FREE-CONVECTION AND STRATIFICATION OF ELECTROLYTE IN THE LEAD-ACID CELL WITHOUT WITH A SEPARATOR DURING CYCLING

The concentration and velocity profiles during discharge and recharge with and without a separator, as an "immobilized" electrolyte, in a lead-acid cell for small and real dimensions and actual conditions were studied experimentally. The electrolyte was an aqueous solution of initially 2.0 M H2SO4 during recharge and 5.0 M H2SO4 during discharge, uniformly distributed in the whole system. The electrolysis was done under galvanostatic conditions with a current density of 94.34 A m-2 during both recharge and discharge. The concentration field was measured by means of Holographic Laser Interferometry (HLI) and velocity profiles by means of Laser Doppler Velocimetry (LDV). The effect of the separator was shown to be dual. It narrows the space between the electrodes, thereby lowering the electrolyte velocity, and act as a barrier which hinders sulphuric acid to freely diffuse out and into the electrode. The effective diffusion coefficient for the electrodes were measured.