Theoretical analysis of the condensation of combustion products in thin gaseous layers

In this paper, a theoretical analysis of the condensation of combustion products in narrow gaps between planar plates is performed. The investigation is motivated by the empirical results shown by Veiga-Lopez [Flame propagation in narrow channels, Ph.D. thesis (Carlos III University of Madrid, 2020)] and the lack of a theoretical description directly applicable to them. In these experiments, he describes how discontinuous condensed water films appeared on the walls of the combustion chamber, forming dry/wet stripes parallel to the flame front at the products region. The formulation developed here is derived from a general approach for condensation, which is simplified considering the conditions of high-temperature combustion products. Notably, the liquid phase disappears from the system of equations, which exclusively contains the gaseous phase. The expressions resulting are analytical, simple, and easy to interpret. They allow us to understand qualitatively the effects of the main physical phenomena of the process, which is described by the interaction between heat exchange, mass transfer, the thermodynamic conditions, and the velocity of the combustion products. The construct is subsequently utilized to perform the numerical parametric studies, to analyze the influence of two main parameters of the problem: gap thickness and flame velocity. Despite the relative simplicity of the model, it predicts similar condensation-vaporization-condensation cycles to those observed at the laboratory. Published under an exclusive license by AIP Publishing.

Automated summary

This paper presents a theoretical analysis of the condensation of combustion products in narrow gaps between planar plates, based on empirical results and lacking theoretical descriptions. The simplified formulation exclusively containing the gaseous phase allows for analytical expressions that qualitatively explain the effects of physical phenomena on the process. Despite its simplicity, the model predicts similar cycles of condensation-vaporization-condensation observed in laboratory experiments.