HSC Aqu – Aqueous Solutions Module

Aqueous solutions are widely used in the process industry in a huge number of applications. Process models may be created using pure substance data and assuming ideal behavior for the aqueous solutions. However, the accuracy of the models may be improved by taking into account the naturally existing non-ideal behavior of the ions in the solution.

Well-known non-ideal models for aqueous electrolyte properties have been included in the new Aqua module. The activity coefficient models include the extended Debye-Hückel model (called here the Davies model), the Pitzer model, and Harvie’s modification. An extensive database including about 1000 Pitzer parameters for different systems have been collected to date. The Pitzer parameter database currently has 425 cation-anion pairs, 114 cation-cation and anion-anion pairs, 199 ternary coefficients, and 293 ion-neutral pairs. Many of these parameters are tabulated as temperature-dependent functions. The user is given the option to choose between simpler and more rigorous models and to select the number of parameters used.

In the HSC Aqua module, the Water Phase sheet is used for calculating the ion activities, mean activity coefficients, the osmotic coefficient of water, enthalpies, and heat capacities of homogenous (single phase) aqueous electrolyte solutions. In addition, the water vapor pressures of electrolyte solutions, boiling point elevation, freezing point depression, relative humidity and osmotic pressure can be estimated. The user specifies the system by inserting the ionic or molecular formulae of the solute species in the Water Species Data column, the temperature in the Temp °C column, and the amounts in the Amount kmol column.

The Aqua module can be combined with the HSC Equilibrium Module just by checking a box, i.e. multiphase (gas-aqueous-solid) calculations where ion activities and speciation can be taken into account in the water phase.

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