1D modelling of a latent heat thermal energy storage prototype using boiling water as heat transfer fluid

Abstract

This paper presents a numerical model to simulate the thermohydraulic behaviour of a shell-and-tubes Latent Heat Thermal Energy Storage (LHTES) during discharging period, involving a boiling heat transfer fluid (HTF). It is based on a 1D homogeneous approach for the HTF (water) and a 1.5D approach for the phase-change material (sodium nitrate) allowing calculation times significantly shorter than those of CFD. This approach has been validated with experimental data in a previous study for a LHTES with a monophasic HTF. The two highlights of this paper are as follows: On the one hand, computational fluid dynamics has been used to develop equivalent homogeneous materials for PCM side, integrating the thermal properties of the phase-change material and the helical and longitudinal fins present in the LHTES. On the other hand, the model uses the asymptotic correlation of Steiner and Taborek to describe boiling heat transfers and usual correlations for single phase heat transfers. The paper focuses on the validation of the model against experimental data from the InPower project. The prototype is a 340 kWh storage that has been tested under different conditions. The model reproduces the total energy retrieved during a system discharge with relative error of 8.5% and an absolute mean error of 8.23 kW on outlet power. The main weakness of the model is the homogeneous model for the HTF that generates error in water level and local temperatures.