Study on the combustion mechanism of molten sodium

熔融钠的燃烧是一种固相燃烧，与传统基础燃烧科学中普遍存在的火焰现象不同。(1)反应区出现吸力。(2)固相产物从反应区扩散和移除的过程较为复杂。(3)固相生成物的辐射换热有重要作用。本文从基础燃烧科学的角度阐明了钠的燃烧过程。详细研究了悬浮固相产物（气溶胶）的辐射换热行为，并对气溶胶对辐射换热的影响进行了广泛的讨论。采用基于输运方程的辐射传热模型作为吸收发射介质。在以上讨论的基础上，通过数值分析得出以下结论：研究了钠池表面燃烧速率和火焰高度，熔钠温度、大气温度、大气氧浓度和钠池表面发射率的影响。研制了一种精密的实验钠燃烧器。它实质上是一个逆流扩散火焰燃烧器。所述燃烧器周围有一对蜂窝，构成辐射反馈燃烧器。在蜂窝表面形成甲烷的预混火焰，保持蜂窝间的空间为受控的高辐射场。在熔钠池表面观察到逆流扩散火焰。计算结果与分析结果基本一致。此外，还分析了逆流驻点附近的轴对称流场，包括对气溶胶的详细检查。通过与实验结果的比较，澄清了这一现象。

The combustion of melting sodium is difficult and different from flame phenomenon widely known in the conventional basic combustion science because product is a solid phase. (1) There appears suction on the reaction zone. (2) The process of diffusion and removal of the solid phase product from the reaction zone is complicated. (3) The radiation heat transfer by the solid phase product has an important effect. In this study, the combustion of sodium is clarified from the viewpoint of the basic combustion science. The behavior of the radiation heat transfer by floating solid phase product (aerosol) was examined in detail and the effect of the radiation heat transfer by aerosol is discussed widely. The radiation heat transfer model based on the transport equation as an absorbing emitting medium was used. The followings were clarified by the numerical analysis based on above discussions ; surface combustion rate and flame height from the sodium pool, the effects of melting sodium temperature, atmosphere temperature, atmosphere oxygen concentration and emissivity of sodium surface. A sophisticate experimental sodium combustor was made. It is substantially a counter flow diffusion flame burner. The burner is surrounded with a pair of honeycomb which composes a radiation feedback burner. The premixed flame of the methane is formed on the honeycomb surface and the space between honeycomb is kept as a controlled high radiation field. Counter flow diffusion flames on the melting sodium pool surface were observed. The results agreed approximately with the analysis. In addition, an axi-symmetric flow field near the stagnation point of the counter flow was analyzed including detailed examination of the aerosol. The phenomena was clarified by comparing with the experimental results.