Evaluation of injection current frequency on molten NaCl solidification images reconstructed by high-temperature electrical resistance tomography

Abstract

The injection current frequency has been evaluated on molten NaCl solidification images reconstructed by high-temperature electrical resistance tomography (htERT). The evaluation is performed by an electrical equivalent circuit consisting of an electrical double layer (EDL), bulk solution and current-voltage path (CV path). The EDL and bulk solution are the elements to indicate electrochemical noise and bulk noise due to random thermally excited vibrations of Na+ and Cl-. The CV path compensates the measurement device errors due to low resistivity of molten NaCl. The molten NaCl solidification images were reconstructed by htERT in an alumina crucible with platinum-wire electrodes under the initial temperature air T 0= 820 ˚C and temperature drop rate γ= 6.67 ˚C/min. As a result, the solid volume fraction of molten NaCl φ was properly obtained in the appropriate injection current frequency of L f < f < H f, which is determined by the electrical equivalent circuit with EDL, bulk solution and CV path. The electrical equivalent circuit was validated by comparing the SNR and Nyquist plot obtained experimentally with an error of resistance. The best frequency range implemented into htERT for molten NaCl solidification images was determined as L f= 1.4 kHz and H f= 41 kHz.