Entropy generation analysis of laminar forced convection with nanofluids at pore length scale in porous structures with Kelvin cells

A numerical investigation on foams in forced convection with Kelvin cell structure is carried out on water/Al2O3 nanofluids. The three-dimensional governing equations are written considering the single-phase model for the nanofluid. The analyzed foams have a porosity of ɛ = 0.95 and four different pore density values, with cells per inch (CPI) equal to 5, 10, 20 and 40, with assigned heat flux on the surface. The nanofluid velocity is in the range 0.003–0.1 m/s and the Reynolds number ranges from 0.6 to 5 × 102. It is observed that thermal development occurs first for the lowest velocities and for highest CPI values whereas the maximum temperature is obtained for the 5 CPI configuration and v = 0.003 m/s. Results show that the highest local entropy generation values are recorded near the points at higher temperature in correspondence with the inlet section and close to the geometric variation of the cells. The local entropy generation density reaches the maximum value at 40 CPI for the maximum velocity considered of 0.1 m/s. Global dimensionless entropy generation decreases for Reynolds number increases and the opposite is related to the dimensionless viscous entropy generation. Thermal dimensionless entropy generation is significantly greater than the dimensionless viscous entropy generation.