本文選題：氣力輸送 + 顆粒-壁面作用��； 參考：《浙江大學(xué)》2016年博士論文

【摘要】：隨著氣力輸送過程研究的深入,特別是密相輸送應(yīng)用的愈加廣泛,人們對于認(rèn)識氣力輸送過程流動本質(zhì)的需求也愈加迫切。從氣力輸送過程的研究現(xiàn)狀來看,無論是對于流型的識別、壓降的預(yù)測還是固體流量的測量,都需要從顆粒運動及受力分析,特別是顆粒-壁面相互作用分析的層面出發(fā),更進(jìn)一步地挖掘氣力輸送過程流動的本質(zhì)。由于輸送管徑一般較小,因此顆粒與壁面作用的壁效應(yīng)就顯得尤為重要。但是,顆粒-壁面相互作用在以往的研究中卻沒有得到足夠的重視,而且局限在柱塞流壓降預(yù)測模型中應(yīng)力轉(zhuǎn)變系數(shù)的離線測定。究其原因,是沒有找到合適的方法來實現(xiàn)顆粒-壁面作用的在線檢測。氣力輸送過程中,顆粒-壁面的相互作用究竟是如何影響管道內(nèi)氣固兩相流體力學(xué)行為、輸送壓降及輸送穩(wěn)定性的呢?這是氣力輸送領(lǐng)域中亟待解決的關(guān)鍵科學(xué)問題,具有重要的理論意義和實際應(yīng)用價值。本研究利用對顆粒運動極為敏感的聲發(fā)射檢測技術(shù),借助小波分解和功率譜分析等信號處理手段,建立了顆粒-壁面作用的在線檢測方法。在此基礎(chǔ)上,利用該方法,結(jié)合壓降、攝像和靜電等多種檢測手段,在實驗室條件下,系統(tǒng)研究了豎直管稀相輸送過程、稀相到密相流型轉(zhuǎn)變過程以及密相柱塞流中顆粒-壁面作用對管道壓降、輸送流型和輸送穩(wěn)定性等流體力學(xué)行為的影響規(guī)律。最后,在實驗室研究的基礎(chǔ)上,基于小波分解和V統(tǒng)計分析,提出了氣力輸送聲發(fā)射信號的多尺度劃分標(biāo)準(zhǔn),闡明了各尺度聲發(fā)射信號的物理意義,進(jìn)一步研究了工業(yè)裝置粉煤高壓密相輸送中顆粒-壁面作用對輸送穩(wěn)定性的影響,并建立了粉煤質(zhì)量流量的聲發(fā)射檢測方法。研究結(jié)果有助于解決如何有效提取聲發(fā)射信號中的有效信息這一聲發(fā)射檢測技術(shù)發(fā)展過程中的難題。同時,對于如何保證在低速下進(jìn)行穩(wěn)定輸送這一氣力輸送領(lǐng)域科研工作者和工程師關(guān)心的關(guān)鍵問題具有重要的指導(dǎo)意義。論文的主要研究內(nèi)容及結(jié)論如下：1.發(fā)現(xiàn)了顆粒-壁面的碰撞(法向作用)和摩擦(切向作用)作用這兩種不同的聲信號產(chǎn)生機(jī)制,提出了顆粒-壁面碰撞和摩擦作用的聲發(fā)射檢測方法�？疾炝祟w粒粒徑、顆粒速度以及法向壓力對碰撞和摩擦聲發(fā)射信號主頻和能量的影響,建立了聲發(fā)射信號的主頻和能量模型。實現(xiàn)了稀相氣力輸送固體質(zhì)量流量和顆粒-壁面碰撞角的聲發(fā)射檢測。(1)顆粒-壁面碰撞和摩擦作用檢測的步驟為：首先,通過實驗研究確定顆粒-壁面碰撞和摩擦信號的主頻范圍和小波能量分率分布等頻域特征。實驗研究發(fā)現(xiàn),對于不同Geldart分類的顆粒,其與壁面碰撞聲發(fā)射信號的主頻均顯著高于摩擦聲發(fā)射信號的主頻。其次,通過小波分析方法對聲發(fā)射信號進(jìn)行分解,并將其中代表顆粒-壁面碰撞和摩擦成分的小波尺度進(jìn)行重構(gòu),提取聲發(fā)射信號中包含的顆粒-壁面碰撞和摩擦成分。(2)基于Hertz接觸理論和分段塑性模型,建立了考慮顆粒塑性形變條件下的顆粒-壁面碰撞聲發(fā)射信號主頻模型,相比于基于完全彈性碰撞下推導(dǎo)的模型,該模型的預(yù)測精度更高。引入接觸時間數(shù)的概念,建立了顆粒-壁面摩擦聲發(fā)射信號的主頻模型。模型可以很好地解釋碰撞和摩擦聲發(fā)射信號的主頻隨顆粒粒徑的增大而降低,摩擦信號主頻隨著顆粒速度的增大和法向壓力的增大而降低的實驗現(xiàn)象。(3)在豎直管稀相氣力輸送過程中,顆粒的呈現(xiàn)形式有分散懸浮的單個顆粒和顆粒聚團(tuán)兩種,這兩種類型的顆粒與壁面的作用方式是不同的。在此基礎(chǔ)上,建立了顆粒-壁面碰撞和摩擦聲發(fā)射信號的能量模型�；诼暟l(fā)射信號的能量模型,建立了豎直管稀相氣力輸送固體質(zhì)量流量和顆粒-壁面碰撞角的檢測方法。碰撞聲發(fā)射信號能量分率與固氣比的關(guān)系為采用該模型測得的固體顆粒質(zhì)量流量與實驗值之間的平均相對誤差為3.78%。顆粒-壁面碰撞角a與碰撞和摩擦聲發(fā)射信號能量比的關(guān)系為2.采用聲發(fā)射、壓降和靜電多種檢測手段相結(jié)合的方式,研究了最小輸送速度附近操作時的流型轉(zhuǎn)變現(xiàn)象,揭示了顆粒-壁面作用對流型轉(zhuǎn)變的影響規(guī)律,建立了基于聲能量和靜電荷累積量的流型轉(zhuǎn)變圖。(1)單一檢測手段無法準(zhǔn)確地識別最小輸送速度附近的流型。恒定質(zhì)量流率下,隨著表觀氣速的降低,壓降、聲能量和靜電荷累積量均呈現(xiàn)先減小再增大的趨勢,但是曲線轉(zhuǎn)折點所對應(yīng)的轉(zhuǎn)變速度各不相同。聲發(fā)射能量得到的轉(zhuǎn)變速度(7.0 m/s)略小于壓降最小輸送速度(7.5-8.0 m/s),而靜電荷累積量的轉(zhuǎn)變速度(6.0 m/s)明顯小于前兩者。(2)壓降最小輸送速度是氣體與壁面摩擦、顆粒-壁面相互作用以及顆粒濃度的變化共同作用的結(jié)果。當(dāng)氣速大于壓降最小輸送速度時,氣相壓降的影響占主導(dǎo)；當(dāng)氣速小于流型轉(zhuǎn)變速度時,氣相壓降的影響幾乎可以忽略,顆粒濃度的變化和顆粒-壁面相互作用對壓降的影響占主導(dǎo)；當(dāng)氣速介于壓降最小輸送速度和流型轉(zhuǎn)變速度之間時,上述三種因素對管道壓降的影響相當(dāng)。(3)當(dāng)氣速等于流型轉(zhuǎn)變速度時,顆粒-壁面的碰撞聲能量分率最小,摩擦聲能量分率最大,顆粒-壁面的碰撞角最小。這是由于流型轉(zhuǎn)變時顆粒的聚集形態(tài)發(fā)生了變化,使得顆粒-壁面的碰撞及摩擦能量分率的變化曲線出現(xiàn)轉(zhuǎn)折點。當(dāng)氣速大于流型轉(zhuǎn)變速度時,顆粒-壁面的作用以懸浮單顆粒的形式為主,隨著氣速的減小,顆粒-壁面碰撞速度降低,顆粒-壁面碰能量降低,導(dǎo)致碰撞能量減小,摩擦能量分率增大；當(dāng)氣速小于流型轉(zhuǎn)變速度時,顆粒-壁面的作用以回落顆粒與柱塞的作用為主,隨著氣速的減小,回落顆粒和柱塞之間的相對速度增大,碰撞能量增加,因此顆粒-壁面碰能量分率增大,摩擦能量分率減小。(4)基于聲能量和靜電荷累積量與壓降的關(guān)系,建立了新的流型轉(zhuǎn)變圖�；诼暷芰颗c壓降的流型圖不僅可以實現(xiàn)壓降最小輸送速度的識別,還能夠反映不同流型下壓力損失方式的不同�；陟o電信號與壓降的流型圖可以同時識別最小壓降速度和柱塞流轉(zhuǎn)變速度。3.研究了密相柱塞流中最基本的流動結(jié)構(gòu)柱塞與壁面的作用及其對管道壓降的影響,發(fā)現(xiàn)當(dāng)柱塞長度較大或者表觀氣速較小時,柱塞流輸送時可能出現(xiàn)壓降二次上升的現(xiàn)象。這一現(xiàn)象的出現(xiàn)是由于回落顆粒與柱塞前端的碰撞導(dǎo)致了額外的壓力損失。通過在模型中引入顆粒與柱塞的碰撞作用,建立了柱塞流輸送的聲能量模型,能夠準(zhǔn)確預(yù)測柱塞流輸送過程中顆粒壁面作用的變化,說明顆粒與柱塞的碰撞作用是柱塞流的典型特征。4.將聲發(fā)射技術(shù)和多尺度分析方法相結(jié)合,用于粉煤高壓密相氣力輸送過程中氣固兩相流體力學(xué)行為的研究,給出了聲發(fā)射信號微尺度、介尺度和宏尺度的劃分標(biāo)準(zhǔn),并進(jìn)一步對各個尺度代表的物理意義進(jìn)行了探討。在此基礎(chǔ)上,建立了粉煤質(zhì)量流量的聲發(fā)射檢測方法,并將其應(yīng)用于工業(yè)裝置中。(1)結(jié)合V統(tǒng)計分析和小波分解,提出了粉煤密相輸送的聲發(fā)射信號的多尺度劃分原則。