Sub-grid models for heat transfer in gas-particle flows with immersed horizontal cylinders

Abstract

Simulating full-scale heated fluidized bed reactors can provide invaluable insight to the design process. Such simulations are typically computationally intractable due to their complex multi-physics and various lengthscales. While it may be possible to simulate some large-scale systems, they require significant computing resources and do not lend themselves well to design optimization methods. To overcome these problems coarse-grid simulations can be used with supplementary constitutive sub-grid models to approximate the unresolved physics. This study details the development, implementation, and verification of a sub-grid model for heat transfer in gas-particle flows with immersed horizontal cylinders. Using the two-fluid model for multiphase flow, small periodic unit-cell domains were simulated over a wide range of flow and geometry conditions. The results were filtered and fit using nonlinear regression to build a Nusselt correlation based on the solids fraction, solids velocity, cylinder geometry (diameter and spacing), and the Peclet number. The proposed model is highly nonlinear and includes power-law contributions from each parameter. The model was verified using a nearly orthogonal experiment design where the input parameters were varied randomly to generate combinations not previously considered. The predicted filtered Nusselt numbers agreed well with the observed (simulated) values. Work is ongoing to further expand the capabilities of the model, including 3D simulations, vertical cylinders, and uncertainty quantification.

Capturing the effects of particle heterogeneity on adsorption in a fixed bed

“…In heterogeneous porous media such as ACs, reactive transport is influenced by the meso‐ and microscale pores and interfaces both inside and between the particles 24–26 . To understand the mesoscale phenomena within an AC bed, numerical models must resolve complex geometrical features arising from microstructures and interfaces 27,28 . CFD techniques can flexibly model the physics underlying gas flow through a fixed bed amidst complicated porous geometry 29 …”

Conventional anddata‐drivenmodeling of filtered drag, heat transfer, and reaction rate ingas–particleflows

“…Recently, some researchers 25–31 have conducted conventional modeling studies on an improved understanding of mesoscale gas–particle heat transport behavior and on development of the filtered HTC (fHTC). Analogous to the drift velocity for fHDC, Rauchenzauner and Schneiderbauer 28,29 proposed a novel concept of drift temperature to model fHTC.…”

Development of a filtered reaction rate model for reactive gas–solid flows based on fine‐grid simulations

“…Therefore, accurate coarse‐grid simulations for a large‐scale reactor by the TFM must account for the effect of unresolved mesoscale structures on the resolved information through appropriate correction to the closures, such as the effective drag, heat, and mass transfer coefficients. Currently, much effort has been invested to construct the constitutive relations for the filtered drag force 5‐14 and the filtered interphase heat and mass transfer 15‐17 . It can be found from these studies that the drag force and the interphase heat and mass transfer coefficient are overpredicted in coarse‐grid simulations when sub‐grid corrections are not accounted for.…”