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Theoretical study of bubble departure and lift-off diameters model for evaporation based on microlayer in flow boiling

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INTERNATIONAL JOURNAL OF THERMAL SCIENCES 2025年 214卷

作者： Dong, Wu-han Gao, Ming Shen, Zhong-xiang Dang, Meng-yuan Zhang, Li-xin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

This study was devoted to the theory of microlayer evaporation and bubble dynamics. In subcooled flowing boiling, a theoretical study of the mechanism of heat and mass transfer in vapor bubbles during boiling heat transfer has been carried out. The forces on mononuclear boiling bubbles during subcooled flow boiling are analyzed. In addition, the effect of microlayer evaporation was considered, and microlayer evaporation force has been introduced. Evaporation of the microlayers as between the bottom of a bubble and the heated wall, evaporation of the layer of superheated liquid around the bubble, the condensation of the vapors at the top of a bubble are taken into account on the basis of the bubble dynamics. The prediction models for bubble forces, departure and lift-off diameters were improved. The influence of force on the bubble under the same working conditions was also investigated. Compared with previous experimental results, it was found that the improved model could forecast the diameters of the bubble departure and bubble lift-off well.

关键词： Bubble Microlayer flow boiling Wall temperature Theoretical model Nomenclature

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Dynamics of post-impact merged droplets under different droplet-droplet interaction modes upon successive impingement on the substrate of different wettabilities

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PHYSICS OF FLUIDS 2025年第1期37卷

作者： Zhou, Junjie Wang, Dongmin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Successive impingement of multiple droplets onto a substrate is common in applications. However, the effects of the substrate properties and droplet-droplet interaction modes on the dynamics of the post-impact merged droplet remain unclear. In this study, we simulate the successive impingement of two droplets and the dynamics of the merged droplet on a superhydrophobic surface and a hydrophilic-hydrophobic patterned surface under different droplet-droplet interaction modes, based on a two-dimensional single-component pseudopotential multiphase lattice Boltzmann model. On the superhydrophobic surface, if the leading droplet is at spreading stages upon successive impingement, the merged droplet's maximum spreading factor, rebounding height, and merged droplet-substrate contact time decrease with the spreading of the leading droplet. Conversely, if the leading droplet is at recoiling stages upon successive impingement, the merged droplet's maximum spreading factor and rebounding height remain a small constant, while the merged droplet-substrate contact time increases with recoiling of the leading droplet. The dynamics of the merged droplet on a superhydrophobic surface under different droplet-droplet interaction modes are attributed to amplifying or suppressing the leading droplet kinetic energy upon successive impingement. However, on the hydrophilic-hydrophobic patterned surface, it is found that the hydrophilic stripes enhance the merged droplet spreading. The relatively large viscous force of the hydrophilic stripes and the energy barrier at the boundary of the pattern stripes significantly dissipate the kinetic energy of the merged droplet. The merged droplet does not rebound on the hydrophilic-hydrophobic patterned surface and has a small oscillation amplitude and fast energy decay rate.

关键词： Kinetic energy

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Lattice Boltzmann simulation of droplets accelerate shedding on an inverted triangular surface with wettability gradient

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NUMERICAL heat transfer PART B-FUNDAMENTALS 2024年

作者： Tao, Ying Gao, Ming Yang, Jian-hua Chen, Lu Zhang, Li-xin Univ Shanghai Sci & Technol Sch Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The droplet combining and shedding on a gradient-wetting inverted triangle surface is investigated using the lattice Boltzmann method based on the Shan-Chen pseudo-potential model. The impacts of the tip angle, wetting gradient, and Bond number are investigated. The study shows that the smaller the tip angle, the better for the droplets to merge and shed. The droplet combining and shedding process can be sped up by the triangular surface's wetting gradient. As the wetting gradient increases, the droplet combining and shedding becomes easier. Applying a wetting gradient to speed drainage is better when the original surface is more hydrophilic. The combination and shedding of droplets on the wet surface are significantly influenced by the Bond number as well.

关键词： Droplet motion inverted triangle surface lattice Boltzmann method shedding wetting gradient

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Process modelling and assessment of thermochemical sulfur-iodine cycle for hydrogen production considering Bunsen reaction kinetics

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CHEMICAL engineering AND PROCESSING-PROCESS INTENSIFICATION 2024年 195卷

作者： Yang, Aoli Ying, Zhi Zhao, Muyang Zheng, Xiaoyuan Dou, Binlin Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H2SO4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0-57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle.

