高压脉冲放电降解水溶液中4-氯酚过程的数学模型(Ⅱ)鼓泡过程中臭氧传质增强因子E与4-氯酚浓度的关系

臭氧从气相传质到废水溶液中并与其中的有机污染物发生氧化还原反应是一个含有化学反应增强的臭氧吸收过程. 在酸性废水中主要发生臭氧与4 -氯酚分子和 4- 氯酚盐离子的反应, 而臭氧在水溶液中分解形成的羟基自由基的氧化作用可以忽略. 提出了由于发生化学反应而形成的臭氧传质增强因子 E与废水中有机物浓度[PCP] 的定量关系的表达式.

细颗粒增强气液传质机理及模型研究

分散细颗粒(包括分散固体颗粒和分散液滴)可以明显增强气液传质。简要叙述了目前提出的三种颗粒增强传质机理:传输作用,边界层混合作用和阻止气泡聚并作用,讨论了每种机理可能适用的体系。评述了近年来发展的有代表性的经验模型和基于不同机理的理论模型,并指出今后模型的建立应以湍流理论为桥梁,综合考虑多种传质机理。

质子交换膜燃料电池流场强化传质研究进展

质子交换膜燃料电池作为车载新型动力源具有广阔的应用前景而备受关注。流场板是燃料电池的核心部件之一,起分配反应气体、移除水分与杂质和传导电子等作用。目前对质子交换膜燃料电池流场方面的研究,大多针对常规流道进行了尺寸和流场布置方式的优化,部分研究在流道内部添加不同形式的堵块以增强气体传质,或将多孔介质材料应用于流场板,或设计新型的三维网格流场结构,通过此类方式来优化燃料电池的水热管理,强化传质效果以提高燃料电池的性能。本文中对这些研究进行归纳总结,并得出若干结论。

气液界面传质过程Rayleigh对流模拟的格子Boltzmann方法

浓度梯度导致的Rayleigh对流是一种通常在传质过程中观察到的界面现象.为了模拟乙醇吸收CO2气液传质过程中界面传质引发的Rayleigh对流现象,提出了描述界面扰动的随机扰动模型,并建立了带有双分布模型的二维格子Boltzmann方法(LBM).模拟二维液相Rayleigh对流过程中,假设界面上CO2浓度为常数.通过模拟研究,确定了随机扰动模型的2个参数:局部扰动概率P和浓度扰动大小ρD.模拟结果表明,当0<ρD≤10-9,kg/m3、10-6≤P≤10-1时,平均液相传质系数存在一个稳定值:(1.09±0.02)×10-5,m/s.通过考察浓度分布结构,分析了Rayleigh对流的时空演化过程.根据模拟结果定义并计算了传质增强因子,其证明了Rayleigh对流能够有效地强化界面传质.

低冷量下强化CO_(2)吸收的甲醇基纳米流体性能

冷甲醇洗法捕集CO_(2)技术要求低温环境,需要大量的冷冻能量,能耗较大。在吸收剂中引入纳米颗粒,可以有效提高气液传质速率,降低能耗。本研究旨在开发冷量需求少,吸收、解吸性能提升的甲醇基纳米流体。实验分别考察了纳米颗粒种类、固含量、尺寸,表面活性剂含量、操作温度和初始CO_(2)浓度等因素对吸收剂捕集CO_(2)性能的影响及机理。结果表明,在0.2~1.0g/L的TiO_(2)、Al_(2)O_(3)、SiO_(2)纳米流体中,0.4g/L的TiO_(2)-甲醇纳米流体的CO_(2)吸收、解吸增强效果最佳。向其中添加0.10%(质量分数)聚乙二醇辛基苯基醚(Triton X-100)后,纳米流体的吸收、解吸增强效果达到最大,且在5次循环后仍呈现良好增强效果。此外,本文对纳米流体增强吸收的机理进行了深入分析,提出了一个经验公式来预测TiO_(2)-甲醇纳米流体的增强因子E和最佳固含量。

