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

Abstract

Abstract The injection current frequency has been evaluated on molten NaCl solidification images reconstructed by high-temperature electrical resistance tomography (htERT). The evaluation was performed using 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 that indicate electrochemical noise and bulk noise due to random thermally excited vibrations of Na+ and Cl–. The CV path compensates for measurement device errors due to the low resistivity of molten NaCl. The molten NaCl solidification images were reconstructed by htERT in an alumina crucible with platinum-wire electrodes under an initial temperature air T 0 = 820 °C and temperature drop rate γ = 6.67 °C min−1. As a result, the solid volume fraction φ of molten NaCl was properly obtained at the appropriate injection current frequency of L f < f < H f , which is determined by the electrical equivalent circuit (EEC) with an EDL, bulk solution and CV path. The EEC was validated by comparing the signal to noise ratio and Nyquist plot obtained experimentally with a resistance error. The best frequency range implemented in htERT for molten NaCl solidification images was determined as L f = 1.4 kHz and H f = 41 kHz.