30 July 2025, Volume 46 Issue 7

    

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  Bypass Control Strategies for the Compressed Air Energy Storage System Expander

  CHEN Zebing, LI Wen, ZHU Yangli, WANG Xing, CHEN Haisheng

  Journal of Engineering Thermophysics. 2025, 46(7): 2091-2105.

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  During the energy release phase of the compressed air energy storage (CAES) system, the air pressure in the storage device gradually decreases. When it falls below a certain threshold, the unit cannot maintain the rated total output power. To address this issue, the study proposes the applications of bypass systems in the CAES system expanders. In this paper, three types of bypass systems are designed for the expander unit of a CAES system: single-stage bypass systems (3 configurations), two-stage bypass systems (3 configurations), and three-stage bypass system (1 configuration), with a total of 7 configurations. By adjusting the openings of the main and bypass valves, the total inlet and outlet pressures of certain turbines are modified, thereby changing their mass flow rates and output powers to achieve the rated total output power. The results show that 5 configurations can achieve the desired performance. The three-stage bypass system enables the lowest terminal air pressure in the storage device, expanding the sliding pressure operation range of the unit. The optimal configuration is the two-stage bypass system that independently controls T1 and T2, which achieves the longest power generation duration and the highest energy density, representing a 71.25% improvement compared to the original unit. Therefore, adopting the bypass control methods can extend the power generation duration and increase the energy density of the CAES system.
  
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  Current Progress and Development Direction of Hydrogen Production by Seawater Electrolysis Assisted by Low-Energy Consumption Oxidation Reaction

  SUN Miaoting, ZHOU Wei, LI Longhao, ZHANG Xuewei, HUANG Yuming, MENG Xiaoxiao, SUN Fei, GAO Jihui, ZHAO Guangbo

  Journal of Engineering Thermophysics. 2025, 46(7): 2106-2127.

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  Hydrogen production is considered to be a promising new hydrogen production method in the future. However, there are high overpotential and slow kinetic process of oxygen evolution reaction (OER), and corrosion of the electrode caused by chlorine evolution reaction (CER), which make the hydrogen production technology of seawater electrolysis face great challenges. In recent years, relevant studies have shown that coupling the anodic oxidation reaction of hydrazine, urea, sulfide, sugars, microplastics and other substances into the seawater electrolysis hydrogen production system can replace OER, avoid problems such as chlorine corrosion and achieve higher economic benefits. This paper systematically reviews the principle, challenges and the research status of related catalysts, focuses on the progress of the oxidation reaction of electrolytic seawater with lowenergy consumption in recent years, and finally discusses the problems that need to be breakthrough and the future research direction.
  
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  Biomimetic Ion Channels Achieve Solar Evaporation-based Selective Crystallization

  BAO Yanqiong, LIU Lang, LIU Chao

  Journal of Engineering Thermophysics. 2025, 46(7): 2128-2135.

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  To address the core challenge of low salt resource utilization in solar desalination, this study designs a biomimetic ion-channel graphene oxide/polyamide (GO/PA) interfacial evaporator. By tuning the charge characteristics of the PA layer, a dual-negative GO/PIP membrane and a heterogeneously charged GO/PEI membrane were developed. The GO/PIP membrane achieves selective separation of Cl−/SO²⁻₄ through the Donnan effect and size sieving effect while inducing NaCl crystallization at the membrane edge via lateral ion channels. In contrast, the GO/PEI membrane forms a vertical electric field within the membrane, driving the directional migration of anions and cations, thereby effectively inhibiting salt deposition in the short term. Experimental results show that the evaporation rate of the GO/PA membrane is more than 2.6 times higher than that of pure water, with the GO/PIP membrane exhibiting the highest evaporation rate of 1.94 kg·h⁻¹·m⁻². The crystallization rate of the GO/PIP membrane reaches 280 g·m⁻²·h⁻¹, and after three cycles, the NaCl purity reaches 96.13% (separation factor 3.5). The anti-salt crystallization dynamic equilibrium strategy proposed in this study provides an engineering-ready solution for achieving zero-liquid discharge treatment of high-salinity wastewater. 
  
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  Effect of Thin-Walled Tube Bundle Structure on Ammonia Condensation Heat Transfer in the Stratosphere

  WANG Kun, ZHANG Jiayu, GAO Shen, ZHAO Yanxing, GONG Maoqiong

  Journal of Engineering Thermophysics. 2025, 46(7): 2136-2141.

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  The operating altitude of the airship is controlled by the large volume change caused by the phase change of ammonia, which is an innovative way to solve the problem of long-term stable airborne stay of the airship. The focus of this method is to strengthen the condensation heat transfer process of ammonia outside the thin-walled wire tube in the stratosphere. In this paper, the condensation heat transfer process of ammonia under 7 different tube row structures at 6.5 kPa was analyzed through numerical simulation. The study found that when the tube bundle arrangement angle is 98◦ and the tube spacing is 2d, the condensation efficiency of ammonia outside the tube is the best under low pressure. Compared with the structure with the tube bundle arrangement angle of 60°, the average condensation heat transfer coefficient around the tube is increased by 49.1%, and the condensation rate is increased by 1.1 times. Compared with the structure with a tube spacing of 1.5d, the average condensation heat transfer coefficient around the tube is increased by 82.9%, and the condensation rate is increased by 89.4%.
  
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  Solar Driven Self-Floating MXene-rGO Aerogel for Hydrogen Production From Formic Acid

  LIU Kun, WANG Rui, LI Yinshi

  Journal of Engineering Thermophysics. 2025, 46(7): 2142-2147.

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  The utilization of abundant solar energy resources in the production of green and clean energy exhibits the characteristics of cost-effectiveness and environmental friendliness, thereby demonstrating a wide range of potential applications. Herein, this work presents the solar-driven floating hydrogen production system, which effectively achieves rapid photothermal conversion and enhances mass transfer rates through interfacial heating and improved mass transfer. The results demonstrate that the system achieves a hydrogen evolution rate of 72.1 mmol g⁻¹ h⁻¹ utilizing formic acid under an irradiation intensity of 1 kW m⁻² and maintains excellent stability even after undergoing five cycles. More importantly, the floating system also demonstrates its potential for the application of solar energy in room-temperature hydrogen production by efficiently saving energy-consuming processes like filtration during catalyst utilization.
  
