確保工業排氣櫃效益之新型流量計設計研究

Abstract

流量計量測是計量科學重要的技術之一，可用於工業生產，環境保護、廢棄處理、能源計量，以流量計作為管理能源的基礎，實施節能降耗。然而ISO-5167所規範之孔口板(orifice plate)標準流量計，礙於其量測壓力孔之位置，造成裝設時需要龐大的體積，這並不適用於狹窄作業場所。因此，本研究要設計一款新型多孔洞式孔板流量計，縮短壓力孔間量測的距離，以縮小整體體積，以方便狹窄作業場所使用。我們自行設計多孔洞的孔口板，利用計算流體力學(Computational Fluid Dynamics, CFD)的方式進行模擬，透過數值模擬，可以得知流場內各個位置的物理量，如速度、壓力、濃度，溫度等分布。經過研究發現，多孔洞的孔口板可以破壞原先在標準流量計後方的大迴流區，而以相同面積之單孔洞相較，多孔洞孔口板量測壓力孔的距離較短，這可使整體體積縮小。而本研究發現多孔洞之間的比例關係確實會影響上下游壓力孔之間的距離，即外圈孔徑/中心孔徑愈大，上下游壓力孔的距離可以愈短，並且各別提供了上游及下游壓力孔位置的預測方程式。另外，新型流量計所造成的壓損也低於標準流量計，其壓力損失較標準流量計可減少10 %到20 %。此外，新型流量計在使用上仍需與標準流量計校正，因在不同吸氣速度下的流量誤差變化程度是相同的，因此只要另外乘上一係數k值，就可以達到校正效果。使用流量計可以穩定控制流體在管道中的流量，避免能源的浪費，進而達到節能效果。

Flow measurement plays an important role in scientometrics. It can be used in industrial production, environmental protection, waste disposal, energy measurement, and energy conservation. The standard (orifice plate) flowmeter in accordance with ISO-5167 is that it requires a huge space for installation because of its position of the pressure taps. It is often limited in narrow work places. Therefore, in this study, we designed a multi-hole orifice plate flowmeter to resolve this problem by reducing the distance between the pressure taps of upstream and downstream. We designed a multi-hole orifice plate. And the computational fluid dynamics (CFD) was conducted to simulate some parameters in each position of flow field, such as velocity, pressure, concentration and temperature. We found that this kind of multi-hole orifice plate could destroy the large recirculation zone, which is generated behind the original plate. The distance of pressure taps of multi-hole orifice plate is shorter than single-hole plate. It could be applied to a smaller area. We also found that the ratio of diameter of outer and central orifice would influence the distance between the upstream and downstream pressure taps. We provide an equation to predict the location of pressure taps in the upstream and downstream. Otherwise, the pressure loss of the new flowmeter can reduce by 10% to 20% compared with a standard flowmeter. The new flowmeter needs to be calibrated with the standard flowmeter. We concluded that the new flowmeter has advantages of lower pressure loss and shorter length of pipe.