Fishbone structures for thermochemical energy storage in porous systems

This paper documents the design of a flow configuration for Thermochemical Energy Storage in a porous medium impregnated with salt. The heat transfer fluid blown through the system is humid air, and the reaction of water vapor with the salt leads to heat storage or release. A thermodynamic analysis reveals the relationship between the pore geometry and the main parameters describing the transfers (mass flow rate, reaction enthalpy and temperature difference). The analysis leads to the proposal of a Fishbone-like architecture allowing the fluid to meander between salt inserts, while the water vapor molecules can diffuse and react with the salt walls. It is shown that such a configuration brings compacteness to the design without loss of heat transfer and mass ex-change performances. Next, we propose a methodology to scale up from the elemental Fishbone unit to an entire module made of layers of parallel salt Fishbones. The layers are separated by channels of heat transfer fluid. For constant porosity and apparent volume of the module we show, in accord with the constructal approach, that an arrangement of the Fishbones exists providing high energy efficiency.