本文選題：降膜流動　切入點：傳質(zhì)　出處：《天津大學》2015年碩士論文

【摘要】：降膜流動由于結(jié)構(gòu)簡單、動力消耗小且在低流量、小溫差的情況下具有高傳熱傳質(zhì)系數(shù)等獨特優(yōu)勢在工業(yè)領(lǐng)域得到廣泛應(yīng)用。本課題研究目的在于探究二組分溶液降膜蒸發(fā)過程中的傳質(zhì)分離效果,通過改進降膜支撐媒介的結(jié)構(gòu)以及改變?nèi)芤罕砻鎻埩Φ确椒◤娀瘹庖簝上嗟膫髻|(zhì)過程,并對其應(yīng)用前景進行了展望。本文設(shè)計了降膜蒸發(fā)裝置對下降液膜進行研究,利用電加熱板對光滑平板和翅片板上的下降液膜加熱,觀察液膜的流動形態(tài),發(fā)現(xiàn)光滑平板上受熱液膜流動面積明顯減小且出現(xiàn)徑向收縮;而翅片板上液膜由于得到再分布,其湍流程度增大,內(nèi)外界面更新速度加快,受熱后流動面積變化很小且在徑向收縮不明顯,這種壁面結(jié)構(gòu)為降膜蒸發(fā)傳質(zhì)的強化提供了很好的依據(jù)。為了考察液膜在不同流動狀態(tài)及受熱狀態(tài)下的降膜蒸發(fā)傳質(zhì)效果,本文通過控制變量法對乙醇-水溶液在不同流量、不同加熱功率以及不同結(jié)構(gòu)降膜流動板上的降膜蒸發(fā)過程進行了實驗。對比不同流量及不同加熱功率下塔頂乙醇出料的質(zhì)量分數(shù),發(fā)現(xiàn)隨著流量的增大及加熱功率的降低,塔頂乙醇質(zhì)量分數(shù)增大。同時,對比不同結(jié)構(gòu)降膜流動板上二組分溶液的分離效果,發(fā)現(xiàn)粗糙平板對乙醇-水溶液的分離程度高于光滑平板,而流經(jīng)翅片板的塔頂乙醇質(zhì)量分數(shù)高于粗糙板,由此證實了通過改進降膜支撐媒介的結(jié)構(gòu)來優(yōu)化降膜流動形態(tài)、增大液膜湍動程度來強化降膜蒸發(fā)傳質(zhì)的可行性。為了考察液膜表面張力對降膜蒸發(fā)效果的影響,本文通過測量加入一定量表面活性劑的溶液在不同溫度下的表面張力,以及該溶液在翅片板上塔頂乙醇出料的質(zhì)量分數(shù),得出加入表面活性劑有利于降膜傳熱傳質(zhì)的結(jié)論。表面活性劑的加入降低了溶液的表面張力,在一定程度上抑制了表面波的形成,增加了有效傳質(zhì)面積,因此明顯提高了降膜蒸發(fā)的效果�；诖�,本文就強化降膜蒸發(fā)傳質(zhì)過程提出以下建議:優(yōu)化降膜支撐媒介的結(jié)構(gòu),加入適當表面活性劑降低液膜表面張力,對降膜流動的流量和加熱量進行優(yōu)化。
[Abstract]:Falling film flow because of its simple structure, low power consumption and low flow rate, In the case of small temperature difference, the advantages of high heat and mass transfer coefficient are widely used in the industrial field. The purpose of this research is to explore the effect of mass transfer and separation in the process of falling film evaporation of two-component solution. By improving the structure of the falling film supporting medium and changing the surface tension of the solution, the mass transfer process of the gas-liquid two-phase was enhanced, and the prospect of its application was prospected. In this paper, the falling film evaporation device was designed to study the falling liquid film. The falling liquid film on smooth plate and fin plate was heated by electric heating plate, and the flow pattern of liquid film was observed. It was found that the flow area of heated liquid film on smooth plate obviously decreased and the radial contraction occurred, while the liquid film on fin plate was redistributed. The turbulence degree increases, the internal and external interface renewal speed accelerates, the flow area changes very little after heating, and the radial contraction is not obvious. This wall structure provides a good basis for the enhancement of falling film evaporative mass transfer. In order to investigate the effect of falling film evaporation mass transfer under different flow and heated conditions, the flow rate of ethanol-aqueous solution in different flow rates is controlled by variable method. Experiments were carried out on the falling film evaporation process with different heating power and different structure. By comparing the mass fraction of ethanol at the top of the tower with different flow rate and different heating power, it was found that with the increase of flow rate and the decrease of heating power, At the same time, compared with the separation effect of two component solution on different structure falling film flow plate, it was found that the separation degree of ethanol aqueous solution on rough plate was higher than that on smooth plate. The mass fraction of ethanol at the top of the column passing through the fin plate is higher than that of the rough plate, which proves that the falling film flow pattern can be optimized by improving the structure of the falling film supporting medium. In order to investigate the effect of liquid film surface tension on the effect of falling film evaporation, the surface tension of solution with a certain amount of surfactant was measured at different temperatures. The mass fraction of ethanol at the top of the column on the fin plate shows that the addition of surfactant is beneficial to the heat and mass transfer of the film. The addition of surfactant reduces the surface tension of the solution. To some extent, the formation of surface wave is restrained, the effective mass transfer area is increased, and the effect of falling film evaporation is obviously improved. Based on this, the following suggestions are put forward for strengthening the falling film evaporation mass transfer process: optimizing the structure of falling film supporting medium, Proper surfactant is added to reduce the surface tension of liquid film, and the flow rate and heat of falling film flow are optimized.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ051.62
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本文編號：1662089