The direct detection of inclusions first became possible for electronically conducting fluids following the development of the LiMCA (Liquid Metal Cleanliness Analyzer) technique. The principle of this technique is based on the R.P.T. (Resistive Pulse Technique), or E.S.Z. (Electric Sensing Zone) method, for counting, and sizing, inclusions in liquids. Its application to steel melts is now studied theoretically, in order to help in the understanding and analysis of in-situ experimental measurements of inclusion size and frequency distributions in steel plant processing operations.
In developing the theoretical model for this technique, a three-step strategy was used to explore physical events that take place within the electric sensing zone, as an inclusion passes through. First, a multiphase flow model was required, in which events that can take place during the passage of the inclusion through the sensor's ESZ were considered. Inclusion trajectories and transit times were predicted using a particle momentum equation. For this, Newton's Second Law of motion was solved, in which the mass and instantaneous acceleration of the particle was balanced against the sum of the various forces acting on the particle/inclusion, during its passage through the ESZ. The forces summed included Stokes's drag, fluid acceleration, particle acceleration with added mass, gravitational and, in particular, the external self-conducting electromagnetic force induced by passing a heavy direct current through the ESZ of an electronically conducting liquid.
In the second step of this theoretical analysis, a numerical potential-integral method was conceived in order to calculate local changes in electrical resistance within an ESZ of variable geometry, and variable location of a traversing particle. This new approach was compared to alternative analytical and numerical estimates of changes in ESZ resistivity with a second phase particle within it, which neglects the effects of radial position of the particle.
In the third and final step in the present analysis, parabolic, fluted, and cylindrical ESZ's were selected, and the influence of fluid properties, ESZ dimensions, electric currents, and the inclusion's properties (electrical conductivity, density, size, shape, etc.), were investigated to determine how these various parameters affect the resistive (or voltage) pulses generated during the passage of an inclusion through the ESZ.