本文提出一新型的微混合器，並使用數值方法模擬微混合器中的混合情況。新型微混合器的第一階段類似於原始T形微混合器，兩個不同的流體進入第一混合流道而產生第一次的匯流混合，離開第一混合流道後，混合流體分離成兩個流 (之後的第二階段和第一階段相連)；兩個流都轉了一個直角彎進入次流道，其中一個流經過兩個順時針的直角彎，另一個流經過兩個逆時針直角彎，然後，兩個流匯流在第二個T形接頭並流入第二個主混合流道。為了提升本微混合器的混合，在高雷諾數下的T形接頭中引發流動捲入現象是必要的，然而在電腦可應付網格尺寸的網格法模擬中，由於高雷諾數下的數值擴散的關係，所以難以得到精確的結果，因此我們使用結合粒子反向追跡與擴散模式的解法和反向隨機漫步蒙地卡羅追跡法來模擬流體混合，兩種模擬在本文中的結果顯示能有很好的一致性。本文研究發現，在高雷諾數下，兩個T形接頭產生的捲入流動提升了混合效果，而分合流道和當中的直角彎道在捲入發生時，也能有助於混合。我們進一步模擬不同主流道長度的微混合器時，可發現在高雷諾數下，當雷諾數升高後，第一主混合流道必須相對應的加長才能產生較好的混合效率。最後，本微混合器與只有一個筆直的主混合流道的原始T形微混合器相比，可發現更能得到較好的混合效率。

A novel micromixer is proposed and fluid mixing in the mixer is investigated numerically. The first stage of the proposed mixer is similar to the original T-shaped micromixers. Two different fluids entering the two inlets have the first confluence at the beginning of the first main mixing channel. At the end of the first main mixing channel, it is connected to the second stage, where the mixing fluid splits into two streams; each of them takes a 90-degree turn into a sub-channel. While one of the stream flows through two clockwise 90-degree bends, the other stream flows through two counterclockwise 90-degree bends. Then, the two streams recombine at the second T-junction and flow into the second main mixing channel. Inducing flow engulfment at high Reynolds number (Re) in the T-junction is necessary for the enhancement of fluid mixing in the present micromixers. However, an ordinary grid-based simulation is hard to generate accurate solutions for fluid mixing with affordable mesh sizes because of the numerical diffusion at high Re. Therefore, a particle tracking method with the diffusion model and a backward random-walk Monte Carlo simulation are applied to the present cases to circumvent numerical diffusion. The results obtained by the two methods show that they are in good agreement. As expected, at high Re, higher mixing performance occurs due to the engulfment flows in the two T-juctions. Moreover, the effect of split-and-recombine sub-channels and 90-degree bends also contribute to the mixing performance at high Re. From further investigation of the different lengths of the two main mixing channels, it is found that the micromixer at higher Re should go with the longer first main mixing channel to generate better mixing performance. The proposed micromixer generates much greater mixing efficiency than the original T-shaped micromixer with only one straight main mixing channel does.

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