Experimental two-phase liquid-metal magnetohydrodynamic generator program. Final report, October 1977-September 1978

The experimental results presented satisfy one major goal in demonstrating the technical feasibility of two-phase LMMHD (liquid-metal MHD), i.e., operating an MHD generator at power densities equal to or above that anticipated for practical power systems. Power densities of up to 32 MWe/m3 and efficiencies higher than 0.6 at high void fractions were attained for a small 20-kWe generator. Slip ratio data, and more-extensive pressure distribution and voltage profile data are also given. Barium has been identified as an attractive additive for the generation of foams with NaK, and bismuth is a back-up for barium. A guiding hypothesis for understanding the phenomena contributing to foamability in liquid metal systems has been developed, and basic data on surface tension obtained. A computer code has been developed that will calculate the electrical end loss for any insulating vane geometry and magnetic flux density distribution, a significant accomplishment. Initial studies with this code have shown that generator efficiencies in excess of 0.8 are attainable. Initial measurements of local flow parameters in a NaK-nitrogen two-phase liquid-metal MHD generator, using hot-film and resistivity probes, are reported. Although the results are preliminary, there is evidence that large electromagnetic force densities have a significant effect on the sixze and distribution of the gas bubbles or voids. All results are very encouraging for the development of large high-efficiency LMMHD generators