Heat recirculation and heat losses in porous micro-combustors: Effects of wall and porous media properties and combustor dimensions

Highlights: • Heat losses and heat recirculation are crucial factors in porous micro-combustors. • Heat transfer through combustor wall and porous media is quantified. • Effects of heat losses and heat recirculation on flame temperature are revealed. • Scale effects on heat transfer in porous micro-combustors are discussed. • Methodology proposed could be readily applied to other configurations. The micro-combustor is a key component of most combustion-based micro power generation devices. Porous micro-combustors stand as a potential promising solution able to sustain reactions under a wider range of conditions. Multiple heat transfer modes co-exist and are closely coupled in porous micro-combustors, and therefore the primary objective of the present study is to analyze various heat fluxes occurring in porous micro-combustors in a quantitative manner in order to reveal their relative importance and provide clues for better design and operation of such devices. Numerical simulations of premixed combustion of H₂/air in porous combustors with the combustor heights from 1.0 mm to 2.0 mm are carried out. By quantifying heat recirculation and heat losses in the preheat zone and the reaction zone, respectively, the effects of the wall thermal conductivity and the porous media properties (thermal conductivity and porosity) on the flame temperature are discussed. Comparing the results of different combustor heights shows that the smaller porous micro-combustor has a higher proportion of heat recirculation relative to heat losses. The flame temperature is found to be inversely related to the ratio of total heat losses to total heat recirculation. The methodology developed in this study could be easily applied to other micro-combustor configurations with or without the porous media with necessary adaptions.