A theoretical study of particule concentration in two-phase flow is presented. The Row is contained in a cylindrical column fitted with an electric sensor on the external surface. We have calculated the capacitance variation as particules of the flow across the space between the electrodes. Taking into account the dielectric constant of the system, the particule concentration is then calculated applying the effective medium theory. These analytical results are compared with experimental results. A good agreement is found and size effects predicted without applying any phenomenological coefficient.