The latest technology of personal computer, including processor, chipset, memory and graphics technology, poses a huge challenge to system designers in terms of heat dissipation. As the market moves towards higher computing speed, more powerful functions and smaller models, the heat and heat density generated by these devices will continue to increase. This increase in thermal energy at the component level forces designers to reconsider cooling solutions at the chip, packaging, motherboard and system levels. Passive and active radiators have proven to be a reliable and relatively economical solution, sufficient to keep up with the challenges of the growing thermal environment. In order to continue to use these heat sink technologies, it is necessary to consider the cooling scheme at the system level.
In the past, system designers focused on improving the thermal environment of the system by increasing the number of fans and optimizing the position of vents. This approach is still an important aspect of system cooling design. However, the cost and complexity of packaging level heat dissipation schemes are getting higher and higher, which requires more advanced system level technologies to find more balanced and cost-effective system countermeasures. If the shell of the computer can provide a lower internal temperature, this cost can be greatly saved. By properly balancing system level solutions with packaging level solutions, integrators can significantly reduce the total cost of the system. In an environment with increasing heat load, processors are usually the most demanding components for system cooling design. Processor cooling solutions typically use copper or aluminum heat sinks with active fans to promote air flow. The processor failure temperature can be directly related to the temperature of the air entering the active fans and radiators. The lower the air temperature, the lower the processor failure temperature. With the introduction of INTEL Prescott Pentium4 4 CPU above 3G, the high power consumption of high frequency processor has brought more heat, and the old chassis cooling scheme can no longer meet its needs. So INTEL has put forward a whole set of solutions to solve the heat dissipation and EMI prevention problems caused by CPU above 3G. The "Air Guide Design" is one of them, and the more significant one is the BTX specification. It also derived EMI proof Wave Guide Design and U-seam Design
Air Guide Design generated by 38 ℃
We all know that the temperature generated by the CPU surface is basically 72 ℃ (INTEL calls it T-case temperature), while at the ambient temperature of 35 ℃, the internal temperature environment provided by most computer cases is generally about 40-45 ℃. However, INTEL must ensure that the T-case temperature is controlled within 72 ℃. According to the heat dissipation capacity brought by the CPU fan, if the temperature rise in the chassis (called T-rise by INTEL) is lower than the target of 3 ℃, the temperature in the chassis must be controlled below the ambient temperature of 35 ℃ plus T-rise 3 ℃ equal to 38 ℃ (called T-ambient temperature by INTEL). The measurement method of this 38 ℃ is: the average temperature of 4 points 2 cm above the heat sink of the CPU fan. The forward and backward air flow direction of the chassis increases the temperature of the air flowing to the CPU fan a lot, so it is necessary to open a separate air duct for the CPU fan, so that the air temperature obtained by the CPU fan is exactly below 35 ℃, so the "chassis air duct" is generated.
以往，系統(tǒng)設計師專注于通過增加風扇的數量和優(yōu)化通風口的位置來改進系統(tǒng)的熱環(huán)境。這一途徑仍然是系統(tǒng)散熱設計的一個重要方面。然而，包裝層次散熱方案的成本和復雜程度越來越高，要求有更先進的系統(tǒng)層次的技術，以發(fā)現更平衡、成本效益更佳的系統(tǒng)對策。如果計算機的外殼能提供較低的內部溫度，就能大大節(jié)省這一開支。通過在系統(tǒng)層次解決方案和包裝層次解決方案之間的恰當平衡，集成商可極大地降低系統(tǒng)的總成本。在熱負荷越來越大的環(huán)境中，處理器通常是對系統(tǒng)散熱設計要求最高的部件。處理器散熱方案通常使用銅質或鋁質的散熱器，并以活躍的風扇促使空氣流動。處理器失效溫度可以與進入活躍的風扇和散熱器的空氣的溫度有直接關系?？諝鉁囟仍降?，處理器失效溫度也越低。隨著INTEL Prescott Pentium4 3G以上CPU的推出后，因為高頻處理器的高功耗帶來了更大的發(fā)熱量，而舊有的機箱散熱方案已經無法滿足其需求。于是INTEL為解決3G以上CPU所帶來的散熱及防EMI問題而提出了一整套的方案，“機箱導風管”的設計(Air Guide Design)就是其中一種，而更為顯著的另外一套方案就是BTX的規(guī)范。并且也衍生出防EMI的Wave Guide Designe和U-seam Design
由38℃而產生的Air Guide Design(機箱導風管設計)
我們都知道CPU表面所產生的溫度基本上是在72℃（INTEL稱之為T-case溫度），而在 35℃的環(huán)境溫度下，大多數計算機機箱提供的機內溫度環(huán)境一般約為 40-45℃。而INTEL必須保證T-case溫度控制在72℃之內，根據CPU風扇所帶來的散熱能力，必須要讓機箱內的升溫(INTEL稱之為T-rise)低于3℃的目標，就必須要求機箱內的溫度控制在環(huán)境溫度35℃加T-rise3℃等于38℃（此38℃ INTEL稱之為T-ambient溫度）之下。此38℃的測量方式是：CPU風扇散熱片(heatsink)上方2cm高取4點的平均溫度。而機箱的前進后出的空氣流向，使得流向CPU風扇的空氣溫度已經有上升很多，所以就需要為CPU風扇單獨開出一條風道，使得CPU風扇得到的空氣溫度正好是在35℃以下，所以就產生了“機箱導風管”。
