快速反應(yīng)體系中流體微觀混合機(jī)理的研究
發(fā)布時(shí)間：2018-12-24 10:13
【摘要】：微觀混合主要是指物料從經(jīng)湍流分散后的最小粘性渦尺度即Kolomogrov尺度到分子尺度的均勻化混合過(guò)程。這種微尺度上的混合對(duì)于快速反應(yīng)體系(如丙烯高溫氯化反應(yīng)、環(huán)己酮肟重排反應(yīng)等)有著非常重要的影響,反應(yīng)體系的物料濃度分布、產(chǎn)品質(zhì)量及系統(tǒng)操作穩(wěn)定性等均與微觀混合過(guò)程有著緊密聯(lián)系。由于這類(lèi)體系的反應(yīng)速率極快,在物料混合尚未達(dá)到分子尺度均勻化之前,反應(yīng)有可能已經(jīng)或者接近完成。因此,研究快速反應(yīng)體系中流體微觀混合的機(jī)理并建立相應(yīng)的理論模型對(duì)于設(shè)計(jì)和優(yōu)化反應(yīng)器、提升目標(biāo)產(chǎn)物選擇性、避免混合不均勻而形成的物料局部過(guò)濃現(xiàn)象以及抑制由此產(chǎn)生的深度副反應(yīng)等具有重要意義。已有文獻(xiàn)中的微觀混合模型主要有經(jīng)驗(yàn)?zāi)Ｐ秃徒Y(jié)構(gòu)模型兩種。經(jīng)驗(yàn)?zāi)Ｐ椭饕芯鄄?擴(kuò)散模型、雙/多環(huán)境模型、IEM模型等,結(jié)構(gòu)模型主要有層狀結(jié)構(gòu)模型、薄層片狀/片狀結(jié)構(gòu)模型、渦旋卷吸模型等。經(jīng)驗(yàn)?zāi)Ｐ痛蠖家肓艘粋�(gè)或者多個(gè)模型參數(shù),且這些參數(shù)常無(wú)實(shí)際物理意義、缺乏流體力學(xué)基礎(chǔ)�，F(xiàn)有的結(jié)構(gòu)模型大都僅考慮物料微團(tuán)的一維壓縮變形,并將模型簡(jiǎn)化為相鄰物料富集區(qū)局部微元內(nèi)的混合過(guò)程。由于這類(lèi)模型過(guò)于簡(jiǎn)化,導(dǎo)致其所描述的混合過(guò)程與實(shí)際情形存在一定偏差。本文針對(duì)前人模型存在的不足,提出了一個(gè)新的微觀混合機(jī)理模型。本文模型考慮了湍流場(chǎng)結(jié)構(gòu)的復(fù)雜性和尺度裂變動(dòng)力學(xué),考慮了物料富集區(qū)在多維對(duì)流和擴(kuò)散協(xié)同作用下的混合過(guò)程,即引入了物料富集區(qū)微元的切向、法向變形和分子擴(kuò)散,構(gòu)建了一個(gè)耦合拉伸、剪切、擠壓、卷吸等多種機(jī)制的微觀混合模型�；谖锪蠞舛鹊膶�(duì)流、擴(kuò)散方程,構(gòu)建了耦合物料濃度輸運(yùn)以及化學(xué)反應(yīng)的數(shù)學(xué)方程,并推導(dǎo)出了渦旋速度分布。并引入了代表性的快速反應(yīng)體系即串聯(lián)-競(jìng)爭(zhēng)反應(yīng)體系(?-萘酚與苯磺酸重氮鹽生成偶氮染料的反應(yīng)系統(tǒng)),分析了物料的摩爾體積比、粘度、分子擴(kuò)散系數(shù)、物料的初始濃度對(duì)反應(yīng)選擇性的影響及其對(duì)微觀混合均勻程度的影響。然后,以快速?gòu)?qiáng)放熱的反應(yīng)體系(即丙烯高溫氯化反應(yīng)體系)為例分析了溫度瞬態(tài)分布及其對(duì)混合過(guò)程的影響。研究表明,當(dāng)物料的摩爾體積比不同時(shí),物料富集區(qū)之間的卷吸厚度和層數(shù)均不同;當(dāng)粘度不同時(shí),反應(yīng)的選擇性隨著粘度的增加而增大;當(dāng)分子擴(kuò)散系數(shù)不同時(shí),反應(yīng)的選擇性隨著擴(kuò)散系數(shù)的增加而減小,且在一定范圍內(nèi)這種趨勢(shì)較明顯;同時(shí)反應(yīng)選擇性隨著物料初始濃度的增加而增大;當(dāng)考慮溫度影響時(shí),局部反應(yīng)區(qū)域內(nèi)存在溫度梯度。上述工作對(duì)于實(shí)際反應(yīng)中微觀混合的過(guò)程調(diào)控具有一定的指導(dǎo)意義。
[Abstract]:Microscopic mixing mainly refers to the homogenization of materials from the minimum viscous vortex scale (Kolomogrov scale) to the molecular scale. This microscale mixing plays an important role in rapid reaction systems such as propene chlorination reaction, cyclohexanone oxime rearrangement reaction and so on. Product quality and system operation stability are closely related to micro mixing process. Because the reaction rate of this kind of system is very fast, it is possible that the reaction has been completed or nearly completed before the material mixing reaches molecular scale homogenization. Therefore, the mechanism of micro fluid mixing in the rapid reaction system is studied and the corresponding theoretical model is established for the design and optimization of the reactor to enhance the selectivity of the target product. It is of great significance to avoid the local overconcentration of materials caused by uneven mixing and to suppress the depth side effects. There are two kinds of microcosmic mixed models in the literature: empirical model and structural model. The empirical models mainly include the aggregation and diffusion model, the double / multi-environment model, the IEM model and so on. The structure models mainly include the layered structure model, the thin lamellar / flake structure model, the vortex entrainment model and so on. Most empirical models introduce one or more model parameters, and these parameters often have no physical significance and lack of hydrodynamic foundation. Most of the existing structural models only consider the one-dimensional compression deformation of the material microclusters, and the model is simplified as the mixing process of local microelements in adjacent material enrichment areas. Due to the simplification of the model, the mixing process described by the model deviates from the actual situation. In this paper, a new microscopic mixing mechanism model is proposed to overcome the shortcomings of previous models. In this paper, the complexity of turbulent field structure and the scale fission dynamics are considered, and the mixing process of material enrichment region under the interaction of multi-dimensional convection and diffusion is considered, that is, the tangential, normal deformation and molecular diffusion of the micro-elements in the material enrichment region are introduced. A micro-mixing model of coupling stretching, shearing, extrusion and entrainment is constructed. Based on the convection and diffusion equations of material concentration, the mathematical equations of coupling mass concentration transport and chemical reaction are established, and the vortex velocity distribution is derived. The representative rapid reaction system, that is, the series competition reaction system (the reaction system of naphthol and benzenesulfonic acid diazo salt to form azo dyes) was introduced. The molar volume ratio, viscosity, molecular diffusion coefficient of the materials were analyzed. The effect of the initial concentration of the material on the selectivity of the reaction and its effect on the microcosmic mixing uniformity. Then, the transient distribution of temperature and its influence on the mixing process were analyzed by taking the reaction system of rapid and intense exothermic reaction (i.e. propylene high temperature chlorination reaction system) as an example. The results show that when the molar volume ratio of the material is different, the entrainment thickness and the number of layers are different among the rich regions of the material, and the selectivity of the reaction increases with the increase of the viscosity when the viscosity is different. When the molecular diffusion coefficient is different, the selectivity of the reaction decreases with the increase of the diffusion coefficient, and the tendency is obvious in a certain range, and the selectivity increases with the increase of the initial concentration of the material. When considering the influence of temperature, there is a temperature gradient in the local reaction region. The above work has certain guiding significance for the process regulation of micro mixing in actual reaction.
