What you are describing is called thermal dynamics. We all know hot air rises, and cool air sinks. As long as the air is moving you have an exchange of energy. As the hot air rises, it creates a vacuum below it that pulls in colder air from below. The cooler air saps energy from the hot parts and gains heat. It then takes the heat and rises with the hot air above creating another vacuum below. That also pulls in fresh new cooler air to surround the hot parts. This continuous movement creates a convection or cycle if you will that keeps air from becoming stagnant. When you have stagnant air the air can only absorb so much heat. Circulating air can absorb more heat away from hot parts do to it being in motion. Thats how fans typically work is to force a convection of cool air to push stagnated hot air out of the way, so cool low energy air can absorb heat energy and travel away from the hot surface.