背向階梯渠道內奈米氣溶膠對流熱傳之研究

Study on nanoaerosol convective heat transfer in a backward-facing step channel

吳春霖(Chun-Lin Wu)

指導教授 ： 翁輝竹

中原大學/工學院/機械工程研究所/碩士(2019年)

https://doi.org/10.6840/cycu201900727

摘要

本論文完成背向階梯渠道中奈米氣溶膠對流熱傳之研究。主要目的在探討在SiO2與Al2O3兩種奈米氣溶膠材料物理性質及粒子濃度，在不同雷諾數以及幾何外型差異下於背向階梯渠道內對流熱傳之影響。首先，驗證網格數量對於再接觸點位置之影響，探討不同數值研究結果之差異，確保數值解的可靠度與精確度。接著，理論建模奈米氣溶膠之材料性質，透過ANSYS-Fluent設定材料性質參數，進行對流熱傳之分析。
研究結果發現，當奈米粒子體積分率增加時，背向階梯渠道中熱傳效果隨之增加。熱傳導係數較低的奈米粒子在高雷諾數下，靠近迴流區域內則有些許的熱傳表現，但並沒有顯著的增強效果，而熱傳導係數較高的奈米粒子，在非迴流區域對努賽爾數有明顯增強效果，在不同雷諾數下，粒子濃度使得努賽爾數增加約27.9%。若改變階梯傾角，傾角越小，此粒子濃度效應幾乎相同；若改變階梯高度，高度越大，粒子濃度使得努賽爾數僅增加約30.7%。

關鍵字

奈米流體 ； 奈米氣溶膠 ； 背向階梯 ； 對流熱傳

並列摘要

This thesis conducts an analysis of nanoaerosol flow and heat transfer in a backward-facing step channel. The main purpose is to explore the influence of the particle volume fraction presented in the SiO2 and Al2O3 nanoaerosols under different Reynolds numbers and channel geometrical shapes on convective heat transfer in a backward-facing step channel. First, we verify the effect of grid number on the position of reattachment point and explore the differences between the results of different numerical studies, so as to ensure the reliability and accuracy of the numerical solutions. Next, we theoretically model the material properties of nanoaerosols and analyze the convective heat transfer by setting material property parameters through ANSYS-Fluent.
According to the results, it was found that as the particle concentration of a nanoaerosol increases, the heat transfer performance in a backward-facing step channel is enhanced. Nanoparticles with lower thermal conductivity could result in a little heat transfer enhancement near the recirculation zone at high Reynolds number, but the enhancement is insignificant; Nanoparticles with higher thermal conductivity could result in a significant enhancement effect (increased Nusselt number) in the non-recirculation zone. Under different Reynolds numbers, the Nusselt number could be increased by increasing particle concentration up to about 27.9%. If the step inclination angle is changed so that the angle is smaller, the particle concentration effects are almost the same for all angles; if the step height is changed so that the height is greater, the Nusselt number could be increased by increasing particle concentration only up to about 30.7%.

並列關鍵字

nanofluids ； nanoaerosols ； backward-facing step ； convective heat transfer

參考文獻

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