Investigation of the heat transfer of non-newtonian pseudoplastic fluids in porous heat exchangers

In this paper, the natural heat transfer of Rayleigh-Benard's non-Newtonian Pseudo-Plastics fluid in a tube heat exchanger with its left wall lined with a porous layer of a thickness of 0.1 is considered numerically for an unstable state of laminar. The lower wall of the heat exchanger is at constant temperature Th and the upper wall at Tc temperature (Th> Tc). The walls are left and right insulated. The equations governing the problem after dimensionless are solved by the finite element method and then the accuracy of the results is compared with previous studies. The results show that, in a large Rayleigh number (Ra=105), the average Nusselt number increases due to the fact that the natural heat transfer is more than conduction heat transfer. Also, in small Darcy numbers (Da = 10-4), the flow permeability is very low which causes a reduces the natural heat transfer convection. The results show that by decreasing the Power-law index, the non-dimensional temperature is reduced and the lowest non-dimensional temperature is obtained for the lowest Power-law index. On the other hand, with the increase of Power-law index in a constant Rayleigh number and the passage of time, the increase of natural heat transfer occurs in the tube. Also, the Rayleigh number decreases with the increase of the Power-law index to start the natural convection in the heat exchanger.