Numerical optimization of cold trap designs for the Karlsruhe Sodium Laboratory

The present study is focused on the numerical analysis of three designs (basic, intermediate and optimized) for the cold trap considered for sodium purification in the KASOLA (KArlsruhe SOdium LAboratory) sodium loop. Given the complexity of the construction the present approach was based on CFD (Computational Fluid Dynamics). The comparison of the designs considered reveals that significant improvements have been obtained regarding the cooling and heat recovery systems. The CFD (Computational Fluid Dynamics) models considered a conjugate heat transfer approach in order to simulate both fluids (air and sodium) and the solid domains (stainless steel walls). The stainless steel wool packages were numerically modelled using a porous domain. For most of the cases the air flow is turbulent and was modelled using the Shear Stress Transport (SST) turbulence model, while the sodium flow was treated as laminar or turbulent, depending on the sodium flow rate. The effect of the turbulent Prandtl number and of the turbulence models (SST and Reynolds-stress models) on the heat transfer has been also investigated. The influence of the buoyancy forces has been also studied. The numerical results are found in very good agreement with the thermal balance analysis of the cold traps. The pressure loss for all designs is similar, nevertheless with a minor improvement for the optimized design. The study compares the advantages of each design and based on this analysis a design was identified and used for the cold trap that was manufactured and installed in the KASOLA facility.