Salt Mixtures in Porous Ceramics for Thermochemical Storage of Low Temperature Heat
Abstract
Long term storage of solar heat or transformation of solar heat into could demands often a thermochemical process with materials having a low charging temperature to meet the requirements of simple inexpensive solar collectors. A number of storage materials are available such as silica gel or so called composites (Levitskij et al. 1996, Jänchen et al., 2004, 2005) hosting a hygroscopic salt hydrate. Those salt hydrates, showing a high potential for thermochemical heat storage, may have disadvantages like slow hydration/dehydration kinetics (magnesium sulfate as an example) or a too low value of the deliquescence relative humidity (DRH) typically for halides. The latter leads to liquefaction of the salts at rather low relative humidity already and may result in leakage problems. We have therefore investigated a new approach of utilization of salt hydrates in porous hosts by using a mixture of salts (Posern and Kaps, 2010) to prevent the disadvantages of the single salts.