固体表面温度对冻结液滴的相变过程与表面润湿特性的影响

doi:10.16085/j.issn.1000-6613.2021-2277

摘要/Abstract

摘要：

通过液滴可视化实验，发现并归纳了冻结液滴在不同基底温度下于铝板表面融化过程的动态表面润湿特性，结合力学分析，总结了液滴润湿面积、体积、接触角等润湿参数与相变时间之间的变化规律。实验结果表明：液滴的润湿性主要受重力、表面张力、热毛细力的影响，重力对液滴的横向扩散促进作用、表面张力与热毛细力受底板温度影响具有抑制液滴润湿过程的作用；两种不同条件下，冻结液滴高度变化规律相同，随着融化的进行，液滴高度骤降，然后缓慢降低；不同冻结条件下，冻结液滴的润湿过程主要发生在融化初始阶段，重力促进液滴的润湿过程，液滴接触角处于65°~85°之间，而在润湿后阶段，接触角减小，重力的作用减弱，表面张力的作用增强，液滴的扩散进程受阻，体积下降的趋势也变缓；不同升温条件下，冻结液滴的润湿过程几乎没有发生，热毛细力与表面张力在润湿过程中占据主导性，随着基底温度的升高，液滴内部与三相线温差逐渐增大，Ma数呈增加的趋势，数值由1802增至22876，热毛细力始终抑制液滴的运动。

关键词: 液滴, 熔化过程, 润湿性, 接触角, 热毛细力

Abstract:

In this paper, through the droplet visualization experiment, the dynamic surface wetting characteristics of the freezing droplets on the surface of the aluminum plate at different substrate temperatures were summarized. Based on mechanical analysis, the article summarizes the changing laws of wetting parameters such as droplet wetting area, volume, contact angle and phase transition time. Experimental results showed that the wettability of droplets is mainly affected by gravity, surface tension and thermal capillary force. Gravity promoted the lateral spread of droplets. The surface tension and thermal capillary force were affected by the temperature of the bottom plate, and have the effect of inhibiting the diffusion process of the droplets. Under the two different conditions, the change of the height of the frozen droplets was the same. As the melting progresses, the height of the droplets dropped sharply and then slowly decreases. Under different freezing conditions, the infiltration of frozen droplets in the initial stage of melting was very obvious. At this stage, gravity promotes the wettability of the droplets, and the contact angle of the droplets was between 65° and 85°. In the later stage, the decrease of contact angle led to the weakening of gravity and the increase of surface tension, which hindered the spread of droplets and slows down the trend of volume reduction. Under different heating conditions, the droplets hardly undergo diffusion movement. Thermal capillary force and surface tension dominated the wetting process. As the substrate temperature increases, the temperature difference between the inside of the droplet and the three-phase line gradually increased, and the number of Ma increased from 1802 to 22876. The capillary force always restrained the movement of the droplet.

Key words: droplet, melting process, wettability, contact angle, thermal capillary force

中图分类号:

TK124

张哲, 郎元路, 陈佳楠, 吴巧燕, 计宏伟, 李星泊, 马妍, 陶柳倩, 王瑾悦. 固体表面温度对冻结液滴的相变过程与表面润湿特性的影响[J]. 化工进展, 2022, 41(9): 4605-4617.

ZHANG Zhe, LANG Yuanlu, CHEN Jia’nan, WU Qiaoyan, JI Hongwei, LI Xingbo, MA Yan, TAO Liuqian, WANG Jinyue. Analysis of effect of solid surface temperature on phase transition process and surface wetting characteristics of frozen droplets[J]. Chemical Industry and Engineering Progress, 2022, 41(9): 4605-4617.

图/表 26

图1 液滴熔融实验装置1—恒温水浴循环箱；2—LED光源；3—DSA-30型液滴形状分析台；4—观测腔；5—水冷头；6—升降部件；7—移动部件；8—CCD高速相机；9—计算机操控主机；10—显示屏；11—GP-10型温度采集仪；12—半导体制冷片

图2 液滴滴定

表1 DSA-30液滴形状观测实验台组件及相关参数

组件名称	参数名称	参数值及名称
摄像头	型号	Allied Vision Stingray F-046B
	精度/μm	8.3
	最大帧率/帧·s^-1	61
	变焦倍率	6.5
	传感器型号	Sony ICX415
	接触角精度/（°）	0.3
	接触角分辨率/（°）	0.01
光源	型号	单色LED照明
观测舱	规格	150mm×150mm×60mm

图3 液滴温度与接触角测量

图4 液滴形貌特征

图5 液滴冻结阶段的形态变化图像（T=-4℃）

图6 液滴融化阶段的形态变化图像（T=-4℃）

图7 液滴冻结阶段的形态变化图像（T=-8℃）

图8 液滴融化阶段的形态变化图像（T=-8℃）

图9 液滴相变流程

图10 融化阶段的形态变化图像（T=16℃）

图11 融化阶段的形态变化图像（T=20℃）

图12 液滴润湿过程中的表面变化

图13 液滴润湿过程示意图（俯视）

图14 润湿表面微观示意图

图15 表面液滴润湿过程受力分布

表2 去离子水的表面张力

基底温度/℃	σ/mN∙m^-1
6	74.78
11	74.07
16	73.34
20	72.75
24	72.59

图16 不同基底温度下的相变时间规律

图17 液滴高度变化

图18 接触角动态变化

图19 液滴润湿面积变化

图20 液滴体积变化

图21 液滴内部温度变化（升温条件）

表3 液滴温度差

基底温度/℃	∆T/℃
6	-0.1
11	-0.2
16	-0.5
20	-0.7
24	-0.9

表4 去离子水的热物性参数

参数	6℃				24℃
ρ/g∙cm^-3	1
c_p /kJ∙kg^-1∙℃^-1	4.186
k/W∙cm^-3	0.548	0.582	0.592	0.60	0.608
μ/10^-3 N∙s∙m^-2	1.4728	1.2713	1.1111	1.0050	0.9142

图22 Ma数与温差变化规律（升温条件）

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