Water-cooled insulating walls for MHD generators

The wall of an MHD generator must insulate electrically along the plane of the wall and, if the wall temperature is less than that of the gas, the wall must conduct heat from the gas into a coolant. The authors believe that the requirements of long life and durability make it necessary, when the actual operating environment (ash, seed, combustion gases) has been considered, to operate the wall at a temperature considerably less than that of the gas. The resultant heat-transfer loss can be minimized by minimizing generator length with high magnetic-field strength. The properties of good electrical insulation and high thermal conductivity are not commonly found in a single material. This paper describes the mechanical development of a composite water-cooled wall consisting of metallic elements separated by thin sections of electrical insulation. Duration tests of up to 140 hr have been experienced by these walls, including over 130 hr with ash and seed and with the walls still in operating condition. Although the water wall requires more endurance testing, it appears to have promise for use in central station MHD power plants.