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Vibration Promotes Mass Transfer of Products in Photoelectrochemical Water Splitting by Enhancing Forced Convection

JOURNAL OF PHYSICAL CHEMISTRY C 2025年第11期129卷 5369-5382页

作者： Nie, Tengfei Xu, Qiang She, Yonglu Luo, Xinyi Wang, Mengsha Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Improving the productivity of photoelectrochemical water splitting hinges on discovering a viable method to facilitate bubble release from the surface of the photoelectrode, which, in turn, enhances the mass transfer of the resulting products. In this study, an experimental platform for photoelectrochemical water splitting to produce hydrogen by a coupled vibration system was built to realize the visualization of bubble behavior. By applying vibration to the electrode through a vibration exciter, this work explored how amplitude and frequency affect the photocurrent and geometric parameters during the bubble evolution process on the photoelectrode surface. Based on the expression of bubble coverage and gas evolution efficiency, mass transfer coefficients of gas products were deduced and calculated. The results showed that the increase in amplitude will increase the onset potential of nucleation, reducing the possibility of nucleation. Increasing the amplitude and frequency helps to release the bubbles from the electrode surface. For stationary electrodes, the mass transfer of gas products mainly depends on single-phase natural microconvection. For the vibrating electrode, macroscopic forced convection plays a dominant role. In this experiment, the average total mass transfer coefficient after applying vibration to the electrode can reach 11.16 x 10-5 m/s, which is about 7.6 times the mass transfer coefficient under static conditions. Therefore, vibration can significantly improve the reaction efficiency and mass transfer during the water splitting process for hydrogen generation.

关键词： Forced convection

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Size Effects on Bubble Dynamics during Photoelectrochemical Water Splitting

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ACS NANO 2025年第8期19卷 8200-8211页

作者： Li, Jinfeng Xu, Qiang Luo, Xinyi Nie, Tengfei Wang, Mengsha She, Yonglu Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

The rapid bubble removal from electrodes diminishes the reaction resistance within photoelectrochemical water splitting, and the coalescence between bubbles accelerates their detachment. To delve into the size effects on bubble coalescence dynamics, the Marangoni effect is utilized as a noninvasively controlling means of bubble sliding and coalescence. The study reveals that the encounter of capillary waves induces bubble detachment. A quantitative correlation has been established to elucidate the relationship between the oscillation time of coalescence and the capillary wave propagation. Then, the bubbles undergo damping oscillations due to fluid resistance after detaching, characterized by the same dimensionless oscillation periods. Additionally, the detachment velocity of the bubbles follows a power law relationship of 1/2 with the ratio of dimensionless surface energy to the equivalent radius. Considering the viscous dissipation and adhesive effect of the electrode on the bubbles, the critical radius of large bubbles enabling jumping is deduced from the perspective of energy conservation. Our research provides a strategy for the management of bubble dynamic behavior and the practical application of electrolysis technology.

关键词： photoelectrochemical water splitting size effect bubble coalescence bubble oscillation bubbledetachment

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Neural network approaches for real-time fatigue life estimation by Surrogating the rainflow counting method

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INTERNATIONAL JOURNAL OF FATIGUE 2025年 197卷

作者： Guo, Yiwen Li, Liangxing Gui, Jiabin Hu, Shurui Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Fatigue life estimation is critical for ensuring the safety and reliability of systems under cyclic loading. Traditional rainflow counting methods require exhaustive traversal of load histories, making them computationally expensive for real-time applications. To address this issue, this present study leverages the increasing demand for efficient high-cycle fatigue (HCF) life estimation methods, combining neural network surrogate modeling with physical principles to enhance both accuracy and computational speed. The Euler neural network (ENN) and the Runge-Kutta 4th-order neural network (RK4NN) for fatigue life estimation are proposed. These approaches are validated by comparing the results of rainflow counting with wind turbine damage ratios, demonstrating the accuracy achieves errors within 15 % for over 74 % of cases in the numerical stability range. Moreover, the RK4NN displayed superior generalization and fitting capacities across varied load conditions, effectively capturing early-stage damage growth while avoiding overfitting with the mean squared error 1.99 x 10- 36. Additionally, the ENN and the RK4NN achieved the acceleration ratio of 19.53 x and 19.38 x respectively in comparison with the modified rainflow counting method (RCM). These findings underscore the practical value of the surrogate models in improving the real-time responsiveness and computational efficiency of fatigue life estimation frameworks, particularly in digital twin applications for industrial systems.

