IMPEDANCE OF LAMINAR FREE-CONVECTION AND THERMAL-CONVECTION AT A VERTICAL ELECTRODE

Simultaneous heat and mass transfer under thermal laminar free convect ion to a Vertical electrode was investigated. On the basis of Marchian o and Arvia's theory developed in steady state, the ac diffusion imped ance for a circular or a rectangular vertical electrode was calculated as a function of frequency. For this calculation, the dimensionless l ocal flux was expressed as a series expansion of the dimensionless loc al characteristic frequency xi in the low-frequency range and proporti onal to xi(+1/2) in the high-frequency range. With 80 terms in the ser ies, the two solutions were shown to overlap fairly well for 1.6 less than or equal to xi less than or equal to 10. The overall impedance wa s then obtained for the different electrode geometries. For a circular electrode these theoretical predictions were successfully tested with different steady temperature differences, Delta T, between the electr ode and the solution (0 degrees less than or equal to Delta T less tha n or equal to 2.65 degrees).