Publikacje

Abstract:

The paper deals with numerical simulation of mass and heat transfer in turbulent flow of Kaolin slurry. The physical model assumes that solid particles are sufficiently small and fully suspended, and a turbulent flow is hydro-dynamically and thermally developed in a straight horizontal pipeline. Based upon the assumptions the slurry is considered to be a single-phase flow with increased density and apparent viscosity. As the slurry exhibits a yield stress, the Bingham rheological model was chosen to calculate its apparent viscosity. The mathematical model uses the time-averaged momentum equation in which the turbulent stress tensor was defined by means of the k- model, which makes use of the Boussinesq eddy-viscosity hypothesis. The turbulence damping function, which has been used in the k- model, was purposely designed for such slurry because the slurry exhibits increased damping of turbulence. In addition, the energy equation has been used. The convective term of the equation was determined from the energy balance acting on a unit pipe length, assuming linear changes of temperature in the main flow direction.
The objective of the paper is to examine the influence of yield stress on the Nusselt number in the turbulent flow of Kaolin slurry in the range of solids concentration between 0% and 38% by volume and in the range of Reynolds numbers from 5,000 to 50,000. The paper shows that there is a substantial influence of the yield stress on velocity profiles and consequently on the temperature profiles and Nusselt number. The results of numerical simulation demonstrate the importance of turbulence damping near a pipe wall. A possible cause of turbulence damping in the near-wall region is also discussed.

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Simulation of a yield stress influence on Nusselt number in turbulent flow of Kaolin slurry