PIV Measurement for Rayleigh Convection and Its Effect on Mass Transfer☆

The velocity distribution in Rayleigh convection caused by acetone volatilization in acetone-ethyl acetate binary system was observed in a vertical cross section of an initially quiescent liquid layer ...     

Validation of Simulation and Mass Transfer Coefficient Prediction with Interfacial Convection

Investigation of interfacial mass transfer by means of numerical simulation is a promising field. In the present work, the Rayleigh convection of the CO₂‐ethanol absorption process was simulated using a random‐disturbance model based on the lattice Boltzmann method and the results were compared with the Schlieren observation for validation. It was found that the simulation method was superior for capturing the characteristics of the absorption process. A correlation was then proposed to predict the mass transfer coefficient based on Reynolds mass flux, scalar fluctuation variance, and its dissipation rate, and the correlation was found to be superior to existing methods in terms of phase difference. In this correlation, the mass transfer coefficient was linked with computational mass transfer for the first time.     

双组分混合有机胺溶液吸收沼气中CO_2的传质性能

在填料塔中,对以二乙醇胺(DEA)为基础溶剂,以N-甲基二乙醇胺(MDEA)、(N-2-羟乙基)乙二胺(AEE)、二乙烯三胺(DETA)、三乙烯四胺(TETA)为添加剂的二元混合胺溶液吸收沼气中高浓度CO2的传质性能进行了实验研究,考察了添加剂浓度及种类对吸收过程中CO2脱除率n、总体积传质系数KGae、气液相传质阻力的影响.结果表明,双组分混合有机胺溶液中,以AEE,DETA和TETA为添加剂时,KGae和随添加剂浓度增加而增大,气相传质系数kG及气相阻力占总阻力的分率减小,液相阻力占总阻力的分率增大;以MDEA为添加剂时趋势相反n和KGae沿塔高方向增大,其在4种溶液中的大小为DEA-TETADEA-DETADEA-AEEDEA-MDEA.     

吸收过程的界面传质机理

以分子热力学为基础 ,对气体吸收过程进行了理论分析 ,导出了传质通量的数学表达式。根据该文分析 ,气液界面传质的源动力来自界面处气液两相的不平衡 ,即只要有传质发生 ,液相界面处的浓度就不会达到与气相呈平衡的浓度。对于气相阻力可以忽略的吸收过程 ,两相传质速率的大小主要取决于液相的溶质界面浓度和液膜厚度 ,影响溶质界面浓度和液膜厚度的主要因素是近界面液相侧的流场分布。利用近界面浓度与液膜厚度的激光测定结果 ,计算了甲醇、乙醇及正丙醇吸收CO2 气泡的传质通量 ,计算结果与实验值吻合良好     

吸收过程的界面传质机理

Based on the method of molecular thermodynamics ,the mass transfer mechanism at gas-liquid interface is studied theoretically,and a nowe mathematical model is proposed,Using laser holographic interference technique,the hydrodynamics and mass transfer characteristics of CO2 absorption are measured,It is shown that the calculated results are in good agreement with the experimental data.     

乳状液膜分离Zn^2＋的界面传质阻力及传质模型

用Ｌｗｅｉｓ恒界面传质池对乳状液膜分离Ｚｎ＾２＋的传质阻力进行实验研究，结果表明由于表面活性剂单分子层的形成，使界面传质阻力占整个传质阻力的８５％。在此基础上所建立的既考虑界面传质阻力又考虑膜破碎的液膜传质模型能使用理论计算值与实验测定值符合较好。     

CO_2在仿生物型等三种吸收剂中传质吸收速率的测定

在研究了CO2 在仿生物型吸收剂和其他吸收剂中溶解度的基础上 ,通过微分实验 ,测定CO2 在仿生物型吸收剂中的传质速率 ,对这种新型吸收剂的动力学特性作出初步评价。     

超声对超临界CO2萃取传质的影响

自行设计了超声强化超临界CO2萃取装置,并以人参为原料,研究了超声的功率密度、频率和超声的辐照方式对超临界CO2萃取人参皂甙传质的影响。萃取压力、萃取温度、萃取时间和CO2流量分别为25 MPa、45℃、4 h和2.5 L/h。实验结果表明,当功率密度、超声频率和辐照方式分别为100 W/L、20 kHz和3 s/6 s时,人参皂甙的萃取率是不使用超声时的1.51倍;皂甙的萃取率随超声功率的增大而升高;低频超声较高频超声更有利于萃取;超声辐照时间对皂甙的萃取率影响较小;在高压下超声对超临界CO2萃取传质强化作用更明显;在适当的低温下更有利于超声强化超临界CO2萃取。     