研究發(fā)現(xiàn),聲發(fā)射信號的d1-d4尺度(18.75-300 kHz)和d8-d10尺度信號(0-2.34 kHz)具有一個典型的周期性成分,而d5-d7尺度信號(2.34-18.75 kHz)具有多個周期性成分。基于信號頻率及其復(fù)雜程度的不同,將粉煤密相輸送聲發(fā)射信號的d1-14尺度、d5-d7尺度和d8-d1o尺度分別劃分為微尺度、介尺度和宏尺度。進(jìn)一步研究揭示了微尺度、介尺度和宏尺度聲信號的物理意義。三者分別代表顆粒-壁面的碰撞和摩擦作用、氣固兩相的相互作用產(chǎn)生的非均勻結(jié)構(gòu)以及氣體與管壁的摩擦。其中,介尺度信號是粉煤密相輸送聲發(fā)射信號中的主要成分。隨著粉煤質(zhì)量流量的增加,微尺度信號能量分率下降,介尺度信號能量分率上升,宏尺度信號能量分率基本不變,說明在高濃度下粉煤更傾向于以聚團(tuán)的形式運動。(2)基于聲發(fā)射信號的多尺度分解理論,結(jié)合信號的時域特征和偏最小二乘回歸方法,建立了粉煤質(zhì)量流量和粉煤濃度的檢測模型。當(dāng)粉煤質(zhì)量流量變化范圍為8000-12000 kg/h時,粉煤質(zhì)量流量檢測值與實際值的平均相對偏差為4.15%,粉煤濃度檢測值與實際值的平均相對偏差為4.78%。利用該模型對粉煤質(zhì)量流量進(jìn)行預(yù)測,發(fā)現(xiàn)流量在5800 kg/h附近變化時預(yù)測值與實際值的平均相對偏差為10.37%,表明該模型具有一定的預(yù)測能力。
[Abstract]:With the deepening of the research on the process of pneumatic conveying, especially the wider application of dense phase transport, the demand for the understanding of the essence of the flow of the pneumatic conveying process is becoming more and more urgent. From the research status of the pneumatic conveying process, the particle motion is required, whether for the identification of the flow pattern, the prediction of the pressure drop or the measurement of the solid flow. And the force analysis, especially the particle wall interaction analysis, further excavate the essence of the flow of the pneumatic conveying process. Because the pipe diameter is generally small, the wall effect of the particle and wall action is particularly important. However, the particle wall interaction has not been sufficiently weighed in the previous study. The off-line determination of the stress change coefficient in the prediction model of the plunger flow pressure drop is considered, and the reason is that there is no suitable method to realize the on-line detection of the particle wall action. In the process of pneumatic conveying, how the interaction between the particle wall surface affects the gas-solid two-phase fluid mechanics behavior, the pressure drop and the transmission in the pipeline. It is the key scientific problem to be solved in the field of pneumatic conveying, which has important theoretical significance and practical application value. In this study, the on-line detection of particle wall action is established by means of signal processing, such as wavelet decomposition and power spectrum analysis, which are very sensitive to particle motion. On the basis of this method, using this method, combined with pressure drop, camera and static electricity and so on, under the laboratory conditions, the fluid mechanics behavior, such as the dilute phase transport process of vertical tube, the transition process of the thin phase to the dense phase flow pattern and the pressure drop of the particle wall surface, the flow pattern and the transport stability in the dense phase plunger flow, are systematically studied. Finally, based on the laboratory research, based on the wavelet decomposition and V statistical analysis, the multi-scale division standard for the acoustic emission signal of the pneumatic conveying is proposed, the physical meaning of the acoustic emission signals of each scale is clarified, and the effect of the particle wall action on the transport stability in the high pressure dense phase transport of the industrial equipment is further studied. Sound emission detection method is established, and the results are helpful to solve the problem of how to effectively extract the effective information of acoustic emission signals, the development process of acoustic emission detection technology. At the same time, the research workers and