交錯潤濕性表面對池沸騰熱傳影響之研究

Abstract

本研究主要探討交錯潤濕性的表面對於池沸騰熱傳之影響，交錯潤濕性表面是由兩種不同潤濕性的表面交錯而成，本研究使用溶膠凝膠法進行表面改質，可成功製備出超親水與未改質的交錯式表面到超疏水與未改質的交錯式表面。實驗共分為三個實驗變數對於池沸騰熱傳之影響，第一部分為交錯式表面之接觸角差異，第二部分為改變中央條紋親疏水性以及表面介面數，第三部分則是改變表面親水面積比，分別檢視以上因素之影響。 改變接觸角差異的實驗結果顯示不論是超親水與未改質，或是超疏水與未改質表面，相較於完全未改質表面可提升臨界熱通量125%至180%，以及降低最大過熱度，並且發現在加熱過程中有熱通量漸大、過熱度卻降低之情況，本研究利用流場觀測去解釋此特殊的沸騰曲線現象。改變中央條紋親疏水性的實驗使用2、4、6三種不同介面數，實驗結果顯示不論使用何種表面，皆為中央為未改質之表面有較佳的池沸騰熱傳，並且介面數越多，池沸騰熱傳效果也越佳。改變面積比的實驗結果則為接近50%親水性面積時，可得到較佳的池沸騰熱傳係數。

This study investigates the effect of interlaced wettability surfaces on pool boiling heat transfer. Interlaced wettability surfaces are composed of two different wettability. This study uses sol-gel method to modify the surface wettability, and successfully generate from superhydrophilic-plain interlaced surface to superhydrophobic-plain surface. Experiment results are divided into three parts to examine the effect of three variables, contact angle difference, the wettability of central region and area ratio of the hydrophilic region. At first, experimental results of contact angle difference show that all of the interlaced surfaces increase the critical heat flux and reduce the maximum superheat. The pool boiling curve shows that the heat flux increases with reduced wall superheat at nucleate boiling regime. Such a reverse trend on pool boiling curve could be explained by the flow visualization. Furthermore, the results of the wettability of central region on the surfaces show that whatever the number of interfaces is, surfaces with plain central region have better boiling heat transfer than the others. Additionally, the higher pool boiling heat transfer can be observed when surfaces increase the number of interfaces. Finally, the results indicate that the best heat transfer coefficient is at 50% area ratio of the hydrophilic coated region.