纳米颗粒强化船舶烟气CO_(2)吸收解吸性能实验

利用鼓泡吸收和解吸实验装置研究TiO_(2)和SiO_(2)纳米颗粒对质量分数为30%的单乙醇胺(monoethanolamine,MEA)溶液CO_(2)吸收-解吸性能的影响。结果表明,质量分数为0.10%的TiO_(2)-MEA吸收剂的吸收增强因子最佳,可以达到1.095。吸收前后纳米颗粒的粒径分布和Zeta电位基本保持不变,具有较好的稳定性。在解吸过程中,相较质量分数为30%的MEA吸收剂,质量分数为0.10%的TiO_(2)-MEA和质量分数为0.10%的SiO_(2)-MEA吸收剂相对热损耗分别降低7.1%和7.0%,解吸容量分别提升7.69%和7.53%。此外,纳米颗粒对其他有机胺吸收剂也具有一定作用,在解吸过程中,显著提高有机胺吸收剂解吸速率的峰值,缩短达到解吸速率峰值的时间,提高解吸效率。

水吸收CO_2过程界面对流的激光诱导荧光观测

建立了采用激光诱导荧光技术观测水吸收CO_2过程中界面对流现象的实验装置,利用荧光素钠作为荧光剂,通过标定获得了CO_2在水中溶解浓度与荧光强度的关系,进而获得了定量测量水中CO_2浓度分布的实验方法。通过建立的实验装置和方法,测量了水吸收CO_2过程中液体近界面Rayleigh对流发生时的浓度分布演化过程。利用实验结果对文献中报道的临界Rayleigh数进行了验证;并对上述吸收体系的界面传质由分子扩散主导逐步转变为对流传质主导的过程,以及Rayleigh对流对吸收过程界面传质的强化进行了定量分析。

气相第2组分对水溶解CO2过程界面对流影响的LIF观测

采用激光诱导荧光(LIF)观测方法考察了在气相中分别添加乙醇和二氯甲烷分别对CO_2在水中溶解过程界面对流的影响,得到了液相中CO_2浓度分布及其演化的观测结果,通过物料衡算得到了相应条件下的液相传质系数。CO_2溶解过程会出现由密度梯度引起的Rayleigh对流。实验结果表明,当添加的乙醇含量小于8.47 mg·L-1时,Rayleigh对流会被增强,进而促进了CO_2的溶解;随着气相中乙醇含量的增大,Rayleigh对流反而被抑制;气相添加二氯甲烷会显著增强Rayleigh对流,提高了CO_2的传质速率,随着气相二氯甲烷含量的增大,CO_2在水中溶解过程的液相传质系数呈现先加强后恒定的趋势。

Enhancement of CO2 Absorption under Taylor Flow in the Presence of Fine Particles

The physical absorption of CO2 in water containing different types of particles was studied in a micro-channel operated under Taylor flow. The maximum enhancement factors of 1.43-2.15 were measured for activated carbon （AcC） particles. The analysis shows that the enhancement effect can be attributed to the shuttle mechanism. Considering the separate contributions of mass transfer from bubble cap and liquid film, a heterogeneous enhance- ment model is developed. According to this model, the enhancement factors Ecap, EFilm and Eov are mainly determined by mass transfer coefficient gL （gL Cap and KL Film）, adsorptive capacity of particles m, and coverage fraction of particles at gas-liquid interface （. With both effects of particle-to-interface adhesion and apparent viscosity included, the model nredicts the enhancement effect of AcC varticles reasonably well.

CFD simulation with enhancement factor of sulfur dioxide absorption in the spray scrubber

A model describing the absorption process of SO2 into limestone slurry with a spray scrubber is presented. Both the physical performance of the spray liquid in the scrubber and the involved chemical reactions are analyzed in the model. A con- tinuous concentration change of H+ was solved by iterative coupling using Matlab, and it was found that there was a remarkable influence on the concentration of the other elements in the process of SO2 absorption. The calculations show that the enhancement factor exponentially grows with an increasing value of pH and logarithmically decays with an increasing value of the driving force. To verify the accuracy of the model, experiments were also carried out, and the results suggest that the model, after combining the physical performance of the spray and the enhancement factor, can more precisely describe SO2 absorption in a spray scrubber. Furthermore, a commercial computational fluid dynamics (CFD) tool is used to perform several simulations which describe and clarify the effects of variables on SO2 absorption. The results of numerical simulation can provide a basis for further design and optimization of the scrubber.

