(572c) A Sub-Grid Model for an Array of Immersed Cylinders in Coarse-Grid Multiphase Flow Simulations of a Carbon Capture Device

A post-combustion carbon-capture system utilizing a bubbling fluidized bed of sorbent particles is currently being developed as a part of the Carbon Capture and Simulation Initiative (CCSI) efforts. Adsorption of carbon dioxide (CO₂) by these amine based sorbent particles is exothermic and arrays of immersed cylindrical heat transfer tubes are often utilized to maintain the lower temperatures favorable for CO₂ capture.  In multiphase computational fluid dynamics (CFD) simulations of the full-scale devices, which can be up to 10 m in size, approximately 10³ cells are required in each dimension to accurately resolve the cylindrical tubes, which are only a few centimeters in diameter.  Since the tubes cannot be resolved explicitly in CFD simulations, alternate methods to account for the influence of these immersed objects need to be developed.   

In this work a sub-grid CFD model is developed to account for the influence of cylindrical arrays on flow dynamics in a multiphase flow.  Highly resolved simulations of flow around a single cylinder are performed in a periodic domain, from which drag measurements are filtered to obtain the sub-grid model.  This model may then be used in coarse-grid simulations where the cylinder array is treated as a uniform porous medium exerting an anisotropic drag on the gas-solid flow.  The influence of these cylinders can appear as drag exerted on the gas and solid phases, or it may change the clustering behavior of particles thereby affecting the gas-particle drag indirectly.  Both mechanisms are investigated to formulate a new sub-grid drag model for the gas-cylinder and solid-cylinder drag and to develop corrections for the existing gas-solid drag due to the presence of cylinders.  Although this work addresses cylindrical rods in a carbon-capture device, the approach can be generalized to model other immersed obstruction geometries in industrial-scale multiphase flow simulations.