engineers on how to ensure the stable transport of the pneumatic conveying field at low speed are closed. The key issues of the heart have important guiding significance. The main contents and conclusions of this paper are as follows: 1. the two different sound signal generation mechanisms are found, the particle wall collision (normal action) and the friction (tangential action) effect are found. The acoustic emission detection method for particle wall collision and friction is proposed. The particle size is investigated. The influence of particle velocity and normal pressure on the main frequency and energy of collision and friction acoustic emission signals, the main frequency and energy model of acoustic emission signals are established. The acoustic emission detection of solid mass flow and particle wall collision angle in dilute phase pneumatic conveying is realized. (1) the steps of particle wall collision and friction detection are: first, pass through The experimental study determines the frequency domain characteristics of the main frequency range and the wavelet energy distribution of the particle wall collision and the friction signal. It is found that the main frequency of the acoustic emission signal with the wall collision is significantly higher than the main frequency of the friction acoustic emission signal for the particles with different Geldart classification. Secondly, the acoustic emission signal is analyzed by the wavelet analysis method. The number is decomposed, and the wavelet scales representing particle wall collision and friction component are reconstructed to extract the particle wall collision and friction components included in the acoustic emission signal. (2) based on the Hertz contact theory and the piecewise plastic model, the main frequency of the particle wall collision acoustic emission signal under the condition of granular plastic deformation is established. The model, compared to the model based on the complete elastic collision, has a higher prediction precision. The main frequency model of the particle wall friction acoustic emission signal is established by introducing the concept of contact time. The model can explain the main frequency of the collision and friction acoustic emission signal with the increase of particle size, and the main frequency of the friction signal. The experimental phenomenon decreases with the increase of particle velocity and normal pressure. (3) in the process of dilute phase pneumatic conveying of vertical tubes, there are two kinds of particle and particle cluster in the form of dispersed suspended particles, which are different between the two types of particles and the wall surface. On this basis, a particle wall collision is established. The energy model of the acoustic emission signal. Based on the energy model of the acoustic emission signal, a method for detecting the mass flow of solid mass and the collision angle of the particle wall in a vertical tube is established. The relationship between the energy fraction of the acoustic emission signal and the solid gas ratio is between the mass flow of solid particles and the experimental value measured by the model. The average relative error is the relationship between the 3.78%. particle wall collision angle A and the energy ratio of the collision and frictional acoustic emission signals. The flow pattern transition in the vicinity of the minimum transport velocity is studied by the combination of acoustic emission, pressure drop and various electrostatic detection methods. The effect of the convective