3D Fully Developed Laminar Mixed Convection in Horizontal Concentric Annuli with the Presence of Porous Blocks

Abstract—This paper reports the results of a numerical investigation to examine the potential of a four porous blocks inserted specifically for augmenting heat transfer from the inner heated wall of concentric horizontal annuli. Results are presented for a range of the values of the Grashof number, for two value of the Darcy number and for three value of the Prandtl number. Results are presented in the form of contours plots of the streamlines and for the temperature isotherms, and in terms of the overall heat transfer coefficients and friction factor. The average Nusselt number ( b N u ) increases significantly with an increase of the Grashof number and the Prandtl number ( Pr ). For pure forced convection, Nub is independent of Pr . With the use of the four porous blocks, the friction factor is consequently increased compared with the situation without porous blocks. The decrease of the Darcy number leads to an increase of the friction factor. If the fully fluid case is taken as a reference, the use of porous blocks is justified only when the ratio of the average Nusselt number to the friction factor is enhanced. At Da =10？3 , the enhancement occurs for all value of Pr , however, at Da =10？4 the improvement is noticeable only for Pr =10 and 5 after a certain threshold value of Grashof number is exceed.