MHD発電器作動ガスの電場による非平衡電離
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概要
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This paper deals theoretically with nonequilibrium ionization of MHD gases in magnetically induced or applied electric fields in MHD devices. It is shown that electron energy in the gases is in a Maxwell distribution with the electron temperature T_e,even in nonequilibrium states. However, the degree of nonequilibrium ionization is much lower than that from the Saha equation based on T_e at low electron temperatures. The enhancements in the electron density n_e, i.e. the electrical conductivity σ, and T_e in electric fields can be calculated from an electron energy balance equation containing radiative energy loss terms. The flow region is divided into two sections. One is a transient section, near the inlet of the device, of which length is an order of 1cm. The other is a steady or generator section, where n_e can be assumed to be locally in equilibrium with T_e, since the relaxation times of T_e and n_e are very short compared with those of heavy species. The current density-electric field characteristics theoretically obtained in K-seeded Ar and Na-seeded Ar are in good agreement with those experimentally obtained. In these experiments, the nonequilibrium conductivity of an order of 100mhos/m has been obtained. Hence, it is concluded that the enhancements in the electrical conductivity of MHD gases in induced or applied fields in MHD devices can be expected according to the results shown in this paper, if the decrease in the fields, e.g. by short circuit in Hall currents near the surfaces of insulators, does not occur. It is also shown that the optimum seeding ratio should be smaller than that in equilibrium states, since the radiation loss increases with the seeding ratio.
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