氣體爆發の限界と傳播速度

Abstract

General properties of gaseous explosion are reviewed and some new simple theories by this author and his collborator are proposed. 1. Characterestics of Explosion. According to the author's opinion, gaseous explosion is essentially heterogeneous. It seems to proceeds through two kinds of stages as follows: (1) Primary stage. ----generation of locally concentrated reaction zone (or a flame) in gaseous phase or on a solid surface by the energy supplied externally. There exist certain limits in the energy and gaseons conditions. (1) Secondary stage. ----propagation of the reaction zone whose activation energy can be supplied by the primary process or every reaction zone. In order to elucidate these characterictics from the atomistic view point, the auther and his collaborator has proposed some theories as follows. 2. Propagation Velocity of a Detonating Flame. It is very complicate to discuss the propagation velocity of a flame theoretically, because it is generally accompanied by thermal or hydrodynamic confusion. But the detonating flame whose velocity is larger than the sound velocity may be considered to be free from such confusion and so its propagation may be treated as a continuity of the secondary activation stage. The energy released by the flame front may be reserved by the reactant melecules as their kinetic energy and parted equally to the every degree of freedom of those molecules. Assuming that the detonation velocity corresponds the mean translational velocity V¯ of the reactant molecules whose tatal mass is M, the following relation might be held; [Figure omitted] where J is the mechanical equivalent of heat, Q heat of reaction, ɛ energy of activation, ft the degrees of freedom of translaion and F the total degrees of freedom. Neglecting ɛ for Q, [Figure omitted] where γ is ƒ●F. Calculated values of V¯ show good agreement with the observed values for 15 kinds of detonation (Table 1). 3. Lower Limit of Composition. If C1 is a lower inflammation limit of combustible gas in volume ratio, number of molecules of supporter-gas (O2 and N2) per one molecule of combustible gas is given by 1/C1 approximately. In the elementary reaction, the sum of the reaction heat and activation energy may be released and distributed among the surrounding molecules as kinetic energy. It is assumed that the flame propagation might occur when the energy distributed for every degree of freedom of the inert molecules (O2 + N2, or O2) exceeds the activation energy ɛ. Accordingly the starting condition of explosion may be given by the equation [Figure omitted] where Q is the heat of reaction, ɛ the activation enrgy, and F the total number of degree of freedom (7 for O2 and N2) of the supporter-gas molecules. If ɛ can be neglected for Q, the equation (3) becomes [Figure omitted] The equation (4) gives the linear relation between C1 ahd T; and the activation energy ɛ can be evaluated from this relation. It has been found that Q×C1 is nearly constant (about ll kcal) for many kinds of organic compounds (Fig 2). It means that the activation energies take almost the same value (about 1.9 kcal/mol). Activation energies for H2 and CS2 are estimated to be exceptionally small. Upper limit of inflammation can be treated in the similar way as above.