Heat Transfer Mechanisms

Convection is the transfer of thermal energy by the motion of a fluid. Water and air are two types of fluids that are most often used as examples. Air/water near the heat source expands (becomes less dense) and rises, carrying energy with it. The more cold/dense air/water sinks until it reaches the heat source, absorbs energy and then rises (Nave 2015). This rising and falling of air/water causes a circular flow, which can be seen in the figure below. While this movement is not as uniform as the figure suggests, it is a good approximation of the process.

(http://kids.britannica.com/elementary/art-177312/When-water-is-heated-convection-causes-the-water-at-the)

While there is no concrete equation established for dealing with convective air movements, the ideal gas law can be used to understand why the gases/liquids rise as they increase in temperature. PV=nRT where P is pressure, V is volume, n is molar mass, R is the gas constant, and T is temperature. If pressure is held constant, an increase in temperature is an increase in volume, which decreases density. This causes the air/water to rise.