25 August 2024, Volume 45 Issue 9

    

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  The Performance Study on La_1−xSr_xFe_0.8Al_0.2O₃ Oxygen Carriers in Chemical Looping Dry Reforming of Methane for Syngas Production

  YANG Tianlong, ZHANG Jinrui, RAO Qiong, GAI Zhongrui, LI Yang, PAN Ying, JIN Hongguang

  Journal of Engineering Thermophysics. 2024, 45(9): 2551-2557.

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  Chemical looping can achieve high product selectivity using lattice oxygen in oxygen carriers for partial oxidation of methane. Oxygen carrier La_1−xSr_xFe_0.8Al_0.2O₃ was prepared by sol-gel method for chemical looping dry reforming of methane. The reaction performance of the oxygen carrier doped with different proportions of Sr was tested by thermogravimetric and fixed bed reactor. The experimental results showed that the oxygen capacity of x=0.4 oxygen carrier in La_1−xSr_xFe_0.8Al_0.2O₃ is as high as 1.88 mmol·g⁻¹, with excellent reaction performance and less carbon deposition. The stability of the oxygen carrier La_0.6Sr_0.4Fe_0.8Al_0.2O₃ was further tested for 20 redox cycles. The oxygen carrier maintained excellent redox performance, achieving 61.2% methane conversion, 97.1% CO selectivity, and 1.81 H₂/CO. The material characterization results displayed that the morphology and crystal structure of the oxygen carrier were stable. The results show that La_0.6Sr_0.4Fe_0.8Al_0.2O₃ is an excellent oxygen carrier suitable for chemical looping dry reforming of methane.
  
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  Experimental Study of the Performance of an Electrically-driven Free-piston Stirling Heat Pump

  WANG Riying, HU Jianying, WU Zhanghua, ZHANG Limin, JIA Zilong, LUO Ercang

  Journal of Engineering Thermophysics. 2024, 45(9): 2558-2564.

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  Heat pump heating technology can effectively reduce the energy consumption and environmental pollution caused by coal-fired heating. However, the low-temperature adaptability of commonly used heat pump heating systems is poor, making it difficult to meet the heating demand in cold regions. Considering that Stirling heat pump technology has a wide range of available temperature zones, an electrically-driven free-piston Stirling air source heat pump is developed in this paper to investigate its heating performance under different climatic conditions. The experimental results show that the overall coefficient of performance of the Stirling heat pump reaches 2.31, 1.97 and 1.78 for normal, cold and very cold regions, respectively. In addition, the relative Carnot efficiency of the Stirling heat pump gradually increases with rising heat-pumping temperature difference. Its advantage is more obvious at large heat-pumping temperature difference.
  
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  Parametric Optimization and Thermo-Economic Analyses of Geothermal ORCs Using HFOs as the Working Fluids

  LIU Qiang, WANG Chunyan, DUAN Yuanyuan

  Journal of Engineering Thermophysics. 2024, 45(9): 2565-2571.

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  A thermo-economic model was used to analyze the thermodynamic and economic characteristics of a geothermal ORC system. The evaporation and condensation temperatures of typical hydrofluoroolefins (HFOs) working fluids including R1224yd(Z), R1233zd(E) and R1336mzz(Z) were optimized to obtain the maximum net power. The thermo-economic characteristics were analyzed and compared with the traditional working fluids R601, R601a and R245fa. The results show that the evaporation and condensation parameters of R1224yd(Z) and R245fa are close under the optimal conditions. When the geothermal water inlet temperature is lower than 130°C, the net output power of R1336mzz(Z) is the maximum among the selected fluids, which is 1.47%∼1.89% more than that of R1233zd(E); but the heat exchanger area increases by more than 17%. When the geothermal water inlet temperature is higher than 130°C, the net output power of R245fa is the maximum, and the power generation cost is reduced by 15.5%∼16.8% compared with R1336mzz(Z).
  
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  Experimental Study on Isobaric Specific Heat Capacity of Ethane and Ethane + Propane at Low Temperature

  SHENG Bowen, ZHAO Yanxing, DONG Xueqiang, GONG Maoqiong

  Journal of Engineering Thermophysics. 2024, 45(9): 2572-2579.

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  In this paper, a flow calorimeter was developed for the measurement of isobaric specific heat capacity (c_p) at low temperature. The calorimeter was composed of four parts: thermostatic bath, flow system, calorimeter and data acquisition system. The calorimeter can measure the c_p in the temperature range of 115 ∼ 340 K, and the pressure can reach 8 MPa. The uncertainty of temperature, pressure and heat capacity were 11 mK, 0.02 MPa and 0.9%, respectively. The c_p data of propane, isobutane, ethane and ethane + propane binary mixtures at low temperature were measured. The measured data showed a good agreement with the calculated values of high-precision Helmholtz equation of state. The average absolute relative deviations of propane, isobutane, ethane and ethane + propane was 0.26%, 0.32%, 0.31% and 0.38%, respectively, which verified the reliability of the device.
  
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  Thermodynamic Characteristics of Phase Transition During Natural Gas Hydrate Decomposition by Depressurization

  TIAN Mengru, DONG Shuang, LI Jing, YANG Mingjun, SONG Yongchen, ZHENG Jia’nan

  Journal of Engineering Thermophysics. 2024, 45(9): 2580-2585.

