SENSITIVITY IN LOCAL CONCENTRATION FLUCTU ATION MEASUREMENT WITH MICRO-ELECTRIC CELL

Sensitivity of the electrode in detecting the concentration mass of st rong electrolyte solution was analysed numerically for the case of a s ingle mass in an electric field between a large spherical or ring elec trode and a concentric micro - spherical electrode. The response curve is spike shaped (large mass) or mountain shaped with a gentle slope ( small mass) when a mass grazes a micro-electrode. The more a mass cove rs and passes concentrically through the micro-electrode, the more the slope and peak of the response curve are sharpened and the peak is fl attened. The peak value, I(M), is not only a nonlinear function of the mass concentration, but also a function of mass size. The real concen tration of mass is larger than that estimated from assuming I(M) linea lly proportional to the concentration. On the contrary, beyond the mid dle stage of turbulent mixing, where there are many of relatively larg e mass in high level of background concentration between electrodes, t he peak value I(M), though small, is approaching to direct proportiona lity to the concentration. Therefore, the reliability of electrical me asurement of the concentration fluctuation is good in the final stage of mixing.