关键词： Hydrogen production Sulfur-iodine cycle Bunsen reaction kinetics Internal heat exchange network Thermal efficiency

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Lignin oxidation reaction kinetics and its conversion into high-value chemicals over self-prepared electrode during lignin-assisted water electrolysis for hydrogen production

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RENEWABLE ENERGY 2024年 237卷

作者： Ying, Zhi Sun, Hao Cao, Jiahao Zheng, Xiaoyuan Dou, Binlin Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Electrochemical oxidation of lignin coupled with water electrolysis forms lignin-assisted water electrolysis (LAWE), which reduces the energy consumption of hydrogen production and achieves the high-value conversion of lignin. However, the kinetics of lignin oxidation reaction (LOR) is slow, and the correlation between operating parameters and LOR kinetics is rarely found. Herein, a vertical self-grown nickel-iron layered hydroxide nanosheet on a nickel foam substrate (Ni1Fe2-LDH@NF) was synthesized for improving LOR kinetics, and the influence of lignin concentration, NaOH concentration, and temperature on LOR kinetics was revealed. A mathematical model correlating LOR kinetics with operating parameters was developed, and based on variance analysis, NaOH concentration was found the biggest factor affecting LOR kinetics. The best LOR kinetics was reached at the lignin concentration of 10 g/L, the NaOH concentration of 0.8 mol/L, and the temperature of 50-80 degrees C. In addition, the LOR over Ni1Fe2-LDH@NF and hydrogen production presented excellent stability during LAWE process at high current density of 200 mA cm(-2) and 65 degrees C. The lignin underwent large skeleton breakage and oxygen-containing functional groups consumption, and successfully converted into value-added chemicals such as 2,4-di-tert-butylphenol. This work highlights the importance of understanding LOR kinetics, providing opportunities for optimized lignin upgrading in LAWE process.

关键词： Hydrogen production Lignin-assisted water electrolysis (LAWE) Lignin oxidation reaction (LOR) Operating parameters Modeling Analysis of variance

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Comparative investigation of numerical simulation and experimental study of electroconvection layer in natural convection heat transfer enhanced by an electric field

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INTERNATIONAL COMMUNICATIONS IN heat AND MASS transfer 2024年 153卷

作者： Gao, Ming Zhang, Ling-shuang Zhang, Bang-hui Lou, Qin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

This article utilizes numerical simulation methods, grounded in experimental data and models to investigate the formation process of the electroconvection layer and its role in enhancing natural convection heat transfer. After verifying the feasibility of the model, the experimental results were compared with the numerical results, and numerical calculations were performed under experimental conditions of voltages ranging from 1000 V to 5000 V and heat fluxes spanning from 4000W/m2 to 10,000W/m2. The findings reveal a correlation between the establishment of the electroconvection layer and the strength of the electric field force with respect to the temperature gradient. Electroconvection not only enhances heat transfer but also modifies the velocity field of the natural convection, resulting a double vortex flow. The electric field force suppresses vertical thermal convection and alters the direction of the horizontal velocity field. Furthermore, electroconvection augments the heat transfer in free convection, with the cooling effect of high voltage surpassing that of low voltage. The electric field force's enhancing impact on low heat fluxes is comparatively diminished compared to high heat fluxes.

关键词： Electrohydrodynamic Electroconvection Free convection heat transfer enhancement

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An innovative damping random walk algorithm with compulsive evolution for the synthesis of heat exchanger networks

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APPLIED THERMAL engineering 2024年第PartB期248卷

作者： Huang, Xiaohuang Liu, Weiwei Duan, Huanhuan Xu, Yue Xiao, Yuan Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

heat exchanger network synthesis in process system engineering poses a significant challenge, primarily because of the intricacies of stream matches and the nonlinear nature of continuous variables. Numerous heuristic methods are frequently trapped in local optima because of their greedy acceptance criteria, which limits their capacity to explore diverse solutions. This aspect of enhancing algorithms through acceptance Criterion has yet to be considered in previous studies. Hence, a damping strategy using damping perfect solutions is proposed and applied to the Random Walk Algorithm with Compulsive Evolution, which has recently received considerable attention. This strategy aims to prevent trapping in local optima and improve global search capabilities, thereby reducing the risk of premature convergence to the local optima. To address the impact of different damping coefficients within the strategy on the optimization process and structural variations in the algorithm, three damping strategies were designed: a fixed damping strategy with a constant damping coefficient, a variable damping strategy featuring variable damping coefficients at different optimization stages, and an adaptive damping strategy that tracks structural changes and selectively delays modifications driven by continuous variables to preserve those driven by integer variables. The results obtained from applying these strategies to three classical industrial HEN cases are 2,890,884 $/yr, 6,650,082 $/yr, and 1,709,205 $/yr, respectively. These results outperformed the optimal outcomes documented in the literature, demonstrating the effectiveness of the new method.

