微重力蜡烛火焰特征数值模拟

Numerical Simulation of Candle Flame Characteristics in Microgravity

建立了微重力蜡烛火焰的数学模型。计算与分析表明 ,火焰的形状由空气动力学特征决定 ,火焰的温度取决于化学反应动力学特征和火焰的热损失。在静止微重力环境中 ,自然对流的消失使火焰为半球形。辐射热损失对蜡烛火焰温度 (颜色 )特征的形成有重要贡献 ,在静止微重力环境下 ,化学反应放热速率受氧气扩散速率控制 ,辐射热损失的冷却使火焰温度低于正常重力温度值。但当环境气体的流动速度加大时 ,辐射热损失的影响逐渐减小 ,蜡烛火焰的温度逐渐接近正常重力蜡烛火焰的温度。当氧浓度较小时 ,火焰峰值温度小于烟黑形成的阈值温度 (130 0K) ;当氧浓度较大时 。

A numerical model of candle flame in microgravity is established.The calculation and analysis show that the flame shape is characterized by the gas dynamics of surrounding atomsphere,and the flame temperature (or flame color) is by the chemical reaction kinetics in the flame as well as the heat loss from the flame.In quiescent microgravity,the disappearance of natural convection leads to a hemi-spherical candle flame.The radiative heat loss from the flame has great contribution to the formation of candle flame characteristics.In quiescent microgravity,the chemical reaction rate is limited by the diffusion of oxygen from the surrounding atmosphere to the candle flame,and the radiative heat loss has strong cooling effect on the flame,leading to a lower peak temperature of candle flame.With the increase of the air-flow velocity in surrounding atmosphere,the cooling effect on the flame becomes weaker and weaker,and the peak temperature approaches to the counterpart value in normal gravity.The peak temperature of candle flame is strongly related to the oxygen concentration in the surrounding atmosphere.For a lower oxygen concentration,the peak temperature may be lower than the soot-formation-threshold temperature,which accounts for the dim blue color of candle flame in microgravity;but for a higher level of oxygen concentration,the peak temperature may be higher than the soot-formation-threshold temperature,and in this case,the color of candle flame may be bright yellow,even if the candle flame is in microgravity.