Two-phase alkali-metal experiments in reduced gravity

Abstract

Future space missions envision the use of large nuclear reactors utilizing either a single or a two-phase alkali-metal working fluid. The design and analysis of such reactors require state-of-the-art computer codes that can properly treat alkali-metal flow and heat transfer in a reduced-gravity environment. Current single and multiphase computer codes rely on the presence of gravity-in the fluid momentum equations, in defining their flow regimes, in specific two-phase flow models, or indirectly in the form of correlations obtained from tests conducted in a 1-g field. New flow regime maps, models, and correlations are required if the codes are to be successfully applied to reduced-gravity flow and heat transfer. A literature search of relevant experiments in reduced gravity is reported on here, and reveals a paucity of data for such correlations. The few ongoing experiments in reduced gravity are noted. General plans are put forth for the reduced-gravity experiments which will have to be performed, at NASA facilities, with benign fluids. A similar situation exists regarding two-phase alkali-metal flow and heat transfer, even in normal gravity. Existing data are conflicting and inadequate for the task of modeling a space reactor using a two-phase alkalimetal coolant. The major features of past experiments are described here. Again, general plans are made for future alkali-metal experiments in normal gravity. Data from the reduced-gravity experiments with innocuous fluids are to be combined with normal gravity data from the two-phase alkali-metal experiments. Analyses undertaken here give every expectation that the correlations developed from this data base will provide a valid representation of alkali-metal heat transfer and pressure drop in reduced gravity.