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  Operating Parameters Optimization for Coal-Fired Power Unit Based on Machine Learning Algorithms

  CHEN Dongchao, LÜ Jiale, QI Lin, WANG Zhong, SI Heyong

  Journal of Engineering Thermophysics. 2025, 46(7): 2148-2159.

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  A parameter optimization method is proposed by integrating multiple machine learning algorithms to ensure safety, energy-saving, and low-carbon operation of coal-fired power unit in this paper. Firstly, the steady-state discrimination algorithm is developed to obtain the steady-state data from the historical operation data. Based on the multi-step clustering algorithm, an improved working condition identification method has been presented which is used for the decoupling of the operating parameters and working conditions. Secondly, outliers in each operation condition are automatically removed to improve data quality by combining particle swarm optimization, Gaussian mixture model and density-based clustering algorithm. Moreover, the parameter optimization model for all operating conditions is established by using fuzzy C-clustering, principal component analysis and extreme gradient boosting algorithms under the constraints of safe, efficient, and low-carbon energy supply. Finally, an actual on-duty 1000 MW unit was taken as study unit, and the benchmark values of the operating parameters were obtained by the proposed method. The results indicated that the energy conservation and carbon reduction potential is remarkable if the operating parameters are adjusted and controlled according to the benchmark values.
  
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  Multi-objective Optimization of Double Evaporation Double Regenerative Organic Rankine Cycle System Based on NSGA-II and Entropy EWM-TOPSIS

  DAI Wenzhi, SHEN Xiongjian, ZHANG Haixing, YANG Xinle, YAN Shuai

  Journal of Engineering Thermophysics. 2025, 46(7): 2160-2171.

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  In order to effectively utilize the waste heat after exhaust of the expander and improve the effective utilization efficiency of the organic Rankine cycle, a dual-stage evaporation dual-stage recuperation organic Rankine cycle (DEDR-ORC) system driven by geothermal energy was constructed. Establish multi-objective evaluation criteria for thermal efficiency, exergy efficiency and levelized electric energy cost, and explore the effects of heat source temperature, evaporation temperature and narrow point temperature of the evaporator on system performance, using NSGA-II and entropy weight-good and bad solution distance methods (TOPSIS) performs multi-objective optimization of the system. Five working fluids were selected for comparative research. The research results show that: the evaporation temperature, heat source temperature and evaporator narrow point temperature increase, and all working fluids of DEDR-ORC are relative to the twostage evaporation recuperation organic Rankine cycle system (DESR-ORC). The thermal efficiency, net output power, exergy efficiency and levelized electric energy cost (LEC) are more advantageous; compared with DESR-ORC, the thermal efficiency and exergy efficiency of DEDR-ORC are increased to 11.365% and 88.632% respectively, and the LEC is reduced to 9.131%. Among DEDR-ORC and DESR-ORC, the working fluid with the best performance is benzene, and the one with the greatest overall performance improvement is hexane.
  
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  Application of Solar Chimney Brine Concentration System in Dangxiongcuo Salt Lake

  LÜ Ruiling, ZHANG Dayu, ZHANG Bin, GUO Penghua

  Journal of Engineering Thermophysics. 2025, 46(7): 2172-2180.

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  A novel solar chimney brine concentration system is proposed for improving the brine concentration rate. A transient thermodynamic model of the system is established. The brine evaporation rate of the system is compared with that of a conventional solar pond by using the weather data of Dangxiongcuo salt lake. Furthermore, the influence of meteorological factors on the evaporation process of the system at different time scales is explored using correlation analysis and multiple regression models. The results show that, compared with the conventional method, the time required for brine concentration can be reduced by 24.4% by applying the solar chimney brine concentration system. At the monthly scale, both the evaporation rate and water temperature are primarily influenced by radiation intensity; at the daily scale, the evaporation rate is mainly affected by the radiation intensity, while the brine temperature shows significant correlations with the ambient temperature.
  
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  Hybrid Optimization of the Flow Path Structure of Small Diameter Finned Tube Type Evaporator for Domestic Air Conditioners

  WANG Wenli, CUI Songlin, WU Junhong, SHAN Lianyu, CAI Shanshan, XIE Junlong

  Journal of Engineering Thermophysics. 2025, 46(7): 2181-2190.

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  Based on the steady-state distributed parameter method, a small-tube finned-tube evaporator model is established, and a method for finding the optimal finned-tube heat exchanger with a mixture of structural and flow path parameters is proposed. A sensitivity analysis is conducted on the small-tube evaporator to study the main factors affecting its heat transfer effect. Based on the non-dominated algorithm with elite strategy (NSGA-II), the neural network model is solved to obtain the optimal structural parameters and the optimal flow pattern of the small diameter finned tube evaporator within a certain range of structural parameter variations.
  
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  Analysis of Erosion Characteristics of Pelton Turbine Based on Cavitation Effect

  LI Chenxi, SHEN Peirong, PAN Jiaping, HUANG Fangzhou, GUO Pengcheng

  Journal of Engineering Thermophysics. 2025, 46(7): 2191-2198.

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  The core issue faced by Pelton turbines is sand erosion, and their critical components may also experience cavitation, which seriously threatens the safe and reliable operation of the unit. This paper studies the erosion characteristics and cavities morphology of Pelton turbines under the influence of cavitation effects, combined with the motion characteristics of sand particles. The results show that there are obvious cavitation regions on the nozzle seat and the back of the bucket. As the particle size increases, the average erosion rate on the nozzle surface gradually increases, while that on the needle surface first decreases and then increases. The erosion rate on the tip of the bucket splitter increases with the particle size due to the direct impact of the jet. Furthermore, under large particle sizes, the particle trajectories are closer to the nozzle wall and the gas-water interface, and the nozzle seat and the back of the bucket which cavitated will accumulate more particles, thereby inhibiting the formation and development of the cavities structure in these regions. 
  
