Spatiotemporal distribution visualization of solid volume fraction during LiCl-KCl molten salt solidification by thermal-compensated electrical resistance tomography (tcERT)

Abstract

Spatiotemporal distribution visualization of solid volume fraction during LiCl-KCl molten salt solidification has been visualized by thermal-compensated electrical resistance tomography (tcERT). The tcERT consists of three steps which are 1) conductivity interpolation step, 2) conventional conductivity reconstruction step, and 3) phase-fraction conversion step. In the first step, the liquid electrical conductivity ${}^L\sigma (x,T)$ under mole fraction $x$ of KCl and measured temperature $T$ is defined by conductivity interpolation diagram (CID). In the second step, the electrical conductivity during solidification is defined by the conventional heat-resistant ERT as the reconstructed solid and liquid conductivity ${}^{S+L}\sigma (r,\theta ,T\left(t\right)$. From both steps, the solidification volume fraction $\phi (r,\theta ,T(t\left)\right)$ is calculated by the solid–liquid conductivity model (SLCM) which converts ${}^{S+L}\sigma (r,\theta ,T\left(t\right))$ into $\phi (r,\theta ,T(t\left)\right)$ by referring to ${}^L\sigma (x,T)$. The tcERT was applied to a composition of 85 mol % LiCl–15 mol % KCl in a crucible with platinum-wire electrodes under the initial temperature ${}^{0}T=$ 700 °C and at cooling rate $\gamma =$ 4.44 °C/min. As the results, inhomogeneous and unsteady $\phi (r,\theta ,T(t\left)\right)$ distributions were precisely visualized with a maximum relative error $\zeta =$ 0.763 of space-mean $〈\phi 〉\left(T\right(t\left)\right)$, where the inhomogeneity refers to the spatial gradient perpendicular to the crucible wall, and the fluctuation describes the transition from the nucleation region to the crystal growth region.