Entropy generation during microcombustion

Abstract

We use an entropy balance to formulate the entropy generation equation in a flame zone of a cylindrical microcombustor tube. In deriving this equation, we define a nondimensional radius as the ratio of the tube radius to the flame thickness, and we set up a thermal model of the flame zone by applying an energy balance for a steady flow system to the flame zone. Based on this model, we obtain a relationship between the flame temperature and the nondimensional radius. Given this relationship, the effects of the fuel, fuel-air ratio, unburned gas temperature, and tube radius on entropy generation are analyzed. The occurrence of minimum entropy generation is predicted. The efficient operating conditions of the microcombustor are suggested.

Progress in the Prediction of Entropy Generation in Turbulent Reacting Flows Using Large Eddy Simulation

“…These include system-level analysis, often termed exergy analysis, to obtain the net rate of exergy destruction [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. More detailed studies involve identification of specific processes contributing to losses by considering the local generation of entropy.…”

Development of 1D model for the analysis of heat transport in cylindrical micro combustors

“…Firstly, the 1D flame model is a simplification as the scale analysis [10] noted that the reacting flow in the micro combustor is 2D in nature. However, the 1D assumption is well established and has been widely applied in studying laminar flame propagation [19][20][21]24,25]. Furthermore, Kaisare and Vlachos [37] compared the 1D and 2D (averaged in the radial direction) simulation results and noted that they were in reasonable quantitatively agreement.…”

“…Aside from these numerical studies, Leach et al [19] extended Mallard and Le Chatelier's (1D) thermal flame model to investigate the H 2 -air combustion in micro channels and noted that the heat exchange through the structure of the micro combustor leads to broadening of the reaction zone. Besides, Li et al applied the 1D flame model coupled with the heat conduction in the combustor wall and used it to correlate the flame temperature to the wall temperature [20] and analyze the entropy generation in the micro combustion process [21]. It should be noted that although Leach [20,21] to quantify two important ratios, namely, the heat loss ratio Q l /Q in (defined as the ratio of the heat loss from the flame to the heat generation in the reaction zone) and the heat recirculation ratio Q recir /Q l (defined as the ratio of the heat recirculation through the solid structure to the upstream to the heat loss from the flame).…”

“…Besides, Li et al applied the 1D flame model coupled with the heat conduction in the combustor wall and used it to correlate the flame temperature to the wall temperature [20] and analyze the entropy generation in the micro combustion process [21]. It should be noted that although Leach [20,21] to quantify two important ratios, namely, the heat loss ratio Q l /Q in (defined as the ratio of the heat loss from the flame to the heat generation in the reaction zone) and the heat recirculation ratio Q recir /Q l (defined as the ratio of the heat recirculation through the solid structure to the upstream to the heat loss from the flame). Q l /Q in determines the relative intensity of heat loss in the flame zone, while Q recir /Q l reflects the significance of heat recirculation.…”

Entropy Transport Equation in Large Eddy Simulation for Exergy Analysis of Turbulent Combustion Systems

“…The vast majority of contributions so far has been on exergy analysis of combustion systems with laminar flow regimes [3,5,6,11,12,19,20]. Despite the prevalence of turbulence in practical combustion devices, the application of exergy analysis to turbulent reacting flows has been very limited [8,10,16,18].…”