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  Thermodynamic Analysis and Turbine Off-design Performance Investigation for S-CO₂ System Driven by Nuclear Energy

  LOU Juwei, WANG Jiangfeng, XIA Jiaxi, ZHANG Guolutiao, ZHAO Pan, DU Yang

  Journal of Engineering Thermophysics. 2025, 46(7): 2199-2207.

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  The efficient utilization of nuclear energy is one of the key approaches to carbon peaking and carbon neutrality due to its characteristic of clean and high energy density. Parametric analysis is carried out based on the S-CO₂ Brayton system. GA algorithm is employed to get optimal system efficiency and corresponding system parameters. One-dimensional design and three-dimensional simulation are presented based on the optimization results. The off-design performance is evaluated based on the three-dimensional simulation method. Results show that the system can obtain maximum thermal efficiency under the optimal parameters combination. The deviation of efficiency and power output for the turbine between one-dimensional design and three-dimensional are 0.85% and 2.98%, respectively. The turbine shows great off-design performance and can operate with high isentropic efficiency in a wide range of mass flow rates under high rotational speed.
  
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  Research Progress of Experimental Technology for Turbine Rotor-Stator Cavity

  WU Lei, YIN Zhao, ZHANG Hualiang, XU Yujie, CHEN Haisheng

  Journal of Engineering Thermophysics. 2025, 46(7): 2208-2222.

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  As an important component of the turbine, the rotor-stator cavity has a significant impact on turbine efficiency, rotor heat transfer and axial force distribution. Through extensive experimental research, people have made significant progress in understanding the internal flow mechanism, performance evaluation and structural improvement of the rotor-stator cavity. This is manifested in the combination of new testing technologies to obtain new perspectives, predictive models and structures. However, there are still challenges such as small space, high speed, high temperature, unsteadiness, and difficulty in observation. Based on literature and research results of relevant experimental teams, this paper introduces the composition of typical turbine rotor-stator cavity facilities, and focuses on the summary of pressure, temperature, speed, and sealing efficiency measurement technologies. Overall, the existing test rigs are distinctive and cover different mainstream ingress forms as well as research priorities, but parameters remain to be improved. At the same time, although there are many new measurement techniques, they need to be further strengthened in reducing the effect of the convective field, improving the ability of anti-jamming, optimizing the visualization techniques and contactless measurement.
  
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  The Investigation of Loss Mechanism in a Steam Compressor in Power Plants

  ZHANG Lei, LEI Tongtong, LANG Jinhua, AN Guangyao, YUAN Wei, ZHANG Qian

  Journal of Engineering Thermophysics. 2025, 46(7): 2223-2233.

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  Steam compressors are recognized as core components of steam pressurization and quality enhancement systems. The investigation of complex flow mechanisms and loss characteristics within the internal flow field is deemed critical for advancing the development of high-performance steam compressors. The loss mechanisms of a steam compressor in power plants under various operating conditions were investigated based on entropy generation theory, with the loss characteristics of the impeller and diffuser being comparatively analyzed across three operating conditions: near choked, peak efficiency, and near stall. The results demonstrated that entropy generation caused by viscous shear was identified as the primary source of losses within the compressor. With increasing flow rate, the losses in both the impeller and diffuser initially decreased and subsequently increased, though the variation in impeller losses remained relatively minor. From peak efficiency to near choked condition, the diffuser losses were substantially amplified, with their proportion of total compressor loss being sharply increased from 35% to 71%. In the impeller, losses were predominantly induced by tip leakage flow and secondary flow near the hub region, with approximately 40% of total impeller losses being localized in this area. Diffuser losses were concentrated in the main flow passage, where under peak efficiency conditions, the blockage at the leading edge and flow separation were mitigated, resulting in a reduction of loss proportion from 48% (near choked) to 24%. Additionally, significant reductions in other loss components were observed except in the inlet region. Theoretical support for the development of high-efficiency and wide-operating-margin steam compressors is provided by this study
  
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  Multipoint Optimization Design for Compressor Plane Cascade

  QIU Qinghui, QIN Kai, HUANG Diangui

  Journal of Engineering Thermophysics. 2025, 46(7): 2234-2241.

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  In this paper, a parameterized method of camber line and thickness distribution is proposed and the formulas for solving the camber line and thickness distribution in the cascade and the coordinates of the back profile of the cascade surface are given. The compressor plane cascade modeling program is realized based on the parametric method. A multi-condition simulation optimization platform is built to realize parallel flow field calculation. The weighted average of the total pressure loss coefficient of cascade under multiple conditions is taken as the constraint conditions, and the objective function of multi-condition optimization is used to optimize the compressor plane cascade by multi-island genetic algorithm. The results show that the proposed parameterized method can be used to fit the compressor plane cascade well. By analyzing the flow field, it can be seen that the flow near the leading edge of the optimized cascade is more uniform, and the diffuser capacity of the leading edge is enhanced. The total pressure loss coefficient is lower than that of the original cascade at multiple angles of attack, indicating that the optimized cascade can maintain good aerodynamic performance in a wider range of angles of attack.
  
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  Design of High Efficiency Fan With Wide Speed Range Based on Adjustable Guide/Stator Blades

  WANG Haoran, ZHAO Shengfeng, LUO Qiaodan, HAN Ge, LU Xingen

  Journal of Engineering Thermophysics. 2025, 46(7): 2242-2253.

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  The stable operating margin and thermal efficiency of the fan decrease significantly at low reduction speed, which fails to meet the requirements for stable and efficient operation of the aeroengine compression system in wide airspace and varying speeds. Therefore, there is an urgent need to develop a control method for optimizing flow within the fan at low reduction speed. This study proposes adjusting the bending angle of the variable camber guide vane and rotation angle of the first stage stator blade to enhance both stable operating margin and thermal efficiency at low reduction speed. Numerical results demonstrate that by altering the attack angle of the rear blade, the variable camber guide vane expands the stable operating margin of the fan while reducing flow loss caused by leakage in tip clearance between rotor blades in order to improve thermal efficiency. Additionally, reverse adjustment of the first stage stator blade further enhances stability; however, it has minimal impact on peak thermal efficiency due to increased loss from rotor tip clearance leakage when rotating in reverse, offset by decreased losses from improved angle of attack on first stage stator blade. Through optimization design encompassing stable operating margin and design point thermal efficiency across various speeds, an efficient working range is achieved throughout this entire spectrum. Design point efficiencies at 100%, 90%, 80%∼70%, and 60%∼40% reduction speeds are found to be superior with values exceeding 0.88, 0.87, 0.855, and 0.84 respectively. Furthermore, stall margin on right boundary within this efficient working range exceeds 18%.
  
