發(fā)布時(shí)間：2018-07-10 11:24

  本文選題：界面?zhèn)髻|(zhì) + 抵達(dá)頻率密度��； 參考：《湘潭大學(xué)》2015年碩士論文

【摘要】：目前關(guān)于氣液兩相界面?zhèn)髻|(zhì)的理論研究尚不成熟和完善。在實(shí)際工業(yè)生產(chǎn)過程中,許多單元設(shè)備的傳質(zhì)效率還較低,難以滿足生產(chǎn)需求,亟待優(yōu)化升級(jí)。因此研究界面?zhèn)髻|(zhì)機(jī)理并構(gòu)建相應(yīng)的理論模型對(duì)于指導(dǎo)單元設(shè)備的設(shè)計(jì)和優(yōu)化、強(qiáng)化傳質(zhì)效率具有重要意義。本文基于現(xiàn)有模型存在的不足,將采用現(xiàn)象學(xué)方法和湍流結(jié)構(gòu)理論,構(gòu)建基于寬能譜分布、隨機(jī)界面作用的流體微元或漩渦傳質(zhì)理論模型。本文分兩個(gè)部分。第一部分為氣-液表面?zhèn)髻|(zhì)機(jī)理模型的構(gòu)建。傳統(tǒng)的傳質(zhì)系數(shù)模型主要是基于滲透理論或表面更新理論的改進(jìn)模型。這些模型考慮傳質(zhì)過程是由非穩(wěn)態(tài)分子擴(kuò)散控制。而基于經(jīng)典的大渦和小渦傳質(zhì)模型預(yù)先假定傳質(zhì)由某波段能譜的流體結(jié)構(gòu)控制。本文則在全能譜的范圍內(nèi)考慮不同尺度流體微元結(jié)構(gòu)對(duì)傳質(zhì)的貢獻(xiàn),因此上述假設(shè)不再需要。本文重點(diǎn)研究了氣泡界面?zhèn)髻|(zhì)過程,采用特征線法以及濃度梯度薄層近似,推導(dǎo)出了一個(gè)新的液相側(cè)傳質(zhì)系數(shù)模型。模型的推導(dǎo)結(jié)合了非穩(wěn)態(tài)濃度對(duì)流擴(kuò)散方程以及氣泡與流體微元的相互作用。該模型考慮了氣泡與旋渦之間的有效相對(duì)運(yùn)動(dòng)才會(huì)促使漩渦與氣泡表面接觸,并基于隨機(jī)基礎(chǔ)作用的概念從理論上推導(dǎo)了不同尺度漩渦抵達(dá)表面的頻率密度分布。該抵達(dá)頻率密度分布可以用來理論解釋全能譜各區(qū)波段的流體微元結(jié)構(gòu)對(duì)傳質(zhì)系數(shù)貢獻(xiàn)的差異性。此外,本文還考慮了氣泡尺寸、氣泡變形與振動(dòng)、以及旋渦數(shù)密度分布對(duì)傳質(zhì)影響。模型預(yù)測(cè)的結(jié)果與文獻(xiàn)報(bào)道的實(shí)驗(yàn)數(shù)據(jù)吻合很好。第二部分首先采用數(shù)值方法驗(yàn)證了特征線以及濃度梯度薄層近似的合理性(濃度梯度層厚度整體上低于漩渦尺寸的3.18%),并證明了即使在單渦的傳質(zhì)過程也應(yīng)看成是非穩(wěn)態(tài)過程。數(shù)值計(jì)算表明:相同界面接觸時(shí)間,處于耗散區(qū)的漩渦能帶走更多的溶質(zhì),傳質(zhì)效率更高。通過推導(dǎo)的LBM模型數(shù)值求解了非穩(wěn)態(tài)的濃度方程,與本文解析模型相比較,發(fā)現(xiàn)界面液相側(cè)的切向分子擴(kuò)散對(duì)傳質(zhì)影響較弱。當(dāng)忽略切向分子擴(kuò)散,傳質(zhì)系數(shù)的誤差低于1%。表明忽略該擴(kuò)散具有一定合理性。
[Abstract]:At present, the theoretical study on gas-liquid two-phase interface mass transfer is not mature and perfect. In the actual industrial production process, the mass transfer efficiency of many unit equipment is still low, it is difficult to meet the production demand, so it is urgent to optimize and upgrade. Therefore, it is of great significance to study the mechanism of mass transfer at the interface and to construct the corresponding theoretical model for guiding the design and optimization of unit equipment and enhancing the efficiency of mass transfer. In this paper, based on the shortcomings of the existing models, the theoretical model of fluid micro-element or vortex mass transfer based on the wide spectrum distribution and random interface action will be constructed by using the phenomenological method and the turbulent structure theory. This paper is divided into two parts. The first part is the construction of gas-liquid surface mass transfer mechanism model. The traditional model of mass transfer coefficient is based on permeability theory or surface renewal theory. These models consider that mass transfer processes are controlled by unsteady molecular diffusion. Based on the classical mass transfer models of large and small vortices, it is assumed that mass transfer is controlled by the fluid structure of a certain band energy spectrum. In this paper, the contribution of fluid micro-element structures of different scales to mass transfer is considered in the range of the omnipotent spectrum, so the above hypothesis is no longer necessary. In this paper, the mass transfer process at the bubble interface is mainly studied. A new model of liquid side mass transfer coefficient is derived by using the characteristic line method and the concentration gradient thin layer approximation. The model combines the convection-diffusion equation of unsteady concentration and the interaction between bubble and fluid element. The effective relative motion between bubble and vortex is considered in this model to promote the contact between vortex and bubble surface, and based on the concept of random fundamental action, the frequency density distribution of vortex arriving at different scales is deduced theoretically. The density distribution of the arrival frequency can be used to explain the difference of the contribution of the fluid microelement structure to the mass transfer coefficient in each region of the omnipotent spectrum. In addition, the effects of bubble size, bubble deformation and vibration, and vortex number density distribution on mass transfer are also considered. The results of the model prediction are in good agreement with the experimental data reported in the literature. In the second part, numerical method is used to verify the rationality of the characteristic line and the density gradient thin layer approximation (the thickness of the concentration gradient layer is lower than 3.18% of the size of the vortex as a whole), and it is proved that even the mass transfer process of the single vortex should be regarded as an unsteady process. The numerical results show that the vortex in the dissipative region can take more solutes away and the mass transfer efficiency is higher at the same interface contact time. The unsteady concentration equation is solved numerically by the derived LBM model. Compared with the analytical model in this paper, it is found that the effect of tangential molecular diffusion on mass transfer at the liquid side of the interface is weak. When tangential molecular diffusion is ignored, the error of mass transfer coefficient is less than 1. It shows that it is reasonable to ignore the diffusion.
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ021.4

【共引文獻(xiàn)】

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本文編號(hào)：2113240