关键词： Fatigue life estimation Rainflow counting method Neural network Euler iteration Runge-Kutta method

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A theoretical model of gas diffusivity in graphene nanochannels

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JOURNAL OF CHEMICAL PHYSICS 2025年第12期162卷 124110页

作者： Zhou, Runfeng Wang, Rui Wu, Tianyu Wang, Qiyuan Sun, Chengzhen Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Gas diffusion in graphene nanochannels is pivotal for applications such as gas sensing and membrane separation, where nanoscale confinement introduces unique transport phenomena. Unlike bulk-phases, diffusion in graphene nanochannels is significantly influenced by adsorption, which modifies density distributions and alters diffusivity behavior. In this study, molecular dynamics simulations are combined with a theoretical framework to comprehensively investigate gas diffusion under varying pressures and channel heights. A modified Chapman-Enskog model, derived from atomistic Lennard-Jones potential parameters, is proposed to account for the effects of confinement. Simulation results reveal that gas diffusivity decreases with increasing gas-phase pressure and decreasing channel height due to enhanced density in the nanochannels. Interestingly, for ultra-narrow channels (h less than or similar to 0.7 nm), the diffusivity correction factor exhibits non-monotonic behavior, initially decreasing but subsequently increasing due to overlapping repulsive potential fields. The proposed model integrates adsorption effects through density predictions based on the Boltzmann distribution and effectively predicts gas diffusivities with relative errors of less than 13%, even under strong confinement. These findings highlight the critical interplay between adsorption and confinement in shaping gas transport within graphene nanochannels. The theoretical model provides a predictive tool for designing graphene-based gas separation and sensing devices, offering fundamental insights for optimizing their performance.

关键词： Lennard-Jones potential

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Entrance effect on supercritical water heat transfer in horizontal tubes: Enhanced heat transfer performance and new correlation development

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2025年 244卷

作者： Hou, Zhenghui Yang, Chaofan Yang, Kuang Li, Qiang Guo, Xinyang Liao, Haifan Wang, Haijun Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

The unique physical properties of supercritical fluids result in a pronounced entrance effect on heat transfer. This study systematically investigates the influence of the entrance effect on heat transfer characteristics of supercritical water in a horizontal tube using both experimental and simulation methods. Based on variations in boundary conditions, the heating process of supercritical water is divided into three stages: the Thermal Establishment Stage, the Axially Asymptotic Developed Stage (AADS), and the Thermal Removal Stage. Each stage is clearly defined, and its heat transfer characteristics are analyzed. The Thermal Establishment Stage, influenced by the entrance effect, exhibits superior heat transfer performance. In horizontal tubes, buoyancy- induced thermal stratification and secondary flow significantly extend the range of the entrance effect and intensify its impact. The influence of the entrance effect extends over 150 times the tube diameter, potentially increasing the overall heat transfer coefficient by >30 %. Higher heat flux, lower mass flux, and more pronounced changes in physical properties enhance the entrance effect. Based on experimental data, a heat transfer correlation is developed that excludes wall temperature parameters or those dependent on wall temperature, while effectively capturing the influence of the entrance effect. This study provides valuable insights into utilizing the entrance effect to mitigate heat transfer deterioration and improve heat exchanger performance.