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  Study on the Aeroelastic Performance of the 15 MW Class Wind Turbine Under Surge Condition

  ZHOU Le, LI Yijia, MA Lu, SHEN Xin, OUYANG Hua, DU Zhaohui

  Journal of Engineering Thermophysics. 2025, 46(7): 2254-2260.

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  Based on the lift-line free vortex wake model and the geometrically exact beam theory model, the aeroelastic coupling characteristics of the IEA-15 MW wind turbine were studied. The results show that the loads of the rotor will fluctuate periodically under surge condition, and there is a certain delay of the load response due to the wake induction effect, airfoil unsteady aerodynamics and blade deformation. After considering the blade flexibility, the deformation of the blade (especially the torsional deformation) will reduce the power and thrust of the wind turbine. In addition, the superposition of the platform motion and blade gravity will make the deformation characteristics of the blade more complicated than that under the fixed condition.
  
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  Investigation on Wind Turbine Nacelle Wind Speed Characteristics Considering the Influence of Wake

  WANG Xiaodong, MA Mengru, WANG Tao, ZOU Jiaxin

  Journal of Engineering Thermophysics. 2025, 46(7): 2261-2268.

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  The power prediction and operation control of horizontal axis wind turbines are based on the nacelle wind speed. Due to the influence of the wind turbine, there are differences between the wind speed measured by the nacelle anemometer and the inflow wind speed, and it is necessary to establish nacelle transfer function for correction. Computational fluid dynamics(CFD) is used to simulate two 2 MW three blade horizontal axis wind turbines in series. We studied the overall performance of two turbines and the nacelle wind speed. It was found that the wake of upstream turbine has not fully recovered at a distance of 7D, resulting in a significant decrease in the power of downstream turbine with periodic small fluctuations. The nacelle wind speed of the upstream turbine with stable inflow exhibits periodic fluctuations, and the separated flow of the blades has a significant impact on the turbines in series. The main influence factor of wind speed changes in downstream turbine nacelle is the rotation of blades/wind turbines. The main factor affecting the variation of nacelle wind speed of both turbines under sinusoidal inflow is the fluctuation of inflow wind speed. Compared to a single turbine, the wake recovery of turbines in series is slower, and the sinusoidal flow will accelerate the wake recovery. 
  
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  Numerical Simulation on Double-Bubble Interaction During Pool Boiling in Low Gravity

  DU Wangfang, ZHANG Liang, HE Falong, LI Huixiong, ZHAO Jianfu

  Journal of Engineering Thermophysics. 2025, 46(7): 2269-2273.

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  Bubble dynamics is closely related to heat transfer performance of nucleate pool boiling, and has always been a hot topic in the field of multiphase flow, heat and mass transfer. Based on OpenFOAM open-source code, µgBCHT, a numerical solver for fluid-solid conjugate heat transfer during microgravity pool boiling process is developed for solving the problems including fluid-solid conjugate heat transfer, gas-liquid phase change heat transfer and flow in both macro- and microregions with random and localized activation of nucleation points. 1D Stefan and Sucking problems are used to validate and verify the solver. A 3D numerical simulation was conducted on the process of double-bubble interaction during nucleate pool boiling of saturated FC-72 in low gravity conditions of 0.1g, revealing the characteristics of bubble growth and the interaction mechanism. The results provide a micro-scale physical picture for understanding the heat transfer mechanism of nucleate pool boiling with low heat flux
  
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  Simulation of Droplet Wetting Transition on Doubly Reentrant Structure

  CHANG Yuxuan, ZHANG Xinlei, CHEN Yanjun, LIU Xiuliang

  Journal of Engineering Thermophysics. 2025, 46(7): 2274-2282.

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  The doubly reentrant structure has attracted extensive attention because of its excellent control ability on superhydrophobicity. However, the research of its wetting transition is mostly based on the continuous Cassie model, and thus the structural discontinuity influence has not been fully understood. In this paper, the wetting transition process of droplets on doubly reentrant structure is simulated and analyzed by three-dimensional pseudopotential lattice Boltzmann method (LBM). It is found that the apparent contact angles distribute step by step depending on the microstructural spacing size, and several Cassie metastable regions exist. We developed the theoretical model based on the relative change of vapor/liquid/solid three-phase interface energy to interpret it. Cassie wettability on doubly reentrant structure is affected by the pinning of the three-phase contact lines and the variation of the interface energy of the suspended liquid level. The step change of the Cassie wettability will lead to a sudden variation of the interface energy, which results in the discrete distribution of the contact angle in different metastable regions.
  
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  Heat Transfer Characteristics of Flexible Flat Plate Heat Pipe With Wick in Strip Gradient Structure

  LU Hongling, JIA Li, WANG Zhou

  Journal of Engineering Thermophysics. 2025, 46(7): 2283-2289.

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  As wearable electronic devices continue to evolve, conventional heat pipes with rigid structure are increasingly struggling to address heat dissipation demands, thereby garnering significant attention in the field of flexible flat heat pipe research. In this work, a flexible flat heat pipe with a thickness of 1.6 mm and a strip gradient structure wick was fabricated, an experimental investigation was conducted to analyze the influence of varying vapor chamber heights, external dimensions, and mesh numbers on the temperature uniformity and thermal resistance of heat pipe. Meanwhile, in order to evaluate the optimal filling ratio for different types of heat pipes, the concept of liquid content per unit volume was proposed. The results showed that, within a unit volume liquid content ranging from 0.0003 to 0.0004 g·mm⁻³, the flexible flat heat pipe featuring a 0.8 mm vapor chamber height and a strip gradient structure wick comprising 7#200 and 2#350 exhibited superior heat transfer performance, attaining a thermal resistance as low as 0.205 °C·W⁻¹ while being able to withstand up to 10 W of heating power.
  
