variavel0=EMMANUEL O. EHIRIM - ehirim@cefetpr.br CEFET-PR Abstract. A mathematical model is presented to describe the behavior of a three-dimensional fluidized bed electrode operating under the condition of electrons transfer. The model is simulated numerically by applying orthogonal collocation method to calculate the electric potential distribution in the particulate and liquid phases, and the overpotential within the electrochemical reactor. The principal results are the effects of the constant current operation, bed width and bed porosity on the system behavior. The developed model is adequate to describe the behavior of these types of electrochemical reactors. Keywords. Mathematical Modeling, Electrochemical reactor, Orthogonal Collocation, overpotential.