Evaporation characteristics of water film over collecting electrode in high-voltage electrical field

doi:10.11949/j.issn.0438-1157.20180546

Abstract

Abstract:

Based on the polarization and force characteristics of water molecules in the electrostatic field, the transport process of water molecules in the liquid film on the surface of the plate in hot dry flue gas is analyzed. Besides, the effect of electrical field parameters on the evaporation characteristics and the dominant influence factors in the evaporation process under multi-field coupling effect (temperature, velocity and electrical field) were all studied. Eventually an evaporation model was proposed. The results showed that the ion wind is the main power source in the process of water film evaporation and the electric evaporation rate is 6.7 higher than the natural evaporation rate (25 kV). Water film evaporated at a constant rate and there was a positive relationship between evaporation rate and electrical field intensity. Evaporation process can be inhibited by the dissolved solute in the water film and the process was divided into two periods: constant rate period and falling rate period. The solute precipitated firstly on the water film surface. Under the coupling effect of velocity and electrical field, the evaporation rate increases slowly (U＜20 kV) and then increases rapidly (U＞20 kV) with increasing the voltage, velocity and voltage is the main influence factor in this two processes respectively. Under the coupling effect of temperature and electrical field, the evaporation rate is higher than the superposition of these two single fields. All these results can provide a theoretic support for the water film forming and consumption, humidity distribution in the unsaturated flue gas.

Key words: evaporation, transport processes, film, flue gas, humidification, electric polarization, electrical field

摘要：

以静电场中水分子的极化和受力特性为基础，对热干烟气中极板表面液膜内水分子输运过程进行分析。考察了电场特征、液膜物性对静态高压电场中液膜蒸发特性的影响并提出了蒸发模型；同时研究了多场（温度、速度和静电）耦合作用下液膜蒸发过程中的主导作用机制。结果表明：离子风为静态高压电场中液膜蒸发的主要动力，蒸发速率是自然蒸发的6.7倍（25 kV）。液膜蒸发为等速过程，蒸发速率与电场强度呈正相关关系；液膜加入溶质，蒸发过程受抑制，蒸发模型变为等速和降速两个过程，最终液膜表面析出溶质；流场耦合静电场作用下，液膜蒸发速率随电压升高先缓慢上升（U＜20 kV）后快速上升（U＞20 kV），流速和电压分别是这两阶段的主要影响因素；温度场耦合静电场作用下，蒸发速率大于单场叠加数值。研究结果为热干烟气中极板表面稳定成膜、系统水耗及空间电场中温湿度分布等问题的研究提供理论支撑。

关键词: 蒸发, 传递过程, 膜, 烟道气, 增湿, 电极化, 静电场

CLC Number:

TK 16

Jingcai CHANG, Xiang WANG, Peng WANG, Lin CUI, Jun LI, Xin ZHANG, Chunyuan MA. Evaporation characteristics of water film over collecting electrode in high-voltage electrical field[J]. CIESC Journal, 2019, 70(3): 865-873.

常景彩, 王翔, 王鹏, 崔琳, 李军, 张鑫, 马春元. 静电场中极板表面液膜蒸发特性研究[J]. 化工学报, 2019, 70(3): 865-873.

Figures/Tables 16

Fig.1 Experimental setup

Fig.2 Schematic of anode and cathode electrode

Fig.3 Force analysis of water film in electrical field

Fig.4 Force analysis of water film in electrical field

Fig.5 Effect of voltage on water film evaporation characteristics

Fig.6 Effect of voltage on water film mass loss rate

Fig.7 Effect of interelectrode distance on water film evaporation characteristics

Fig.8 Effect of interelectrode distance on water film mass loss rate

Fig.9 Effect of electrode interval on water film evaporation characteristics

Fig.10 Effect of electrode resistivity on water film evaporation characteristics

Fig.11 Distribution of electric field

Fig.12 Effect of water film properties on evaporation characteristics

Fig.13 Effect of concentration of water film on evaporation characteristics

Fig.14 Crystals on water film surface

Fig.15 Effect of coupling action of velocity and electrical field on water film mass loss rate

Fig.16 Effect of coupling action of temperature and electrical field on water film mass loss rate

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