Sodium chlorate electrosynthesis cell under natural convection: simulation of the transient and steady state working behaviour

摘要

A model based on mass, voltage and mechanical energy balances is proposed for predicting the behaviour of an electrochemical reactor under natural convection due to gas evolution. It takes into account the slipping between gas and liquid phases. The friction pressure drops related to the two-phase flow are evaluated by using an empirical relation as proposed by Lockhart and Martinelli while the changes in electrolyte velocity and direction in the cell are estimated by adding equivalent fittings. The gap between electrodes is described as a stack of elementary stirred-tank electrochemical reactors in which gas evolution leads to a gas fraction varying with height. The theoretical model for hydrodynamics is successfully validated from experiments and then the complete model is applied to predict the transient behaviour of a chlorate electrosynthesis cell. Practical conclusions are obtained from the model: the cell productivity decreases when the electrode length increases and an optimal value is found out for the distance between electrodes.