Heat PipeFor computer users who often modify the PC is primarily concerned with cooling processors or other chips, of course no stranger to the heat pipe. Simple meaning of the heat pipe is a device that can move large quantities of heat with relatively constant temperature conditions. Heat pipe does not require external power and no moving mechanical parts. Compare with water cooling which requires a variety of tools and inputs such as pump power and others.
In principle, heat pipe is a tube that was isolated, whereas in the inner wall Wick structure (woven porous) and there is liquid as conductor of heat. Heat pipes used to cool electronic components, used in air conditioners, refrigerators, and others. Heat pipes are also used in laptop / notebook to reduce the working temperature of components. Heat pipe technology patented in 1942 by RS Gaugler of the General Motors Corp., but the heat pipe is not much mention until the year 1962 when this technology is used on the space shuttle!
Heat Pipe Construction
Materials often used for heat pipe technology is a pipe made of copper, stainless steel, or aluminum.
While working fluids used must consider the design of the working temperature of the heat pipe. The most liquid used is water and ethanol / alcohol. There are certain characteristics associated with fluids that are used for example when using water, it should be noted that the water will only be suitable when used in working temperatures between 5 and 230 C. The following table shows the working temperature range for several fluids used in heat pipes.| Liquids | Temperature Range ( C) |
| Helium | -271 until -268 |
| Hidrogen | -259 until -240 |
| Neon | -248 until -230 |
| Nitrogen | -210 until -150 |
| Methanol | -182 until -82 |
| Amoniak | -78 until 130 |
| Water | 5 until 230 |
| Mercury | 200 until 500 |
| Cesium | 400 until 1000 |
| Sodium | 500 until 1200 |
| Lithium | 850 until 1600 |
Before selecting a liquid to be used it is necessary to an understanding of the relationship of temperature and pressure. Suppose the heat pipe filled with water designed to remove heat at a temperature of 70 C, the pressure in the container must be maintained at 31.2 kPa, the pressure where the water will boil at a temperature of 70 C. The pressure so far below the atmospheric pressure of 101 kPa, so in theory heat pipe will operate in a vacuum (could be broken). Conversely if the pressure in the pipe is now guarded in accordance with atmospheric pressure, then at a temperature of 70 C water will not boil, because the new atmospheric pressure boiling water if the temperature reaches 100 C. If the temperature heat pipes so new work, then the equipment will be cooled is first charred.
Meanwhile, he played an important role to return liquid to the evaporator. Wick performance depends on the structure. He can be made from porous ceramic or stainless wire net. Can also be made by extrusion along with the tube.
Capillarity effect allows heat pipe capable of working on all positions, even against gravity. However, the best performance was obtained when the direction of Capillarity pressure in the direction of gravity, in other words the position under the evaporator. On the other hand the worst performance if the evaporator is above. While in the horizontal position, the force has no effect on garavitasi Capillarity. Thus the performance can be folded when the evaporator is positioned vertically below, because the effect of Capillarity assisted by gravity.
How it Works Heat pipe
Heatpipe consists of three parts: Evaporator (lawyer-steam vapor = steam) which is at one end, where the heat is absorbed and the liquid is evaporated; then Condenser (lawyer-dew) which lies on the other end where the vapor at the dew-and heat is released; and final adiabatic section that lies between the two. Adiabatic is a state which does not happen (or very small, negligible) heat transfer to or from the surrounding environment. Adiabatic can occur under two possibilities: the system completely isolated, or the temperature inside and outside the same.
Working heat pipe based on the following physical principles :
- At a certain pressure, the liquid will evaporate, while the steam will melt at a given temperature (saturation temperature can not rise again), so that will happen in the pressure setting heat pipe which in turn will regulate the working temperature and liquid phase change to vapor and from vapor to liquid.
- At a certain pressure or temperature, the amount of heat energy is absorbed when the liquid evaporates will be equal to the amount of heat energy released when water vapor condenses.
- Capillary pressure in Wick will move the liquid in the channel he was, even against gravity, due to Capillarity effects.
- The liquid in a channel move toward the lower pressure.
Because of the difference in pressure between the tip of the tip evapotaror condenser, the vapor will move toward the lower the pressure, the condenser section. In the condenser cooling fins are usually installed to help heat dissipation. Part of the cooler condenser, or cold conditioned, will result in steam \ "lost \" heat energy and discharged into the surrounding media, and the steam going to the dew. Liquid product of this condensation then into the channel because of the Wick Capillarity effect, returned to the evaporator. So complete a cycle occurs, and so on.
Why a Heat Pipe?
Empirically, heat pipe has a thermal conductivity (ability to deliver heat) is far more effective than aluminum, copper or even silver. Let us consider two materials with respective temperatures TH and TC. A simple heat pipe with water as working fluid has a heat conductivity (k) of about 100,000 W / (m. C). Comparing with the copper that \ "only \" 400 W / (m C). So for the copper thickness TH and TC distance when replaced with heatpipes filled with water with the same length, will be obtained heat transfer 250 times bigger!
Is common when a heat pipe having an effective conductivity of 400,000 W / m C) which means it a thousand times copper. For example, the horizontal heat pipe length 15 cm, diameter 6 mm with a working fluid of water, able to transfer heat of 300 W. Because it is based on the cycle phase 2 (liquid-vapor) are closed and Capillarity effects, so the heat pipe is no longer needed such extra power pump. This will reduce maintenance and power consumption. Temperature variation will be minimal or awake because governed by the phase change. Heat pipe also has a high response and heat capacity of heat transfer. Heat pipe also serves as a thermal diode, which enables the transfer of heat in one direction only.Then why not use heat pipes?
Although it is theoretically simple but it works principle in its implementation, is difficult. This reflects the difficulty of manufacturing processes and result in high costs required. Other difficulties are also highly heat loss depends on the ability of the condenser and the selection of fluid used. Then at very low temperatures, the liquid will thicken irritant Capillarity work on him. Not ideal conditions can also occur if not enough Capillarity pressure pushes the liquid, as a result of loss of pressure during a phase change from vapor to liquid.
