A Simplified Analytical Method for Assessing Fluid Mixing Homogeneity in Flow Battery Storage Tanks

Abstract

The electrolyte storage tank, as a key component in the vanadium redox flow battery (VRFB) system, directly influences the battery’s operational performance and the accuracy of state-of-charge (SOC) estimation through the mixing homogeneity of the internal electrolyte. To address the challenge in engineering applications of rapidly evaluating mixing processes in storage tanks, this paper proposes a simplified analytical method for assessing fluid mixing homogeneity in VRFB tanks. The proposed method is a computational fluid dynamics (CFD)-based methodology that combines an internal flow-field simulation with monitoring of outlet parameters. It provides a qualitative and semi-quantitative analysis of the tank’s overall mixing performance by comparing the simulated inlet electrolyte scalar concentration curve with the theoretical response curve under ideal, complete-mixing conditions. The research focuses on a multi-inlet conical-bottom self-mixing tank, and a traditional cylindrical flat-bottom tank was used for comparison, with their internal flow fields and mixing mechanisms analyzed using simulation software. The simulation results suggest that the flow streamlines within the conical-bottom self-mixing tank are more uniformly distributed, and its outlet response curve more closely matches the theoretical complete-mixing curve, indicating superior mixing homogeneity compared with the conventional structure. The simulation results were further confirmed by experiments using scaled-down physical models, and the experimentally measured characteristics of the conductivity distributions were in good agreement with the numerical inferences. The paper demonstrates that the suggested approach has the following strengths: simplified modelling, low computational cost, intuitive criteria, and utility as a guide for structural design optimisation of VRFB tanks and for system-level modelling.