A review of salt hydrates for seasonal heat storage in domestic applications

Trouton’s Rule for Vapor Sorption in Solids

“…Table 2 shows ∆s for these transitions. Sometimes different values of ∆s are given [5]. For these cases, the last column gives the alternative ∆s values.…”

“…As anticipated, the vapor pressure line of ammonia does not intersect at 1/T = 0 and therefore does not belong to this collection. Figure 10 illustrates Trouton's rule for a collection of salt hydrate transitions, calculated from collections of parametrized pT-lines [5,10]. Instead of the normal boiling point at 1 atm, we considered a pool evaporator-condenser at 20 °C, giving an H2O vapor pressure of 23.4 mbar.…”

“…Examples of salt hydrates that could be used for heat storage are Na 2 S·5H 2 O (cf. [1][2][3][4]) and K 2 CO 3 ·1 1 ⁄2H 2 O [5], but there are many other candidate reactions [6][7][8][9]. Selecting a suited salt hydrate depends on a number of its properties, which are obtained from experimental data.…”

“…Selection criteria are, for instance, a high heat storage density at favorable operating temperatures, sufficient output power, cycling stability, and low costs and low toxicity [1][2][3][4][5][6][7][8][9]. Examples of salt hydrates that could be used for heat storage are Na 2 S·5H 2 O (cf.…”

“…For instance, for the transition K 2 CO 3 ·(1 Fortunately, tables of ∆s 0 and ∆h 0 have been published for many salt hydration transitions [5,10,12], as well as for salt ammoniate transitions [11]. However, hydration states as well as ∆s 0 and ∆h 0 values of different references are sometimes contradictory, and hydration states are not always confirmed by X-ray diffraction data from, e.g., the online database of the ICDD (International Centre for Diffraction Data) [13].…”