, W. (2009). From micro-scale to technical dimension—Challenges in the simulation of dense gas-particle flows. Particuology, 7(4), 231–232. https://doi.org/10.1016/j.partic.2009.06.006

From micro-scale to technical dimension—Challenges in the simulation of dense gas-particle flows

Joachim Werther ^a *, Ernst-Ulrich Hartge ^a, Jinghai Li ^b, Wei Ge ^b

a Institute of Solids Process Engineering and Particle Technology, Hamburg University of Technology, Hamburg, Germany
b State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, China

10.1016/j.partic.2009.06.006

Volume 7, Issue 4, August 2009, Pages 231-232

Available online 18 July 2009.

E-mail: werther@tuhh.de

Highlights

Abstract

Supported by the Sino-German Center for Research Promotion, an organization jointly founded by the National Natural Science Foundation of China (NSFC) and the German Research Foundation (DFG), a joint Sino-German workshop on particle fluid systems was held for the fourth time on May 19–20, 2008 in Hamburg. Previous workshops were held on August 30–31, 1999 in Hamburg, Germany (Li and Werther, Chem. Eng. Technol. 23 (4): 378, 2000), on May 18–19, 2001 in Beijing, China (Li, Ge, Werther and Bruhns, Chem. Eng. Technol. 24 (11): 1097, 2001) and on October 24–31, 2004 in Beijing, China (Li and Werther (Eds.), China Particuology 3: 1–2, 2005). This time, 26 scientists from China and Germany (including one collaborator in The Netherlands) gathered to have an in-depth discussion on a critical issue in multi-phase systems—multi-scale simulation of dense gas-particle flows.

Gas-particle flows are typically aggregative, featuring remarkable heterogeneity over a broad range of spatio-temporal scales. On the micro-scale, the difference between gas and solid phases presents the intrinsic heterogeneity in the system, and the solid particles are usually irregular and even porous in shape, with various forces between them. The meso-scale features dynamic dense clusters immersed in dilute “broth”, which deform, interact, breakup and merge constantly, to strongly impact the transport and reaction behaviors. On the macro-scale, a variety of flow regimes present and the characteristics of meso-scale structures vary in space and time due to boundaries, inlets and outlets, etc. These heterogeneous flow structures and the related interactions are difficult to describe and have been a focus in the study of multi-phase flow.

To meet the difficulties originated from the multiscale nature of gas-particle flows, many approaches or methods are presented with different domains of interest. The most rigorous simulation of gas–solid flow theoretically should start from below the scale of solid particles and that of the dissipative eddies in turbulent gas, i.e., the micro-scale. Direct use of this approach is unacceptable for industrial systems; however, they can provide micro-scale flow information and possible closures for other approaches. The coarse-grid approach using the two-fluid model (TFM), and the hybrid approach, which combines continuum description for gas and discrete particle method (DPM) or discrete element method (DEM) for particles, are more apposite for reactor simulation of industrial interest.

Therefore, how to improve existing simulations, through their extensions or combinations, so that industrial applications can take advantage of the efficiency of macro-scale methods without overlooking of the effect of microscopic details of the system, becomes a key issue and grand challenge in the simulation of gas-particle flows, and even in the application of fluidization technology and particle engineering. In this workshop, the participants have had extensive discussions on the topic, ranging from simulation methods and typical applications, to experimental findings and validation.

In the final discussion, the participants came to the conclusion that a multi-scale approach is necessary and effective to cope with complexity of gas-particle interactions in industrial systems. For this approach, micro-scale phenomena, for example, intra-particle transport, internal particle structure, particle shape, surface properties and wide particle size distribution, etc., need more investigation. On the other hand, despite its remarkable progress, multi-scale modelling methodology should be connected to phenomenological modelling to facilitate industrial applications.

For further development of simulation methods and their effective application, the interaction between measurement and modelling methods was considered to be increasingly important. Modelling can guide measurements in large CFB reactors by providing a general picture of the reactor, while modelling needs validation by measurement. In particular, a freely accessible database of well-documented precise experimental data, with quality insurance by participation of several research groups could be very helpful to model validation. Some potential databases and their producers and sharing groups were proposed on the workshop.

As to the modelling methods, while the classical drag correlations (e.g. Wen, Yu and Ergun's correlations) are still applicable to homogeneous structures, the EMMS drag model discussed extensively in this workshop seems to be a better choice for heterogeneous gas-particle flows. An EMMS user group was formed among the participants to further expand its application and to develop EMMS model versions that are simpler and easier in application.

The present issue of PARTICUOLOGY contains a selection of contributions to the workshop which after review were considered to be suitable for publication. We would express our sincere thanks to the authors and reviewers for their support.

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