奈米氣溶膠衝擊噴流於平板之數值熱傳研究

Numerical investigation for heat transfer performance of nanoaerosol jet impinging onto a flat plate

范皓俞(HAO-YU FAN)

指導教授 ： 翁輝竹

中原大學/工學院/機械工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000753

摘要

本論文完成奈米氣溶膠衝擊噴流對平板表面熱傳特性之數值分析，主要目的在探討高雷諾數下，奈米粒子濃度、無因次衝擊高度及噴嘴直徑比對衝擊平面努賽爾數的影響。首先，本研究以圓管式噴流作為基本外型，對特定無因次衝擊高度下第二峰值現象進行驗證，接著以Standard k-epsilon、RNG k-epsilon、兩種紊流模型對文獻實驗數據進行比對，之後對其進行網格獨立性測試，以找出符合時間成本及準確性的模擬方式。最後將兩種奈米氣溶膠作為工作流體，探討濃度、無因次衝擊高度及噴嘴直徑比對加熱壁面努賽爾數分布圖的影響。
結果發現，努賽爾數值隨著奈米氣溶膠體積分率的提升而增加，在無因次高度0.25時較其他無因次高度有更高的局部努賽爾數及平均努賽爾數。此外，當奈米氣溶膠濃度提升至0.4%時，其平均努賽爾數值與使用水為工作流體時相當，具有取代水應用於工業領域的潛力。

關鍵字

圓管式衝擊噴流 ； 無因次衝擊高度 ； 奈米氣溶膠 ； 第二峰值

並列摘要

This thesis was conducted to study the numerical analysis of heat transfer characteristics during air jet impingement cooling on a heated flat plate using nano aerosol. The main purpose is to investigate the influence of nanoparticle concentration, dimensionless nozzle height, and dimensionless radial position from the center of the jet on the Nusselt number of the impinging plane under high Reynolds numbers. First of all, the cylindrical nozzle jet was used in this study and numerical simulations were conducted to observe the occurrence of secondary peaks in Nusselt profiles in a specific dimensionless nozzle height, and then different RANS turbulence model namely, Standard k-epsilon, RNG k-epsilon, were used to validate the numerical results with experimental results. Secondly, the grid independence test was carried out to find a simulation method that meets the time cost and accuracy. Finally, two nano-aerosols were used as working fluids to discuss the influences of changing the concentration, dimensionless nozzle height, and nozzle diameter ratio on the Nusselt number distribution.
It was found that the Nusselt number increases with the increase of the nano aerosol volume fraction, and the local Nusselt number is higher at the dimensionless nozzle height 0.2 than others, so as to the average Nusselt number. In addition, when the volume fraction of nano-aerosol is increased to 0.4%, the average Nusselt numbers are equivalent to that when water is used as the working fluid, which has the potential to replace water in the industrial field.

並列關鍵字

cylindrical nozzle jet ； nano aerosol ； dimensionless nozzle height ； secondary peaks

參考文獻

Baughn, J. W., Hechanova, A. E., and Yan, X., 1991, “An experimental study of entrainment effects on the heat transfer from a flat surface to a heated circular impinging jet,” Journal of Heat Transfer, 113, 1023-1025

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Fénot, M., Vullierme, J.J., and Dorignac, E., 2005, “Local heat transfer due to several configurations of circular air jets impinging on a flat plate with and without semi-confinement,” International journal of thermal sciences, 44, 665-675.

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