EFFECT OF OXYGEN ON THE OPERATION OF A PLANAR THERMIONIC CONVERTER FOR ISOTHERMAL AND ISOFLUX HEATING CONDITIONS

In this paper, the effects of oxygen on the performance of and the emi tter material transport in a planar thermionic converter were investig ated. The oxygen and cesium partial pressures in the interelectrode ga p were varied parametrically, and their effects on the operational cha racteristics of the converter were quantified for both isothermal and isoflux emitter heating conditions. With isothermal heating, a signifi cant increase in the electric power density in the presence of oxygen (by a factor of 3-10, depending on the emitter temperature and the ini tial composition of the collector surface) was predicted. The load vol tages corresponding to the maximum output power were similar to 0.3-0. 5 V lower than those corresponding to the optimum efficiency. With an isoflux emitter heating of 20 W/cm(2), the introduction of oxygen into the interelectrode gap of a converter with an initially pure tungsten collector increased the electric power density by only similar to 19% ; however, no improvement occurred for-an initially oxidized tungsten collector. (C) 1997 Elsevier Science Ltd.