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  Experimental Study of Frosting Behavior on Cold Airfoil Under Strong Convection

  XIA Bin, XU Xianghua, LIANG Xingang, ZHANG Haoyuan, ZENG Lei, FENG Yi

  Journal of Engineering Thermophysics. 2025, 46(7): 2290-2295.

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  To address the frosting issue encountered by aircraft bodies at low temperatures when entering warm and humid environments, the fundamental problem is refined to the frosting behavior of low-temperature airfoils under strong convection conditions. This study investigates the characteristics of frosting and the impact of frosting on the NACA0012 airfoil using a wind tunnel to provide the experimental environment. The frosting features on the airfoil surface were observed and summarized, and the morphological changes and frosting rates of the frost layer were monitored. The effects of incoming flow velocity, airfoil temperature, and incoming flow humidity on the frosting behavior of the airfoil were studied quantitatively. The results indicate that the lower the airfoil temperature or the higher the incoming flow humidity, the faster the frost layer grows and the thicker it becomes. Conversely, the higher the incoming flow velocity, the slower the frost layer grows and the thinner it becomes. Additionally, when the incoming flow humidity exceeds the saturation humidity at the freezing point, wet-mode frosting occurs, resulting in a liquid water film on the frost surface and a wavy morphology of the frost layer.
  
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  Radiation Characteristics of TiO₂/SiO₂ Composite Materials in Response to Various Contents of Doped Particle

  YIN Jinying, SUN Longzhen, BAO Weifang

  Journal of Engineering Thermophysics. 2025, 46(7): 2296-2300.

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  The radiation characteristics parameters of TiO₂/SiO₂ composite materials were calculated using the Finite Difference Time Domain (FDTD) method, and effects of the doped particle’s content and structure on the radiation characteristics were investigated and analyzed. The analytical results revealed that the spectral radiation characteristics of TiO₂/SiO₂ composite materials without substrate were governed by the peak pattern and wavelength variation of TiO₂ and SiO₂ based on the infrared spectra. Owing to the mixtures of polystyrene and polyimide groups, where the TiO₂ fiber composite materials containing 20% volume proportion of SiO₂ particle, the absorption crosss0ection was about twice in comparison with that of the SiO₂ fiber composite materials containing 20% volume proportion of TiO₂ particle. Furthermore, the thermal radiation barrier performance was also be significantly improved.
  
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  Study on Deep Potential Molecular Dynamics of Ternary Chloride Molten Salts

  HE Can, DONG Wenhao, TIAN Heqing, GUO Chaxiu, ZHOU Junjie

  Journal of Engineering Thermophysics. 2025, 46(7): 2301-2308.

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  NaCl-MgCl₂-CaCl₂ ternary chloride molten salt is a promising thermal storage material in the next-generation concentrated solar power technology. In this study, first-principles simulation results are utilized as a dataset to develop interatomic potentials for ternary chloride molten salts using neural network machine learning techniques. Deep Potential Molecular Dynamics (DPMD) simulations are employed to predict the local structure and thermal properties of NaCl-MgCl₂-CaCl₂ molten salt within the temperature range of 773∼1173 K. The results demonstrate that DPMD simulations can accurately compute the local structure and thermophysical parameters of ternary chloride molten salts. The binding affinity of anions Cl⁻ with cations varies in the order of Mg²⁺ > Ca²⁺ > Na⁺, with the coordination number decreasing gradually with increasing temperature, leading to a progressively looser and disordered molten structure. Additionally, thermal properties such as density, heat capacity, and thermal conductivity, exhibit excellent agreement with experimental measurements, and the variation in ionic self-diffusion coefficients conforms to experimental observations. These findings indicate that DP potentials can accurately simulate the liquid phase structure and thermophysical properties of molten salts by appropriately describing the complex interatomic interactions.
  
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  Effects of Non-radiative Recombination on the Saturation Current of Near-field Thermophotovoltaic System

  WANG Tianbing, LI Song, ZHAO Junming

  Journal of Engineering Thermophysics. 2025, 46(7): 2309-2315.

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  In near-field thermophotovoltaic systems, the near-field radiation has a significant effect on the saturation current under radiative recombination, and analytical approximation model of the J-V characteristics under constant saturation current condition isn’t applicable. However, the effect of near-field radiation on saturation current density when with inevitable non-radiative recombination is unclear. In this work, the effect of near-field radiation on the saturation current of W-GaSb NFTPV systems is investigated considering radiative-only and full recombination. To determine the range of applicability of the analytical approximation model, the condition of constant saturation current should be satisfied with moderate cell thickness and emitter temperature. The results show that the effect of near-field effect on saturation current is weakened by the non-radiative recombination compared to case of radiative recombination only, and the analytical approximation model is applicable when the non-radiative composite dominates with a constant saturation current density. Increasing the cell thickness strengthens the non-radiative recombination due to the fact that increasing thickness of the cell enhances the carrier diffusion path. Decreasing the emitter temperature enhances the non-radiative recombination because below the optimal operating temperature of the system, the mismatching of the near-field radiative spectrum with the bandgap suppresses radiative recombination. The emitter temperature should be lower than 1200 K for 0.4 µm cell thickness to satisfy the condition of constant saturation current. The present work is useful as a guide for designing thermophotovoltaic systems.
  
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  Investigation on Flow Boiling Heat Transfer in an Interconnected Counter-Flow Microchannel

  HUANG Boqiao, WANG Dahai, ZHANG Chaoyang

  Journal of Engineering Thermophysics. 2025, 46(7): 2316-2323.

