WEB Packing geometry and Macrostructural evolution relationship in a K2CO3 tablets bedWednesday (23.09.2020) 11:50 - 12:05 P: Processing and Synthesis 1 Part of:
The most desirable thermochemical energy storage system is based on the reversible absorption of water vapor by salts. Compaction and permeability are the key words to design a heat battery bed that can provide high energy densities (200-500 kWh/m3) and quick reaction dynamics. In a packed bed of tablets, salt is compacted into a restricted volume and porous channels are intrinsic to the packing geometry.
K2CO3 tablets of different shapes, sizes and compositions (salt in matrix - SIM) have been manufactured from a starting material of ± 900 µm granulometry by compression in a tableting mold. Density was measured by a Buoyancy method, according to Archimedes’ principle, and always equaled roughly ~ 2 g/cm3. These tablets proved to be stable when charged and discharged three times in a thermal gravimetric set up at 12 mbar from 120 oC to 30 oC and further studies are ongoing to identify the hydration rate limiting phenomena.
Depending on to their geometric symmetry, tablets were packed according to an oriented repetitive fashion (blister flat, blister rotated, fish-scale…) into a monolayer and their cycling dynamics and stability where studied through a quasi 2D set up. The set up allows to produce a unidirectional laminar air flow (ml/min) through a small (≈ 16 cm3) Plexiglas/Teflon chamber, control moisture levels (relative humidity (%), PH2O (mbar)) and ensure either isothermal conditions or the analysis of temperature gradients, by providing combined heat through a metal plate and/or the air flow. The set up is such to allow easy sampling of the material and direct visualization.
In the end we are able to predict and interpret the macrostructural evolution caused by the developed characteristic heat (infra-red imaging) and water vapor distribution (NMR), which is proved to be dependent on the packing fashion and composition of the tablets. Eventually it is assessed whether common powder and grain beds drawbacks (local deliquescence and agglomeration), are alleviated or still hamper the performance of the tablet bed and a new research direction is presented based on this results.