O_2/CO_2气氛下有边界层空间反应时传质系数的修正

Correction to Mass Transfer Coefficients Considering Volumetric Reaction in Boundary Layer of a Char Particle in O_2/CO_2

考虑炭粒表面氧化和还原反应、边界层CO气相反应、Stefan流和多组分扩散,建立了O2和CO2气体传质系数的修正表达式.炭球燃烧实验表明,对传质系数进行修正是必要的.考虑边界层CO气相反应后,O2传质系数降低,CO2传质系数升高.CO火焰锋面离炭粒表面越近,O2传质的修正系数越小,CO2传质的修正系数越大.当炭粒表面仅有氧化反应时,O2的修正系数最小值为0.5,比不考虑边界层反应的结果又增加了32.5%的修正量.如果同时考虑表面氧化和表面还原,反应的增多都会降低O2和CO2的传质系数,而且对CO2扩散的影响比对O2的影响大.传质系数的这些变化可归因于气相反应、表面反应和Stefan流的综合作用.

Corrections to mass transfer coefficients were presented with surface oxidation and reduction of a char particle, CO volumetric reaction in the boundary layer, Stefan flow and multi-component diffusion taken into consideration. The combustion experiments on a char sphere indicated the necessity of modifying mass transfer coefficients. Compared with the case without CO reaction considered, the mass transfer coefficient of O2 decreases while that of CO2 increases. The closer the CO flame sheet, the smaller the correction factor for O2 mass transfer while the larger that for CO2 mass transfer. When only surface oxidation is considered, the minimum correction factor for O2 is 0.5, which is 32.5% lower than that in the absence of CO gas reaction. If surface oxidation and reduction are considered at the same time, the increase in reaction number will decrease the mass transfer coefficient of both O2 and CO2, and its influence on CO2 transfer is greater than that on O2 transfer. These changes of mass transfer can be attributed to the combined effects of gaseous reaction, surface reaction and Stefan flow.