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    Title: Investigation of micronozzles flow
    Other Titles: 微噴嘴流之研究
    Authors: 許欽淳;Hsu, Chin-chun
    Contributors: 淡江大學機械與機電工程學系博士班
    康尚文;Kang, Shung-wen
    Keywords: 微文氏管;微噴嘴;壓損係數;壓損係數比;Micro venturi;Micronozzle;Pressure loss coefficient;Ratio of pressure loss coefficient;FLUENT
    Date: 2008
    Issue Date: 2010-01-11 06:42:30 (UTC+8)
    Abstract: 本文主要是針對微噴嘴的空氣流場進行研究與探討,研究分為兩部分進行,分別是探討微文氏管的流力特性及曲面微噴嘴邊界對流力效能的影響,並將實驗結果與CFD軟體的分析結果相互比較,藉以觀察微文氏管內之流場分佈並探討微噴嘴較佳之流力性能。
    在微文氏管的研究部分,首先利用微機電製程技術製造出兩種不同尺寸的微文氏管,寬度分別為150及200微米,開口角度各為45°,總長則為10 mm,再以空氣作為工作流體,利用不同質量流率來量測微文氏管進出口的壓力差並配合FLUENT軟體分析觀察其流場分佈的情況。結果顯示,當流量小時,此兩種不同外型的喉部出口處都會因回流的關係產生相對稱的分離渦流,但隨著流量增大,分離區會持續擴大導致渦流相互影響,此時渦流之間的吸引力造成分離區不再對稱進而使流場的分佈偏向於一邊。而在速度分佈部分,當流量為5.338 mg/min時,寬度為150微米的喉部區流速已經高於聲速,隨後因速度不斷增加,空氣黏滯力影響了速度分佈而產生了速度衝擊現象。
    第二部份是討論微噴嘴的流力特性,主要是利用FLUENT軟體來分析三種不同外型的單一曲面微噴嘴/擴大器,藉由分析的結果來比較各種外型的微噴嘴/擴大器之壓損係數及壓損係數比。模擬結果顯示,微噴嘴/擴大器的壓損係數會隨著雷諾數的增加而減少,但壓損係數比反而隨著雷諾數的增加而提高。而在相同雷諾數下,擴大器的壓損係數則會低於噴嘴的壓損係數。
    另外,吾人同時將文獻中之理論解和實驗數據與FLUENT之模擬值相互比較,發現曲面形貌(a= 5⁄3)之微噴嘴/擴大器有著較高的壓損係數,同時壓損係數比也比直線邊界來的高,因此結合此外型微噴嘴/擴大器之元件有較高之流體驅動力並能有效提高其效率。而模擬值與實驗值亦符合理論值,因此對於微噴嘴/擴大器的設計與應用提供了一明確的參考依據。
    This study presents the investigating of microchannels flow. It is divided into two parts, the flow characteristics of micro venturi and the performance of straight-walled and curved-walled micro nozzle/diffuser respectively. The experimental results are also compared with the simulation results whereby we can observe the flow field in micro venturi and discuss the bounder effect of micro nozzle/diffuser.
    First, we adopt MEMS technology to fabricate micro venturis with different widths of 150 and 200 um respectively and utilize FLUENT software to analyze the flow fields. Air was set as the working fluid and the air mass flow rate of inlet is changed to obtain the pressure drop between inlet and outlet.
    When a flow passes through the throat, the backflow results in the symmetric separations occur and grow with the increase of mass flow rate. As the separation is large enough, the suction between both separations will be larger than the resistance of flow, the larger separation will appear on one side and leads the flow to slant to the other side. The result also shows the complicated shock wave flow structure was generated by the effect of viscosity.
    The second part of this paper presents a CFD-simulation of the performance of straight-walled and curved-walled micro nozzle/diffuser by FLUENT software. Such nozzle/diffusers are mainly used in micro venturi and also applied to valveless micropumps.
    The results show that the pressure loss coefficient for the micro nozzle/diffuser decreases with the Reynolds number whereas the ratio of the pressure loss coefficient increases with the Reynolds number. At the same Reynolds number, the pressure loss coefficient of micro nozzle is higher than that of the micro diffuser.
    The model is also compared with different previously experimental measurements and shows a good agreement. For a fixed volumetric flow rate, the results show the curved profile bounder (a = 5/3) micro nozzle/diffuser has higher pressure loss coefficient and higher ratio of the pressure loss coefficient than that of the straight profile bounder. The theoretical analysis and design basis can then be formulated as a reference and applied to the fabrication of micro nozzle/diffuser from this study.
    Appears in Collections:[機械與機電工程學系暨研究所] 學位論文

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