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鄭澤明22

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鄭澤明、曾憲中、羅婷尹

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水平加熱平板置於上吹式單孔合成噴流上之混合對流熱傳特性

Mixed Convection Heat Transfer on the Horizontal Heated Plate above the Single-Nozzle Upward-Blown Synthetic Jet

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2014精密機械與製造科技研討會論文集－PMMT 2014

2014 Precision Machinery and Manufacturing Technology Symposium-PMMT

Keywords：合成噴流、水平加熱平板、混合對流熱傳、實驗

Synthetic jet,horizontal heated plate,mixed convection heat transfer,experiments

Abstract：本研究以實驗方法探討水平加熱平板置於下式單孔合成噴流之上的混合成噴流之上得混核對流熱傳特性，合成噴流裝置係以功率5W支小型揚聲器置於垂直之中空援助腔體的下端面，利用放大器與訊號函數產生器輸入不同平率與振幅的電壓函數訊號給揚聲器，此揚聲器模面產生不同位移量與頻率的震動，進而在中空圓柱腔體的上端面之3mm圓孔噴嘴產生合成噴流(吹出與吸入腔體的淨氣流量為零)，此上吹式合成噴流衝擊於上方加熱平板，理論上將形成正增強之混合對流熱傳效應。本研究固定圓孔噴嘴直徑(d)，影響混合對流熱傳特性的因子包刮相對衝擊距離(c/d)、合成噴流吹出(或吸入)頻率(f)、合成噴流出口處之平均吹出雷諾數(Rej)及加熱面與合成噴流間之葛拉秀夫數(Gr)，實驗結果指出混合對流紐塞數Numix與Gr值的關係並不規則；Rej與f應為相依關係，Numix會隨Rej增大而上升；(Numix)會先隨(c/d)增加佳增大，當c/d增大到特定臨界值時，Numix會產生最大值，然後Numix會隨c/d而減少，此臨界c/d增隨(Rej)、(f)而變動。

This work experimentally investigated the mixed convection heat transfer of the horizontal heated plate above the single-nozzle upward-blown synthetic jet. The present synthetic-jet device  was made of a 5W loudspeaker and a acrylc circular-cylinder chamber.Using the signal function generator and the amplifier,the periodical voltages of various frequencies and amplitudes could be input to the loudspeaker,installed in the acrylic circular-cylinder chamber,to generate vibrations of different levels at the membrane of the loudspeaker.Conseqently,the 3mm-diameter circular hole at the tip side of the acrylic circular-cylinder chamber would blow the synthetic jet (the net flow rate of blowing and sucking flows equals zero).Since that the horizontal heated plate was above the upward-blown synthetic jet,the superposition mixed convection heat transfer would be generated theoretically.This work fixed the diameter(d) of the jet hole.The influencing factors includes the relative impinging distance(c/d),the frequency(f) of the blown or sucked synthetic jet,the average Reynolds number (Rej)of the blown synthetic jet and the Grashof number (Gr) between the heated surface and the synthetic jet.The experimental results indicated that the relationship between the mixed-convction Nusselt number Numix and Gr value was not irregular.The Rej was dependent on the f.The Numix increased with Rej.The Numix firstly increased and then dropped as increasing the c/d value.The critical value of c/d to generate the maximum Numix was dependent on Rej and f.

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