Jinghai Li

Exploring complex systems in chemical engineering—the multi-scale methodology

Challenges in quantitative design of chemical processes mainly reside in their complex structures, which are usually multi-scale in nature, and are difficult to analyze by the average approach as commonly used. The multi-scale methodology has thus received more and more attention in recent years. There are three kinds of multi-scale methodology: descriptive for distinguishing the phenomenological difference of structures at different scales; and correlative for formulating phenomena at higher scales by analyzing the mechanisms at lower scales; and variational for revealing the dominant mechanisms of the structure aid the relationship between the scales. This paper presents an overview of multi-scale methodologies with emphasis on the variational methodology, and proposes the possibility of establishing a generalized multi-scale methodology, effective for analyzing single-phase turbulent flow in pipe, gas-solid two-phase fluidization, and gas-solid-liquid three-phase fluidization. The variational multi-scale methodology consists of the following steps: Phenomenological resolution with respect to scales of structures. Identification of dominant mechanisms. Establishment of conservation conditions with respect to different scales and correlation between different scales. Formulation of variational criterion to identify what dominates the stability of structure and what compromise exists between different dominant mechanisms. Integration between conservation conditions with stability conditions

The EMMS model — its application, development and updated concepts

Circulating fluidized beds (CFB) operate with a heterogeneous structure consisting of a solid-rich dense phase and a gas-rich dilute phase, the variational criterion and the critical condition of which are indispensable for CFB quantification. With such a strategy, a comprehensive model is developed on the basis of the energy-minimization multi-scale (EMMS) approach. The model is capable of predicting the saturation carrying capacity and the steady states at both the top and the bottom of an S-shaped axial profile. Comparison between the model prediction and available experimental data shows reasonable agreement. In addition, the overall strategy adopted in the EMMS approach is also discussed with updated concepts. It is concluded that the variational criterion (or something equivalent) in analyzing heterogeneous two-phase systems is indispensable unless the observation scale can be sufficiently small.

Physical mapping of fluidization regimes: the EMMS approach

The existence of multiple regimes of distinctive flow structure is a remarkable characteristic of fluidization, which is far from being physically interpreted under a unified approach. The energy minimization multi-scale model (Particle-Fluid Two-Phase Flow, the Energy Minimization Multi-Scale Method, Metallurgical Industry Press, Beijing, 1994) is potentially such an approach in which the inclusion of stability criteria enables the prediction of heterogeneity and non-linear behaviors in fluidized beds. However, fully analytical solution of the model is impossible so far, and numerical solutions have resorted to general optimizing software. Therefore, the detailed characteristics of the solutions and their theoretical implications have not been fully explored. In this paper, we have achieved this by a rigorous numerical approach and by retrieving all missing roots, which leads to physical mapping of fluidization regimes. The model is also extended to unsteady conditions with acceleration and simplified by employing a single stability criterion, which identifies choking as a jump between two branches of the stable solution. Calculations based on this version are in reasonable agreement with measurements on bench, pilot and commercial scale circulating fluidized beds.

Wavelet analysis of dynamic behavior in fluidized beds

Wavelet analysis has been used for studying dynamic behavior of fluidized beds, which proved effective in resolution of time series into different scales of components with distinct structure and in identification of transition from the dense phase to the dilute phase. By examining wavelet spectrum functions of various dynamic signals measured from fluidized beds, it is indicated that the signals can be decomposed into three scales of components: micro-scale (particle size), meso-scale (cluster size) and macro-scale (unit size). The principal component method was employed for phase separation from concentration signals measured by the optical probe. In this method, the maximum scale parameter s(0) of the wavelet spectrum function was chosen as the optimum scale parameter. The principal component method can reduce the computation time significantly and remain the benefit offered by the direct method described in our previous publication (Ren & Li, in: L. S. Fan, T. M. Knowlton (Eds.), Fluidization, Vol. IX, Engineering Foundation, New York, 1998, p. 629.). The method was also extended to detect the boundaries of clusters in 2-D digital images acquired from fluidized beds

Dissipative structure in concurrent-up gas-solid flow

The necessary condition for the formation and dissolution of the dissipative structure in particle-fluid two-phase flow has been investigated, revealing its origin in the compromise between the movement tendencies of the particles and the fluid. As soon as either the particles can dominate the fluid, or the fluid can dominate the particles, the dissipative structure either dissolves or a newly formed coexisting uniform structure appears. At this transition point, operating conditions and material properties alone become insufficient to ensure the steady state. Quantification of such a complicated structure calls for some mode of multiple resolution, for instance, it could be resolved with respect first to scale and then to amplitude and periodicity

