Laminar natural convection heat transfer from isothermal spheres

Steady-state natural convection over a sphere has been studied numerically. Heat transfer and drag coefficients for a wide range of Grashof numbers (101 ⩽ Gr ⩽ 108) and Prandlt numbers 0.72 and 7.0 have been obtained. A plume with a mushroom-shaped front forms above the sphere whose length and thickness decrease with increasing Gr. At high Gr (Gr ⩾ 107 and Pr = 0.72), flow separation and an associated recirculation vortex exist in the wake of the sphere. The vortex size increases with Gr. The local Nusselt number along the sphere surface first decreases, reaches a minimum, and then increases steeply at the rear of the sphere.

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