【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(lèi)號(hào)】：TQ027.1
本文編號(hào)：2390497
[Abstract]:Microscopic mixing mainly refers to the homogenization of materials from the minimum viscous vortex scale (Kolomogrov scale) to the molecular scale. This microscale mixing plays an important role in rapid reaction systems such as propene chlorination reaction, cyclohexanone oxime rearrangement reaction and so on. Product quality and system operation stability are closely related to micro mixing process. Because the reaction rate of this kind of system is very fast, it is possible that the reaction has been completed or nearly completed before the material mixing reaches molecular scale homogenization. Therefore, the mechanism of micro fluid mixing in the rapid reaction system is studied and the corresponding theoretical model is established for the design and optimization of the reactor to enhance the selectivity of the target product. It is of great significance to avoid the local overconcentration of materials caused by uneven mixing and to suppress the depth side effects. There are two kinds of microcosmic mixed models in the literature: empirical model and structural model. The empirical models mainly include the aggregation and diffusion model, the double / multi-environment model, the IEM model and so on. The structure models mainly include the layered structure model, the thin lamellar / flake structure model, the vortex entrainment model and so on. Most empirical models introduce one or more model parameters, and these parameters often have no physical significance and lack of hydrodynamic foundation. Most of the existing structural models only consider the one-dimensional compression deformation of the material microclusters, and the model is simplified as the mixing process of local microelements in adjacent material enrichment areas. Due to the simplification of the model, the mixing process described by the model deviates from the actual situation. In this paper, a new microscopic mixing mechanism model is proposed to overcome the shortcomings of previous models. In this paper, the complexity of turbulent field structure and the scale fission dynamics are considered, and the mixing process of material enrichment region under the interaction of multi-dimensional convection and diffusion is considered, that is, the tangential, normal deformation and molecular diffusion of the micro-elements in the material enrichment region are introduced. A micro-mixing model of coupling stretching, shearing, extrusion and entrainment is constructed. Based on the convection and diffusion equations of material concentration, the mathematical equations of coupling mass concentration transport and chemical reaction are established, and the vortex velocity distribution is derived. The representative rapid reaction system, that is, the series competition reaction system (the reaction system of naphthol and benzenesulfonic acid diazo salt to form azo dyes) was introduced. The molar volume ratio, viscosity, molecular diffusion coefficient of the materials were analyzed. The effect of the initial concentration of the material on the selectivity of the reaction and its effect on the microcosmic mixing uniformity. Then, the transient distribution of temperature and its influence on the mixing process were analyzed by taking the reaction system of rapid and intense exothermic reaction (i.e. propylene high temperature chlorination reaction system) as an example. The results show that when the molar volume ratio of the material is different, the entrainment thickness and the number of layers are different among the rich regions of the material, and the selectivity of the reaction increases with the increase of the viscosity when the viscosity is different. When the molecular diffusion coefficient is different, the selectivity of the reaction decreases with the increase of the diffusion coefficient, and the tendency is obvious in a certain range, and the selectivity increases with the increase of the initial concentration of the material. When considering the influence of temperature, there is a temperature gradient in the local reaction region. The above work has certain guiding significance for the process regulation of micro mixing in actual reaction.
【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(lèi)號(hào)】：TQ027.1
【參考文獻(xiàn)】
相關(guān)期刊論文 前1條
1 李希;陳甘棠;戎順熙;;微觀混和問(wèn)題的研究——(Ⅲ)物質(zhì)的細(xì)觀分布形態(tài)與變形規(guī)律[J];化學(xué)反應(yīng)工程與工藝;1990年04期
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