What is a heat pipe?
A heat pipe is a heat transfer device with an extremely high effective thermal conductivity. Heat pipes are evacuated vessels, typically circular in cross section, which are back-filled with a small quantity of working fluid. They are totally passive systems, with no moving parts, and transfer heat from a heat source to a heat sink with minimal temperature gradients, or to isothermalize surfaces.
How does a heat pipe work?
Through the evaporation and condensation of the working fluid. As heat is input at the evaporator, fluid vaporizes, creating a pressure gradient in the pipe. This forces the vapor to flow along the pipe to the cooler section where it condenses, giving up its latent heat of vaporization. The working fluid is then returned to the evaporator by capillary forces in the porous wick structure or by gravity.
Do heat pipes work against gravity?
Yes, a heat pipe is said to be operating against gravity when the evaporator is located above the condenser. In this orientation, the working fluid must be pumped against gravity back to the evaporator. All heat pipes have wick structures that pump the working fluid back to the evaporator using the capillary pressure developed in the porous wick. The finer the pore radius of a wick structure, the higher against gravity the heat pipe can operate. A thermosyphon is similar to a heat pipe, but has no wick structure and will only operate gravity aided.
What fluids are used in heat pipes?
Heat pipe working fluids range from Helium and Nitrogen for cryogenic temperatures, to liquid metals like Sodium and Potassium for high temperature applications. Some of the more common heat pipe fluids used for electronics cooling applications are ammonia, water, acetone, and methanol.http://www.thermacore.com/frequently-as ... fault.aspx