Liquid-liquid mixing characteristics of Bunsen reaction products in microchannels

doi:10.11949/0438-1157.20240918

Abstract

Abstract:

In order to solve the key technical problems of the thermochemical sulfur-iodine (S-I) cycle and the H₂S splitting cycle for hydrogen production, the mixing characteristics of the Bunsen reaction products (HI/H₂SO₄/H₂O/toluene liquid-liquid two-phase mixture) in the microchannel were investigated by numerical simulation using ANSYS-FLUENT. The relationship between the two-phase mixing in the microchannel and the inlet mode, inlet flow rate, and two-phase flow rate ratio was systematically analyzed, and the strengthening effect of adding obstacles in the microchannel on the two-phase mixing was discussed. The results show that the mixing is more effective when two phases enter the channel in an upper and lower stratified manner. Increasing the flow rates of two phases can significantly increase the mixing degree but the channel pressure loss increases accordingly. When the two-phase flow rate ratio is 1∶1 and the flow rate is 0.035 m/s, the mixing degree reaches the maximum value of 88.72% while the pressure loss is relatively low. Setting obstacles inside the channel can form periodic eddy currents, which can effectively shorten the two-phase mixing time and strengthen the two-phase mixing. Compared to semicircular barriers, rectangular barriers provide a greater promotion of mixing but have a greater pressure loss.

Key words: thermochemical cycle for hydrogen production, Bunsen reaction products, two-phase flow, mixing, microchannels, numerical simulation

摘要：

为了解决热化学硫碘循环和硫化氢化学反应循环制氢的关键技术问题，提出使用ANSYS-FLUENT对Bunsen反应产物（HI/H₂SO₄/H₂O/甲苯液-液两相混合物）在微通道内的流动混合特性进行数值模拟研究。系统分析了微通道内两相混合与入口方式、入口流速、两相流速比的关系，探讨了微通道内加入障碍物后对两相混合的强化作用。结果表明，当两相以上下分层方式进入通道时，混合效果更佳；提高流速可以显著增大两相流的混合程度，但是通道压力损失随之增加；两相流速比为1∶1、流速为0.035 m/s时，混合程度达到最大值88.72%，同时压力损失相对较小；在通道内部设置障碍物可以形成周期性的涡流，有效缩短两相混合时间，强化两相混合。与半圆形障碍物相比，矩形障碍物可以更有效地促进两相混合，但是压力损失更大。

关键词: 热化学循环制氢, Bunsen反应产物, 两相流, 混合, 微通道, 数值模拟

CLC Number:

TQ 027.1

Ke ZHANG, Weijie REN, Mengna WANG, Kaifeng FAN, Liping CHANG, Jiabin LI, Tao MA, Jinping TIAN. Liquid-liquid mixing characteristics of Bunsen reaction products in microchannels[J]. CIESC Journal, 2025, 76(2): 623-636.

张珂, 任维杰, 王梦娜, 范凯锋, 常丽萍, 李佳斌, 马涛, 田晋平. Bunsen反应产物在微通道中的液-液两相混合特性[J]. 化工学报, 2025, 76(2): 623-636.

Figures/Tables 28

Fig.1 3D structure of the serpentine microchannel

Table 1 Two-phase physical property parameters

液相	密度/(kg/m³)	动力黏度/(Pa·s)	表面张力/(mN/m)
HI/H₂SO₄混酸	1080.3	9.067×10^-4	28.9
甲苯	860.4	5.345×10^-4	55.4

Fig.2 Schematic diagram of the experimental setup

Table 2 Simulation conditions

边界条件	边界类型/名称	参数设置
入口	平均速度入口	0.014 m/s
出口	自由出流出口	0 Pa
壁面	无滑移壁面	—
对称轴	AXIS	—

Table 3 Mesh size

网格划分方案	全局网格尺寸	网格单元数/个
方案1	0.35	1433700
方案2	0.4	948300
方案3	0.5	487872
方案4	0.6	278620
方案5	0.8	149523

Fig.3 Grid diagram of the channel

Fig.4 Effect of mesh number on the mixing degree

Fig.5 Effect of different time steps on the mixing degree

Fig.6 Comparison of the flow patterns in the simulation and the validation experiment

Fig.7 Cloud images of two-phase volume proportion in the channel of solution 1

Fig.8 Cloud images of two-phase volume fraction distribution of solution 2

Fig.9 Variations of the mixing effect at different entry modes

Fig.10 Cloud images of pressure distribution of fluid in channel

Table 4 Pressure losses of the channel at different inlet modes

方案类型	压力损失/Pa
方案1	174.28
方案2	166.52

Fig.11 Variations of the mixing effect at different velocity ratios

Fig.12 Variations of the mixing degree at different flow rates of two phases

Table 5 Pressure losses of the channelat different flow rates

流速/(m/s)	压力损失/Pa
0.014	172.85
0.035	296.53
0.070	498.26
0.140	1087.72
1.400	29786.82

Table 6 Pressure losses of the channel at different flow ratios

两相流速比	两相流速/(m/s)		压力损失/Pa
两相流速比	甲苯	混酸	压力损失/Pa
1∶3	0.014	0.042	285.69
1∶2	0.014	0.028	215.36
1∶1	0.014	0.014	142.29
1∶0.5	0.014	0.007	53.94

Fig.13 Parameter diagram of rectangular obstacle

Fig.14 Cloud images of two-phase volume ratio and velocity flow diagrams at different obstacle heights (Ⅰ: H=1 mm; Ⅱ: H=2 mm; Ⅲ: H=2.5 mm)

Table 7 Mixing degrees and pressure losses at different obstacle heights

障碍物高度/mm	混合程度/%	压力损失/Pa
1	90.22	81.14
2	97.41	89.23
2.5	99.85	157.16

Fig.15 Cloud images of two-phase volume ratio and velocity flow diagrams at different obstacle widths (Ⅰ: W=1 mm; Ⅱ: W=2 mm; Ⅲ: W=3 mm)

Table 8 Mixing degrees and pressure losses at different obstacle widths

障碍物宽度/mm	混合程度/%	压力损失/Pa
1	97.28	89.15
2	97.41	90.57
3	97.46	93.26

Fig.16 Cloud images of two-phase volume ratio and velocity flow diagrams at different obstacle separation distances (Ⅰ: D=4 mm; Ⅱ: D=6 mm; Ⅲ D=8 mm)

Table 9 Mixing degrees and pressure losses at different obstacle separation distances

障碍物间距/mm	混合程度/%	压力损失/Pa
4	98.62	99.40
6	97.41	89.52
8	96.29	87.11

Fig.17 Semicircular obstruction layout diagram

Fig.18 Cloud images of two-phase volume ratio and velocity flow diagrams at different semicircular obstacle radius (Ⅰ: R=1 mm; Ⅱ: R=2 mm; Ⅲ: R=2.5 mm)

Table 10 Mixing degrees and pressure losses at different semicircular obstacle radius

半圆形障碍物半径/mm	混合程度/%	压力损失/Pa
1	89.40	81.12
2	95.84	83.32
2.5	97.68	94.22

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