Heat transfer and entropy generation analysis of three-dimensional nanofluids flow in a cylindrical annulus filled with porous media

摘要

Laminar natural-convection flow and entropy production within a vertical porous annulus filled with nanofluids are examined. The vertical walls of the external and internal cylinders are maintained at different temperatures T_H and T_C (T_H > T_C), respectively. In contrast, the bottom and top of the annulus are adiabatic. Equations of continuity, momentum, energy, and entropy are resolved using the finite volume approach. Our FORTRAN-language programming code is well-validated with other works. The effects of porosity 0.2 ≤ ε ≤ 0.99, nano-particles 0 ≤ Φ ≤ 0.08, nanofluid types, Rayleigh 10~3 ≤ Ra ≤ 10~5 and Darcy 10~(-4) ≤ Da ≤ 10~(-1) numbers on the flow, heat transfer, and entropy production are examined. We find that nanoparticles' inclusion improves heat transfer and increases total entropy production St. Da and ε affect flow structure, thermal field, and entropy generation. Besides, increasing Da and ε, St, the average Nusselt (Nu)_(in,out), and Bejan Be numbers increase. However, in the opposite case, St and Be decrease. For Ra = 10~5, the best Nusssetl number is maximum for the Ag-water nanofluid, which increases up to 9.50%. Adding TiO_2 nanoparticles, on the other hand, results in a lower (Nu)_(in,out) value. The increase of the inner cylinder size reduces (Nu)_(in,out) and St.