Comparison Of Thermodynamic Models In Design Of Phase Change Materials Using Hydrated Molten Salts As Agents

Phase diagram prediction in a thermodynamic model is an effective way for the design of phase change materials using molten salt hydrates as agent, and strong prediction ability of the model used is a precondition for this work.In this work, five widely used typical thermodynamic models were selected to describe and predict the thermodynamic properties of five binary salt-water systems, which are often used as possible phase change materials. After systmatical comparison of prediction ability of these models, following conclusions have been drawn:â‘´The primitive Pitzer ion interaction model, which is used to represent accurately the component activity properties of a binary salt-water system in relatively low salt concentration, shows bad extrapolation prediction ability.⑵The extended Pitzer model, which can reproduce the activity properties of a binary system to quite high salt concentration although, however, shows weak extrapolation prediction ability.⑶The Clegg-Pitzer model can reproduce and predict activity properties of some binary systems with satisfactory, says the systems MnCl2-H₂OandMn(NO3)2-H₂O.However,when the salt concentration range,on which the water activities are used for the parameterization of the thermodynamic models, is far away from the saturated salt concentratiion, the Clegg-Pitzer model cannot give accurate property prediction of the saturated solution.â‘·The density of a solution in question, which is needed for the application of a MSA model, will limit the wide application of the model. But even if the density data are known, for example in the system LiCl-H₂O, the S-MSA model didn't give accurate property prediction of the saturated solution.⑸The BET model shows strong prediction ability in all five systems studied, so, it would be recommended for application in the theoritical design of phase change materials.