关键词： Entrance effect Correlation Heat transfer improvement Supercritical water Horizontal tubes

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Control mechanism of compressible volume for transcritical CO2 cycle power system

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ENERGY 2025年 319卷

作者： Feng, Jiaqi Wang, Junpeng Zhang, Enbo Bai, Bofeng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Compressible volume control is one of the key control strategies of S-CO2 Brayton cycle system. In this paper, the compressible volume control of buffer tank and inventory tank is proposed for transcritical CO2 closed cycle. To clarify its control response characteristics, the dynamic simulation models are established. Its control mechanism and the influence of initial conditions on system response is investigated. The results show that the volume of buffer tank is appropriately 20 % of the system volume, which can play a buffering role and has a negligible impact on system response rate. The initial parameters and volume of the inventory tank determine its total mass of injection/extraction, which in turn determine the adjustment range of the system parameters. It is appropriate to set the initial pressure of inventory tank to the middle value of cycle maximum/minimum pressure and its volume to about 25 % of the system volume. Compared to the system response without inventory control, inventory control can control the stability of compressor inlet pressure, and it can increase the rate by 1.4 %/min when the load decreases and by 1.8 %/min when the load increases. This study provides insights into compressible volume control in transcritical CO2 closed cycle.

关键词： CO 2 closed cycle system Compressible volume control Control mechanism Dynamic simulation analysis System operation control

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The effects of thermal properties on the interphase drag of supercritical water-particle flow

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POWDER TECHNOLOGY 2025年 456卷

作者： Li, Xiaoyu Zhang, Bowei Li, Yi Jin, Hui Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

The drag of particle clusters is important for the investigation of fluidized beds, but there is no accurate correlation available. The effects of nonlinear physical properties on the drag of particle clusters in supercritical water (SCW) fluidized beds cannot be overlooked either. This work conducts a simulation investigation on the interphase drag of SCW-particle flow. The results reveal that an increase in density leads to a decrease in the drag coefficient Cd. This results in a positive correlation between the drag coefficient and particle temperature. The effects of Reynolds number (Re) and void fraction (epsilon) on the density distribution further influence the normalized drag coefficient C. The distributions of dimensionless velocity and kinetic energy indicate that the conversion rate of pressure potential energy to kinetic energy in SCW is lower than that in constant property flow (CPF). The distributions of Cd and C of sub-particles show that downstream particles are most influenced by variations in density under different conditions. A model for the effects of nonlinear physical properties is established based on the C. Analysis of the results from CPF reveals that the exponent (1 in this work is primarily a function of epsilon. A correlation between the exponent (1 and epsilon is established. A drag coefficient model for particle flow in SCW is developed through the coupling of multiple models.

关键词： Supercritical water Drag coefficient Particle flow Fluidization

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Influence of pipeline structure on flow pattern classification and void fraction in offshore riser systems

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OCEAN engineering 2025年 318卷

作者： Cao, Yeqi Xu, Qiang Wang, Chan Yu, Haiyang Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

It is essential to study the influence of pipeline structure on flow pattern distribution and void fraction in riser systems to ensure the safe and stable operation of offshore pipelines. This paper reports the riser's local flow structures and average void fraction data at different overall flow patterns in a 1722 m long-distance pipeline Sshaped riser system. A flow pattern database is constructed for various riser systems including vertical upward pipe, horizontal/downward/upward-riser, and horizontal-downward-riser, totaling 4326 samples. When a horizontal/downward inlet is added to the vertical upward pipe, unstable flow is distributed in the region of slug flow in the vertical upward pipe;when a horizontal inlet is added to the downward-riser, the right boundary of unstable flow is moved to higher superficial gas velocity. The increase of riser height in the horizontal- downward-riser leads to the expansion of unstable flow to higher superficial gas-liquid velocities. The empirical flow pattern maps of vertical upward pipe and pipeline-riser for various pipe structures and fluid properties are proposed respectively, with accuracies of 93.1% and 80.3%. The correlation for predicting void fraction of the riser in the pipeline-riser system is established, and 92.43% of the data are within the error interval of +/-