采用格子Boltzmann方法模拟解吸过程中的Rayleigh对流

应用二维非稳态格子Boltzmann方法研究了异丙醇-水溶液和丙酮-乙酸乙酯溶液解吸过程中Rayleigh对流的临界开始时间、流动特征及其对界面传质的影响,并与相关文献对比. 结果表明,临界开始时间随界面浓度增加呈先缓慢增大再迅速增大最后趋于稳定的变化趋势. Rayleigh对流结构经历了从有序到无序的发展过程,是不断更新的耗散结构. Rayleigh对流主要作用于液相主体,使液相主体具有较大的湍动速度(10-4~10-3 m/s). 液相主体中存在许多循环流动,促进了界面更新及界面与液相主体之间液体的交换与混合. 传质增强因子(介于2~6之间)表明Rayleigh对流能有效提高解吸过程传质速率,强化界面传质过程.     

格子Boltzmann方法模拟咸水吸收CO2的Rayleigh对流过程

由溶解的CO₂引发的Rayleigh对流,对咸水层中CO₂的捕获与封存至关重要。为了更加直观地了解该过程的混合规律和盐浓度变化带来的影响,本文采用格子Boltzmann方法（LBM）对该过程进行了模拟。通过建立包含密度和浓度分布函数的双分布模型,同时引入静电力和体积力等外力项,对293.15K、101kPa下有多个离散的CO₂扩散源时的浓度分布进行了模拟。结果表明,模拟得到的Rayleigh对流结构、对流发生时间、流场速度和瞬时传质通量的数量级与前人研究结果一致;在咸水吸收CO₂过程中,Rayleigh对流结构可有效强化传质;瞬时传质通量随着时间增长先减小后增大再减小,对应了Rayleigh对流结构产生、发展、稳定的变化过程。同时模拟CO₂在纯水和不同盐浓度咸水中的溶解过程结果表明,盐浓度的增加会延迟Rayleigh对流的开始时间、降低传质效率,这与前人的实验结果一致,模拟结果可为不同盐浓度咸水层中CO₂的封存提供指导。     

二氧化碳传质系数KG.a计算公式的经验回归

采用非线性最小二乘法对本菲尔溶液ＣＯ２吸收传质系数ＫＧ．ａ的数学模型ＫＧ．ａ＝Ａ（Ｌ／０．１０２ｕｌ）＾Ｂ「１＋Ｃ（ＦＣ２－ＦＣ１）Ｍｅ＾（０．０１２ｔ－９．８６９ｐＣＯ２）」中的参数Ａ、Ｂ、和凯洛格Ｂ厂,东洋工程公司和赫尔公司的生产数据进行经验回归,回归后得到Ａ、Ｂ、Ｃ的值分别为０．２７４４,０．２３７６,２．１０９,结果ＫＧ．ａ公式的计算值与实验值的相地残差均在１０％以下。     

气相中乙醇对水吸收CO_2过程界面对流的影响

考察了在气相中加入少量乙醇对水吸收CO2过程中液相界面对流的影响。采用粒子成像测速仪(PIV)测定了这一气体吸收过程中液体瞬时流场。通过对液体流场信息进行处理,得到了不同条件下速度和湍动能的数据及其分布;根据流场内速度和湍动能及其分布结构,定量分析了气相中加入乙醇对气液传质过程界面对流的影响,发现气相中乙醇的加入导致了局部Marangoni效应,很大程度上增大了界面附近的对流,为促进气液传质提供了依据。     

微通道内二乙醇胺/乙醇溶液吸收CO2的传质性能

利用高速摄像仪实验研究了微通道内二乙醇胺（DEA）/乙醇溶液吸收CO₂的传质过程。采用图像法得到微通道内气泡的体积变化,根据微通道进出口压力,计算得到了气液两相从开始接触到平衡时的平均传质系数k。分别考察了气液相流量和DEA浓度对传质系数的影响。结果表明：传质系数随着液相流量和溶液中DEA浓度增大而增大。对于给定的液相流量和DEA浓度,k随着气相流量增大而增大并逐渐趋于一个恒定值。提出了一个传质系数预测式,预测值和实验结果吻合良好。     

Convection Heat Transfer of CO2 at Supercritical Pressures in Microtubes

Convection heat transfer of supercritical pressure CO₂ in microtubes as well as characteristics of fluid flow and heat transfer were investigated. Alterations of physical properties of supercritical CO₂ and the impact of buoyancy on the heat transfer were analyzed when the inlet Reynolds (Re) number of CO₂, diameter of heat exchanger, and inlet Re of cooling water were changed. The temperatures of hot fluid in numerical simulations from several classical turbulence calculation models were compared with experimental results from the literature. The physical properties of CO₂ changed significantly around the critical point, causing a distinct decline of buoyancy and strengthening of heat transfer.     