transformation on the particle wall surface action is revealed. The flow pattern transformation diagram based on the sound energy and the static charge accumulation is established. (1) the single detection method can not accurately identify the flow patterns near the minimum transport velocity. Under the constant mass flow rate, with the decrease of the apparent gas velocity, the pressure drop, the accumulation of acoustic energy and static charge first decrease and then increase, but the curve turning point corresponds to the flow pattern. The transformation speed is different. The transformation velocity of acoustic emission energy (7 m/s) is slightly smaller than the minimum pressure drop velocity (7.5-8.0 m/s), while the transition velocity of the static charge accumulation (6 m/s) is obviously less than the previous two. (2) the minimum pressure drop velocity is the friction between the gas and the wall, the interaction of the particle wall and the change of the particle concentration. The effect of gas pressure drop is dominant when the gas velocity is greater than the minimum pressure drop. When the gas velocity is less than the flow velocity, the influence of the gas pressure drop is almost negligible. The influence of the particle concentration and the particle wall interaction on the pressure drop is dominant, while the gas velocity is between the minimum pressure drop and the flow pattern change. The influence of the above three factors on the pressure drop of the pipe is equal. (3) when the velocity of the flow pattern is equal to the velocity of the flow pattern, the particle wall surface has the smallest sound energy fraction, the maximum friction energy rate and the smallest collision angle of the particle wall. This is due to the change of the particle aggregation shape when the flow pattern changes, making the particle wall face collide. When the velocity of gas is larger than the velocity of the flow pattern, the effect of the particle wall is mainly in the form of a single particle when the velocity of gas is larger than the flow pattern. With the decrease of the gas velocity, the velocity of the particle wall collision is reduced, the particle wall collision energy is reduced, resulting in the decrease of the collision energy and the increase of the fraction of the friction energy; when the gas velocity is less than the gas velocity, the velocity of the friction energy is increased. When the velocity of the flow pattern is changed, the effect of the particle wall surface is dominated by the falling particles and the plunger. With the decrease of the gas velocity, the relative velocity between the falling particles and the plunger increases and the collision energy increases, so the particle wall collision energy fraction increases and the friction energy fraction decreases. (4) the relationship between the sound energy and the static charge accumulation and the pressure drop is based on the increase of the velocity of the particle and the plunger. A new flow pattern transformation diagram is set up. The flow pattern based on the acoustic energy and pressure drop can not only realize the identification of the minimum pressure drop velocity, but also reflect the different pressure loss modes under different flow patterns. The flow pattern based on the electrostatic signal and pressure drop can identify the minimum pressure drop velocity and the plunger flow velocity.3. at the same time to study the dense phase column The most basic flow structure in plug flow and the effect on the wall surface and its