Ap. Washabaugh et M. Zahn, A CHEMICAL REACTION-BASED BOUNDARY-CONDITION FOR FLOW ELECTRIFICATION, IEEE transactions on dielectrics and electrical insulation, 4(6), 1997, pp. 688-709
A physical model is developed for the charge transfer boundary conditi
on in semi-insulating liquids. The boundary condition is based upon in
terfacial chemical reactions and extends established relations for the
interface by including the effects of interfacial surface charge and
charge desorption at the interface. A steady state model for now elect
rification in a rotating cylindrical electrode apparatus incorporated
this boundary condition and described polarity changes in the open-cir
cuit voltage and short-circuit current as a function of the fluid velo
city, the volume charge density dependence on the terminal constraints
, and the charge density dependence on applied de voltages. Previously
used boundary conditions are shown to be special cases of the chemica
l reaction rate boundary condition. A general methodology is developed
for combining the volume charge density and voltage/current terminal
measurements to estimate the parameters describing the interfacial cha
rge transfer kinetics. Volume charge densities rho(omega) on the liqui
d side of the interfaces of 1 to 20 mC/m(3) were estimated from the op
en-circuited electrode measurements,with the stainless steel rho(omega
) typically larger than that of copper but smaller than that of transf
ormer pressboard. Activation energies for an Arrhenius temperature dep
endence of similar to 0.16 eV for pressboard, 0.25 eV for stainless st
eel and 0.28 eV for copper were obtained. Interfacial adsorption react
ion velocities, estimated to be 10(-5) mis, were not large enough to m
ake the terminal current transport limited which contradicts the often
used assumption that the reaction velocities can be considered 'infin
ite'. Estimated surface reaction rates at a 70 degrees C stainless ste
el/oil interface of similar to 20 mu m/s for adsorption and similar to
0.5 s(-1) for desorption were obtained. The additive BTA reduced the
rho(omega) for pressboard and stainless steel at concentrations > 8 pp
m in transformer oil.