A Numerical Study On Heat Transfer Of Impinging Methane-air Laminar Premixed Flame

Combustion is the main way of energy utilization.Flame impinging heat transfer is the most direct and effective way to use the combustion heat.Laminar Bunsen flame is the basis of turbulent flame.Thus,The relevant research of the flame structure and combustion characteristics of laminar premixed Bunsen flame is significant to the research on the turbulent premixed flame.In this thesis,flame structure,thermal flow field,species distribution and heat flux distribution of laminar premixed methane-air flame were simulated at different nozzle-plate distance(H=6mm,18mm,30mm,42mm),equivalence ratios(φ=0.8,1.0,1.2)and Reynolds numbers(Re=1500,2000)by using Fluent.Comparing of the result of the flame structure,thermal flow field,the species distribution and heat flux distribution by two methane-air reaction mechanisms,with the experiment,the research results are summarized as follows:Both mechanisms over predicted the height and maximum temperature of the flame,and the "hot spots" where temperatures over the adiabatic flame temperature were found at different positions of the flames,and the "hot spots" will influence the impingement heat transfer under the flow field at large nozzle-plate distances.Overall,the Chemkin mechanism gives a more reasonable temperature field and better predicts flame height and flame structure than the Fluent mechanism due to the more species and radical reactions considered.The heat transfer results showed a close relation between flame structure,temperature and heat transfer.Although the heat fluxes predicted by the two reaction mechanisms are lower than the experiment,both mechanisms can follow the experimental heat flux variation.Especially,both mechanisms can accurately predict the radial position of heat flux peak.Similarly,due to the better predicted flame structure and temperature,the Chemkin mechanism predicts the heat transfer better than the Fluent mechanism.The study reveals that the reaction mechanism used plays a vital role for modelling flame impingement heat transfer.Though a detailed mechanism improves the prediction accuracy,the running time may be too long.So a reduced mechanism can be used in industrial applications.However,if more accurate data is needed to analyze the thermal flow field,a more detailed mechanism is needed.The combustion model of this thesis can be used as the basis of the flow field and pollution discharge simulation.