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  With the advancement of technology, traditional single-phase flow heat dissipation can no longer satisfy the needs of cooling high-power electronic devices. Therefore, two-phase flow in microchannel structure has increasingly attracted attention. In this study, two interconnected counterflow microchannel heat sink structures are designed. The heat transfer performance, the wall temperature and the pressure drops of the two structures are investigated experimentally with a pump-driven two-phase flow experimental circuit system where we choose R1233zd(E) as the working fluid. We find that due to the enhanced mixing effect of the hot and cold fluids in adjacent channels, these two microchannel structures exhibit better heat transfer performance at high mass flow rate when the heat flux is high. Moreover, at high heat flux area, both structures can significantly reduce the wall temperatures on both end of the channels and can help maintain nucleate boiling at the middle of the microchannels. Also, both structures exhibit better temperature uniformity compared to CCM structure. In terms of the pressure drop, both structure have a significantly better performance compared to CCM structure at high heat flux area.
  
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  Permeability Study of Microscale Copper Inverse Opals With Gradient Pore Sizes

  LIU Dongcheng, WU Yongjia, ZHANG Peng, GAO Yahui, MING Tingzhen

  Journal of Engineering Thermophysics. 2025, 46(7): 2324-2331.

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  Copper inverse opal (IO), a microporous metal that allows fine control of the pore structure, has attracted much attention for its high capillary force, high permeability and low thermal resistance. Inspired by the structure of plant vascular bundles, this paper fabricated gradient-pore copper IO using template assembly and electrochemical deposition techniques. The structure combined the capillary driving force of small pores with the fluid mobility and vapor expulsion ability of larger pores. A test rig was constructed for characterization to evaluate its permeability, and a mathematical physical model of permeability was developed. The comparison between simulated and experimentally measured values verified the optimized permeability of the gradient-pore copper IO.
  
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  Theoretical Calculation and Experimental Study on the Thermo-physical Properties of Ternary Carbonates

  MAO Shuai, AN Zhoujian, DU Xiaoze, ZHANG Dong

  Journal of Engineering Thermophysics. 2025, 46(7): 2332-2340.

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  In order to solve the problems of easy decomposition of carbonates at high temperatures and narrow working temperature range, the formulation of ternary carbonate Salt 1 (31.5%(wt) Na₂CO₃-31.5%(wt) Li₂CO₃-37%(wt) K₂CO₃) was obtained by theoretical calculations in the present study and experimentally investigated. Four sets of carbonates with different ratios were also prepared and examined for their thermophysical properties. The results showed that Salt 1 had better integrated thermophysical properties with melting point and latent heat of phase transition of 668.72 K and 322.06 J·g⁻¹, respectively. The specific heat capacity of the carbonate increased slowly when melting started at 653.15 K. The specific heat capacity of the carbonate increased slowly at 766.15 K. The specific heat capacity of the carbonate increased slowly at 766.15 K. At 766.15 K, the specific heat capacity remained around 1.5 J·g⁻¹·K⁻¹, and the viscosity was below 0.01 Pa·s above 783.15 K, with good flow properties. The decomposition temperature and thermal conductivity of sample Salt 1 were 1158.88 K and 1.325 W·m⁻¹·K⁻¹, respectively). Finally, the mixed carbonates showed good thermal stability when held at 873.15 K for 100 h and cooled/heated from room temperature to 873.15 K for 100 times.
  
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  Preparation and Properties of Al-12Si/Al₂O₃ High-temperature Form-stabilized Phase Change Composite Thermal Storage Material

  SHENG Nan, LU Shasha, SHI Songcen, LIU Quansheng, ZHU Chunyu, RAO Zhonghao

  Journal of Engineering Thermophysics. 2025, 46(7): 2341-2347.

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  This study reports the preparation of Al-12Si/Al₂O₃ high-temperature form-stabilized composite phase change thermal storage material, by employing Al-12Si microspheres as phase change materials and Al(OH)₃ powders as composite matrix raw material. The composites are prepared by three steps including boiling water treatment, compressing for cylinder sample formation, and high temperature heat oxidation treatment. The morphology, microstructure, phase change properties, thermal cycling properties and the anti-leakage performance of the sample are investigated. When 50% Al(OH)₃ is added, the as-obtained composite sample indicates the best encapsulation effect which can avoid the leakage of molten metal at high temperature. At the same time, the sample also shows good thermal cycling stability, in which after 100 cycles of melting and solidification cycling test, the sample is still entire without leakage and obvious degradation of the phase change properties. The as-explored composite phase change material shows good application prospect in the area of high temperature thermal storage.
  
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  Numerical Simulation of Heat Transfer and Flow Characteristics in a Circular Tube Equipped With Rotors

  OU Gen, LIU Zhichun, LIU Wei

  Journal of Engineering Thermophysics. 2025, 46(7): 2348-2352.

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  In response to the limitation of traditional numerical models for self-rotating inserts, the six degree-of-freedom model is introduced in this research to enhance the computation of rotational speed. Subsequently, a novel numerical simulation is proposed to investigate the heat transfer and flow characteristics in a circular tube equipped with rotors. The accuracy of the model is validated through comparison with experimental data. Compared with the fixed rotor, it is observed that the rotation of the rotor decreases the heat transfer coefficient slightly while reducing the flow resistance effectively in the tube, thereby indicating the superior overall performance of the self-rotating rotor. Furthermore, the impact of structural parameters on the heat transfer and flow characteristics in the tube is analyzed, potentially guiding the optimization of these parameters.
  
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  Research on L-shaped Metal Foam Flow Field in Proton Exchange Membrane Fuel Cells

  GONG Anyishi, XIA Yuzhen, HU Guilin

  Journal of Engineering Thermophysics. 2025, 46(7): 2353-2360.

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  Metal foams are used as the flow field of proton exchange membrane fuel cells (PEMFC), in which the gas distribution is uneven. There are some dead zones where reactants cannot reach and the flooding occures under higher humidity. An L-shaped metal foam combined with different porosity is designed for the cathode flow field. The mass transfer and water management is studied based on the numerical simulations considering multiphase flow. It is shown that at 1.8 A·cm⁻², the average oxygen concentration at the interface between the cathode gas diffusion layer and the catalyst layer of the L-shaped flow field (LSF) increases 5.9%, 2.4%, and 4.6%, respectively, compared to the values of three uniform porosity metal foam flow fields (ε=0.9, 0.8, 0.7). To improve the water discharge capacity, the L-shaped flow field with drainage zones (LSF-D) is established. Comparatively, the oxygen concentration increases 13.5%, 9.7%, and 12.0%, respectively, and the average water saturation decreases 24.0%, 25.9%, and 35.9%, respectively. The LSF-D flow field could enhance the mass transfer of reactants; meanwhile improve the ability of drainage in cathode. It is proved to be helpful for higher performance and longer life time of PEMFC. 
  
