An Investigation of the Fluid Dynamics Aspects of Thin Liquid Film Protection Schemes for Inertial Fusion Energy

Experimental and numerical studies of the fluid dynamics of thin liquid film wall protection systems have been conducted in support of the ARIES-IFE study. Both the porous “wetted wall” concept, involving low-speed injection through a porous wall normal to the surface, and the “forced film” concept, involving high-speed injection through slots tangential to the surface, have been examined. These initial studies focus upon the “preshot” feasibility of these concepts, between chamber clearing and the fusion event. For the wetted wall, a three-dimensional level contour reconstruction method was used to track the evolution of the liquid film on downward-facing walls for different initial conditions and liquid properties with evaporation and condensation at the free surface. The effects of these parameters on the film dynamics, the free surface topology, the frequency of liquid drop formation and detachment, the minimum film thickness between explosions, and the equivalent diameter of detached drops have been analyzed. Initial experimental results are in reasonable agreement with the numerical predictions. Generalized nondimensional charts for identifying appropriate “design windows” for successful operation of the wetted wall protection concept have been developed. The results demonstrate that a minimum repetition rate is required to avoid liquid dripping into the reactor cavity and that a minimum injection velocity is required in order to maintain a minimum film thickness over the first wall. For the forced film concept, experimental investigations of high-speed water films injected onto downwardfacing flat and curved surfaces at angles of inclination up to 45 deg below the horizontal were conducted. Mean detachment length and the lateral extent of the film were measured for a wide range of liquid-solid contact angles at different values of the initial film thickness, liquid injection speed, and surface orientation. The results show that the film detaches earlier (i.e., farther upstream) for nonwetting surfaces and for flat (versus curved) surfaces. The nonwetting flat surface data are therefore used to establish a conservative “design window” for film detachment. Initial observations of film flow around cylindrical obstacles suggest that cylindrical dams are incompatible with forced films.