Effect of Membrane Structural Characteristics on Mass Transfer in a Membrane Absorption Process

Carbon dioxide is absorbed by de-ionized water or NaOH aqueous solution in the unsteady-state membrane absorption process. A theoretical model has been developed to describe the mass transfer behavior in the liquid phase, in which the effects of membrane structural characteristics are investigated. The concentration profiles in the liquid phase are calculated as a function of time. When the membrane porosity is relatively high or the pore size is relatively small, the solute concentration profile near the membrane surface can get homogeneous instantly due to the short distance between adjacent pores. In this case, the existence of the porous membrane has less effect on the mass transfer process. However, when the membrane porosity is relatively low or the pore size is relatively large, the distance between the adjacent pores is large, so the concentration profile near the membrane surface is hard to get homogeneous during the absorption process. Therefore, the concentration profile can be influenced significantly by the membrane structural characteristics, which means that the membrane structure has a significant effect on the mass transfer in liquid phase. Moreover, the chemical reaction in the liquid phase makes it difficult for the concentration profile near the membrane surface to get homogeneous. The disturbance in the liquid phase caused by the gas flow and pressure fluctuation is also taken into account in the model, and the model results agree well with the experimental data.     

Scale Effects on Hydrodynamic and Mass Transfer Characteristics of External Loop Airlift Reactors

Gas hold-up and oxygen transfer have been investigated in two geometrically similar external loop airlift reactors of linear scale ratio of 2. In mass transfer experiments, the sampling location was found to be important as significantly different k_La values can be obtained. The variations of k_La with probe location have been explained in terms of non-uniform hydrodynamic properties and the results obtained have been validated by means of high speed video camera recordings. At higher gas flowrates, the gas hold-up was significantly higher in the large-scale reactor. It was found that in order to maintain the gas hold-up or k_La constant in both the small- and large-scale reactor, the small-scale reactor required 25% and 27% more power input per unit volume of liquid respectively. © 1997 SCI.     

竖直平面上的传热传质复合自然对流

用数值方法研究了竖直平面上因热及物质扩散引起的传热传质复合自然对流,得到了速度、压力、温度和浓度的分布及传热传质速率随浮力比的变化规律。研究结果表明：Ｎｕ与Ｓｈ在随浮力比Ｂ的变化过程中出现最小值,此时的浮力比Ｂｍｉｎ仅是Ｐｒ／Ｓｃ的函数;流型取决于浮力比和Ｐｒ／Ｓｃ,根据流型不同可在Ｂ－Ｐｒ／Ｓｃ坐标系中将流场划为４个区域。     

臭氧吸收及反应过程的传质系数与增强因子

从双膜理论、溶质渗透理论、膜－渗透理论和表面更新理论出发，研究分析了臭氧气体在液相中的物理吸收过程传质系数，臭氧与液相中的污染物化学反应过程的吸收系数。基于双膜模型理论，推导出在不同pH值区间内伴随着臭氧与污染物化学反应过程的增强因子表达式。     

Comparison of Overall Gas‐Phase Mass Transfer Coefficient for CO2 Absorption between Tertiary Amines in a Randomly Packed Column

The mass transfer performance of CO₂ absorption into an innovative tertiary amine solvent, 1‐dimethylamino‐2‐propanol (1DMA2P), was investigated and compared with that of methyldiethanolamine (MDEA) in a packed column with random Dixon‐ring packing. All experiments were conducted under atmospheric pressure. The effects of inert gas flow rate, amine concentration, liquid flow rate, CO₂ loading, and liquid temperature on mass transfer performance were analyzed and the results presented in terms of the volumetric overall mass transfer coefficient (K_Ga_v). The experimental findings clearly indicate that 1DMA2P provided better mass transfer performance than MDEA. For both 1DMA2P and MDEA solutions, the K_Ga_v increased with rising amine concentration and liquid flow rate, but decreased with higher CO₂ loading. The inert gas flow rate only slightly affected the K_Ga_v. A satisfactory correlation of K_Ga_v was developed for the 1DMA2P‐CO₂ system.     

界面性质对气液传质的影响

界面性质对气液传质有重要影响。分子通过界面时需克服界面自由能，界面两侧的浓度不一致。本文导出了两者之间的关系