The effect of turbulent clustering on particle reactivity

TL;DR

This paper uses DNS to study how turbulence-induced particle clustering affects reaction rates in solid-fluid systems, revealing that turbulence can significantly slow reactions at high Damköhler numbers and proposing a model for CFD simulations.

Contribution

It introduces a turbulence-based model for heterogeneous reaction rates considering particle clustering effects, validated through DNS.

Findings

Particle clustering by turbulence controls reaction rates at high Damköhler numbers.

Reaction rates reach an asymptotic limit due to clustering effects.

A new model for heterogeneous reaction rates in turbulent flows is proposed.

Abstract

The effect of turbulence on the heterogeneous (solid-fluid) reactions of solid particles is studied numerically with Direct Numerical Simulations (DNS). A simplified reaction system is used, where the solid-fluid reaction is represented by a single isothermal reaction step. It is found that, due to the clustering of particles by the isotropic turbulence, the overall reaction rate is entirely controlled by the turbulence for large Damk\"ohler numbers. The particle clustering significantly slows down the reaction rate for increasing Damk\"ohler numbers which reaches an asymptotic limit that can be analytically derived. This implies that the effect of turbulence on heterogeneously reacting particles should be included in models that are used in CFD simulations of e.g. char burnout in combustors or gasifiers. Such a model, based on the chemical and turbulent time scales, is here proposed for the heterogeneous reaction rate in the presence of turbulence.