Heat Pipe StructureA heat pipe is a sealed tube with an inner wall that features a wicking structure. The wicking structure can be, for example, a wiry mesh, a sintered powder, or deep and repeating grooves. A set amount of working fluid wets the inner wall. The working fluid (typically water in e-cooling applications) evaporates when subjected to a heat source. In practice, you place one end of the heat pipe near a heat source and the other end at a heat sink. The heat source end contains mostly vapor, and the heat sink end contains mostly liquid. Energy TransferThe structure of a heat pipe allows heat energy to be transferred from the heat source to the heat sink. First, the inner wall wicking structure promotes capillary action, allowing the working fluid to travel along the inner walls from the heat sink to the heat source. When the working fluid arrives at the heat source, it absorbs enough energy to evaporate, filling the center of the pipe with vapor. As the vapor travels down the temperature gradient toward the heat sink end, it transfers some of its energy to the inner walls of the heat pipe. By the time it reaches the heat sink end, it transfers enough energy to condense. The working fluid repeats the cycle, as shown below. Heat source Heat sink Vapor movement Fluid movement Dry wicking structure Wet wicking structure |