Résumé:
In the present work, we numerically study the three-dimensional mixed
convection heat transfer between tow concentric horizontal pipes, the external pipe is
heated by an electrical intensity passing through its small thickness while the inner cylinder
is insulated. The convection in the fluid domain is conjugated to thermal conduction in the
pipes solid thickness. The physical properties of the fluid are thermal dependant. The heat
losses from the external outside pipe surface to the surrounding ambient are considered.
The model equations of continuity, momenta and energy are numerically solved by a finite
volume method with a second order spatiotemporal discretization. The obtained results
show the three dimensional aspect of the thermal and dynamical fields with considerable
variations of the viscosity and moderate variations of the fluid thermal conductivity. As
expected, the mixed convection Nusselt number becomes more superior to that of the
forced convection when the Grashof number is increased. At the solid-fluid interface, the
results show clearly the azimuthal and axial variations of the local heat flux and the local
Nusselt numbers. Following these results, we have tried modelling the average Nusselt
number as a function of Richardson number. With the parameters used, the heat transfer is
quantified by the correlation: NuA = 12.8678 Ri 0.1426