关键词： heat exchanger network synthesis Total annual cost Structure evolution Damping Random Walk Algorithm with Compulsive Evolution Heuristic method

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Electrochemical upcycling of biochar particles at anode-electrolyte interface in biochar-assisted water electrolysis for hydrogen production

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CHEMICAL engineering JOURNAL 2024年 498卷

作者： Ying, Zhi Chen, Xinyue Gu, Xufei Sun, Hao Zheng, Xiaoyuan Dou, Binlin Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Biochar-assisted water electrolysis (BAWE) exhibits potential in reducing electricity consumption for hydrogen production and is beneficial to biochar upcycling. However, it remains a huge challenge to increase biochar oxidation reaction (BOR) kinetics and deliver upgraded biochar with high selectivity. Herein, we demonstrate the correlation between the BOR kinetics and physicochemical properties of biochar, the laws of energy and mass transfer at anode-electrolyte interface, and the evolution of biochar structure during its electrooxidation. The biochar was derived from the pyrolysis of mixed cellulose and lignin at 500-800 degrees C, and based on Pearson correlation analysis, the physicochemical properties such as functional groups abundance, contact angle, and electric conductivity of biochar showed significant influence on electron transfer rate during biochar oxidation. Oxygen evolution reaction (OER) was found the main competition to BOR, only biochar oxidation occurred at potential below 1.6 V vs. RHE, but OER became dominant at potential above 1.6 V vs. RHE. Biochar underwent three stages including oxygen consumption, oxygen enrichment, and deep oxidation during its electrochemical oxidation. The easily-oxidized carboxyl, hydroxyl, and aldehyde were primarily oxidized, followed by the transformation of methyl into hydroxyl and aldehyde, and aldehyde further oxidized into carboxylic acids and CO2. These findings provide new inspiration on electrochemical upgrading of biochar coupled with efficient hydrogen production.

关键词： Biochar-assisted water electrolysis (BAWE) Biochar Biochar oxidation reaction (BOR) Kinetics Physicochemical properties

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Investigation on dynamic characteristics of droplet impact on surfaces with different rough microstructures based on lattice Boltzmann method

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CASE STUDIES IN THERMAL engineering 2024年 63卷

作者： Yang, Jianhua Gao, Ming Dang, Mengyuan Liang, Jia Zhang, Lixin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Constructing microstructures on smooth surfaces is significant for 3D printing technology and surface self-cleaning effects in engineering applications. This paper uses the lattice Boltzmann method (LBM) to study the droplet impact behavior on different microstructured surfaces: righttriangle, semicircular, and rectangular microstructures. The formulas for calculating the surface wetting characteristics of different microstructures are derived theoretically, the difference between simulation results and those from theoretical analyses is less than 5 %. The increase of the microstructure column height h may eventually lead to the disappearance of the Wenzel mode. The droplet impact on the microstructured hydrophilic surface can accelerate the droplet to the stable stage and reduce the excessive impact effect. The droplet impacts on the superhydrophobic microstructured surface can accelerate the rebound separation and shorten the time to reach the stable stage. When droplets impact the superhydrophobic surface of the right-triangle microstructure, a secondary separation phenomenon will occur, resulting in the maximum rebound height and the maximum reduction of the near-wall density. The superhydrophobic right-triangle microstructured surface can more effectively promote self-cleaning.

关键词： Lattice Boltzmann method Droplet impact Microstructure Hydrophilic surface Superhydrophobic surface

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Analysis of stability and internal flow mechanisms in spiral annular flow with different swirlers

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EXPERIMENTAL THERMAL AND FLUID SCIENCE 2024年 158卷

作者： Wang, Haoyu Yang, Yang Yang, Bin Tang, Yu Jing, Wenjie Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Spiral annular flow within ducts is widely utilized in modern industry, with the swirler serving as a critical component in generating such flow patterns. The structure of the swirler significantly influences the generation and stability of the spiral annular flow. This study selected four different swirler structures with outstanding performance from previous research and analyzed their characteristics through visual image processing combined with numerical simulations. By analyzing the amplitude information of the wave fluctuations in the annular swirling flow liquid film under different operating conditions using probability density functions, it was found that the swirler A(Flat-vane swirler) and swirler B(Flat-vane swirler with hub) produced smaller fluctuations in the annular swirling flow liquid film, indicating better stability compared to the swirler C(Arc-vane swirler) and swirler D(Spiral-vane swirler), which exhibited poor performance. Combining the numerical simulation results with the analysis of the internal mechanism of the swirlers, it was discovered that within the swirler A and swirler B, the fluid between the swirler vanes experienced a larger pressure gradient, resulting in phenomena such as "jump" and "pull" under this pressure gradient. This, in turn, contributed to the generation of greater tangential velocity and radial pressure gradient after the fluid exited the swirler. Due to the influence of the swirler structure, the swirler A and swirler B did not completely separate the fluid region into four independent spaces. Instead, in the central connection area of the rear section of the swirler, the gas phase components aggregated earlier, greatly promoting the downstream generation of spiral annular flow. This study analyzed the two-phase flow process and mechanism inside the swirler, filling a gap in previous research and providing important references for the optimization and selection of swirlers.

关键词： Gas-liquid two-phase flow Swirler Spiral annular flow flow characteristics Probability Density Function

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