Triggering Xylitol crystallization in a 42 kWhth shell and tubes latent heat thermal energy storage system

Xylitol is a very promising Phase Change Material for district heating networks decentralized Latent Heat Thermal Energy Storages. However, it presents a high and persistent supercooling that requires the implementation of specific ways to trigger its crystallization. In previous works, the coupling of bubbling and seeding has been successfully tested as an efficient way to trigger Xylitol crystallization in small-scale crystallizers. The present work first studies the feasibility of using Xylitol as PCM in a 42 kWhth shell and tubes Latent Heat Thermal Energy Storage prototype integrating a bubbling and seeding system. Then, the benefits of optimizing the seeding step is discussed. Indeed, if the coupling between bubbling and seeding results in a fast and reproducible PCM crystallization, optimizing the seeding step allows to completely remove the effects of Xylitol supercooling on the restituted temperature levels. Another effect of bubbling in a Latent Heat Thermal Energy Storage is also brought to light: during the beginning of the discharge, a vertical temperature homogenization is observed in the liquid PCM. The consequences of this vertical temperature homogenization on the heat transfers and the performances of the storage are discussed.