完全發展入口狀況平滑壁面平行四邊形雙通道之流場與熱傳表現研究

Flow Field and Heat Transfer Performance in Stationary Two-Pass Smooth Parallelogram Channels with Fully Developed Inlet Flow

林安(Lin, An)

指導教授 ： 劉通敏 ； 張始偉

國立清華大學/工學院/動力機械工程學系/碩士(2016年)

摘要

本文運用質點影像測速儀與紅外線熱像儀量測在靜態完全發站入口條件下平行四邊形渦輪機葉片內冷卻通道之紊流流場、與熱傳分佈，並與前人數據比較探討入口幾何形狀與雷諾數(Re)變化對紊流流場、入出口壓力變化與熱傳分佈之影響。實驗通道模型由兩平行四邊形截面之直通道與180度銳轉之轉彎區組成，通道截面為45度傾角、45.5mm等邊之平行四邊形，等效水力直徑為32.17mm。於流場量測實驗中，為了達到實驗光學條件要求，實驗模型由厚度15mm之透明壓克力板構成，實驗雷諾數固定在10,000；而於熱傳實驗中，構成通道模型材料改為耐熱、低熱傳導係數之電木，實驗有六個雷諾數變化，分別為5,000, 7,500, 10,000, 12,500, 15,000 以及20,000。本研究也比較兩種入口幾何形狀(完全發展入口條件與仿真實葉片入口條件)下對紊流流場與熱傳分佈所造成之影響，實驗主要量測結果以通道內主流、二次流流場向量分佈、紊流動能、壓損係數以及通道壁面之紐賽數(Nu)分佈來量測與探討，在全展入口條件下，量測得到單純平行四邊形截面所導致上下壁面不對稱之流場與熱傳表現，並與前人所研究之典型正方形、矩形截面雙通道比較後，發現平行四邊形通道熱性能係數與之相近，因此在內冷卻流道設計之可行性上獲得驗證。再者，從實驗數據之量測與比較可得知入口效應對內冷卻流道的熱傳表現增益顯著，尤其在第一通道可達到近70%的熱傳表現提升，影響可越過轉彎區並達到第二通道，對通道整體可達40%之熱傳表現提升。

關鍵字

質點影像測速儀 ； 紅外線熱像儀 ； 平行四邊形通道 ； 入口幾何形狀 ； 紊流 ； 熱傳

並列摘要

PIV and Infrared Thermometry measurements are respectively conducted to study the effects of entrance geometry and Reynolds number (Re) on the detailed flow fields and local heat transfer distributions in a stationary two-pass smooth parallelogram channel with 180-deg sharp turn. Two entrance geometries, including a fully developed inlet condition (FDI) as well as an asymmetrically and suddenly contracted inlet condition (ASI), are investigated. The smooth parallelogram channel has equal adjacent sides of 45.5 mm in length and two pairs of adjacent angles are 45-deg and 135-deg. Local (Nu0) and regionally averaged ((Nu) ̅_0) Nusselt numbers over entire top and bottom walls along the first and second passages and through the bend region with the associated pressure drop are examined at Re ranging from 5,000 to 20,000. Moreover, cross-sectional secondary- flow patterns as well as the near-wall streamwise mean velocity components and turbulent kinetic energy are analyzed to correlate the relationship between flow characteristics and heat transfer distributions at Re=10,000. The most distinct finding of present study is the asymmetric thermal and fluid flow features on the top and bottom wall side, in contrast to symmetric ones in the corresponding square and rectangular channels. The Nu0 distributions over top and bottom walls of ASI channel respectively extends downstream to the mid-turn and the middle of second pass. Compared with FDI channel, the (Nu) ̅_0 for ASI are elevated to the levels about 65.3-70.1%, 14.2-13.7%, and 23.9-14.0% in the first passage, turn region, and second passage, respectively, under constant flow rate condition. Thermal performance factors of the ASI channel are about 43.5% and 53.7% higher than the FDI channel at Re=5,000 and 20,000, respectively. Moreover, the correlations of Nu0 and fanning friction factor (f0) with Re as the controlling parameter are obtained and validated by those of the comparable square channels available from the literature.

並列關鍵字

PIV ； Infrared Thermography ； Parallelogram Channel ； Entrance Geometry ； Turbulent flow ； Heat Transfer

參考文獻

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