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

Abstract

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 TH and TC (TH > TC), 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, nanoparticles 0 ≤ ϕ ≤ 0.08, nanofluid types, Rayleigh 103 ≤ Ra ≤ 105 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 = 105, the best Nusssetl number is maximum for the Ag-water nanofluid, which increases up to 9.50%. Adding TiO2 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.