No abstract

The unsteady forced and free mixed convection around a sphere immersed in a uid-saturated porous medium is investigated at low Peclet numbers with Gr=Re = O(1). Darcy ow model is used for the velocity ÿeld. The sphere is suddenly heated, and subsequently, maintains a constant temperature over the surface. Asymptotic solutions for small Peclet numbers are obtained using the method of matched asymptotic expansions, and the e ects of the buoyancy force on the transient velocity and temperature ÿelds are examined in detail.