Viscosity model of KCl-NaCl-H₂O and CaCl₂-NaCl-H₂O brines, in the temperature range from 273.15 to 333.15 K

This article concerns the determination of viscosities for specific ternary brine systems, namely KCl–NaCl–H₂O and CaCl₂–NaCl–H₂O, using a mathematical fitting model based on a power-series expansion. The independent continuous variables are molality (moles of solute per kilogram of solvent) and temperature. The molality spans the dilution range of the salts, while the temperature varies from 273.15 K to 333.15 K. The proposed model interpolates the available literature data with an average absolute deviation (%AAD) of 1–5 % in both systems, at constant atmospheric pressure. The dissolution range was selected to avoid precipitation phenomena; for example, in the case of NaCl, the interval extends from 0 to 6.5 mol kg⁻¹, and a similar range applies to KCl. However, for CaCl₂ the range extends up to 9.2 mol kg⁻¹. Since adequate experimental data are not available over the full ranges of temperature and concentration, an approximate model was developed that—at least in principle—can provide extrapolated data that follow the trend of the isothermal surface variations as the system composition changes. This approach is justified because some isotherms are sufficiently populated with reliable experimental data. The proposed model is highly efficient and competitive, and it can serve as a basis for developing predictive viscosity models with a greater number of components.