Lattice Boltzmann modeling and simulation of velocity and concentration slip effects on the catalytic reaction rate of strongly nonequimolar reactions in microflows

Abstract

A lattice Boltzmann (LB) interfacial gas-solid 3D model is developed for isothermal multicomponent flows with strongly non-equimolar catalytic reactions, further accounting for the presence of velocity slips and concentration jumps. The model includes diffusion coefficients of all reactive species in the calculation of the catalytic reaction rates as well as an updated velocity at the reactive boundary node. Lattice Boltzmann simulations are performed in a catalytic channel-flow geometry under a wide range of Knudsen (Kn) and surface Damköhler (Das) numbers. Comparisons with simulations from a computational fluid dynamics (CFD) Navier-Stokes solver show good agreement in the continuum regime (Kn < 0.01) in terms of flow velocity and reactive species distributions, while comparisons with literature Direct Simulation Monte Carlo (DSMC) results attest the model's applicability in capturing the correct slip velocity at Kn as high as 0.1, even with significantly reduced number of grid points (N = 10) in the cross-flow direction. Theoretical and numerical results demonstrate that the term Das × Kn × A2 (where A2 is a function of the mass accommodation coefficient) determines the significance of the concentration jump on the catalytic reaction rate. The developed model is applicable for many catalytic microflow systems with complex geometries (such as reactors with porous networks) and large velocity/concentration slips (such as catalytic microthrusters for space applications).

A Pore-Level 3d Lattice Boltzmann Simulation of Mass Transport and Reaction in Catalytic Particles Used for Methane Synthesis

“…The basic features of the multicomponent 3D LB model and the accompanying catalytic boundary condition are introduced. This is a condensed review of four of the authors' past works [28,[31][32][33] emphasizing on the specific model features crucial to the present work, but also including new information not previously reported.…”

“…Special treatment is required for the nodes located at the catalyst surface. The catalytic boundary condition initially introduced by Arcidiacono et al [28] was extended in our previous works for arbitrarilylarge Damköhler numbers [32] and then for strongly nonequimolar catalytic reactions [33]. In the original model [28], applied here for a D3Q27 lattice, the incoming particle distribution function 𝑓 𝑖𝑛 𝑗𝑖 (see Fig.…”

“…Second, strongly nonequimolar reactions lead to noticeable variations in mixture density and velocity before and after catalytic reaction and this is crucial for the presently studied CO methanation reaction. This limitation can be removed by introducing a correction term such that the constant pressure condition at the reactive boundary is satisfied [33]. Third, micron-sized pores may create slip phenomena.…”

“…The models proposed by Arcidiacono et al [27,28] were extended by Kang et al for 2D thermal non-reacting binary mixture flows [30] and 2D thermal multicomponent flows with catalytic reactions [31]. More recent developments were introduced by Khatoonabadi et al [32,33], where the foregoing 2D models [28,31] were first extended to 3D within the framework of a D3Q27 lattice (27 discrete velocities). Furthermore, the local catalytic boundary condition of [28] and [31] was replaced by a non-local one (using information from the near-wall node), to ensure accurate simulations at affordable grid sizes for arbitrarily-high Damköhler numbers [32].…”

“…Furthermore, the local catalytic boundary condition of [28] and [31] was replaced by a non-local one (using information from the near-wall node), to ensure accurate simulations at affordable grid sizes for arbitrarily-high Damköhler numbers [32]. Lastly, Khatoonabadi et al [33] augmented the catalytic boundary condition to account for velocity slips and concentration jumps in microflows, as well as for strongly nonequimolar reactions since the resulting reaction-induced large volume change impacts the LB momentum and pressure balances at the catalytic boundary.…”