Numerical investigation on natural convection of Al2O3/water nanofluid with variable properties in an annular enclosure under magnetic field
Abstract
Numerical investigation of the natural convection of water nanofluid is carried out in a differentially heated vertical annulus under a uniform magnetic field. An in-house Fortran code has been developed to solve the system of equations governing the magneto-hydrodynamic flow. Computations are carried out for different Rayleigh numbers (10 # ≤ '(≤ 10 $), nanoparticle diameter () % = 13 and 47 /0), nanoparticle volume fraction (0 ≤ 3 ≤ 0.09), radius ratio (2 ≤ 7 ≤ 10), and different Hartmann numbers (0 ≤ 8(≤ 100). According to the simulation data, nanoparticle size is crucial for evaluating nanofluid properties, such as viscosity and thermal conductivity. The computational results reveal that, for nanoparticles with a diameter) % = 47 /0, the average Nusselt number 9: ;;;; & on the inner cylinder wall decreases as the nanofluid volume fraction increases. This decrease in 9: ;;;; & number is observed up to a volume fraction 3 = 0.05, after which it increases again. For the full range of volumetric fractions, it is shown that increasing '(number causes 9: ;;;; & to increase, while increasing 8(number and increasing the magnetic field causes 9: ;;;; & to decrease. Furthermore, as the 8(number increases, the heat transfer enhancement ratio =/ increases mainly when the magnetic field is oriented radially. Finally, new correlations of 9: ;;;; & versus '(, 3, 8(, and 7 are derived for the axial and radial magnetic fields cases.
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