You are cooking by convection when circulating molecules of a gas or liquid transfer their heat directly to your food. These gas or liquid molecules are set in motion by a heat source, which is usually at the bottom of your oven or pot. As the assemblage of molecules closest to the heat source is warmed, it becomes lighter and rises above the heavier, cooler batch of molecules, which is simultaneously sinking. The cooler molecules, upon reaching the bottom of the oven or pot, are heated and begin their journey upward, displacing the top molecules, which have cooled slightly. This ongoing process creates air or water currents, an essential for convection cooking. Food cooked in an oven or pot of liquid, incidentally, is also heated by radiation (emitted by the heated interior surfaces of the oven or pot) and by conduction.
** Asian Recipes