TECHNICAL PAPERS ELECTROCHEMICAL SCIENCE AND TECHNOLOGY Impedance of Laminar Free Convection and Thermal Convection at a Vertical Electrode

Simultaneous heat and mass transfer under thermal laminar free convection to a vertical electrode was investigated. On the basis of Marchiano and Arvia's theory developed in steady state, the ac diffusion impedance for a circular or a rec-tangular vertical electrode was calculated as a function of frequency. For this calculation, the dimensionless local flux was expressed as a series expansion of the dimensionless local characteristic frequency in the low-frequency range and proportional to h/2 in the high-frequency range. With 80 terms in the series, the two solutions were shown to overlapfairly well for 1.6 10. The overall impedance was then obtained for the different electrode geometries. For a circu-lar electrode these theoretical predictions were successfully tested with different steady temperature differences, AT, between the electrode and the solution (0 ° s AT 2.65°).