THE DISCREPANCY OF CONCENTRATION MEASURED BY THE ELECTRIC CONDUCTIVITY METHOD COMPARED TO THAT OF THE VOLUMETRIC MEAN IN A FLUCTUATING CONCENTRATION FIELD

Maxwell''s equation was applied to a current line between electrodes to measure the mean concentration by the electric conductivity method. It is concluded that this method may cause fatal error of measurement in a field of fluctuating concentration if the relative concentration differences are large. The discrepancies between measured and mean concentrations were evaluated for the complete segregated model and Gaussian distribution models of concentration with a flowrate ratio of 1 :1 to 1 :9. The use of pure water to measure mean concentration in the mixing process must be avoided. The lower/upper concentration ratio is recommended to be around 0.5 for all flow rates ratios in order to measure the meanconcentration within errors of 5% even in the most extreme cases.