Research on liquid film flow characteristics of vertical porous plate

doi:10.11949/0438-1157.20201737

Abstract

Abstract:

The pore structure is widely used in mass transfer tower packing, which has a great influence on the liquid film flow and mass transfer behavior on the packing. However, no relevant research has been conducted on the wetted area and wave characteristics of the porous plates. In this work, three-dimensional simulations of the liquid film flow on the vertical smooth and porous plates were carried out and verified by experimental results. The effects of the holes on the liquid film flow behavior were studied. The results show that the flow patterns on the vertical porous plates and the smooth plate are almost the same, namely droplet, rivulet, and closed film flow. Dry holes will hinder the spreading of the liquid film, while the wet holes will promote it. Compared to the smooth plate, the liquid film on porous plates has sinuous waves, which will affect the distribution of film thickness and the wave velocity. The sinuosity of liquid film thickness and the horizontal velocity will increase with the increase of hole diameter, while the vertical flow velocity will decrease with the increase of hole diameter. When the hole diameter increases to certain value, capillary waves will appear on the liquid film in the hole, which will greatly enhance the horizontal wave velocity and reduce the vertical velocity in the hole. When the hole depth is 0.5 mm, a hole with a diameter of 4 mm will produce capillary waves. However, if the hole diameter continues to increase to a critical value, the liquid film will rupture. There are vortices on the in-hole and gas side of the porous plate, which can promote the internal liquid exchange and enhance the gas side disturbance, thus enhance mass transfer.

Key words: liquid film, hole plate, wettability, wave characteristic, flow pattern

摘要：

孔结构被广泛应用于传质塔填料中，对填料上的液膜流动和传质行为影响较大。对竖直光板和多孔板上的液膜流动进行了三维模拟，并通过实验验证了模拟的准确性。通过模拟研究了孔结构对液膜流动特性的影响。结果表明，干燥孔会阻碍液膜的铺展，而润湿孔促进液膜的铺展。与光板相比，多孔板上的液膜具有起伏波，这将影响液膜的厚度分布和速度分布。液膜厚度波动和水平方向的速度波动随着孔径的增加而增加，而竖直流动方向的速度随着孔径的增加而降低。当孔径增加到一定值时，毛细波将出现在孔中的液膜中，这大大增加液膜水平方向上的波动速度，而降低流动方向上的速度。当孔径继续增加到临界值时，液膜将破裂。多孔板上孔内和气侧区域存在涡旋，能够促进内部液体交换和增大气侧扰动，从而增强传质能力。

关键词: 液膜, 孔板, 润湿性, 波动特性, 流型

CLC Number:

TQ 026.2

Yeming ZHU, Jinping LIU, Xiongwen XU, Dandan ZHU. Research on liquid film flow characteristics of vertical porous plate[J]. CIESC Journal, 2021, 72(8): 4081-4092.

朱业铭, 刘金平, 许雄文, 朱丹丹. 竖直多孔平板上液膜流动特性的研究[J]. 化工学报, 2021, 72(8): 4081-4092.

Figures/Tables 16

Fig.1 Schematic diagram of calculation domain

Table 1 Model boundary conditions

Zone name	Boundary conditions
inlet	velocity-inlet(UDF, Nusselt velocity distribution)
outlet	pressure-outlet (0 Pa)
top	symmetry
plate	no-slip wall with contact angle
side	no-slip wall with contact angle
hole	symmetry

Fig.2 Experimental setup

Fig.3 Equilibrium contact angle between water and aluminium plate

Fig.4 Photo by infrared thermal imager

Table 2 Mesh size of nonporous and porous plates

光板			H=0.25 mm) 多孔板，(D=1 mm,S=1 mm,
网格数/万	最小网格体积/mm³	最大网格体积/mm³	网格数/万	最小网格体积/mm³	最大网格体积/mm³
5.2	0.1	0.35	43	0.0029	0.082
11.8	0.022	0.16	91	0.0013	0.058
22.5	0.016	0.12	143	0.0004	0.056
55.7	0.0065	0.065	200	0.0004	0.04

Fig.5 Grid independence

Fig.6 Comparison of wetted area between experiment and simulation

Fig.7 Comparison of liquid film coverage between smooth plate and porous plate

Fig.8 Comparison of flow patterns between smooth plate and porous plate

Fig.9 Phase interfaces with different diameters

Fig.10 Closed film morphology with different diameters

Fig.11 Closed film thickness distribution with different diameters

Fig.12 Experiments of liquid film flow pattern with different diameter

Fig.13 Velocity distribution of closed film

Fig.14 Streamline of closed film

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