Development of CDI two-dimensional concentration mass transfer model and experimental validation

doi:10.11949/0438-1157.20220033

Abstract

Abstract:

Capacitive deionization (CDI) is an emerging technology for water treatment and desalination, which has received much attention because of its excellent performance. To this end, a new two-dimensional concentration transfer model of CDI was proposed in this paper by analyzing the existing empirical models, which considers the electric field migration and mass transfer diffusion from both along and vertical flow directions. The ion diffusion and concentration distribution of CDI in the process of desalination were simulated and explored. According to the actual experimental results, the model is verified experimentally and its parameters are corrected. The results show that the two-dimensional model can simulate the CDI desalination process well. This two-dimensional model was simulated using COMSOL software to observe the internal concentration changes of CDI during the desalination process. And rationalization suggestions are made for the existing problems to provide theoretical support for the future development of CDI technology.

Key words: capacitive deionization, electro-adsorption, two-dimensional model, desalination, experimental validation

摘要：

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。

关键词: 电容去离子, 电吸附, 二维模型, 脱盐, 实验验证

CLC Number:

O 646

Luyue HUANG, Chang LIU, Yongyi XU, Haoruo XING, Feng WANG, Shuangchen MA. Development of CDI two-dimensional concentration mass transfer model and experimental validation[J]. CIESC Journal, 2022, 73(7): 2933-2943.

黄陆月, 刘畅, 许勇毅, 邢浩若, 王峰, 马双忱. CDI二维浓度传质模型的建立以及实验验证[J]. 化工学报, 2022, 73(7): 2933-2943.

Figures/Tables 13

Table 1 Comparison of pros and cons of CDI mass transfer model

名称	模型	优点	缺点
Biesheuvel等的模型	一维	理论模型的预测与离子去除步骤的实验结果一致性很高	离子解吸步骤的实验结果与模型不吻合，说明模型存在缺陷
Suss等的模型	一维	能预测随着时间的推移，浓度和电位在电极间隙和电极上的变化	不适合用于预测确切的电池性能；忽略了表面传导和电渗流的影响
Perez等的传质模型	一维	很好地预测了低流速和高流速下溶液的脱盐率	只适用于低浓度的溶液；使用了Nernst层近似
Hemmatifar等的模型	二维	模型结果与实验数据一致性较好；模型是充分模块化的	假设恒定的微孔电容不够精确；忽略了系统是动态变化的

Table 2 The parameters setting in 2D mass transfer model

R/Pa	T/K	d/m	z	F	D/(m²/s)	E/V	t₁	t₂	$η$ /%
8.314	298	0.005	1	96500	1.48×10^-9	1.2	0.623	0.97	100

Table 2 The parameters setting in 2D mass transfer model

R/Pa	T/K	d/m	z	F	D/(m²/s)	E/V	t₁	t₂	$η$ /%
8.314	298	0.005	1	96500	1.48×10^-9	1.2	0.623	0.97	100

Fig.1 The predicted curve of concentration vs distance by model

Fig.2 The predicted curve of concentration vs time by model

Fig.3 The predicted curve of concentration vs distance by modified model

Fig.4 The fitting curve of concentration change in vertical direction

Fig.5 Comparison of 2D model and dynamic experiment results

Fig.6 COMSOL model structure

Fig.7 Electric field intensity distribution by COMSOL simulation

Fig.8 Streamline distribution by COMSOL simulation

Fig.9 Concentration distribution in the X direction by COMSOL simulation

Fig.10 Concentration distribution in the Y direction by COMSOL simulation

Fig.11 Concentration distribution in the XY direction by COMSOL simulation

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