influence on the pressure drop of the pipe. It is found that when the plunger length is larger or the apparent gas velocity is small, the pressure drop may rise two times when the plunger flow is transported. This phenomenon is due to the additional pressure loss caused by the collision between the falling particles and the front end of the plunger. By introducing the collision between the particles and the plunger in the model, the acoustic energy model of the plunger flow is established. It can accurately predict the change of the effect of the particle wall in the process of the plunger flow. It shows that the collision between the plunger and the plunger is the typical characteristic of the plunger flow..4. combines the acoustic emission technique with the multi-scale analysis method and is used in the coal powder. The study on the mechanical behavior of gas-solid two-phase fluid in high pressure dense phase pneumatic conveying process has given the standard of acoustic emission signal micro scale, mesoscale and macro scale, and further discusses the physical significance of the representative of each scale. On this basis, a method of acoustic emission detection for the mass flow of coal powder is established and applied to the work. (1) combined with V statistical analysis and wavelet decomposition, the multi-scale division principle of acoustic emission signals for dense phase transport of coal is proposed. The research shows that the D1-D4 scale (18.75-300 kHz) and d8-d10 scale signal (0-2.34 kHz) of the acoustic emission signal have a typical periodic component, and the d5-d7 scale signal (2.34-18.75 kHz) has many weeks. Based on the difference of signal frequency and its complexity, the d1-14 scale, d5-d7 scale and d8-d1o scale are divided into microscale, mesoscale and macro scale respectively. Further studies have revealed the physical significance of the microscale, mesoscale and macro scale acoustic signals. The three ones represent the particle wall surface respectively. Collision and friction, the non-uniform structure of gas-solid two-phase interaction and the friction between gas and tube wall. Among them, the mesoscale signal is the main component in the acoustic emission signal of the dense phase transport of coal powder. With the increase of the mass flow of coal, the energy fraction of the microscale signal decreases, the energy fraction of the mesoscale signal rises, and the macro scale signal The energy fraction is basically the same, indicating that the pulverized coal is more inclined to move in the form of cluster at high concentration. (2) based on the multi-scale decomposition theory of acoustic emission signals, combining the time domain characteristics of the signal and the partial least squares regression method, a test model for the quality flow of pulverized coal and the concentration of pulverized coal is established. The change range of the mass flow of the pulverized coal is 8000-1200. At 0 kg/h, the average relative deviation between the measured value of coal quality flow and the actual value is 4.15%. The average relative deviation between the measured value of coal concentration and the actual value is 4.78%. using this model to predict the mass flow of coal powder. It is found that the average relative deviation between the predicted value and the actual value is 10.37% when the flow rate is changed near 5800 kg/h, indicating the model. Have a certain ability to predict.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ022
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本文編號：1873658