The objective of the proposed work is to develop theoretically a comprehensive mathematical model of the zinc/bromine (Zn/Br2) cell which will aid designers in the development of this battery. The Zn/Br2 flow battery has been receiving increased interest in recent years as a durable, rechargeable storage battery for use as a peak levelling device by utility companies. The need in the utility industry for some means to reduce the surge of the daily electrical load demand on generating facilities has existed for many years. Demand is high during the daytime when schools, factories, and businesses are open whereas during the night and early morning hours the demand is at a minimum. Generating facilities need be continuously operated at 100% of their rated power to be most cost-effective. To achieve this 100% operation and at the same time satisfy cyclic demand, peak shaving (load levelling) devices, such as the Zn/Br2 battery, must be employed. The Zn/Br2 battery has several attractive features for use as a shaving device. Batteries are compact and truckable and therefore can be optimally located at distributed sites near substations to yield a decrease in transmission line costs. In case of problems such as transmission line outages the batteries can supply at least enough power for vital loads in the area such as hospitals. The Zn/Br2 battery is relatively efficient, inexpensive, and clean compared to the conventional load levelling devices, coal fired units and gas turbines. This model development is based on the conservation of mass and charge supplemented by a transport equation, which includes a migration term for charged species in an electric field, and an electrode kinetic expression. The proposed model will be developed by augmenting a previously published model to include a porous layer on the bromine electrode, zinc complexation, predictions for discharge mode, a second bromine-rich phase, time dependence, and a recirculation system. Model parameters, kinetic and thermodynamic, will be estimated from those used in previous work and by comparing model predictions with experimental data in the literature. Also, the model will be used to investigate the effects of cell dimensions, physical parameters such as the void fractions of the porous regions, and operating conditions on cell performance. The resulting model will be a set of algebraic and three dimensional partial differential equations, two dimensional in space and one dimensional in time. The model development should lead to a better understanding of the physical phenomena which affect the performance of eletrochemical cells in general.
