Studies about mineral oils maintenance in NPP

The maintenance of mineral oils, used as lubricating agent or insulating fluids is a very important problem for the reducing of operating costs in the Nuclear Power Plants. Their maintenance means the maintaining of their solid particles and water content between the allowed limits given by the international standards. A modern dehydration technology is the film desorption of water from mineral oils. The paper presents a mathematical model of the falling film dehydration process of mineral oils in a cylindrical film desorber. The model's equations were solved numerically using a FORTRAN programme made by the authors. The model allows the determination of water concentration radial and longitudinal profiles in the oil film. The simulation results are compared with the experimental results obtained by the authors on their own laboratory experimental plant and the good agreement found validated the mathematical model. The model was solved using a fully implicit numerical scheme, in which the longitudinal convection terms were approximated by the upstream difference and the transverse diffusion terms by the central difference to transform the governing equations into finite-difference equations. The finite-difference system obtained is an algebraic system with a tridiagonal matrix that can be efficiently solved by the Thomas algorithm. To account for the drastic variations of velocity and concentration in the regions near the inner boundary and interface, a nonuniform spatial grid in the r-direction was chosen. A grid with 401 gridpoints was used in the computations.The model allows the determination of water concentration radial and longitudinal profiles in the oil film. The simulation results are compared with the experimental results obtained by the authors on their own laboratory experimental plant and the good agreement found validated the mathematical model. (authors)