Generation and evolution of bubbles in channels of bipolar plates of alkaline water electrolyzers for producing hydrogen

doi:10.11949/0438-1157.20250180

Abstract

Abstract:

In alkaline water electrolyzers, the generation and coalescence of gas bubbles on the bipolar plates will change the flow pattern of electrolytes and affect the velocity and temperature fields of the electrolytes, leading to local overcurrent and hot spots, further reducing the overall electrolysis efficiency. The gas-liquid two-phase flow state in the plate channel is simulated by the level set coupled volume of fluid (CLS-VOF) numerical technique. The generation, growth, and detachment of individual bubbles on the surface of the bipolar plate and the coalescence between bubbles are investigated in detail. The effects of current density, electrolyte flow rate, and cross-sections of channels on the gas content, surface gas coverage, and pressure drop in the polar plate channel are explored. The results showed that the bubble size, gas content, and surface gas coverage increase with the increase of current density and decrease with the growth of electrolyte flow rate.

Key words: alkaline water electrolyzers, hydrogen production, bipolar plates, channel, bubble, two-phase flow

摘要：

碱水制氢电解槽极板上气泡的生成和合并会改变电解液的流动状态，影响电解液的速度场、温度场分布，导致局部过电流和热点出现，进而降低电解槽的电解效率。采用水平集耦合流体体积（CLS-VOF）数值技术对极板通道中的气液两相流动状态进行了模拟研究，考察了气泡在极板通道表面上的生成、成长和脱落过程，以及气泡之间的合并规律，研究了电流密度、电解液流量和通道截面形状对极板通道中含气率、表面气体覆盖率和压力降的影响。结果表明，气泡合并尺寸、含气率、表面气体覆盖率随着电流密度增大而增大，随着电解液流量增大而减小。

关键词: 碱水电解槽, 制氢, 双极板, 通道, 气泡, 两相流

CLC Number:

TQ 028.8

Jiaqing ZOU, Zhaoyu ZHANG, Jianguo ZHANG, Boyu ZHANG, Dingsheng LIU, Qing MAO, Ting WANG, Jianjun LI. Generation and evolution of bubbles in channels of bipolar plates of alkaline water electrolyzers for producing hydrogen[J]. CIESC Journal, 2025, 76(9): 4786-4799.

邹家庆, 张肇钰, 张建国, 张博宇, 刘定胜, 毛庆, 王挺, 李建军. 碱水制氢电解槽极板通道中气泡的生成及演化性质[J]. 化工学报, 2025, 76(9): 4786-4799.

Figures/Tables 26

Fig.1 Schematic diagrams of the simulations: (a) polar plate model; (b) boundary conditions; (c) geometry dimension

Table 1 Physical parameters and operation conditions （current density of 0.5 A/cm2）

参数	数值
工作温度/K	298
工作压力/Pa	101325
KOH溶液密度^[26]/（kg/m³）	1216.11
O₂密度/（kg/m³）	1.29
5 mol/L KOH动力黏度^[27]/（kg/(m·s)）	1.6549×10^-3
O₂动力黏度/（kg/(m·s)）	1.919×10^-5
表面张力^[28]/（N/m）	0.0871
KOH入口流量/（ml/min）	15
出口表压/Pa	0
接触角^[29]/（°）	150

Fig.2 Schematic diagram of different types of channel structures

Table 2 Variation of bubble size with mesh size at B4 and B5 at 0.7 ms

网格尺寸/mm	网格总数/个	B4气泡y方向尺寸/mm	B5气泡y方向尺寸/mm
0.030	528160	0.475	0.474
0.025	741280	0.480	0.488
0.020	2000000	0.483	0.482

Fig.3 Comparisons of bubble shapes between the experiment[30] (left) and the present simulation (right) for model validation

Fig.4 Bubble generation process at orifice B1 (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 1.0)

Fig.5 Bubble generation process at orifice B1 (J = 0.5 A/cm2, QL = 5 ml/min, θ = 150°, W/H = 1.0)

Fig.6 Effects of current density and electrolyte flow rate on the detachment time of bubbles at B1 hole (W/H = 1.0)

Fig.7 Generation process of a bubble at orifice B1 (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 0.5)

Fig.8 Generation process of a bubble at orifice B1 (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 2.0)

Fig.9 Generation process of a bubble at orifice B1 (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, trapezoidal cross-section channel)

Fig.10 Variation of bubble volume with time (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 1.0)

Fig.11 Detachment and coalescence of bubbles at orifices B1—B9 (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 1.0)

Fig.12 Variation of bubble volume with time (J = 3.0 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 1.0)

Fig.13 Detachment and coalescence of bubbles at orifices B1—B9 (J = 3.0 A/cm2, QL = 15 ml/min, θ = 150°, W/H = 1.0)

Fig.14 Detachment and coalescence of bubbles at B6 (J = 0.5 A/cm2, QL = 10 ml/min, θ = 150°, W/H = 1.0)

Fig.15 Change in bubble volume with time (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°)

Fig.16 Variation of gas fraction with time under different current densities (W/H = 1.0, QL = 15 ml/min, θ = 150°)

Fig.17 Variation of surface gas fraction on GDLwith time under different current densities (W/H = 1.0, QL = 15 ml/min, θ = 150°)

Fig.18 Pressure drop over time (W/H = 1.0, QL = 15 ml/min, θ = 150°)

Fig.19 Variation of gas fraction with time under different electrolyte flow rates (W/H = 1.0, J = 0.5 A/cm2, θ = 150°)

Fig.20 Variation of surface gas fraction on GDL with time under different electrolyte flow rates (W/H = 1.0, J = 0.5 A/cm2, θ = 150°)

Fig.21 Pressure drop over time (W/H = 1.0, J = 0.5 A/cm2, θ = 150°)

Fig.22 Variation of gas fraction with time in channels with different cross-sections (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°)

Fig.23 Variation of surface gas coverage with time in channels with different cross-sections (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°)

Fig.24 Pressure drop over time (J = 0.5 A/cm2, QL = 15 ml/min, θ = 150°)

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