Mathematical Modeling Of Transport Phenomena Research Articles

Immobilization of 137Cs and 60Co in concrete matrix. Part 2: Mathematical modeling of transport phenomena

There are two fundamental issues that must be addressed in an attempt to isolate low-level waste in a disposal facility on land. The first is the isolation of waste from water, or hydrologic isolation. The second is prevention of radionuclide leakage from the disposal facility, or radionuclide migration. We have investigated here the latter modified scenario. Transport phenomena involved in the leaching of a radioactive material from a cement composite matrix have been investigated using an empirical method employing a polynomial equation. The results presented in this paper are examples of the results obtained from a 25-year mortar and concrete testing project, which will influence the design of the engineered trench system for a future central Serbian radioactive waste storage center.

Mathematical Modelling of Transport Phenomena in Continuous Casting of Steel.

A steady state, two dimensional mathematical for continuous casting of steel has been developed. Towards this, governing partial differential equations of fluid flow and thermal energy transport together with the appropriate set of boundary conditions were derived and a procedure for their non-dimensional representation outlined. The modelling of (1) turbulence, (2) flows and energy transport within the mushy region, and (3) bulk motion of the descending strand on liquid steel flow and heat transfer phenomena were also discussed. The governing p.d.e's and the associated boundary conditions were solved numerically via a control volume based finite difference procedure. To this end, incorporating the SIMPLE algorithm, a computational procedure was developed in double precision, FORTRAN 77. Finally, three different industrial billet casting operations reported in the literature were mathematically modelled and direct comparison were made between predicted and experimental solidified shell thickness. Such comparisons demonstrated reasonable to excellent agreement between the two. Present estimates were also compared with our earlier predictions derived via an effective thermal conductivity based model. This indicated that for mathematical modelling of transport phenomena in continuous casting of steel, a conjugate heat and fluid flow model is the most appropriate.

Mathematical Modeling of Transport Phenomena During Alloy Solidification

Mathematical modeling of mass, momentum, heat, and species transport phenomena occurring during solidification of metal alloys is reviewed. Emphasis is placed on the incorporation of the effects of the solid structure and the interactions between the solid and liquid phases on a microscopic scale into a (macroscopic) model of the transport phenomena occurring at the system scale. Both columnar and equiaxed growth structures, as well as laminar convection of liquid and solid crystals are considered. The macroscopic conservation equations are introduced via a volume averaging approach and commonly made simplifications are examined. Basic constitutive relations for the phase interactions occurring in alloy solidification are presented. Recent progress in including nucleation, microsegregation, undercooling and other microscopic phenomena in the macroscopic equations is reviewed. The specific areas where future theoretical and experimental research is needed are identified.

The Mathematical Modelling of Transport Phenomena in Non-Transferred Plasma Systems: Accomplishments and Unresolved Problems

ABSTRACTAn overview is presented of transport phenomena in non-transferred plasma arc systems. It has been shown that while the modelling of these systems involves the standard application of computational fluid mechanics techniques, numerous pitfalls may be encountered in practice. A detailed discussion of these is presented, with emphasis on the torch inlet conditions, the effect of swirl, the temperature dependence of the system properties and the laminar-turbulent transition in the system. A critical comparison is presented with experimental measurements, and the necessary future work is also outlined.