RESUMO
In this paper, a theoretical numerical analysis of the thermodynamics second law in ammonia/ethylene counter-flow diffusion flames is carried out. The combustion process, which includes heat and mass transfer, as well as a chemical reaction, is simulated based on a detailed chemical reaction model. Entropy generation and exergy loss due to various reasons in ammonia/ethylene and argon/ethylene flames are calculated. The effects of ammonia addition on the thermodynamics efficiency of combustion are investigated. Based on thermodynamics analysis, a parameter, the lowest emission of pollutant (LEP), is proposed to establish a relationship between the available work and pollutant emissions produced during the combustion process. Chemical reaction paths are also analyzed by combining the chemical entropy generation, and some important chemical reactions and substances are identified. The numerical results reveal that ammonia addition has a significant enhancement on heat transfer and chemical reaction in the flames, and the total exergy loss rate increases slightly at first and then decreases with an increase in ammonia concentration. Considering the factors of thermodynamic efficiency, the emissions of CO2 and NOx reach a maximum when ammonia concentration is near 10% and 30%, respectively. In terms of the chemical reaction path analysis, ammonia pyrolysis and nitrogen production increase significantly, while ethylene pyrolysis and carbon monoxide production decrease when ammonia is added to hydrocarbon diffusion flames.
RESUMO
In studies on the combustion process, thermodynamic analysis can be used to evaluate the irreversibility of the combustion process and improve energy utilization efficiency. In this paper, the combustion process of a laminar oxy-fuel diffusion flame was simulated, and the entropy generation due to the irreversibilities of the radiation process, the heat conduction and heat convection process, the mass diffusion process, and the chemical reaction process was calculated. The effect of the oxygen concentration in the oxidizer on the entropy generation was analyzed. The results indicated that, as the oxygen concentration in the oxidizer increases, the radiative entropy generation first increases and then decreases, and the convective and conductive entropy generation, the mass diffusion entropy generation, the chemical entropy generation, and the total entropy generation gradually increase.
RESUMO
In this paper, a three-dimensional (3-D) high-temperature furnace filled with a gas-solid medium was investigated, and the radiative transfer equation and the radiative entropy transfer equation in the chamber were applied in order to analyze the effect of coal deposits on thermal radiation. The heat flux on the walls of the furnace and the entropy generation rate were determined due to the irreversibility of the radiative heat transfer process in the furnace. Furthermore, the effect of ash deposits on the wall surface on the irreversibility of the radiation heat transfer process was investigated. The numerical results show that when burning bituminous and sub-bituminous coal, ash deposits in the furnace led to a 48.2% and 63.2% decrease in wall radiative heat flux and a 9.1% and 12.4% decrease in the radiative entropy rate, respectively. The ash deposits also led to an increase in the entropy generation number and a decrease in the thermodynamic efficiency of the radiative heat transfer process in the furnace.