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  The Significant Regulatory Effect of Pressure on the Thermal Transport Properties of Wurtzite XN (X=Al, Ga) Materials

  TIAN Peng, SONG Xin, LI Qinggang, LI Wenhe, GAO Yufei, TANG Dawei

  Journal of Engineering Thermophysics. 2025, 46(7): 2361-2367.

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  This paper systematically investigates the changes in lattice thermal conductivity of wurtzite GaN and AlN under uniaxial (along the z-axis) and biaxial (within the xy-plane) pressures, based on first-principles calculations and the phonon Boltzmann transport equation method. The study reveals that with increasing axial pressure, GaN exhibits a non-monotonic trend in thermal conductivity (initially increasing, then decreasing), with maximum increases of 25% and 48% under uniaxial and biaxial compression, respectively. In contrast, AlN shows a monotonic pressure dependence, with its thermal conductivity achieving a maximum increase of up to 60% under both uniaxial and biaxial compression. Furthermore, we found that pressure can effectively modulate the anisotropy of thermal conductivity in both materials: for GaN, thermal conductivity can change from the isotropic to the anisotropic under pressure, while for AlN, it can become anisotropic in the opposite way compared to its zero-pressure state. Additionally, we analyze the impact of isotopic scattering on the thermal transport properties of these materials, as well as the effect of axial compression on the electronic structures of GaN and AlN, and compare these findings with the results under hydrostatic pressure. This study provides meaningful insights into the pressure regulation of thermal transport properties and band gaps in semiconductors, offering some directional suggestions for the engineering applications of these materials.
  
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  Study on the Flow and Heat Transfer Characteristics of a Micro Straight Ribbed Tube With Vortex Generator Inserts

  WANG Chongzhao, WU Linkai, LI Xinpeng, LIN Zhimin, HOU Bo, WANG Liangbi

  Journal of Engineering Thermophysics. 2025, 46(7): 2368-2381.

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  To investigate the flow and heat transfer characteristics of the micro straight-ribbed tube with vortex generators (VGs) and the parametric effects including the twisted ratio (T_r = 3, 4, 5 and 6), the pitch ratio of VGs (S_t/W = 0.83, 1, 1.25 and 1.67), and the base tape width ratio (W_b/W = 0.3, 0.45, 0.6 and 0.75), a comprehensive study is carried out by using numerical methods. The results show that: in the range of Re from 3000 to 30000 and the studied geometric parameters, the Nu_m/Nu₀ and f/f₀ of the micro straight-ribbed tube with VGs are 1.17∼2.16 and 3.87∼5.07, respectively, and the heat transfer enhancement factor named as JF can reach up to 1.3; for the micro straight-ribbed tube placed with VGs, the average Nussle number Num increases with the decrease of T_r, while both W_b/Wand S_t/W have little effects on Num, particularly at the lower studied Re, however at higher Re, Nu_m decreases slightly with increasing S_t/W; the friction factor f increases with the decrease of T_r and S_t/W and with the increase of W_b/W. Compared with the smooth circular tube, the micro straight rib tube, and the circular tube fitted with VGs or with twisted tape, the combination of the respective advantages of micro straight ribs and VGs together play a role in strengthening the heat transfer, and thus have a better heat transfer effectiveness. 
  
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  Enhanced Thermal Transport at the Graphene/Silicon Substrate Interface via Heat Treatment

  LIU Wenxiang, SUN Qiangsheng, HUANG Dezhao, HUANG Xiaona, YUE Yanan

  Journal of Engineering Thermophysics. 2025, 46(7): 2382-2387.

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  This study investigates the impact of annealing on the thermal transport at the interface between graphene and a silicon substrate, addressing the issue of interface thermal regulation. Raman thermometry was employed to measure the interfacial thermal resistance between graphene and the silicon dioxide/silicon substrate under different annealing cycles. Experimental results show that the interfacial thermal resistance decreased by an order of magnitude from 9.51 × 10⁻⁵ K·m²·W⁻¹ before annealing to 5.00 × 10⁻⁶ K·m²·W⁻¹ after annealing. The primary reason for this reduction is that annealing causes the monolayer graphene to adhere more closely to the substrate. Atomic force microscopy measurements indicate that the surface roughness of graphene decreased from 0.609 nm to 0.433 nm after annealing.
  
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  Research on Mass Transfer Characteristics of CO₂ Reduction Electrolytic Cell Based on Membrane Electrode Assembly

  YANG Kang, XU Guoliang, DUAN Jingjing

  Journal of Engineering Thermophysics. 2025, 46(7): 2388-2393.

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  Membrane electrode assembly (MEA) is a key part of electrocatalytic carbon dioxide reduction (eCO₂RR), which converts carbon dioxide into valuable chemicals and fuels. This paper proposes a structural design of a CO₂ reduction electrolyser based on a membrane electrode assembly to simultaneously achieve the diffusion of CO₂ and the timely discharge of the product carbon monoxide (CO). The experiment investigated the effects of different flow channel configurations on the catalytic activity, product distribution and current density of the reaction system. The results showed that the vein-shaped bionic flow channel achieved a CO Faraday efficiency of up to 96.72 % at a cell voltage of 2.5 V and a current density of 115 mA·cm⁻². Combined with numerical simulation, the coupling relationship between CO₂ mass transfer and electrochemical reaction was established. 
  
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  Study on Double-Diffusive Characteristics of the Rolling Process Based on the Schlieren Method

  HU Zhihao, DONG Liang, ZUO Zhongqi, TONG Lige, WU Ping, WANG Li

  Journal of Engineering Thermophysics. 2025, 46(7): 2394-2400.

