Flow Battery

From Cell to Stack to System

Flow batteries separate the storage of electrical energy from the charge/discharge process; power and energy can be scaled independently of each other to meet the needs of many different applications. Very few technologies are realistically applicable to utility-scale electrical energy storage (EES); flow batteries are in an elite category. But they are also scalable to home and building applications for peak shaving or peak shifting, or for emergency backup power.

In a flow battery, energy storage is accomplished in arbitrarily large tanks full of electrolytes, while separate stacks of cells convert electricity into and out of different electrochemical (redox) states of those electrolytes. The tank on the left contains the catholyte, and the tank on the right contains the anolyte.

By Nick B, benboy00 - https://commons.wikimedia.org/wiki/File%3ARedox_Flow_Zelle_Deutsch_Farbverlauf.png, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=35143999

Of course, the single cell in the above diagram is actually a stack of about 14-19 cells in a real battery, a few of which are shown expanded below with both the membrane (typically DuPont NafionTM 117) and the porous graphite fiber electrode pads visible.

The charge collector plates also contain a serpertine "flow field" in the picture below, which is used to assure uniform distribution of electrolyte within the cell for minimum overpotential and reduced pumping losses.

There are many such plates in a stack, and many stacks are then plumbed in parallel in a battery. Time scales within a cell are on the order of fractions of a second, but any simulation of a flow battery must cover many days of charge/discharge scenarios.

This means that the complexities of modeling a realistic flow battery involve more than just combining fluid flow, thermal energy, electrical networks, and electrochemical treatment of redox reactions. They must also involve handling multiple time and distance scales simultaneously: you need to be able to zoom in on the fast time-scale multiphysics within a cell, while at the same time zooming out to the full system as it moves through its daily operational cycle.

Vanadium Redox Flow Batteries (VRFB) represent the current state-of-the-art, with 20+ years of reliable and safe operation demonstrated. Many research projects are underway to find alternate electrochemistries or membranes, or to reduce the cost and increase the performance of VRFBs.

Or just enjoy the diurnal variations of temperature gradients within a single cell of a 17-cell stack in a 6-stack battery over the course of a typical day:


Click here to fetch the VRFB case study on our User Forum


flow regimes

Introduction to Two-phase Flow

September 24, 2-3pm MDT

This webinar introduces basic concepts in two-phase flow modeling including quality, void fraction, flow regimes, slip flow, pressure drops and accelerations, and heat transfer.

No knowledge of CRTech software is required. However, references to the corresponding FloCAD features will be made to assist users of that product.

Click here to register

Introductory FloCAD Training

Class times: September 5, 10, and 12, 2019, 9:00 am to 12:00 pm MDT daily
Cost: no charge (attendees must have an active support contract)

CRTech will be hosting introductory training for FloCAD (Flow Modeling in Thermal Desktop). This is our standard FloCAD class previously hosted in a classroom environment and now restructured for an online teaching environment.

The class will introduce single-phase fluid modeling concepts and how to build fluid models within the FloCAD work environment. Topics covered include an introduction to fluid modeling components, geometric versus non-geometric modeling options, working with FloCAD Pipes, solution control, and an introduction to path and pipe libraries.

The class will be broken into three two- to three-hour sessions held over a 3 day period. The format will be online lecture and demonstration with opportunities to ask questions. Hands-on lab work will be provided to students to work on after each session. To gain the most from this class, students are encouraged to attend all three sessions.

Prerequisites: Attendees must have basic working knowledge of Thermal Desktop as many of its base features will not be covered in this class but their usage is required for FloCAD.

Eligibility Requirement: This class is a service to our customers. All attendees must have an active support contract. If you are unsure of your support status, please contact CRTech.

Click here to register