Résumé:
In this work, we numerically study the three-dimensional mixed convection heat transfer in a horizontal pipe
equipped by longitudinal and transversal attached fins on its internal surface for the solar application such as the
water or air heating with solar panel. The pipe and fins are heated by an electrical intensity passing through their
small thickness. The longitudinal fins studied number is: 2 vertical, 4 and 8 fins, while the number of transversal fins
is 8 fins. The considered heights fin are H=0.12 cm and H=0.24 cm. The convection in the fluid domain is conjugated
to thermal conduction in the pipe and fins solid thickness. The physical properties of the fluid are thermal dependant.
The heat losses from the external 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. As expected for the longitudinal fins, the axial Nusselt number increase with increasing
of number and height of fins. For Gr= 5.1 105, the average Nusselt number without fins is equal to 13.144. The
introduce of longitudinal fins gives an average Nusselt number equal to 16.83, 22.523 and 32.066 for 2 vertical, 4
and 8 fins respectively. The participation of fins located in the lower part of the tube on the improvement of heat
transfer is higher than the participation of the upper fins. On the other hand, the longitudinal fins participate directly
on increase of the heat transfer; this is justified by the large local Nusselt number along the interface of the fins. This
participation is moderate in the case of transverse fins, these latter are used to mix the fluid for increased the local
Nusselt number to the interface in the cylindrical axial sections following the transversal fins
