Mesoscopic simulations of transport phenomena in reactive systems

The scope of the project is to study the interplay of transport phenomena (convection, diffusion) and reactions taking place near surfaces in structured reactors and porous media.

In many catalytic reactors, a fluid flow is used to enhance the mass transfer to and from catalytic sites dotted on solid surfaces. Computational Fluid Dynamics techniques can be used to investigate the mass transfer, but the boundaries between the solid surface and the fluid are usually corrugated on length scales much smaller than the CFD grid (sub-micrometer scale), leading to sub-grid-scale effects that are not included in CFD simulations. Moreover, the pore spaces in catalytic pellets may become so small that non-continuum (molecular) effects such as Knudsen diffusion start to play a role. On the other hand, the relevant scales where these phenomena take place are usually so large that detailed Molecular Dynamics simulations are also out of the question. In such cases it will be advantageous to use mesoscale particle-based simulations methods to investigate the coupled convection-diffusion-reaction mechanisms taking place in boundary layers and in porous media.

In particular, the technique of Stochastic Rotation Dynamics will be used, which can automatically account for thermal fluctuations and hydrodynamics, and extend it with reactions on surfaces. In Stochastic Rotation Dynamics, which was co-developed by Prof Padding, the fluid (gas or liquid) is coarse-grained to a set of point particles, which interact with each other though highly efficient multi-particle collision rules. The resulting dynamics of the fluid obeys the Navier-Stokes equations at larger scales, but has the advantage of automatically accounting for thermal fluctuations and (coarse-grained) molecular diffusion. Reactive surfaces will be implemented by probabilistic rules for particle adsorption and desorption, with reaction kinetics that can be linked to microkinetic models obtained from quantum-mechanical (DFT) calculations. The simulations will give an insight in the interplay of convection, diffusion, and reaction mechanisms, and clearly pinpoint the conditions under which transport limitations become important. This will allow for optimization of the design of new catalytic structures to be used in large scale industrial operations.

Complex Fluid Processing

Involved People:
Rong Fan
Johan Padding
Remco Hartkamp

Facilities used: