Modeling formation and transport of clusters at high temperature and pressure gradients by implying partial chemical equilibrium

TL;DR

This paper presents a theoretical model for cluster transport in gases under high temperature and pressure gradients, emphasizing partial chemical equilibrium and deriving analytical expressions for diffusion coefficients.

Contribution

It introduces a novel collective description of cluster transport assuming local partial chemical equilibrium, applicable to high-temperature plasma processes.

Findings

Thermal diffusion can be significant even when molecular diffusion is negligible.

Analytical formulas for effective diffusion and thermal diffusion coefficients were derived.

The model successfully accounts for sulfur clusters in H2S conversion processes.

Abstract

A theoretical approach to describing transport of an entire ensemble of clusters with different sizes as a single species in gas has been developed. The major assumption is an existence of local partial chemical equilibrium between the clusters. It is shown that thermal diffusion emerges in the collective description as a significant factor even if it is negligible when transport of the original molecular species is considered. Analytical expressions for the effective diffusion and thermal diffusion coefficients at temperature, pressure, and chemical composition gradients have been derived. The theory has been applied to a technology of H2S conversion in a centrifugal plasma-chemical reactor and has made it possible to account for sulfur clusters in numerical process modeling.