New scientific article !

The researchers of IMDEA Energy and ENEA published the article “CFD-based numerical investigation of a thermal energy storage tank driven by natural convection” on the Journal of Energy Storage. 

Abstract

This work addresses a numerical investigation of a thermal energy storage tank driven by natural convection. The innovative tank design consists of a single molten salt reservoir with two indirect heat exchangers that transfer heat between thermal oil and molten salt. During discharge, hot molten salt transfers heat to the cold thermal oil in the upper heat exchanger and flows down through an internal channel (a vertical shell that crosses the thermocline layers) due to buoyancy force. During charging, hot thermal oil from the solar field flows through the bottom heat exchanger, heating the molten salt and causing it to rise to the top due to buoyancy force. To analyse this concept, a two-dimensional computational fluid dynamics (CFD) model is used to evaluate the performance under different discharging and charging conditions of the heat exchangers. The study investigates the molten salt mass flow rate in the channels, the inlet and outlet temperatures of the heat exchangers, and temperature and velocity distributions in the tank for different flow resistances and heat exchanger operating conditions. The results reveal that the mass flow rate of the molten salt in the channel follows a three-stage pattern during both discharge and charge, and its magnitude is influenced by the heat exchanger design, the temperature gradient, and heat sink/source profile. The bulk mean inlet and outlet temperatures in the heat exchangers serve as key indicators of discharge and charge duration, providing insight into the ability of the tank to function as a thermocline. The analysis shows that a heat exchanger with a momentum sink coefficient of 10⁷ m⁻² and a rate of change of volumetric heat sink/source of approximately −800 W m⁻³ s⁻¹ extends the constant outlet temperature period to approximately 8 min, indicating behaviour similar to that of a typical thermocline system and resulting in a thermocline thickness of around . These findings highlight the crucial role of heat exchanger design and operating conditions in optimizing natural convection-driven thermal energy storage systems, offering valuable insights for future research directions and their integration with renewable energy technologies such as concentrating solar systems.

Citation:

Germilly Barreto, José González-Aguilar, Manuel Romero, Giampaolo Caputo, Alberto Giaconia,
CFD-based numerical investigation of a thermal energy storage tank driven by natural convection,
Journal of Energy Storage, Volume 132, Part B, 2025, 117782, ISSN 2352-152X, DOI: 10.1016/j.est.2025.117782.

Read the article here: https://www.sciencedirect.com/science/article/abs/pii/S2352152X25024958?via%3Dihub