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  With the development of energy storage technology in recent years, the demand for cryogenic liquid air and liquefied natural gas tanks has been increasing. Researchers mainly explore the rollover phenomenon induced by double-diffusive convection in cryogenic mixtures through numerical methods. However, due to the lack of experimental data, the credibility of numerical simulation models in practical applications still needs to be improved. This paper innovatively applies the Schlieren method to study double-diffusive convection at the stratified interface of multi-component mixtures. A visualization experimental system for double-diffusive stratification of mixtures at room temperature was designed and constructed. By adjusting the concentration difference of the saltwater solution, the intensity of external heat flux, and the heating position, along with PIVlab postprocessing images, parameters such as rolling time, velocity, and vorticity at the density-stratified interface were obtained. The relationships between these parameters and heating power, concentration difference across the interface, and heating position were analyzed. A fitting relationship between heating power, Rayleigh number and the occurrence time of mixture rolling was proposed, providing an effective reference for preventing rolling in cryogenic mixtures.
  
  
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  Review of the Formation and Evolution of Fuel Film During Spray-wall Impingement

  LUO Hongliang, XU Ru, LU Chao, WANG Huaiyu, LIU Dai, WANG Yang, XIONG Qian, LIU Long

  Journal of Engineering Thermophysics. 2025, 46(7): 2401-2414.

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  Internal combustion engines are confronted with great challenge of global carbon reduction. Their main development directions will be the green and low-carbon, energy conservation and emission reduction, as well as high-power density. With the application of high-pressure direct injection, regardless of whether traditional fuels or green and low-carbon or zero-carbon fuels are used in the future, the wet wall phenomenon caused by direct injection in the cylinder will be inevitable. This paper provides a comprehensive review of published literatures concerning the quantitative measurement methods for fuel film, film formation mechanism and computational simulation model, etc. This review is concluded with recommendations concerning future work that is needed to address attention on the green methanol direct injection impingement problem in internal combustion engines and characteristics of the wet wall. Besides, research on the construction of fuel film models for methanol fuel engines, simulation calibration and high-precision calculation, as well as the fuel film reduction strategies, are all key and difficult issues in the future of engineering thermos-physics.
  
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  Flashback Characteristics of Premixed Rich Hydrogen Fuel/Pure Oxygen Jet Flames Under Water Vapor Dilution

  QIN Sibo, YAO Qiang, LÜ Hailu, ZHANG Yang, ZHANG Hai

  Journal of Engineering Thermophysics. 2025, 46(7): 2415-2426.

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  Rich hydrogen fuels, as a typical low-carbon energy source, have attracted significant attention under the “dual carbon” strategy. Micromixing combustion and water vapor dilution can significantly reduce the risk of flashback in rich hydrogen fuels. This study investigates the flashback boundaries of various rich hydrogen fuels under water vapor dilution through experiments with micromixing single-nozzle jet flames. The experiments reveal that the flashback processes of the tested rich hydrogen fuels exhibit boundary-layer flashback characteristics. Parameters such as the water vapor dilution ratio, hydrogen content in the fuel, and equivalence ratio significantly affect the mean outlet velocity, laminar flame propagation speed, and nozzle edge temperature at the flashback onset, thereby influencing the flashback process. A predictive model for the flashback boundary of micromixing single-nozzle jet flames under water vapor dilution was developed based on the critical velocity gradient theory of boundary-layer flashback. The model predictions qualitatively and quantitatively match the experimental results, with a prediction error of less than 17%.
  
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  Experimental and Numerical Study on the Effect of Diluent on Laminar Flame Speeds of Hydrogen

  LÜ Senlin, HU Erjiang, YIN Geyuan, HUANG Zuohua

  Journal of Engineering Thermophysics. 2025, 46(7): 2427-2434.

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  In this paper, the near-limit laminar flame speeds of H₂/air at different N₂ and CO₂ dilution ratios were measured on a constant volume combustion bomb. Six H₂ mechanisms were verified against the experimental data using numerical simulation. Finally, the NUIG 2013 mechanism was adopted and the chemical, physical and global effects of four diluents(N₂/AR/HE/CO₂) were investigated by using the pseudo dilution gas method. Furthermore, the chemical reaction kinetics was analyzed. The results indicate that the minimum laminar burning velocity measured for H₂/air/diluent premixed flame is about 2 cm/s. In the near-limit condition, the predicted values of different mechanisms are low, which are significantly lower than the experimental values. Dilution inhibition ability CO₂>N₂>AR>HE, CO₂ dilution gas exists the strongest inhibition effect on the chemical effect, and HE exists the weakest inhibition effect, which is due to its higher thermal diffusivity and lower specific heat capacity than the other three diluents. The analysis of chemical reaction kinetics showed that the sensitivity of reaction H+O₂+M ⇔ HO₂+M increased with the increase of diluent ratio. Diluent, as the third body m of the system, controlled the reaction rate. The difference of reaction rate of this reaction may be the reason for the difference between mechanism prediction and experimental value at the near-limit condition.
  
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  Effect of the Bluff-body Temperatures on the Lean Premixed Flame Behavior and Structure

  CAI Siqi, YANG Wenquan, LI Lang, WAN Jianlong

  Journal of Engineering Thermophysics. 2025, 46(7): 2435-2439.

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  To enhance the bluff-body stabilized lean premixed flame performance and reveal the impact of bluff-body temperature on the lean premixed flame dynamics, the effect of bluff-body temperature on the lean methane-air premixed flame behavior and structure are investigated via experiment and numerical simulation. Three bluff-body temperatures are employed: natural heatconducting bluff-body (NHB), heated bluff-body at 600 K (HB-600), and heated bluff-body at 900 K (HB-900). The results indicate that in the case of HB-900, the flammability limit of the lean premixed mixture is significantly expanded, and a stable residual flame is observed for the first time in the case of Lewis number of 1.0. Furthermore, the flame structures are revealed at various bluff-body temperatures via numerical simulation. In the case of NHB, the flame structure includes the adiabatic zone and mixed zone. By contrast, in the case of HB-600 and HB-900, the flame structure includes the adiabatic zone, excess reaction zone, and weak reaction zone. The present study provides the theoretical foundation for improving the lean premixed flame performance based on the high-temperature bluff-body.