水电解制氢中气泡生长及磁场对气泡行为和两相流动特性影响

发布时间：2018-07-05 07:56

本文选题：电解水制氢 + 气液两相流　；参考：《重庆大学》2016年博士论文

【摘要】：氢气以其来源广泛、清洁燃烧、能量密度高等突出优点成为最有潜力的清洁能源之一,也是重要的食品化工原料。虽然目前水电解制氢在所有制氢手段中所占的比例并不高,但电解水制氢是目前不可替代的超纯氢来源和分布式能源构成部分,未来有着光明前景。采用电解水制氢还可以作为中间媒介,有效整合风能、太阳能等时域和地域性强的清洁能源构建持续清洁能源供应系统,实现氢能的更广泛应用。在如超大规模集成电路制造和浮法玻璃生产等行业中,与其他制氢方法相比,通过水电解制取高纯氢是一些工业用氢必要的制氢手段。电解过程的高能耗是制约水电解制氢发展的瓶颈,电解水产生1 Nm3氢气能耗为4.5~5.0 k Wh,效率在60%以下,因此如何强化水电解制氢,提高其电解效率非常必要。在水电解过程中,气相产物的管理是一项重要的工作。及时排除电极表面气相产物有利于电解槽能耗的降低。现有工业电解槽中主要依靠循环泵驱动电解液流动来排出气相产物。有报道表明,在磁场作用下,电解液中存在洛伦兹力引发的多尺度对流,利用磁场可驱散气相产物。但磁场在有气相存在条件下作用在电解质的机制还不清楚,如何强化这个磁场作用来达到提升电解效率还亟待研究。为分析磁场对水电解过程的影响及作用机制,本文在理论分析的基础上,通过实验和数值模拟相结合的方法,重点针对电极表面的气泡行为及磁场驱动下电极间的气液两相流动进行分析,主要包含以下几个方面的内容:1、通过数值模拟,基于Fluent计算平台,采用VOF(volume of fluid)模型对电极表面的析氢过程进行模拟。根据法拉第定律计算电极表面的氢组分的生成速率,建立了基于过饱和氢组分质量传递的气泡生长模型,通过UDF(user define function)接口编译到计算模型中,并进行了实验验证。研究还发现,在气泡成核与生长阶段,电极表面存在多种形式的对流作用,包括电解液中由于氢组分浓度梯度引发的对流和由于气泡界面扩张引发的电解液扰动。通过对不同对流形式下电极表面传质系数的计算,量化了单气泡演化过程对于局部传质的强化效果。2、在分析电极表面氢气泡演化过程的基础上,采用微电极和常规尺寸的局部疏水电极实验分析了外部磁场对于电极表面气泡行为的影响。在微电极表面,通过高速摄像记录了气泡的生长过程,给出了气泡生长曲线和磁场对于气泡生长的影响。分析了不同电流条件下,电极表面氢组分过饱和浓度的变化。采用光刻—电沉积的方法制作了局部疏水电极,并实验观测了气泡在局部疏水位置的生长和脱离行为特性。分析了导致疏水点处大气泡随机脱离的原因。对比磁场作用下微电极和常规尺寸电极表面气泡脱离行为的差别,并通过数值模拟的方法揭示了因micro-MHD流动使氢气泡周围压力分布变化而导致气泡行为改变的磁场作用微观机制。3、采用平行光亮铂电极,测试了磁场对电解槽电势差的影响。同时,基于Fluent计算平台,采用Euler-Euler模型,对磁场驱动下电极间的电解液流动方式和气相产物的分布规律进行了分析,揭示了因MHD驱动减小了电极间气相产物份额和电极表面气相覆盖度的磁对流影响电极电势差的物理机制。
[Abstract]:Hydrogen is one of the most potential clean energy sources with its wide source, clean combustion and high energy density. It is also an important raw material for food and chemical industry. Although the proportion of hydrogen production in all hydrogen making means is not high at present, hydrogen production by electrolysis is an irreplaceable source of ultra pure hydrogen and a distributed source of energy. The future has a bright future. The use of electrolysis water to produce hydrogen can also be used as intermediate medium, effective integration of wind energy, solar energy and other time-domain and regional strong clean energy to build a continuous clean energy supply system to achieve a more extensive application of hydrogen energy. In such industries as large scale integrated circuit manufacturing and float glass production, and other systems Compared with hydrogen, making high pure hydrogen by water electrolysis is a necessary means of hydrogen production for industrial hydrogen. The high energy consumption of electrolysis process is the bottleneck restricting the development of hydrogen production by electrolysis. The energy consumption of 1 Nm3 hydrogen is 4.5~5.0 K Wh and the efficiency is below 60%. Therefore, it is necessary to strengthen the water electrolysis and improve the efficiency of electrolysis. In the process of solution, the management of gas phase products is an important work. Eliminating the gas phase products on the surface of the electrode in time is beneficial to the reduction of the energy consumption of the electrolyzer. The existing industrial electrolysis cell mainly relies on the circulation pump to drive the electrolyte flow to expel the gas phase products. It is reported that under the effect of the magnetic field, there are many feet caused by Lorenz force in the electrolyte. It is not clear that the mechanism of the magnetic field acting on the electrolyte under the presence of gas is not clear. How to strengthen the effect of this magnetic field to improve the electrolysis efficiency is still urgently needed to be studied. The method combined with numerical simulation focuses on the bubble behavior on the surface of the electrode and the analysis of gas-liquid two phase flow between the electrodes driven by the magnetic field. The main contents are as follows: 1, the hydrogen evolution process on the electrode surface is simulated by the VOF (volume of fluid) model by numerical simulation and based on the Fluent computing platform. According to Faraday's law, the formation rate of hydrogen components on the surface of the electrode is calculated. A bubble growth model based on the mass transfer of the supersaturated hydrogen component is established. The model is compiled into the calculation model by UDF (user define function) interface, and the experimental verification is carried out. Convection, including the convection caused by the concentration gradient of the hydrogen component in the electrolyte and the electrolyte disturbance caused by the expansion of the bubble interface. By calculating the mass transfer coefficient of the electrode surface under different convection forms, the enhanced effect of the single bubble evolution process for local mass transfer was quantified, and the evolution process of hydrogen bubbles on the surface of the electrode was analyzed. On the basis of the microelectrode and the conventional size local hydrophobic electrode, the effect of the external magnetic field on the bubble behavior on the surface of the electrode was analyzed. The growth process of the bubble was recorded on the microelectrode surface by a high-speed camera. The bubble growth curve and the influence of the magnetic field on the growth of the bubble were given. A local hydrophobic electrode was made by photolithography and electrodeposition, and the growth and disengagement behavior of the bubbles in the local hydrophobic position were observed. The reasons for the random separation of the large bubbles at the hydrophobic point were analyzed. The surface gas of the microelectrode and the conventional electrode was compared with the magnetic field. The difference in bubble separation behavior was obtained by numerical simulation, and the micromechanism.3 of the magnetic field action caused by the change of the pressure distribution around the hydrogen bubble caused by the micro-MHD flow was revealed. The effect of the magnetic field on the potential difference of the electrolyzer was tested by the parallel bright platinum electrode. At the same time, the Fluent calculation platform was used for Euler-Euler. The model, the flow mode of electrolyte between the electrodes driven by the magnetic field and the distribution of the gas phase products are analyzed. The physical mechanism of the influence of the magnetic convection on the potential difference between the gas phase and the surface gas coverage of the electrode has been revealed by the MHD drive.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ116.21

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