Study on the combustion mechanism of molten sodium

熔融钠的燃烧很困难，与传统基础燃烧科学中广为人知的火焰现象不同，因为产物是固相。(1)反应区出现吸力。(2)固相产物从反应区的扩散和去除过程是复杂的。(3)固相产物的辐射换热对传热有重要影响。本研究从基础燃烧科学的观点阐明了钠的燃烧。本文详细研究了悬浮固相产物（气溶胶）的辐射换热行为，并对气溶胶的辐射换热效应进行了广泛的讨论。采用基于输运方程的辐射传热模型作为吸收-发射介质。在此基础上，通过数值分析，得到了表面燃烧速率和火焰离钠池高度，以及熔融钠温度、大气温度、大气氧浓度和钠表面发射率对表面燃烧速率和火焰高度的影响。研制了一台小型实验钠燃烧器。它基本上是逆流扩散火焰燃烧器。该燃烧器的四周环绕着一对蜂窝体，构成辐射反馈燃烧器。在蜂窝表面形成甲烷预混火焰，蜂窝间隙保持受控的高辐射场。在熔融钠池表面观察到逆流扩散火焰。结果与分析基本一致。此外，一个轴对称的流场附近的停滞点的逆流进行了分析，包括详细检查的气溶胶。通过与实验结果的比较，对这一现象进行了解释。

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.