Measurements of vapor flow regimes in liquid metal pools

There is significant ongoing research within the APEX project to develop innovative first wall/blanket concepts capable of efficiently extracting useful thermal energy from magnetic fusion devices that can substantially improve the attractiveness of fusion energy systems. Among the several different ideas are solid and liquid wall concepts. One solid wall concept being considered is the EVOLVE concept. This concept relies on liquid lithium filled tungsten trays to act as a heat transfer and tritium breeding media. In this design, liquid lithium flows into tungsten trays and is brought to the saturation temperature by volumetric neutronic heating of the liquid lithium and tungsten trays. The lithium vapor generated could then be used as the heat transfer media for the thermal power cycle. Key to this design is the vaporization and boiling of the lithium in the presence of a strong magnetic fields (∼7 T). Initial analysis of the boiling phenomena lead to many questions regarding the void fractions and boiling flow regime (void distribution) that may exist in the trays [Fusion Technol. 39 (2001) 810]. Since it is necessary to know the void fraction and flow regime present during the boiling process to determine the neutronic heating and energy removal capability, experiments have been initiated to examine this issue. This paper presents initial experiments and scaling analysis conducted in a new test section, which provides real time X-ray determination of flow regimes and void fractions within a pool of low-density liquid metal (NaK) during gas injection inside a horizontal magnetic field. Data will be presented from a first series of tests with gas injection of volumetric flow rates from 0 to 5 SCFH (0<Jg<0.06 m/s) with no field.