THE EFFECT OF STIRRING ON DIFFUSION MEASUREMENTS USING THE DIAPHRAGM CELL SETUP

摘要

This article presents a systematic study to quantify the limiting parameter of the stirring on the reliability of the diffusion test. The effect of the stirring energy and the stirring velocity were justified by performing a series of diffusion tests (using the diaphragm cell setup under the quasi-steady-state boundary conditions) with six bars (of different dimensions) magnetically stirred. It was concluded that the validity of the diffusion coefficient with respect to solution stirring was better linked to the rotational velocity of the probe used rather than the generated energy. The diffusion tests were considered valid when the rotational velocity was lower than 2000 rpm, irrespective of the dimensions of the stirrer bar used. To solve the problems of solution homogeneity and the formation of the stagnant liquid layers (adjacent to the diaphragm at both sides) without forcing the chemicals to flow by advection (rather than diffusion), it was suggested to use a stirrer bar with 25-40 mm length and 6-8 mm diameter with a rotational velocity of less than 2000 rpm.