穩態液晶量測高旋轉數對於缺失鰭片之熱傳變化研究

Abstract

本實驗透過液晶可視化技術，觀察矩形冷卻通道(寬高比為4)在高旋轉數狀態下，缺失鰭片結構對內部熱傳變化影響，內部鰭片以交錯方式排列。各鰭片間距，在軸向與側向間距之鰭片直徑比值皆為2。實驗透過替換第4排中間鰭片的方式，形成三種不同鰭片結構，分別為完整鰭片、分割式鰭片和拔除鰭片。實驗利用雷諾數分別為5000、10000與20000的冷卻空氣，通過加熱的通道壁面，藉此觀察各鰭片通道在旋轉狀態下，迎風面與背風面的表面熱傳分佈(實驗旋轉數為0~0.65，密度比值固定為0.1)。在旋轉數為0.65時，通道受旋轉效應影響，造成在兩面熱傳的不均勻現象，其底端的熱傳值高於頂端，且觀測區域鰭片尾流明顯向底端偏移。此現象分別對完整鰭片與拔除鰭片，在迎風面上兩側熱傳差異為10%與40%；在背風面上兩側熱傳差異則為15%與42%。另外隨旋轉數上升時，三種鰭片結構的背風面的熱傳值跟著提高，其相較在靜止狀態下，分割式鰭片與拔除式鰭片分別提升約61%與57%，完整鰭片則為三種結構中最差的熱傳表現只提升43%。

The study investigates the heat transfer of a rectangle cooling channel with pin-fin array at high rotation numbers using thermochromic liquid crystal. The channel aspect ratio is 4 and angle of channel orientation is 150°. Eight rows of staggered circular pin-fins are used with the spanwise and streamwise spacing of 2. Various fin array configurations (full fin, partial fin, and missing fin) is studied by changing the fin geometry at the fourth row of the fin array. The Reynolds numbers in the current study are 5000, 10000, and 20000. The rotation number ranges from 0 to 0.65, and the density ratio is maintained at 0.1. At high rotation number, the rotation effect influences fluid flow in the channel, which causes different heat transfer near the top and bottom side of the channel. The wake flow behind the pin fin moves towards the bottom side. For the trailing surface, the heat transfer difference of the full fin and missing fin is 10% and 40%, respectively. For the leading surface, the heat transfer difference of the full fin and missing fin is 15% and 42%, respectively. The heat transfer on the trailing surface from the three fin configurations significantly enhances with an increase of rotation number. Comparing to the stationary state, increases of heat transfer from the partial fin and missing fin are 61% and 57%, respectively. The full fin has the lowest heat transfer enhancement of 43% among the three configurations.