Modelling nanoparticle deposition rate in iron particle combustion

Abstract

Iron powders attract increased interest as energy carrier as they can provide high temperature heat during combustion. The combustion products can be recycled using renewable energy leading to a carbon free and fully closed energy cycle. However, nanoparticles are formed as by-products. They are difficult to remove from the exhaust gases, and the slip of iron nanoparticles reduces cycle efficiency and compromises sustainability. Nanoparticle slip is reduced by their deposition onto the fuel microparticles that act as a spherical collector, but the fraction of the nanoparticles that do not escape due to deposition is totally unknown. In this study, Lagrangian and Eulerian simulations are performed to evaluate the deposition of nanoparticles onto microparticles due to inertial impaction and diffusion. The simulation results are validated with analytical solutions from the literature. Then, the effects of a positive and a negative Stefan flow occurring at the microparticle’s surface during combustion are investigated. A model for the collection efficiency in the diffusion-dominated regime and in the presence of positive or a negative Stefan flows is proposed. This collection efficiency model can then be used to augment the classic kernel of Smoluchowski such that its validity is extended to flow conditions prevalent in iron combustion.