Mass Transfer Enhancement of Propane Absorption into Dodecane-Water Emulsions

A one-dimensional unsteady heterogeneous parallel mass transfer(ODUHPMT) model was developed for the absorption enhancement of volatile organic compounds(VOC) by the dispersed droplets.An analytical solution for enhancement factor was obtained based on surface renewal theory and the Laplace domain transformation. The absorption rate of propane into water at different stirring speeds with the added micro dodecane droplets was investigated experimentally in a thermostatic stirred tank.The mass transfer flux across the gas-liquid interface and the enhancement factor were measured.The results showed that the dodecane has an obvious enhancement effect on propane absorption into water,the maximum enhancement factor reached 11.The enhancement factor increased with increasing dodecane volume fraction and decreased with increasing stirring speed.The experiment data agreed well with the model predictions and showed high prediction accuracy of ODUHPMT model.

Enhancement Factors in Ozone Absorption Based on the Surface Renewal Model and its Application

Based on the Danckwerts surface renewal model, a simple explicit expression of the enhancement factor in ozone absorption with a first order ozone self-decomposition and parallel second order ozonation reactions has been derived. The results are compared with our previous work based on the film theory. The 2,4-dichlorophenol destruction rate by ozonation is predicted using the enhancement factor model in this paper.

Effect of Marangoni Convection on Mass Transfer in Liquid Phase

Marangoni convection and its influence on the mass transter in the liquid phase were investigated. Marangoni convection was visualized using laser Schlieren technique, Orderly polygonal convection patterns and random interfacial turbulence were observed. The effect of Marangoni convection on the mass transfer rate was studied by desorbing ethanol from aqneous solution in the falling film. The experimental results show that Marangoni convection can speed up the surface real and enhance the mass transfer rate in the liquid phase.The liquid mass transfer coefficient can be enhanced by as much as 3 folds. The corresponding empirical correlations are given in terms of the mass transfer enhancement factor. Furthermore, in considering the Marangoni effect, the conventional mass transfer correlation was modified, The differences between the values predicted by the correlation and the experimental data are within ±8.2% and the average difference is 4.2%.

Gas Absorption Enhancement of Carbon Dioxide into Ca(OH)_2 Slurries

Chemical absorption of CO2 into aqueous slurries of Ca(OH)2 was studied in a stirred thermostatic reactor. The influence of solid loading and stirring speed on absorption rate were investigated experimentally, and the results show that the enhancement factor increases with particle content due to the increase of reactive particles in the gas-liquid interfacial region. The absorption process was controlled by the diffusion of gas molecules in slurry. The influence of stirring intensity on enhancement factor is an integration of gas-liquid and liquid-solid mass transfer variation. A novel prediction model of enhancement factors was proposed with the partition of interface into two various zones, and the prediction values by the presented model are in agreement with the experimental data.

Porousizing catalysts for boosting CO_(2) electroreduction

Facing soaring global energy demand and intensifying environmental problems,the search for sustainable energy alternatives has become imperative.The efficient conversion of carbon dioxide(CO_(2)),one of the primary greenhouse gases,plays the crucial role in mitigating global climate change.The electrocatalytic CO_(2) reduction reaction(eCO_(2)RR)provides an effective solution for its conversion into high-value-added chemicals,promoting the development of the carbon cycle and green chemistry.Porous materials of distinctive physicochemical properties have demonstrated substantial potential in eCO_(2)RR.In this review,various strategies of porousizing catalysts for boosted eCO_(2)RR are briefly summarized.Subsequently,the functionalities of porous materials including enrichment effect,modulating microenvironmental pH,stabilizing key species,facilitating mass transfer and tuning the nature of active sites to improve the efficiency and selectivity of eCO_(2)RR are categorized.Furthermore,we discuss the principal challenges confronting current electrocatalytic systems and propose future research directions.Insights from this review are expected to benefit broad communities of chemical and material research for rationalizing porous electrocatalysts and optimizing eCO_(2)RR performances.

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(10-4～10-3m/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.