电场对竖直微槽润湿及毛细流动特性影响

doi:10.11949/0438-1157.20220427

摘要/Abstract

摘要：

竖直微槽群毛细结构广泛应用在重力热管、蒸发器等散热设备内，但受重力等因素影响易达到毛细极限。引入电场的主动强化方式来提高竖直微槽的毛细极限，并通过实验和建立数学模型研究电场对竖直微槽内液体润湿及毛细流动特性的影响。结果表明，电场可以提高竖直微槽内液体润湿高度，当电场为5.0 kV时与无电场时相比，润湿高度强化比可达到30.0%。同时，电场作用下流体在微槽道内的毛细润湿流动呈分段效应：润湿流动初期，润湿高度与时间的1/2次方呈线性关系，即h-t^1/2，润湿速率与润湿高度的倒数呈线性关系，即v-1/h；润湿流动中后期，润湿高度与时间的1/3次方呈线性关系，即h-t^1/3，润湿速率与润湿高度平方的倒数呈线性关系，即v-1/h²，且润湿速率随时间呈下降趋势。

关键词: 微通道, 流动, 数学模型, 电场, 润湿高度, 润湿速率

Abstract:

Vertical microgroove capillary structures are widely used in heat transfer devices such as gravity heat pipes, evaporator and other heat transfer devices. The capillary rise in microgrooves attracts increasing attentions since it affects capillary limit significantly, which is easy to be reached due to the structure, gravity and other factors, and has a great influence on the heat transfer performance of the heat pipes. Thus, to improve the capillary limit of the vertical microgrooves, electric field, as one of the active enhanced technology, is introduced to the experiment system. The influence of the electric field on the wetting and capillary flow characteristics of the liquid in the vertical microgroove is studied experimentally and a mathematical model is established to understand the wetting and flow mechanisms of liquid in the vertical microgrooves under the action of electric field. The results show that the electric field can improve the wetting height of the liquid in the vertical microgrooves. When the electric field is 5.0 kV, the wetting height enhancement ratio can reach 30.0% compared with no electric field. Besides, the liquid wetting and capillary flow in the microgrooves under electric field are segmented: at the beginning of the capillary wetting flow, the square of the wetting height is linearly related to time, that is, h-t^1/2, and at the long-term of the wetting flow, the wetting height is linearly related to the 1/3 power of time, that is, h-t^1/3. Besides, the relationship between the wetting velocity and the wetting height first follows v-1/h, then is governed by v-1/h². Moreover, the wetting velocity decreases with time.

Key words: microchannels, flow, mathematical modeling, electric field, wetting height, wetting velocity

中图分类号:

TQ 021.1

董宜放, 于樱迎, 胡学功, 裴刚. 电场对竖直微槽润湿及毛细流动特性影响[J]. 化工学报, 2022, 73(7): 2952-2961.

Yifang DONG, Yingying YU, Xuegong HU, Gang PEI. Electric field effect on wetting and capillary flow characteristics in vertical microgrooves[J]. CIESC Journal, 2022, 73(7): 2952-2961.

图/表 13

图1 微槽群测试单元

Fig.1 Microgrooves testing unit

图 2 微槽群实验件截面图

Fig.2 Cross section of microgrooves

图3 电场布置情形1—负极(接地电极);2—高压电源;3—微槽群实验件;4—高压电极;5—微槽群固定装置

Fig.3 Electric field arrangement

表1 工质物性

Table 1 Physical properties

变量	数值
液体密度 $ρ l$ /(kg/m³)	997
液体表面张力 $σ l$ /(N/m)	0.072
液体动力黏度 $μ l$ /(Pa·s)	8.9×10^-4
液体介电常数 $ε l$ /(C²/(N·m²))	78.4 $ε 0$
蒸汽介电常数 $ε v$ /(C²/(N·m²))	$ε 0$ ，8.854×10^-12
电导率 $σ e$ /(S/cm)	<1×10^-6

表1 工质物性

Table 1 Physical properties

变量	数值
液体密度 $ρ l$ /(kg/m³)	997
液体表面张力 $σ l$ /(N/m)	0.072
液体动力黏度 $μ l$ /(Pa·s)	8.9×10^-4
液体介电常数 $ε l$ /(C²/(N·m²))	78.4 $ε 0$
蒸汽介电常数 $ε v$ /(C²/(N·m²))	$ε 0$ ，8.854×10^-12
电导率 $σ e$ /(S/cm)	<1×10^-6

图 4 润湿高度数据处理

Fig.4 Image processing of the wetting height

图5 4.0 kV时微槽润湿高度随时间的变化

Fig.5 Wetting height variation with time under 4.0 kV

图6 不同电场作用下微槽内润湿高度随时间的变化

Fig.6 Wetting height variation with time under different electric field

图7 有无电场作用时毛细流动初期h2-t曲线

Fig.7 h2-t curve at the beginning of the capillary flow with or without electric field

图8 不同电场下微槽最大润湿高度沿x方向分布

Fig.8 Distribution of maximum wetting height along with x direction under different electric fields

图9 不同电场下最大润湿高度强化比对比

Fig.9 Comparison of EHD enhanced ratio of maximum wetting height under different electric fields

图10 不同电场作用下微槽内液体润湿速率与时间(a)和润湿高度(b)的关系

Fig.10 Wetting velocity variation with time (a) and wetting height (b) under different electric fields

图11 有无电场时微槽润湿初期和中后期v-1/h曲线

Fig.11 v-1/h curve for the beginning and long-term period under different electric fields

图12 不同电场下平均润湿速率强化比对比

Fig.12 Comparison of EHD enhanced ratio of wetting velocity under different electric fields

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