(425b) Validation of Filtered Two-Fluid Models Using NETL-PSRI Bubbling Fluidized Bed Challenge Problem

Filtered two-fluid models offer a promising practical alternative to microscopic two-fluid model for the simulation of gas-particle flows in industrial systems generally characterized by heterogeneous structures ranging from micro-scale to macro-scale. In our prior studies [1,2] we performed highly resolved simulations of gas-particle flows using microscopic two-fluid model and extracted constitutive models for filtered drag coefficient and filtered particle phase stresses in terms of filtered particle volume fraction and filter size as markers that classify inhomogeneity of sub-filter scale flow structures. In our recent study [3] we further investigated various markers and identified filtered fluid-particle slip velocity as an important additional marker for filtered drag coefficient. In that study new constitutive models were proposed. Filtered drag coefficient was expressed in terms of filtered particle volume fraction, filter size and filtered slip velocity while pressure and viscosity of both phases were expressed in terms of filtered particle volume fraction, filter size and filtered scalar shear rates. 

In present study, we focus on validation of Milioli et al. filtered models [3] using NETL-PSRI bubbling fluidized challenge problem [4].  Simulations were performed using different levels of relatively coarse grid resolutions and differential pressure gradient (also indicator of bed expansion) data from experiments was used for comparison.  It was found that Milioli et al. filtered models predicted correct bed expansion and differential pressure gradient predictions compared well with experiments while microscopic two-fluid model and Igci et al. filtered models [1] predicted unphysical bed expansion thereby clearly demonstrating the relative importance of filtered drag and its dependence on filtered slip velocity.  Milioli et al. filtered models were also tested under different flow conditions including initial static bed depth and gas superficial velocity. Overall, model predictions were found to be in good agreement with experiments.

1. Y. Igci and S. Sundaresan, Ind. Eng. Chem. Res., 50, 13190–13201 (2011).

2. Y. Igci and S. Sundaresan, AIChE J., 57, 2691-2707 (2011).

3.  C.C. Milioli, F.E. Milioli, W. Holloway, K. Agrawal, S. Sundaresan, Accepted to AIChE Journal (2012).              

4. NETL-PSRI Bubbling Fluidized Bed Challenge Problem 2010, https://mfix.netl.doe.gov/challenge/index_2010.php.