Analysis of the outcome of blow-out operation in EAST manifold

Abstract

Prior to equipment maintenance and “baking” operation, the Experimental Advanced Superconducting Tokamak (EAST) carries out a “blow-out” operation. Utilizing a manifold structure, pressurized nitrogen gas is driven into the Plasma Facing Components (PFCs)' cooling channels to eject residual cooling water. The “outcome” of the blow-out operation, the final steady-distribution of the gas-liquid two-phase in the manifold, significantly influences the efficiency, the time and energy cost of the subsequent drying process and indirectly shapes the quality of the vacuum environment required for plasma operation. In this context, this paper presents a theoretical analysis and simulation of the outcome of blow-out operation of EAST manifold. The analysis discusses three kinds of steady distribution state within a manifold branch: “Stagnant", “Two-phase flow", and “Near-dry flow". It is observed that stable “Two-phase flow” cannot be maintained when multiple branches flow concurrently due to the unstability of parallel flows. Thus, in such scenarios, the branch primarily exhibits only “Stagnant” and “Near-Dry” states. Furthermore, the total gas flow rate plays a significant role in determining the number of “Near-Dry” branches. Simulation provides specific quantities prediction of “Near-Dry” branches under varying gas volume flow rates. Finally, the theoretical analysis and simulation results is validated through experimental data. This study offers valuable insights for optimizing future blow-out operations of the EAST manifold.