CDI二维浓度传质模型的建立以及实验验证

电容去离子技术(CDI)作为一种新兴的水处理脱盐技术,因其具有诸多优异性能而受到广泛关注。厘清CDI的传质机制是理论研究的焦点。通过对已有经验模型的分析,从沿流向方向和垂直流向方向两个方面,考虑了电场迁移以及传质扩散等因素,提出了一种新的CDI二维浓度传质模型,对CDI在除盐过程中的离子扩散及浓度分布规律进行模拟探究,根据实际实验结果对该模型进行实验验证及参数修正。结果表明,该二维模型可以较好地模拟CDI除盐过程。将该二维模型利用COMSOL软件进行模拟,观测CDI在除盐过程中的内部浓度变化。并针对存在问题提出合理化建议,为CDI技术的未来发展提供理论支撑。     

蒸发结晶盐配制电解盐水工艺研究

介绍以氯碱厂隔膜法烧碱生产中产生的蒸发结晶盐配制的盐浆为原料，并利用离子膜法烧碱生产中的副产淡盐水，在溶盐塔内进行盐溶解制饱和盐水实验，取得了良好的效果；在适宜的实验条件下，制得盐水中的NaCl质量浓度达到305～320 g/L，且不含固体悬浮物；并根据传质理论，建立了盐颗粒溶解过程模型。实验结果表明，溶盐过程是盐浆沉降、盐浆分散、盐颗粒扩散溶解的过程；盐浆浓度对溶盐效果影响不大。     

通气强化气隙式膜蒸馏质量传递数值模拟

采用计算流体动力学(CFD)方法对通气强化气隙式膜蒸馏(AGMD)过程进行了数值模拟,并探讨了强化过程的传质机理。利用FLUENT软件结合流体体积函数(VOF)模型,以通气强化过程膜管内的气液两相流体为研究对象,设定氯化钠溶液为分离介质,氮气为强化介质进行模型建立与模拟分析。结果表明:渗透通量模拟数据与实验数据基本吻合;通气可增大渗透通量(J)与传质系数(k),降低浓度极化率(CPC),有利于膜蒸馏过程;浓度分布模拟结果可用于预测局部浓度极化程度;由拟合出的通气强化过程传质系数关联式的形式,可知过渡扩散-泊肃叶流传质机理比过渡扩散传质机理更接近于通气强化膜蒸馏真实传质过程。基于气体在多孔介质中的传质理论,通过合理建模并设定模拟参数,可研究通气强化传质过程的影响因素(文中为气含率)对强化效果的影响,该方法也可推广应用于研究多影响因素的膜蒸馏强化传质过程。     

石灰石湿法脱硫的传质模型

石灰石/石灰-石膏湿法烟气脱硫是控制二氧化硫排放的最常用方法,本文以单个石灰石颗粒为研究对象,根据双膜理论建立碱性溶液脱硫的传质模型,并利用 matlab软件进行模拟.通过对气相中的SO2向液相中(相界面)的传质扩散、石灰石的溶解扩散、液相中的化学反应进行理论分析,并对该过程进行合理假设,进而推导出了传质模型,该模型可以推导出传质速率,得到的模型计算结果与实验相吻合,拟合程度高达97%,从而为湿法脱硫机理的研究提供理论参考.     

不可压热流体中气体传质扩散过程的数值模拟

控制流体流动中溶解的气体分子浓度能有效控制流动过程中的化学反应,而由热产生的自然对流能够加强气体分子的传递,因此研究气体分子在热流体流动中的扩散混合过程有重要意义。应用格子Boltzmann方法,耦合热效应和扩散效应,数值模拟了一个简化的容器中随着自然对流的发展,溶解的氧气分子在整个容器中的扩散过程。首先建立了二维9速模型的双扩散模型来模拟热量和质量的双扩散对流。为了考察不同自然对流流动对气体分子传递的影响,设计了3种不同给热条件,对不同热流动的形成过程和气体分子扩散过程进行了模拟,与文献结果吻合良好。通过详细分析热边界如何影响流动和传质过程,证实了模拟的速度场与文献数据差异的合理性,同时为控制气体传质过程提供给热条件的设计依据。     

熔融盐膜法脱除航天舱中CO2传质模型

基于电化学理论、膜分离与传质理论，采用非平衡态热力学，建立了熔融盐(43．5％ Li2CO2 25％K2CO3 31.5?Na2CO3)(mol.?膜法脱除C02数学模型。首先，根据熔盐体系离子的Hittorf迁移数、比电导、扩散系数等独立实验参数，计算得到体系的Onsager系数和模型参数，然后用计算机求得该模型的数值解。解的结果表明：影响CO2传质通量的因素主要有电流密度及C02在膜两侧的浓度差。在低电流密度下，浓差推动力起主导作用：在较高电流密度下，膜两侧浓差推动力对C02传质影响甚微，电流密度对C02的传质则起着决定性作用。为了进一步验证数学模型，在823K及常压条件下，模拟航天舱中的气体成分，进行了熔融盐膜法脱除CO2的实验研究。实验结果与模型理论解吻合较好。     

