Combustion characteristics and stability of millimeter-scale energy systems with premixed propane flames for hydrogen production
18 Pages Posted: 18 Aug 2022
Date Written: August 9, 2022
Millimeter-scale energy systems are of importance in the study of flame structure. However, the development of millimeter-scale energy systems is hindered by the lack of a clear concept of the critical role that energy considerations play in an accurate explanation of combustion within very small spaces. Computational fluid dynamics simulations were performed to elucidate the energy aspects of combustion within very small spaces, which in turn contributes to an understanding of the nature of flames. Physical flame phenomena were studied, and the effect of wall material properties on combustion characteristics and stability was evaluated. Heat transfer analyses were made to investigate the oxidation characteristics of combustibles on a catalytic surface accompanied by the release of heat but without flame. Combustion phenomena were predicted over wide temperature and concentration ranges. Design recommendations with backside cooling were made for hydrogen production. The results indicate that combustion occurs at higher temperatures, accompanied by hot flames. Physical processes that transfer mass and energy by diffusion or convection occur in gaseous combustion. The process of diffusion is of great importance in combustion reactions. Investigation of burning velocities and study of flame temperatures play a vital part in the refinement of theories concerning the mechanism of combustion within very small spaces. The complex combustion process depends heavily upon the properties of the combustible substance and wall material. The combustion spreads from the ignition source near the wall to the adjacent layer of gas mixture. Cavities greatly contribute to their ease of combustion. Combustion terminates when excessive heat is lost to the surroundings. A relationship exists between the wall temperature and the wall thermal conductivity. The mechanism of the reaction determines the flammability limits. The knowledge of temperature and reaction rates makes possible a quantitative description of combustion characteristics. Great amounts of heat losses extinguish the flame, and the same result is achieved when substances that remove any of the active species are added to the flame. Conditions must be such that the flame is fixed in the combustion chamber. Flame temperatures depend on the chemical and thermodynamic properties of the mixture and on pressure and temperature, under given conditions of heat loss. Both heat transport and diffusion of active radicals must be considered essential for ignition.
Keywords: Combustion characteristics; Flammability limits; Chemical reactors; Catalytic reactions; Energy systems; Heat conduction
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