Having the physical properties of paraffin wax in mind, we test a new application strategy, which is somewhat contrary to its established way of use: the application as thermal insulation of thermal energy storage systems. The main rationale is that the low thermal conductivity of solid paraffin will restrain lateral heat loss. When heating up the water-saturated gravel in the pit, phase change of paraffin can occur and absorb energy, and thus the outward thermal gradient will remain lower than without. Additionally, heated paraffin fluid may actively seal voids, cool again and as a hydrophobic material, it may be able to impede flow and leakage of water.
With the given experimental configurations, we test the effect of periodical heating the water-saturated gravel beyond the melting point of paraffin, and cooling the system again. By monitoring temperature and moisture evolution at different positions inside and outside the TES, the thermal and hydraulic isolation efficiency is inspected and design variants (individual layer widths, need for additional devices such as foils between paraffin layer and granulate, etc.) are compared and optimized. A numerical (coupled thermal-hydraulic) model is set up to simulate the transient effects from heating and cooling on the temperature evolution, phase change and leakage effects.