硅酸二钙烧成过程中的数学模型研究

提出了一种无烧结条件下硅酸二钙烧成过程的数学模型,在给定模型初始和边界条件下运用软件MATLAB/pdetool模拟了某一粒径下颗粒的传热和传质过程。模拟发现,反应是在一个明显界面上进行,温度和钙离子浓度随着反应的进行无限趋近于设定的模型边界值,模拟结果同笔者的实验结果基本符合。同时在该模型的基础上运用煅烧动力学方程对几种不同粒径颗粒的烧成过程进行了数值计算,计算结果同样与笔者的实验结果较为符合,在误差允许的范围之内。因此可以认为该模型能用来模拟粒径在微米到毫米级范围内二氧化硅颗粒的煅烧过程。     

电渗析过程传质模型的研究进展

电渗析是一种利用离子交换膜和电势差从溶液及其他不带电组分中分离出离子的物质分离过程，该技术具有适应性强、预处理简单、能耗低、环境污染小等优点，被广泛应用于化工、生物等领域的分离纯化过程。本文主要介绍了用于电渗析分离过程的6种传质模型，总结了各模型的优势及存在的问题，指出限制电渗析技术进一步发展的主要原因是对包含物质传递、浓差极化、流体流动行为、电解质溶液-膜平衡等复杂现象的电渗析过程进行理论和实验研究难度大，而传质模型化为电渗析分离过程的物质传递研究提供了一条有效途径，有助于深入研究电渗析过程中物质的传递机理，准确预测分离性能并导向性优化电渗析结构设计和操作工艺。并且提出未来电渗析传质模型的研究方向是结合经验方程或传质系数进一步优化传质模型，并采用仿真工具模拟传质过程，提高模型的准确性和普适性。     

氨基酸中空纤维膜分配色谱模型

以色氨酸为例,考虑氨基酸解离和在中空纤维膜内扩散传质建立了氨基酸中空纤维膜分配色谱理论模型.该模型采用完全独立的模型参数,模拟结果与实验数据吻合较好,验证了模型的可靠性.理论计算表明流动相的pH值与局部氨基酸浓度密切相关;理论和实验结果表明,流动相离子强度对氨基酸的保留行为有很大影响,采用梯度洗脱的方式可以改善洗脱峰形,提高色谱柱的分离度.     

基于吸附-扩散机理研究钒离子透膜传质过程(I)——离子膜吸附-扩散模型

钒离子透膜传质是导致钒电池能量损失的关键因素之一,在分析钒离子透膜传质过程的基础上,根据离子交换膜固定电荷理论提出钒离子透膜传质的吸附-扩散模型.由膜内离子Donnan平衡,引入选择性系数研究膜内钒离子吸附过程;考虑膜面浓差电势影响,由Nernst-Planck方程描述膜内钒离子和氢离子交互传质过程,将钒离子透膜扩散过...     

ZIF衍生多孔碳纳米纤维用于高效电容去离子的研究

作为一种环保节能的新兴脱盐技术，电容去离子技术正在成为替代反渗透脱盐和电渗析脱盐的一项重要的脱盐技术。各种碳基材料被广泛地应用于电容去离子电极材料的研究，然而大多数碳基材料为粉末状材料，需要添加黏结剂，这必将导致电极材料电吸附能力的下降。利用静电纺丝技术，将ZIF纳米颗粒和聚丙烯腈混纺，并通过分段高温热处理过程，成功合成了具有柔性结构的整体性多孔碳纳米纤维。由于其具有孔道结构的分级分布和较强的亲水性等优良特性，所制得的多孔碳纳米纤维在1.2 V电压下于500 mg/L NaCl溶液中表现出良好的电吸附性能，脱盐量达到了19.92 mg/g，比普通碳纳米纤维提高了一倍以上。     

电渗析脱盐过程离子传递现象的数值模拟

建立了电渗析脱盐过程离子传递稳态模型，研究了离子电荷数、离子扩散系数和离子交换膜电导率对脱盐过程传质的影响，描述了离子浓度分布、电势分布和离子传递通量分布的变化情况。研究表明：相较于一价离子，二价离子在电渗析过程中膜两侧浓度差较小，跨膜电压降较高，各项传递通量较小；当离子扩散系数增大时，膜两侧浓度差减小，跨膜电压降升高，总传递通量和电迁移通量增大；当离子交换膜电导率增大时，膜两侧浓度差增大，跨膜电压降降低，各项传递通量均增大。     

