Heat Pipe
For computer users who often modify PCnya mainly related to cooling the processor or other chip, would be familiar with the heat pipe. Simple meaning of the heat pipe is a device that can move heat in large quantities with relatively constant temperature conditions. Heat pipes do not require external power and no moving mechanical parts. Compare with water cooling which requires various tools and resources such as pumps and other inputs. In principle, the heat pipe is a tube that was isolated, which on the inner wall has a wick structure (woven porous) and there is fluid as heat registers. 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 when in 1962 the technology is used on the space shuttle!
Heat Pipe Construction
Materials often used for heat pipe technology is a hollow pipe made of copper, stainless steel, or aluminum.
While the working fluid used must consider the design of the working temperature of the heat pipe. The most
widely used fluid is water and ethanol / alcohol. There are certain characteristics associated with fluids that are used for example if using water, it should be noted that the water will only be suitable when used at temperatures of between 5 to 230 ° C. The following table shows the working temperature range for some fluids used in heat pipes
Fluid Temperature Range (° C)
Helium -271 to -268
Hydrogen -259 to -240
Neon -248 to -230
Nitrogen -210 to -150
Methanol -182 to -82
Ammonia -78 to 130
Water from 5 to 230
Mercury 200 and 500
Cesium 400 to 1000
Sodium 500 to 1200
Lithium 850 to 1600
Before choosing a fluid to be used it is necessary to an understanding of the relationship of temperature and pressure. Suppose that heat pipes filled with water is designed to release heat at a temperature of 70 ° C, the pressure in the container must be maintained at 2.31 kPa, the pressure where the water will boil at a temperature of 70 ° C. The pressure so far below the atmospheric pressure is 101 kPa, so that in theory will heat pipes operate in vacuum (can be broken). Conversely, if the current pressure in the pipe which is maintained in accordance with atmospheric pressure, then at a temperature of 70 ° C water will not boil, because the atmospheric pressure boiling water only if the temperature reaches 100 ° C. If the heat pipe at temperatures of many new works, the equipment to be cooled is first charred.
Meanwhile, he played an important role to restore the liquid to the evaporator. The performance of the wick depends on the structure. He can be made from porous ceramic or stainless wire mesh. Can also be made by extrusion together with the tube.
Capillarity effects allows heat pipes can work in all positions, even against gravity. However, the best performance will be obtained when the capillarity pressure in the direction of gravity, in other words the position of the evaporator is below. Conversely the worst performance if the evaporator is above. While in the horizontal position, the force garavitasi no effect on capillarity. Thus the performance can be folded when positioned vertically with the evaporator below, because the effect of capillarity is assisted by gravity.
How it Works heat pipe
Heatpipe consists of three parts: Evaporator (lawyer-vapor, vapor = steam) located at one end, where the heat is absorbed and the liquid is evaporated, then Condenser (lawyer-dew) located at the other end where the steam is out and the dew heat release; and final adiabatic section that lies between the two. Adiabatic is a state where there is no (or very small, negligible) heat transfer to or from the surrounding environment. Adiabatic can occur under two possibilities: the system is isolated with a perfect, or the temperature inside and outside the same.
Animation workings of heatpipes can be found at:
http://www.dynatron-corp.com/images/products/heatpipe/heatpipe06.gif
Working heat pipes based on the principle of physics follows:
- At a certain pressure, the liquid will evaporate, while the steam also will melt at a given temperature (saturation temperature that can not ride anymore), so that there will be pressure regulation in the heat pipes which in turn will regulate the working temperature and the 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 the wick will move the liquid in the wick channel, even against gravity, due to the capillarity effect.
- The liquid in a channel move toward the lower pressure.
At first wick filled with fluid and the bottom of the heat pipe (the evaporator) filled with steam. When the tip comes in contact with the surface of the evaporator heat, heat energy will flow into the heat pipe. In saturated conditions (where the addition of heat does not raise the temperature, but makes the liquid phase change into steam), liquid in the tip of the evaporator will evaporate as a result of heat transfer earlier, causing the vapor pressure rises. Because of the difference in pressure between the tip of the tip evapotaror condenser, the steam will move into the lower pressure, namely the condenser. In the condenser is usually mounted cooling fins to aid heat dissipation. The cooler condenser section, or cold conditioned, will result in steam \ "lost \" thermal energy and discharged into the surrounding media, and the steam going to the dew. Fluid results from condensation is then entered into the wick channel because of the capillarity effect, returning to the evaporator. So that happened one complete cycle, and so on.
Why Should Heat Pipe?
Empirically, heat pipe has a thermal conductivity (ability to deliver heat) are far more effective than aluminum, copper or even silver. Let us consider two media with respective temperatures TH and TC. A simple heat pipe with water as working fluid has a thermal conductivity (k) of approximately 100,000 W / (m. ° C). Comparing with the copper that \ "only \" 400 W / (m. ° C). So for a distance of TH-thick copper and TC when replaced with heatpipe containing water of equal length, heat transfer will be obtained 250 times bigger!
Is prevalent if a heat pipe having an effective conductivity of 400 000 W / m ° C) which means a thousand times its copper. As an example, the horizontal heat pipe length of 15 cm, diameter 6 mm with the working fluid of water, capable of transferring the heat of 300 W. Because based on the cycles of 2-phase (liquid-vapor) are closed and the capillarity effect, then the heat pipes are no longer needed additional resources such pumps. This will reduce maintenance and power consumption. Temperature variation will be minimal or awake because governed by phase changes. Heat pipes also have a response to high heat and large heat transfer capacity. Heat pipes are also functions like a thermal diode, which allows the transfer of heat in one direction only.
Then why not use heat pipes?
Although it is theoretically simple but working principles in implementing it, tough. This impact on the difficulty of the process of manufacture and resulting high costs required. Other difficulties are also highly dependent heat release by the ability of the condenser and the selection of fluid used. Then at very low temperatures, the liquid will thicken irritant capillarity work on wick. Not ideal conditions can also occur when the pressure is not enough to encourage fluid capillarity, as a result of loss of pressure during the phase change from vapor to liquid.
