Turbulent heat transport in two- and three-dimensional temperature fields

Abstract

A fundamental numerical study of turbulent heat and mass transport processes in two- and three-dimensional convective flows is presented. The model of turbulence employed is the type referred to as a second-order closure. In this scheme transport equations for all nonzero components of the Reynolds stress tensor, for the isotropic dissipation rate of turbulent kinetic energy, for all nonzero scalar flux tensor components and for the mean square scalar fluctuations are solved by a finite difference method along with the mean momentum and mean enthalpy (or concentration) equations. The model used for the stresses was developed earlier. Parallel ideas were utilised in obtaining a model for turbulent heat and mass transfer processes. The study has focused especially on the problem of nonaxisymmetric convective heat and mass transport in pipes, which arises when the boundary conditions are not axisymmetric. The few available experimental data on such situations have indicated anisotropy in effective diffusivities. To expand the available data base an experiment was conducted to obtain heat transfer measurements in strong three-dimensional heating conditions. Numerical procedures especially suitable for incorporation of second-order turbulent closure models have been developed. The effect of circumferential conduction in the tube material, which is influential in the asymmetric heating data currently available, was accounted for directly by extending the finite difference calculations into the pipe wall. The principal goal of predicting three-dimensional scalar transfer has been achieved.