FC-72在水平加熱板上之過熱流動沸騰熱傳特性研究

Abstract

近年來由於半導體製程技術之快速發展，使得IC chip上之元件密度大幅增加，進而造成微電子系統中微電流流動所產生的熱量( Dissipation Heat ) 也增加很多。為了維持這些系統能穩定正常運作，我們需要發展有效的冷却方法去移除這些熱量。也因此，具有液-氣相變化的冷却方法(如沸騰和冷凝)，常被運用於電子系統冷却。目前為了更進一步滿足未來的需求，各種不同提升沸騰熱傳的方法正被積極的研究。這其中，在加熱面表面上做各種微結構去提升沸騰熱傳已有一些研究。而在上一期的國科會專題研究計畫(99年8月至102年7月)，我們的實驗量測探討如何利用氣泡運動所造成之細線移動來增加池沸騰與流動沸騰熱傳，已得到不錯的結果。 介電液如FC-72及FC-87常被選用作為電子系統冷却之工作流體。由於介電液屬於親水性流體，其在加熱面上核沸騰起始溫度經常有很高之Temperature Overshoot。因此可將上游處之介電液維持在些許的過熱狀態，這種過熱狀態的介電液如何影響加熱面上的沸騰熱傳特徵目前尚未被學界討論。是否有可能利用介電液的過熱度來增加沸騰熱傳？值得學界深入研究探討。 在本三年期的專題研究計畫中(102年8月至105年7月)，我們將建立實驗系統來探討FC-72介電液在加熱面上之過熱流動沸騰熱傳，主要將量測液體過熱度對沸騰曲線( Boiling curve ) 及沸騰熱傳係數的影響。另外也將量測相關之氣泡特徵來釐清過熱度對核沸騰過程之影響。在第一年計畫中，我們將探討經由FC-72流量之突然下降而造成之FC-72液體過熱如何影響沸騰熱傳。而在第二年的計畫中，我們將直接加熱上游的FC-72液體至過熱狀態，研究液體過熱度對FC-72沸騰熱傳之影響。最後在第三年之計畫中，我們將進一步探討是否可以利用加裝於加熱面上之可移動彈性細線來加強FC-72的過熱沸騰熱傳。

The quick advance in the semiconductor technology in recent years has resulted in the huge increase in the component density integrated in an IC chip. Thus, in turn, causes a large increase in dissipation heat in the microelectronic systems. Certain effective cooling methods are thus needed to remove the high dissipation power density to maintain the systems in stable normal operation. Therefore, methods based on phase change such as boiling and condensation are employed in the electronics cooling because of latent heat involved in the heat removal processes. Besides, various techniques to enhance the boiling heat transfer to meet the future need are currently under intensive investigation. Especially, the use of some surface microstructures to augment boiling heat transfer has received some attention. In our last research project sponsored by NSC (August 2010 to July 2013), we explore how passively movable and flexible wires driven by the bubble motion only can enhance the pool and flow boiling heat transfer over a small heated surface. Good boiling heat transfer enhancement has been noted. The dielectric liquids such as FC-72 and FC-87 are often employed as working fluids in electronics cooling. It is well known that the temperature overshoot at Onset of Nucleate Boiling of the dielectric liquids on a heated surface is rather significant since they are hydrophilic. Hence it is possible to maintain the liquid layer above the surface at a slightly superheated state. How the slightly superheated liquid layer affects the boiling heat transfer characteristics of dielectric liquids remains essentially unexplored. Is it possible to enhance the boiling heat transfer by superheating the liquid layer above the boiling surface? This needs to be explored. In this three-year research project (August 2013 to July 2016) an experimental system will be established to explore the superheated flow boiling heat transfer of FC-72 liquid on a heated plate by measuring the boiling curves and boiling heat transfer coefficients for various degrees of liquid superheating. Besides, the associated bubble characteristics in the boiling flow will be examined to elucidate the boiling processes affected by the liquid superheating. Specifically, in the first year of the project we will investigate the superheated flow boiling heat transfer resulting from a sudden reduction of the FC-72 flow rate. Then in the second year of the project the superheated flow boiling heat transfer of FC-72 resulting from heating the upstream liquid to a superheated state will be unraveled. Finally, in the third year of the project the possible enhancement of the superheated boiling heat transfer of FC-72 by installing flexible / movable strings on the heated surface will be examined.