## 1 Introduction  
With the increasing severity of environmental problems worldwide, renewable energy resources are becoming more critical. However, based on the natural environment, renewable energy exhibits severe output fluctuations [1], which hinders normal energy supply. To address this problem, studies on energy storage systems (ESSs) have been conducted worldwide. ESSs are classified into physical and electrochemical energy storage devices based on their application. As one of the electrochemical energy storage devices, redox flow batteries (RFBs) generate or store electricity through redox reactions between the active materials constituting the electrolytes. They are classified into various types according to the electrolytes, and their output characteristics are determined by the redox reactions of each electrolyte. Moreover, RFBs can be designed for specific applications, because the size of the stack that determines their output and the size of the electrolyte tanks that determine their capacity are independent of each other; they are suitable for medium- and large-energy storage devices [2]. Large capacity batteries for the MegaWatt class currently engaged for ESS include the lead-acid battery, NaS battery, lithium battery, and RFBs. Among them, the RFB is more recyclable and environmentally friendly than the equivalent lead-acid battery. In addition, The RFB has the advantage of a large capacity, safety, and reliability over the lithium battery. The redox couple used in the RFB includes various chemical species such as vanadium, bromine-polysulfide, and zinc-bromine. The Zn/Br is highly efficient, as it has a higher standard electrode potential of about 1.8 V compared with that of the vanadium (1.4 V) and the bromine-polysulfide (1.5 V) [3; 4]. One of the key technologies of the flow frame manufacturing process, the flow path design, significantly affects the overall system efficiency of RFBs [5]. When developing the flow frame for RFBs, two aspects improve the output and efficiency of the batteries, namely: the output of RFBs is maximized by increasing the active surface area through the flow path design (inducing uniform flow of the electrolytes that pass through the electrodes), and the pressure drop is minimized, reducing the power consumptions of the pumps used in RFBs [6]. Electrolyte flow uniformity is important in order to ensure the performance of the redox cells. If the flow is reversed or the velocity is negligible in any part of the redox battery, the overall efficiency of the redox battery will decrease [7]. Previous studies on the improvement of RFB efficiency are as follows. [PERSON] et al. [8; 9] defined an equation for evaluating electrolyte nonuniformity by analyzing the RFB flow characteristics, and proposed a cell design that minimized nonuniformity using the commercial code. This code was verified by comparisons with experimental pressure drops for various flow rates. [PERSON] et al. [10] analyzed the capacity and system efficiency of vanadium RFBs, according to the flow rate of the electrolytes, and [PERSON] et al. [11] analyzed the electrical efficiency and pressure drop according to the electrode type, in addition to analyzing the capacity and pressure drop of the batteries according to the electrolyte flow rate. [PERSON] et al. [12] performed experimental and numerical studies to check the uniform distribution of electrolytes on the porous electrodes of vanadium. This work describes the development and experimental validation of a three dimensional computational fluid dynamics (CFD) model for a vanadium RFB in a half-cell configuration. [PERSON] et al. [13] introduced a method including several performance indicators, by using CFD simulation to determine the pressure drop and flow distribution of membrane electrode assembly (MEA). Although many studies have been conducted on this subject, most of them use vanadium electrolytes, and few have considered the Zn/Br RFB, which has the aforementioned advantage over vanadium.