ABSTRACT
This chapter examines the natural-convection problems where the body force is gravitational and the density gradient is due to a temperature gradient. It considers the natural-convection heat transfer from a heated flat plate, a cylinder, a sphere, and other miscellaneous systems. Compared to forced-convection problems, natural-convection systems are characterized by smaller velocities, small convection coefficients, and correspondingly smaller heat-transfer rates. Natural-convection boundary layers in contact with a vertical surface can experience transition and exhibit turbulent flow. Natural convection itself is caused by a thermal instability. Turbulence is a series of hydrodynamic instabilities. The natural-convection problems considered thus far had a principal body dimension aligned primarily with the direction of action of the gravity force. For the case of a horizontal flat surface, the principal body dimension is perpendicular to the gravity vector and hence to the direction of action of the buoyant forces.