Particle-motion-resolved discrete model for simulating gas–solid fluidization

This paper presents numerical simulations of two-dimensional gas-solid fluidized beds by establishing the so-called particle-motion-resolved discrete model in which the motion of the solid phase is calculated by considering individual particle motions while gas flow is described by the Navier-Stokes equation. The particle-motion-resolved method is used to treat the interparticle interaction and particle/fluid interaction, resolving the overall movement of particles into the collision process accounting for the interparticle interaction and the suspension process related to the interaction with the fluid. It was assumed that momentum conservation of collision mechanics controls the interaction between colliding particles, while the state of each suspended particle is fully dominated by fluid/particle interaction. Comparing a two-dimensional hexagonal lattice with a three-dimensional hexagonal packed structure, an unreal porosity calculated on area basis is transformed into a three-dimensional porosity in order to give reasonable simulation results. The above model has been used for simulating bubbling, slugging and cluster behavior in gas-solid fluidization, resulting in more reasonable phenomena such as distinct eddies, particle-free slugs and the dynamic clusters

Axial Voidage Profiles of Fast Fluidized Beds in Different Operating Regions

ABSTRACT Investigation on the effects of operating parameters on axial voidage profiles in fast fluidized beds resulted in the identification of three operating regions on the basis of the relation between the solids rate Gs and the saturation carrying capacity of the flowing gas K * : 1 Gs = K * , 2 Gs * , and 3 Gs > K * Each region possesses its own unique hydrodynamic characteristic. These three operating regions can be demonstrated in the regime diagram of particle-fluid two-phase flow.

Macro-scale phenomena reproduced in microscopic systems—pseudo-particle modeling of fluidization

eDespite its,wide applications, fluidization is not understood enough to satisfy our technical or academic interests. Cascading simulation approaches on different scales, with small-scale approaches provide constitutional correlations to larger scale approaches, is considered a practical way toward this direction. However, by physically reproducing many macro-scale phenomena in fluid flow and fluidization on micro-scales even below the traditional continuum limit, pseudo-particle modeling (PPM,. Ge and Li (Proceedings of the Fifth International Conference on Circulating Fluidized Bed, Beijing, China, Science Press, Beijing, 1996) has suggested the possibility of a more straightforward and penetrating way. In this paper, traditional approaches are reviewed first and then PPM is discussed in full length and validated further. We demonstrate that it has maintained all necessities on the molecular level for comprehensive flow description, and the reproduced phenomena, such as bubbling, clustering and radial heterogeneity, have reflected the fundamental mechanism of their macro-scale counterparts despite the vast scale difference. With this digital miniature, every detail of the flow can be traced non-intrusively until the lowest level in classic physics and experiment with flexible parameters, which provides a unique tool for, theoretical study and engineering predictions. Therefore, PPM is at least a useful complement, if not substitute, to traditional approaches

Compromise and resolution - Exploring the multi-scale nature of gas-solid fluidization

Research strategy in studying gas-solid fluidization at the Institute of Chemical Metallurgy (ICM) is outlined. Particle-fluid compromise is recognized to be the origin of the multi-scale dissipative structure in the system, to which multiple resolution is applied, leading to the establishment of the variational criterion for stability and the critical condition for choking. The dynamic behavior of such a heterogeneous structure in fluidized systems is formulated by carrying out wavelet analysis and resolving the whole process with respect first to scale, and then, to time and amplitude. Average approaches, as commonly used, are considered to be inadequate to describe transport behaviors in gas-solid fluidization. Discrete computer simulation on micro-scale is regarded to be a promising approach to further understanding of the complicated mechanism of particle-fluid interaction

From Multiscale Modeling to Meso-Science

Multiscale modeling is becoming essential for accurate, rapid simulation in science and engineering. This book presents the results of three decades of research on multiscale modeling in process engineering from principles to application, and its generalization for different fields. This book considers the universality of meso-scale phenomena for the first time, and provides insight into the emerging discipline that unifies them, meso-science, as well as new perspectives for virtual process engineering. Multiscale modeling is applied in areas including: multiphase flow and fluid dynamicschemical, biochemical and process engineeringmineral processing and metallurgical engineeringenergy and resourcesmaterials science and engineeringJinghai Li is Vice-President of the Chinese Academy of Sciences (CAS), a professor at the Institute of Process Engineering, CAS, and leader of the EMMS (Energy-minimizing multiscale) Group. Wei Ge, Wei Wang, Ning Yang and Junwu Wang are professors at the EMMS Group, part of the Institute of Process Engineering, CAS. Xinhua Liu, Limin Wang, Xianfeng He and Xiaowei Wang are associate professors at the EMMS Group, part of the Institute of Process Engineering, CAS. Mooson Kwauk is an emeritus director of the Institute of Process Engineering, CAS, and is an advisor to the EMMS Group.