發(fā)布時間：2018-09-11 07:33

【摘要】：海水和苦咸水淡化為解決淡水資源短缺問題提供了行之有效的方法,由于水平管降膜蒸發(fā)具有小溫差換熱、較低的蒸發(fā)溫度、較高的傳熱系數(shù)等諸多優(yōu)點,從而得到了廣泛的應(yīng)用。研究水平管降膜蒸發(fā)技術(shù),可為設(shè)計生產(chǎn)更加高效的水平管降膜蒸發(fā)器提供重要的技術(shù)依據(jù)和理論基礎(chǔ)。本文利用高速攝像的實驗方法研究了四種布液器孔間距在不同噴淋密度和管形下的管間流型和柱狀流的降膜波長;采用激光誘導(dǎo)熒光技術(shù)研究了開孔參數(shù)為單孔和三孔時液膜在管表面的鋪展分布。結(jié)果表明:同一個管形的孔間距小時,流型轉(zhuǎn)變Re數(shù)小;光管的滴-滴柱、滴柱-柱流型轉(zhuǎn)變Re數(shù)小于螺旋翅片管的轉(zhuǎn)變Re數(shù),兩管形的柱-柱簾流型轉(zhuǎn)變Re數(shù)相似。同一管形的液柱波長隨Re數(shù)的增大而降低;波長隨孔間距的增大而增大;Re數(shù)一定時螺旋翅片管的波長小于光管的波長。在一定的Re數(shù)范圍內(nèi),液膜軸向鋪展存在極限。單孔下隨Re數(shù)增大,液膜在管表面頂端和底部的軸向鋪展長度差值減小。三孔下兩液柱中心距隨時間呈周期性變動,Re=302時兩液柱中心距較Re=172時大。最厚液膜在兩液柱中心位置略微左右移動,出現(xiàn)在中心位置的幾率為30%。利用VOF方法模擬了水平管外液體的降膜流動,研究了單孔和三孔時液膜在管壁的鋪展規(guī)律。隨著接觸角從10°增大到60°,水在管表面各周向角的軸向鋪展長度減小,達(dá)到鋪展長度最短時對應(yīng)的周向角越小,液膜鋪展長度穩(wěn)定的周向區(qū)域增大,相應(yīng)周向角的液膜厚度增大,即液膜厚度與鋪展長度呈相反的分布。隨著入口速度的增大,同一周向角的鋪展長度呈增大的趨勢,且增大的幅度較小。管徑32mm的液膜厚度大于管徑19mm和25mm的液膜厚度,管徑32mm的液膜鋪展長度較另兩管徑的鋪展長度短。三孔下周向角90°時XZ平面的液膜厚度分布,出現(xiàn)兩個波峰和三個波谷,波峰位于兩孔之間,波谷位于液體入口處,在液膜鋪展的兩側(cè)邊緣處液膜厚度突起。當(dāng)液體入口速度小,液膜軸向鋪展長度較短,液膜厚度波動較小,波峰和波谷的差值小。
[Abstract]:Desalination of seawater and brackish water provides an effective method to solve the problem of shortage of fresh water resources. Due to its advantages such as small temperature difference heat transfer, low evaporation temperature, high heat transfer coefficient and so on, horizontal tube falling film evaporation has many advantages, such as small temperature difference heat transfer, low evaporation temperature, high heat transfer coefficient, etc. Thus it has been widely used. The study of horizontal tube falling film evaporation technology can provide an important technical and theoretical basis for the design and production of a more efficient horizontal tube falling film evaporator. In this paper, the flow patterns between tubes and the falling film wavelengths of columnar flows with different spray densities and tube shapes are studied by means of high speed camera. Laser induced fluorescence technique was used to study the spreading distribution of the liquid film on the surface of the tube when the opening parameters were single hole and three hole. The results show that the Re number of flow pattern transition is small when the hole spacing of the same tube is small, the Re number of drip-drop column and drip-column flow pattern transition is smaller than that of spiral finned tube, and the Re number of flow pattern transition from column to column curtain is similar between the two tubes. The wavelength of the same tube decreases with the increase of the Re number, and the wavelength of the helical fin tube is smaller than that of the light tube when the number of re increases with the increase of the hole spacing. In a certain range of Re numbers, there is a limit for the axial spreading of liquid film. The axial spreading length difference of the liquid film at the top and bottom of the tube surface decreases with the increase of the Re number under the single hole. The center distance of the two liquid columns under the three holes varies periodically with time: re = 302.The center distance of the two liquid columns is larger than that of Re= 172. The thickest liquid film moves slightly around the center of the two columns, and the probability of appearing in the center is 30. The liquid falling film flow outside the horizontal tube was simulated by VOF method, and the spreading law of the liquid film in the tube wall was studied with one hole and three holes. With the increase of the contact angle from 10 擄to 60 擄, the axial spreading length of water at each circumferential angle on the surface of the pipe decreases, and the corresponding circumferential angle becomes smaller when the spreading length is the shortest, and the circumferential region of the stable spreading length of the liquid film increases, and the thickness of the liquid film at the corresponding circumferential angle increases. That is, the thickness of liquid film is opposite to the spreading length. With the increase of inlet velocity, the spreading length of the same circumferential angle tends to increase, and the amplitude of increase is smaller. The liquid film thickness of diameter 32mm is larger than that of 19mm and 25mm, and the liquid film spreading length of 32mm is shorter than that of the other two diameter. Two peaks and three troughs appear in the liquid film thickness distribution of the XZ plane at 90 擄angle of the three holes next week. The wave peaks are located between the two holes and the trough is located at the inlet of the liquid, and the thickness of the liquid film protrudes at the edge of the liquid film spreading. When the inlet velocity of the liquid is small, the axial spreading length of the liquid film is short, the thickness of the liquid film fluctuates less, and the difference between the peak and the trough is small.
【學(xué)位授予單位】：內(nèi)蒙古工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P747;TK172

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