Process simulation of desalination by electrodialysis of an aqueous solution containing a neutral solute

A model was developed to describe the desalination process of an aqueous solution consisting of a salt and a neutral solute using electrodialysis (ED). Under the assumption of plug flow in compartments, the ED process was analyzed in two-dimensional directions of the electric field and flow to get the differential equations of mass balance in the flow length. Then the transport equations of solutes and water through the membrane were deduced by the irreversible thermodynamics approach. Under the limited condition of uniform current density, the model composed of a first-order differential equation set was developed. While the model parameters such as transport coefficients, dimensions of ED equipment, operation conditions and characteristics of solutes are given, the model was solved by the numerical method. The variations of current density, concentrations of solutes and velocities in dilute and concentrated compartments vs. flow length can be simulated by the model. While there was no neutral solute, the model was used to simulate the desalination process of a salt solution. By comparing the ED experiments to the simulations, it is shown that the model is well suited to describe the actual desalination process. The effects of the initial values of variables in the model on the desalination process were simulated to attempt to construct the actual ED process; and the general simulation of desalination process can be realized by the model. While the effect of concentration polarization on the desalination process is reflected by the variation of membrane conductivity, the model was verified to describe the ED process successfully under low velocity.     

Complexation-Enhanced Boron Removal in a Dual-Stage Nanofiltration Seawater Desalination Process

A complexation-enhanced boron removal method in a dual-stage nanofiltration (NF) seawater desalination process was investigated. A comparative experiment of five different polyols was carried out. Sorbitol was chosen as the complexation additive because of its higher equilibrium constant. The reaction between boron and sorbitol was rapid and only slightly affected by the other ions. Due to the complexation reaction, boron rejection of dual-stage NF seawater desalination process was increased from 35% to 62% in the first stage and from 42% to 55% in the second stage. Boron concentration reached 0.1 mg/L by adjusting the complexation and pH value. Molecular structures were simulated using the molecular simulation technology. The results indicated that molecular structure and molecular size played significant roles in enhancing boron removal. Meanwhile, NaOH and sorbitol had no evident effect on the chemical structure of the membrane surface. The results indicated that complexation is an effective method to reduce boron concentration in a dual-stage NF seawater desalination process.     

Computational modeling of the template-assisted deposition of nanowires

In the present paper we developed and simulated a two-dimensional model for the electrodeposition inside the porous anodic alumina template, which deals with one only potentiostatic pulse applied to one pore. The potential distribution within the oxide is described by Laplace equation and the diffusion equation takes into account the transport of the metal ions in the solution. These equations are coupled by time-dependent boundary conditions at the deposition interface. The charge transfer process is described by a Butler-Volmer relationship. Two limit situations corresponding, respectively, to a completely insulating template and to a metallic cavity are described by the model. The first case corresponds to the ideal condition for a truly one-dimensional deposition because there is no current on the pore wall. In the second limit situation, the reacting interface is treated as an equipotential and the deposition kinetic is limited by the charge transfer process. Furthermore, in this case one has a bi-dimensional electrodeposit growth. Between these limit situations, the charge transfer process and the voltage drop inside the oxide are equally significative. In this case, the model captures the dynamic interaction between the concentration gradients and the potential distribution inside the oxide which allows us to explain several experimental observations.     

Hybrid Reverse Osmosis‐Capacitive Deionization versus Two‐Stage Reverse Osmosis: A Comparative Analysis

Reverse osmosis (RO) is a high‐pressure single‐phase desalination process used to obtain freshwater from seawater/brackish water. The RO system shows high energy consumption for a given unit volume of pure water produced. The reported hybrid system of RO and capacitive deionization (CDI) aims at improving the RO water recovery and minimizing energy consumption. The RO‐CDI system is simulated and compared with two‐stage RO, to determine the effectiveness of the new hybrid system. The energy recovery from RO brine was also studied. The specific energy consumption by two‐stage RO for two different arrangements of the energy recovery device is higher than for RO‐CDI. The hybrid RO‐CDI system is energy efficient for the production of freshwater from brackish water.     

有限元方法求解化学气相淀积反应器模型(Ⅰ)——冷壁反应器模型及有限元解

建立了冷壁化学气相淀积反应器的数学模型,用Galerkin有限元方法对模型予以求解.计算中考虑了温度对物性参数的影响及自然对流因素,计算值和实验结果基本上一致.     

有限元方法求解化学气相淀积反应器模型(Ⅰ)——冷壁反应器模型及有限元解

建立了冷壁化学气相淀积反应器的数学模型,用Galerkin有限元方法对模型予以求解.计算中考虑了温度对物性参数的影响及自然对流因素,计算值和实验结果基本上一致.