Numerical analysis and optimization of divertor cooling system

Novel divertor cooling system concept is currently under development at Princeton Plasma Physics Laboratory (PPPL). This concept utilizes supercritical carbon dioxide as a coolant for the liquid lithium filled porous divertor front plate. Coolant is flowing in closed loop in the T tube type channel. Application of CO
₂
eliminates safety concerns associated with water cooling of liquid lithium systems, and promises higher overall efficiency compared to systems using He as a coolant Numerical analysis of divertor system initial configuration was performed using ANSYS software. Initially conjugated heat transfer problem was solved involving computational fluid dynamics (CFD) simulation of the coolant flow, and heat transfer in the coolant and solid regions of the cooling system. Redlich Kwong real gas model was used for equation of state of supercritical CO
₂
together with temperature and pressure dependent transport properties. Porous region filled with liquid lithium was modeled as a solid body with liquid lithium properties. Evaporation of liquid lithium from the front face was included via special temperature dependent boundary condition. Results of CFD and heat transfer analysis were used as external conditions for structural analysis of the system components. Simulations were performed within ANSYS Workbench framework using ANSYS CFX for conjugated heat transfer and CFD analysis, and ANSYS Mechanical for structural analysis. Initial results were obtained using simplified 2D model of the cooling system. 2D model allowed direct comparison with previous cooling concepts which use He as a coolant. Optimization of the channel geometry in 2D allowed increase in efficiency of the cooling system by reducing the total pressure drop in the coolant flow. Optimized geometrical parameters were used to create a 3D model of the cooling system which eventually can be implemented and tested experimentally. 3D numerical simulation will be used to validate design variants of the divertor cooling system.