Thermodynamics of crystallization of sodium sulfate decahydrate in H2O-NaCl-Na2SO4: application to Na2SO4 center dot 10H(2)O-based latent heat storage materials

In this paper, we present a methodology for the prediction of the crystalli zation enthalpy of mirabilite (Na2SO4. 10H(2)O) from supersaturated H2O-NaC l-Na2SO4 solutions. Required thermodynamic properties of H2O-NaCl-Na2SO4 su ch as dissolution enthalpies, phase equilibria and heat of hydration of Na2 SO4 are represented or determined using Fitter's ion-interaction model. Mea surements of crystallization enthalpies at various temperatures and concent rations were made in a SETARAM C80D calorimeter by mixing H2O-Na2SO4 and H2 O-NaCl-Na2SO4 solutions supersaturated relatively to mirabilite with a seed crystal of Na2SO4. 10H(2)O once the thermal equilibrium was reached. Good agreement was obtained between experimental and predicted values of cr ystallization enthalpies. Furthermore, we have studied the influence of NaC l used as an additive regarding the heat storage capacity of supersaturated H2O-Na2SO4 solutions. (C) 2000 Elsevier Science B.V. All rights reserved.