Wall impact on efficiency of packed-bed thermocline thermal energy storage system
Résumé
Packed-bed single-tank thermocline system with reduced cost is an alternative to the conventional two-tank system for thermal energy storage. This work systematically explores the wall impact on thermocline behavior of packed-bed tanks. For this purpose, adapted transient models were developed and fully exploited for the first time. Two tank configurations were investigated and compared: a high-temperature pilot-scale tank with a steel wall and a low-temperature lab-scale tank with a polycarbonate wall, both tanks being insulated by mineral wool. Results showed that the maximum energy stored in the wall at fully charged state can be up to 10% of the total stored energy. This part of stored energy has a negative impact on the discharging, causing up to 15% increase of the thermocline thickness. The energy stored in the insulation is very small so that this phase can be simplified as a thermal resistance in the modeling. The optimal wall parameters for packed-bed TES tanks were obtained that a thinner wall has a smaller impact on the energy and exergy efficiencies at the discharging cutoff time. The findings of study could provide useful design guideline for pack-bed thermocline TES tanks for different industrial applications.
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