Experimental and numerical investigation of combined sensible-latent heat for thermal energy storage at 575 °C and above

The design, testing, and modelling of a high-temperature thermocline-type thermal energy storage (TES) are presented. The TES concept uses air as the heat-transfer fluid and combines sensible and latent heat for stabilizing the discharging outflow air temperature. A 42 kWh(th) lab-scale prototype of 40 cm diameter was fabricated, containing a 9 cm high layer of encapsulated phase change material (AlSi12) on top of a 127 cm high packed bed of sedimentary rocks with a mean diameter of about 3 cm. A two-phase transient heat transfer model of the thermal storage cycle was numerically formulated and experimentally validated with measured thermoclines during charging and discharging obtained with the lab-scale prototype. The thermal inertia of the experimental setup and the radial variation of void fraction due to the small tank-to-particle diameter ratio affected the validation process. The outflow air temperature during discharging was stabilized around the melting temperature of A1Si(12) of 575 degrees C. The thermal losses stayed below 3.5% of the input energy for all the experimental runs. (C) 2015 Elsevier Ltd. All rights reserved.