發(fā)布時間：2018-05-20 23:10

  本文選題：網狀靜電傳感器 + 流化床　； 參考：《華北電力大學(北京)》2017年碩士論文

【摘要】：流化床因為其出色的傳熱和傳質效率與處理大量顆粒的能力而被廣泛應用于很多工業(yè)場合。流化床中顆粒的速度與濃度等運行參數是保障其正常運行的關鍵性因素。通過對這些運行參數進行實時測量與監(jiān)測,可實現工業(yè)過程的優(yōu)化控制,提高生產效率并且有助于降低環(huán)境污染等問題。靜電法是針對顆粒運動特征參數的一種新型測量方法,且該方法具有成本低、性能穩(wěn)定、靈敏度高、測量裝置簡單和適用于惡劣的工業(yè)生產環(huán)境等優(yōu)點,現己被用于氣力輸送的過程中。本論文基于靜電測量原理,采用一種靈敏度更高且分布更加均勻的網狀靜電傳感器,對固體顆粒動態(tài)參數的測量進行了相關的理論和實驗研究,并得出了一定的實驗結果,主要結論如下:1.為了驗證網狀靜電傳感器的測量性能,在實驗室規(guī)模氣力輸送管道的彎管處進行了實驗研究。通過對氣力輸送管道彎管附近上下游平面對應位置不同網狀電極所得靜電信號進行互相關計算,得出顆粒在彎管處的流速分布。從流速分布可以看出彎管徑向方向從左到右的速度廓型是相對均勻的。由于顆粒在經過彎管的過程中,會受到離心力的作用,從而使得沿著彎管外壁附近運動的顆粒速度更高。利用網狀電極一個平面上靜電信號的RMS值可以重建出彎管處固體顆粒的相對濃度分布。重建結果表明,重建后的相對濃度分布可以反映出固體顆粒通過彎管時在彎管外壁處的繩狀流流型。2.網狀靜電傳感器被安裝在實驗室規(guī)模鼓泡流化床上,用于測量流化床中固體顆粒的速度廓形和電荷分布。網狀靜電傳感器上下游對應位置的電極上靜電信號作互相關計算可以得到固體顆粒的速度廓形,并分析了隨著氣體流量的變化,沿著徑向方向的互相關系數的變化情況。加權平均速度可以在一定程度上表征流體的流動狀態(tài),因此在本文中被用來增加測量的可靠性。靜電信號的RMS值被用于估算所有電極上的感應電荷量,并利用所得結果重建出電荷在截面處的分布情況。由于流化床內顆粒速度廓形的影響,中心處電極上的感應電荷量大于管壁附近電極上的感應電荷量。并且截面處電荷分布相對均勻,相對于平均值的最大偏差小于24%。除此之外,還結合鼓泡床中顆粒的運動特性,對管壁附近下落顆粒的測量作了一定的研究。數據表明鼓泡流化床中大部分的下落顆粒都在管壁附近。利用傳感器獲得的顆粒速度廓形和電荷分布,可以對流化床的運行狀態(tài)進行監(jiān)測,提高運行效率和產品質量。
[Abstract]:Fluidized bed is widely used in many industrial fields because of its excellent heat and mass transfer efficiency and its ability to deal with a large number of particles. The operation parameters such as velocity and concentration of particles in fluidized bed are the key factors to ensure their normal operation. Through the real-time measurement and monitoring of these operating parameters, the optimization control of industrial process can be realized, the production efficiency can be improved and the environmental pollution can be reduced. Electrostatic method is a new method for measuring the characteristic parameters of particle motion. The method has the advantages of low cost, stable performance, high sensitivity, simple measuring device and suitable for bad industrial production environment. It has been used in the process of pneumatic transportation. Based on the principle of electrostatic measurement, a network electrostatic sensor with higher sensitivity and more uniform distribution is adopted in this paper. The measurement of dynamic parameters of solid particles is studied theoretically and experimentally, and some experimental results are obtained. The main conclusions are as follows: 1. In order to verify the measurement performance of the network electrostatic sensor, an experimental study was carried out at the bend of the pneumatic conveying pipeline in laboratory. Based on the cross-correlation calculation of the electrostatic signals obtained from different grid electrodes near the upper and lower plane of the curved pipe in the pneumatic conveying pipeline, the velocity distribution of the particles in the bend pipe is obtained. From the velocity distribution, it can be seen that the velocity profile is relatively uniform in radial direction from left to right. Because the particle is subjected to centrifugal force in the process of passing through the pipe, the velocity of particles moving along the outer wall of the bend pipe is higher. The relative concentration distribution of solid particles in the curved tube can be reconstructed by using the RMS value of a plane electrostatic signal of the grid electrode. The reconstruction results show that the relative concentration distribution after reconstruction can reflect the flow pattern of rope flow at the outer wall of the bend pipe when the solid particles pass through the bend pipe. A netted electrostatic sensor is installed on a laboratory scale bubbling fluidized bed to measure the velocity profile and charge distribution of solid particles in the fluidized bed. The velocity profile of solid particles can be obtained by cross-correlation calculation of electrostatic signals on the electrode corresponding to the upstream and downstream position of the network electrostatic sensor. The variation of the cross-relation number along the radial direction with the change of gas flow rate is analyzed. The weighted average velocity can represent the flow state of the fluid to a certain extent, so it is used in this paper to increase the reliability of the measurement. The RMS value of the electrostatic signal is used to estimate the inductive charge on all electrodes and to reconstruct the distribution of the charge at the cross section using the obtained results. Because of the influence of particle velocity profile in fluidized bed, the inductive charge at the center electrode is larger than that on the electrode near the tube wall. The charge distribution at the cross section is relatively uniform, and the maximum deviation from the average value is less than 24. In addition, the measurement of falling particles near the tube wall is also studied in combination with the motion characteristics of the particles in the bubbling bed. Data show that most of the falling particles in the bubbling fluidized bed are near the tube wall. The particle velocity profile and charge distribution obtained by the sensor can be used to monitor the operating state of the fluidized bed and to improve the operation efficiency and product quality.
【學位授予單位】：華北電力大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TP212.9

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本文編號：1916646