Heat pipe
|
|
A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hot and cold interfaces. Practical heat pipes vary from around 0.5cm diameter and 10cm long to devices 10cm or more in diameter and several metres long.
Each pipe is sized and designed to work at a particular temperature with a certain heat flow capacity. Heat pipes are sealed hollow tubes lined with a wick or capilar ridges containing a little bit of fluid. The pressure in the tube is near the vapour pressure of the fluid, which means the fluid will evaporate out of the wick quickly if heat is applied. In doing so, the fluid absorbs significant latent heat from the hot part(s) of the tube. The vapour finds little resistance in the low pressure environment of the tube, and moves (very) quickly to normalise the pressure in the tube. When it reaches a colder part, the vapour will condense onto the wick, releasing its latent heat to its surroundings. The fluid is then transported through the entire wick by capillary action. Some heat pipes have been known to use a roll of paper as a wick.
Not only are there no mechanical parts and no energy required to transport the heat but because of the significant amount of energy involved in latent heat, the devices are very effective at heat transfer and can carry heat quantities many times that which could be carried by an equivalent metallic conductor.
Applications of heat pipes are often found in space technology, where they are the standard method used to transfer heat from the electronic units to the radiators, and in laptop computers to assist cooling the processor.