Multiphysics simulation of electrically driven molten-salt heat exchangers under renewable energy supply

The integration of renewable electricity such as photovoltaic (PV) systems into industrial heating processes requires efficient thermal energy storage (TES) and reliable heat exchange. This study uses transient Computational Fluid Dynamics and Heat Transfer (CFD&HT) simulations to investigate a 7.5 kW electrically driven heat exchanger (eHX) containing a quaternary molten salt, designed to function as a thermal buffer tank for managing solar power intermittency. The analysis employs a multi-region conjugate heat transfer model and a detailed simulation of the temperature field within the internal electrical filament to assess safety and prevent component-degrading hot spots. The eHX performance is evaluated across various tank diameters (154 mm to 600 mm) and in both horizontal and vertical orientations, under steady-state, transient daily solar, and power perturbation scenarios. Results show that buoyancy-driven flow plays a dominant role in shaping the thermal distribution and inducing stratification. Optimizing the outlet position helps confine stratification, limiting the average salt temperature rise and reducing the thermal load on the heating elements. Transient results revealed that smaller tanks exhibited a faster thermal response and higher maximum average temperatures, while larger tanks introduced a significant time lag in reaching peak temperature due to thermal inertia. • Models conjugate heat transfer across the internal resistance filament and fluid. • Demonstrates tank size influence on thermal inertia and transient response. • Captures transient heater-fluid interactions under intermittent PV power input. • Analyzes molten salt natural convection driven by buoyancy effects.