富氧燃烧中斯蒂芬流对碳粒热平衡的影响

Effect of Stefan Flow on Heat Balance of a Char Particle in Oxy-Fuel Combustion

斯蒂芬流不仅影响组分的质量传递，还对能量传递有影响，而后者通常为研究者所忽略．本文通过建立具有明确物理意义的热流公式，推导出包括斯蒂芬流影响的能量守恒方程，深入研究了斯蒂芬流对碳粒热平衡及其着火的影响．结果表明，考虑斯蒂芬流后，总的化学反应热会随气体温度的升高而增大，辐射热流几乎不变；碳粒着火延迟，着火温度比无斯蒂芬流时约高30K，氧气浓度（体积分数）约高7％．忽略斯蒂芬流导致碳粒（50μm）燃烧速率和表面温度分别高出23％。40％和7％～10％，而熄火粒径偏低，约为28μm．与文献中的修正能量方程相比，新的能量方程更适合碳粒的富氧燃烧计算．

Stefan flow has influence not only on the mass transfer of gas components but also on the heat transfer that is often neglected in the research of char combustion. The heat flux equation, which has definite physical meaning, was established in this work. The energy conservation equation including the Stefan flow was then derived and used to study the effect of Stefan flow on the heat balance and ignition of a char particle in O2/CO2 atmosphere. The results showed that if the Stefan flow was considered, the total chemical reaction heat flux would increase with the gas tem- perature while the radiation heat hardly changed. The ignition of char was retarded, requiring a gas temperature of about 30 K higher or an oxygen molar fraction of 7% larger than those with the Stefan flow reglected. For a carbon particle of 50 μm, compared with the case of considering the Stefan flow, neglecting the Stefan flow would lead to 23%-40% larger in the combustion rate and 7%--10% higher in the surface temperature and to a smaller burnout di- ameter（28 μm）. Compared with the modified energy equation from the literature, the equation developed in the pre- sent work is more suitable for the oxy-fuel combustion of char particle.