暫態液晶熱顯像技術 應用於旋轉內冷卻彎道區之熱傳研究

Abstract

將冷卻流體導入冷卻通道內部，藉以帶走大量熱能達到降溫之功用，此為內部冷卻技術，廣泛應用於渦輪葉片內部冷卻通道中。而渦輪葉片內部冷卻通道，部分通道以180度之彎道相連接，因此本實驗模型選用矩形的內冷卻雙通道。本實驗內冷卻通道的寬高比(aspect ratio)為0.67，e/Dh為0.125，肋條與肋條之間距(p/e)為10，肋條(Rib)與主流方向的攻角呈45度。 渦輪葉片常處在旋轉的環境中，為了符合真實流場之模擬情況，本文研究旋轉效應所造成流場之熱傳影響，並比較靜止情況以及旋轉狀態下，各區域熱傳分佈(第一通道區、流體轉向區以及第二通道區)之差異，並研究肋條(Rib)對於不同區域之熱傳效應。溫度量測採用平面式暫態液晶熱顯像技術，藉以得知模型各區域溫度的熱傳值，以及各種效應所引起之熱傳分佈情形，並配合閃頻攝影技術的使用，完整呈現流道內熱傳的分佈形態，結果顯示，隨著雷諾數增加，紐賽數比值有下降的趨勢。

This study experimentally investigates the effects of rotation on heat transfer in a two-pass rotating rectangular channel. The experiments are conducted with two surface conditions: smooth walls and 45°angled ribbed walls. The channel aspect ratio is 0.67. Three Reynolds numbers are studied: 15000, 20000 and 25000. The rotational speed is fixed at 360 rpm for all tests. Rib turbulators are placed on the leading and trailing walls of the channel at an angle of 45°to the mainstream flow direction. The ribs height to hydraulic diameter ratio (e/Dh) is 0.125, and the rib pitch-to-height ratio (p/e) is 10 for all tests. Detailed measurements are presented in the first pass, in the turn region, and further downstream in the second pass. This study presents the transient liquid crystal technique for local heat transfer coefficient measurements in an internal cooling channel. Stroboscope is used as the photography technique. In this study, the author is able to systematically analyze, and conclude the heat transfer comparison with both smooth walls and ribbed walls. The Nusselt number ratio decreases with increasing Reynolds number in both non-rotating and rotating channels with smooth and ribbed walls.