In an air cooler, the heat is transferred from the IHS of the CPU, through the applied thermal paste, and into a conductive baseplate that is usually made from copper or aluminum. From the baseplate, that thermal energy moves into the attached heat pipes.
The heat pipes are designed to conduct heat from one location to another. In this case, the heat moves to a heatsink that is elevated off of the motherboard, freeing up space for other components, such as RAM. These pipes deliver the energy in the form of heat to the thin metal fins that make up the heatsink. These fins are designed to maximize exposure to the cooler air, which then absorbs the heat from the metal. An attached fan then pushes the warm air away from the heatsink.