Determination of the convective mass transfer coefficient in the dissolution of NaCl particles in non-Newtonian fluids

Abstract

The main objective of this work was to study the dissolution of salt (NaCl) particles in water and in non-Newtonian fluids that contain xanthan gum. In an agitated tank, experimental profiles of salt concentration as a function of time in the liquid phase were obtained. The experimental data were used to evaluate the mass transfer coefficient in different operational conditions and to validate the mathematical model. It was found that the dissolution kinetics of the salt particles was affected by both the fluid's xanthan gum concentration and initial salt concentration. Adding xanthan gum to the fluid decreased the salt dissolution kinetics. The mass transfer coefficient for a system with xanthan gum was smaller than the one for pure water. The values of the mass transfer coefficient for pure water base fluids varied from (0.836 ± 0.003) × 10−4 to (1.110 ± 0.003) × 10−4 m/s, and for xanthan gum solutions from (0.526 ± 0.003) × 10−4 to (0.865 ± 0.003) × 10−4 m/s. The mathematical model based on the mass conservation equations for the liquid and solid phases predicts the salt concentration profiles simulating the dissolution process. In addition, it was proposed an equation to model the decrease in the diameter of the particles due to dissolution. The mathematical model fitted the experimental data with an average relative error of 2.2%.