Understanding thermal stratification or mixing in liquid metal pools due to penetrating colder jets

High fidelity experimental results are presented for understanding the thermal stratification or mixing in a low Prandtl number (Pr) pool due to the injection of a colder (higher density) jet at the bottom of the pool. While work has already been established for fluids like air and water, research on low Pr fluids (<< 1) (e.g. liquid metals) has fewer experimental data sets. In liquid metals, the higher volumetric thermal expansion enhances buoyant forces, aiding in thermal stratification, while the low Pr extends the thermal boundary layer. To quantify the amount of mixing, the empirical parameter eddy thermal diffusivity (κ_τ) is used. Distinct regimes of mixing efficiency (K = [κ_τ + κ_mol] / κ_mol) are seen: molecular (κ_τ << κ_mol), transitional (κ_τ ≈ κ_mol), & energetic (κ_τ >> κ_mol). Rayleigh and acoustic backscattering techniques are used to generate the high fidelity distributed temperature and flow field data, respectively. The high spatial and temporal resolution of the sensors are required to capture the temperature gradient and fluctuations of temperature and velocity to allow a more complete understanding of stratification or mixing within the pool.