Experimental investigations on the design of a dual-media thermal energy storage with liquid metal

Abstract

Liquid metals are a promising heat transfer fluid with stability over a wide temperature range and high thermal conductivity. In concentrating solar energy power plants, as well as in the steel processing facilities heat is generated at high temperature level. Many fluids begin to decompose at such high temperatures and gases have poor thermal conductivity, making it difficult to effectively store and extract heat from the source. Liquid metal heat transfer fluids are able to effectively transport energy at a wide range of temperatures (150 ∘C–1000 ∘C). Existing heat transfer fluids, such as molten salts, have a working range between 290 ∘C and 565 ∘C for example. Depending on the metal selected, thermal conductivity can be 30 to 100 times higher than molten salts, but liquid metals have lower energy density. The liquid metal can be paired with a filler material having a higher energy density to develop a system with high energy transport and storage capability. The first lab-scale experiment of thermocline energy storage with liquid metal as a heat transfer fluid and a zirconium silicate filler, called VESPA [Vorversuch EnergieSPeicher Aufbau (ger.), engl. Preliminary test for energy storage setup], was carried out to prove the concept. So far, there are promising, yet only numerical investigations of thermocline energy storage with liquid metal as heat transfer fluid. The storage system under investigation was a dual-media thermocline energy storage system with liquid lead–bismuth eutectic as heat transfer fluid and zirconium silicate as filler material. The experiments were executed at temperatures from 180 ∘C to 380 ∘C, and focused on design aspects of the energy storage system. Different modes of operation of the storage system were investigated, including charging, discharging, and stand-by. Results are presented showing changes in the vertical temperature profile of the energy storage while varying mass flow, inlet temperature, and filler material.