关键词： Pipeline-riser system Two-phase flow flow pattern classification Void fraction Pipeline structure Acronyms

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Study on potassium recovery of coal gasification process in supercritical water

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JOURNAL OF ENVIRONMENTAL CHEMICAL engineering 2025年第2期13卷

作者： Zhou, Chenchen Jin, Hui Ge, Zhiwei Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Potassium carbonate (K2CO3) has been proved to be a good catalyst for coal gasification in supercritical water (SCW). However, catalyst deactivation occurs during supercritical water gasification (SCWG) of coal, resulting in large consumption and being unfriendly to the reaction system. In this paper, experiments on recovering potassium were investigated to find a suitable catalyst recovery method for coal gasification process in supercritical water. In the water washing method, prolonging the washing time, increasing the number of washes, increasing the water-slag ratio, and grinding the residue can effectively improve the recovery rate of potassium, which can reach 70.24 %. Acid washing can dissolve the oxides in the residue, and the maximum recovery rate of potassium can reach 89.75 %. The alkali washing method can replace the potassium in the solid residue with calcium through chemical reaction, and the total recovery rate of potassium can reach 96.51 %. It was found that the catalytic effect of the recovered liquid obtained by the water washing method and the alkali washing method in a carbon dioxide atmosphere is best. The potassium solution recovered by the acid washing method is the least effective. Because the liquids obtained by water washing and alkali washing in a carbon dioxide atmosphere can be regarded as potassium carbonate solutions, while the liquids obtained by the acid washing method is mainly potassium chloride solutions, so its catalytic effects is weaker. Through the catalytic effect of the recovered liquid, it can be seen the catalytic effect of the residue obtained: alkali washing method approximate to water washing method > acid washing method. A potassium recovery system coupled with a supercritical water gasification system is put forward through the in-depth study and comprehensive comparison of different methods.

关键词： Supercritical water Coal gasification Potassium carbonate Potassium recovery Alkaline washing

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Solutal Marangoni effect influencing bubble dynamics with varied electrolyte compositions

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ELECTROCHIMICA ACTA 2025年 512卷

作者： Wang, Mengsha Xu, Qiang Li, Jinfeng Nie, Tengfei She, Yonglu Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

In the photoelectrochemical (PEC) water splitting system, the intricate interplay between bubble evolution and charge transfer at the electrode-electrolyte interface underscores the paramount importance of studying electrolyte properties. In this paper, the bubble dynamics and gas-liquid interface mass transfer on TiO2 nanorod and nanotube film electrodes are investigated by changing the cation types (K+, Na+, Li+) and concentrations (0.1 M-1.5 M) in alkaline electrolytes. The results indicate that the photocurrent and gas production follow the order of K+ > Na+ > Li+ under the same concentration, which is affected by the solvation of metal cations in aqueous solution and the adsorption on the photoanode surface. Compared with the nanotube electrode, the nanorod electrode enables the bubble to detach at a smaller size and faster rate. The trend of bubble detachment diameter variation with concentration in different cation electrolytes is the same, and follows the order of K+ > Na+ > Li+, which indicates that the force caused by Marangoni effect shows similar rules. The results reveal that the surface tension variation rate induced by ion concentration gradient varies significantly under different cation concentrations, while the variation rate driven by temperature gradient remains notably stable. This confirms that the bubble growth and detachment depend on the Solutal Marangoni effect caused by the surface tension variation rate of different alkaline electrolytes with concentration. Therefore, the suitable choice of electrolyte composition is pivotal for regulating the bubble evolution at the electrode-electrolyte interface and improving the PEC system efficiency.

关键词： Solutal Marangoni effect Electrolyte Bubble dynamics Photoelectrochemical Mass transfer

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