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http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/60271
標題: | 數值模擬加熱元件上方強制與混合熱對流及其於剪應力指示器開發之應用 Numerical Simulation of Forced and Mixed Convection over a Heated Surface Element and its Application in Shear-Stress Indicator Development |
作者: | Shih-Hsin Hsieh 謝時昕 |
指導教授: | 楊馥菱(Fu-Ling Yang) |
關鍵字: | 熱感應器,應變規,自然熱對流,混和熱對流,庫葉流, thermal sensor,strain gauge,natural convection,mixed convection,Couette flow, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | 近年來出現許多關於將熱感應器應用於量測穩流強度的研究。最近在實驗中發展出將應變規黏貼於高熱膨脹係數的材料上,並利用其自體發熱原理來發展熱感應器,其兼具便宜以及體積微小等優點。藉由將溫度變化所引發的熱應變Δε與其週遭流體的相對運動強度 做連結,使Δε能作為其相對運動強度的指標。經過實驗發現Δε隨流動強度呈單調對數遞減。
熱應變規無法直接測表面剪應力。因此,本論文利用數值計算模擬庫頁流及準穩態振盪流流經熱原件之熱傳行為以估計熱元件表面上的溫度變化(ΔT)及剪應力值之關係。首先,我們利用在實驗中得到的Δε-log 關係驗證了模擬的結果ΔT-log 。接著,將空間上溫度變化作平均 並與其表面剪應力的做連結,並進一步探討不同重力場方向所造成強制熱對流與混和熱對流中熱交換的現象。最後,欲根據自體發熱應變規所量測到的訊號用於剪應力的量測。 Thermal sensors have been investigated for measuring the strength of steady liquid flows. Recently, a conventional strain gauge has been developed as a thermal sensor in experiment using its self-heating by bonding the gauge on a substance of high thermal expansion rate. Thus, the induced apparent thermal strain, Δε can be measured to infer a subsequent relative motion between the gauge and its ambient liquid of magnitude . In previous experiments, it is observed that Δε drops monotonically with the logarithm of flow strength log and hence Δε can be applied to indicate . A limitation of strain gauge is that it cannot be applied to measure surface shear-stress directly. Hence, this thesis adopts numerical simulation to investigate the problem with steady Couette flow and quasi-steady oscillating flow over a heating element to compute the desired surface shear stress. First, the experimentally mearsured Δε-log correlation is applied to validate the simulation. The correlation between space-averaged temperature variation (linear relation with Δε) and surface shear-stress is presented to be used for design of shear-stress indicator. We further simulated the cases when gravity is included in differenced direction relative to to investigate the possible influence of forced and mixed convection. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/60271 |
全文授權: | 有償授權 |
顯示於系所單位: | 機械工程學系 |
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