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標題: 具連續移動平板之三維紊流噴射撞擊流場之熱傳數值分析
Numerical Analysis of Convective Heat Transfer of 3-D Turbulent Impinging Jets with a Continuous Moving Plate
作者: 鍾毓煒
Chung, Yu-Wei
關鍵字: three-dimensional turbulent
moving impinging surface
upwash fountain
recirculation region
出版社: 機械工程學系
摘要: 本文主要是針對於具連續移動平板之三維紊流噴射撞擊流的流場與熱傳特性作數值模擬與分析。採用計算流體力學PHOENICS軟體來模擬衝擊表面的熱傳分佈。分別就主噴射流雷諾數(Re)、噴嘴與噴嘴的間距(L)、噴嘴的高度(H)、衝擊面移動的速度比(Vp)、橫向流的速度比(M)以及噴嘴排列方式(直線排列與三角形排列)等參數變化對衝擊表面局部紐塞數、平均紐塞數、整體平均紐塞數與摩擦係數的影響逐一探討。 由研究的結果顯示,兩主噴射流撞擊衝擊面後,將產生上沖噴泉流,且經由流體間的交互作用而導致兩個低壓迴流區的存在。各參數的變化對於流場結構與衝擊表面熱傳效率有很大的影響。當衝擊面移動的速度增加時,衝擊表面摩擦係數及局部紐塞數的峰值變小且位置略有向衝擊面移動方向偏移的現象。另外,衝擊表面的壁合流區與停滯線呈現彎曲狀,其上沖噴泉流也產生偏向。引進橫向流後,當橫向流與主噴射流速度比(M)逐漸增加時,產生主噴射流的偏向,進而導致衝擊表面停滯區的熱傳效率有顯著地減少。 綜合言之,忽略衝擊面移動與橫向流的效應,將導致衝擊表面熱傳效率的高估。為了設計出性能更加的冷卻或加熱系統,瞭解上述的因素對熱傳效率的影響是非常必要的。
This study presents the numerical simulation and analysis on the fluid flow and heat transfer characteristics of three-dimensional turbulent impinging jets with a continuous moving plate. The computational fluid code, PHOENICS, is used to simulate the distribution of heat transfer on the impinging surface. The effect of the jet Reynolds number Re, nozzle-to-nozzle distance (L), two plates distance (H), the ratio of impinging surface velocity (Vp), the ratio of crossflow velocity (M), and nozzle arrangements (in-line and triangular array) on plate heat transfer and friction coefficient will be studied one by one. It is found that upwash fountain flow between the two nozzles is generated when impinging jets directed outward or normal to the plate. Two lower pressure recirculation regions are induced due to the interaction between impinging jets and fluid surroundings. The flow structure and the rate of heat transfer on impinging surface are significantly affected by relevant parameters. Maximum value of local Nusselt number and shear stress on impinging surface is decreased and shifted the direction of plate moving a little while the plate motion is increased. Specially, combined wall jet and stagnation line region on impinging surface is curved, and the upwash fountain will produce deflection. In the case with crossflow, heat transfer rate on the impinging surface is decreased while the ratio of crossflow velocity to mean jet velocity (M) is increased. In summary, the results show that neglecting impinging surface motion effects can lead to the heat transfer is overestimated. It is very important to understand the heat transfer rate from relevant factors for designing a cooling or heating system with better performance.
Appears in Collections:機械工程學系所



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