The natural convection is a process, in which the fluid motion results from heat transfer. When a fluid is heated or cooled, its density changes and the buoyancy effect produce a natural circulation in the affected region, which causes itself the rise of warmer fluid and the fall of colder fluid: therefore, energy transfer from hotter region to colder region and such process is repeated as long as the temperature difference in fluid exist.

We know that a hot boiled egg (or a hot baked potato) on a plate eventually cools to the surrounding air temperature. The egg is cooled by transferring heat by convection to the air and by radiation to the surrounding surfaces. Disregarding heat transfer by radiation, the physical mechanism of cooling a hot egg (or any hot object) in a cooler environment can be explained as follows:

As soon as the hot egg is exposed to cooler air, the temperature of the outer surface of the egg shell will drop somewhat, and the temperature of the air adjacent to the shell will rise as a result of heat conduction from the shell to the air. Consequently, the egg will soon be surrounded by a thin layer of warmer air, and heat will then be transferred from this warmer layer to the outer layers of air. The cooling process in this case would be rather slow since the egg would always be blanketed by warm air, and it would have no direct contact with the cooler air farther away.