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  The exploitation of natural gas hydrate is a major strategic demand of the country, and further improvements in 
  production and efficiency are needed before its commercial development. How to realize its efficient exploitation depends on the thermodynamic mechanism of the hydrates. Traditional hydrate thermodynamics studies are limited to phase equilibrium characteristics and lack the consideration of non-equilibrium thermodynamics in the hydrate decomposition process. At the same time, the hydrate decomposition process may be accompanied by icing and melting. The thermodynamic characteristics of hydrate exploitation under complex heat and mass transfer conditions need to be clarified. In this study, a 2 L natural gas hydrate depressurization decomposition experimental system was used to simulate the hydrate reservoirs with different distributions and perform long depressurization (to 1.0 MPa) at a constant exhaust rate of 0.55 L·min−1(normal conditions). The results show that there is a non-equilibrium thermodynamic relationship (T[°]=8533.8/{38.98−ln(1000p[MPa])}−275.25) between the temperature and pressure in the hydrate-bearing area during the depressurization process, which is only controlled by the hydrate decomposition and is not affected by the reservoir temperature gradient. According to the Gibbs phase law, the thermodynamic freedom of phase transition process is 1. As a result, the natural gas hydrate decomposition belongs to the phase transition process, and the quantitative relationship between temperature and pressure is consistent with the thermodynamic theory. When the hydrates depressurize to about 2.1∼2.3 MPa, instantaneous icing occurs in the reservoir, leading to a sudden increase in temperature and accelerating the hydrate decomposition. Due to the constant exhaust rate, the accumulated gas increases the pressure up to 2.36 MPa. It is found that the temperature and pressure of hydrate-bearing reservoir still satisfy the non-equilibrium thermodynamic phase diagram of hydrates before and after icing. This study illustrates the thermodynamic mechanism of phase transition in the presence of heat and mass transfer in the natural gas hydrate decomposition process, which can provide a more practical theoretical basis for the process of exploitation site monitoring.
  
  
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  High-Temperature Condensation Heat Transfer Characteristics of R245fa in a Horizontal Plain Tube

  WU Zhantao, XIA Yangkai, LUO Xianglong, HE Jiacheng, CHEN Jianyong, LIANG Yingzong, YANG Zhi, CHEN Ying

  Journal of Engineering Thermophysics. 2024, 45(9): 2586-2592.

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  High-temperature heat pump is recognized as an effective solution for industrial decarbonization. R245fa has widely employed in high-temperature heat pump systems for its favorable thermal properties. Nevertheless, there is currently a dearth of reported research on the condensation heat transfer characteristics of R245fa under high-temperature conditions. This study experimentally investigated the condensation heat transfer characteristics of R245fa within a 9 mm horizontal circular tube at vapor quality range of 0.1∼0.9, mass flux range of 218∼393 kg·m⁻²·s⁻¹, saturation temperature range of 80∼100°C, and heat flux range of 11300∼22500 W·m⁻². Based on a comparison between experimental data and existing heat transfer correlations, modifications are made to the existing correlations. The revised correlations exhibited a mean prediction deviation of 6.11%, signifying a significant improvement in prediction accuracy.
  
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  Construction of Three-Dimensional Moisture Swing Adsorption Cycle and Energy Efficiency Analysis

  XIE Renyu, YONG Jinyuan, JIANG Long, ZHANG Xuejun

  Journal of Engineering Thermophysics. 2024, 45(9): 2593-2598.

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  Moisture swing adsorption (MSA) method uses water as a lever to efficiently drive direct air carbon capture. At present, its cycle theory and energy efficiency research are relatively scarce. In this paper, MSA process is analyzed from the perspective of thermodynamic cycle, and a 6-step MSA cycle is constructed in the three-dimensional coordinate system of temperature, humidity, and adsorption capacity. Ideal specific energy consumption, thermodynamic efficiency and adsorbent efficiency of basic isothermal MSA cycle and the 6-step MSA cycle are compared, and the effects of temperature and humidity on each indicator are analyzed. Under the adsorption condition of 25°C and 30% RH, the introduction of temperature swing process can reduce capture energy consumption by 28% at most, and increase the limit of thermodynamic efficiency by 119%.
  
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  Optimal Ecological Performance of Three-Heat-Reservoir Thermal Brownian Heat Transformer

  QI Congzheng, CHEN Lingen, GE Yanlin, FENG Huijun

  Journal of Engineering Thermophysics. 2024, 45(9): 2599-2604.

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  A finite-time thermodynamic model of three-heat-reservoir thermal Brownian heat transformer with heat transfer loss is established, and the heat flow balance equations, heating load, coefficient of performance (COP) and ecological function are derived. The ecological performance characteristics of the cycle are studied by numerical calculation, and the advantages of ecological function as optimization objective are explained. The results show that external heat transfer can only reduce the cycle performance quantitatively, but not change the performance qualitatively. The system performance can be improved effectively by increasing the total thermal conductance of heat exchangers. The three-heat-reservoir thermal Brownian heat transformer can work under maximal ecological function by adjusting the thermal conductance distributions and internal parameters properly. When the heat loading is substituted by ecological function as optimization objective, the heating load decreases less, but the corresponding COP increases more. 
  
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  Investigation of Deviation Model Correction for Transonic Compressor Rotors

  WANG Xiaochen, REN Xiaodong, LI Xuesong, GU Chunwei, QUE Xiaobin, ZHOU Guoyu

  Journal of Engineering Thermophysics. 2024, 45(9): 2605-2611.

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  This paper proposes a theoretical analysis method of deviation angle correction in transonic rotors considering the changes in mean streamline curvatures of S1 stream surfaces. Classical deviation models for subsonic cascades and transonic correction lack the instruction of shock-structure parameters, and causes obvious prediction errors in flow turning and loading characteristics. Based on classical transonic correction method, this paper describes the transonic correction of deviation angle as the outcome of changes in mean streamline curvatures due to transverse pressure difference in the post-shock region of S1 stream surface. The analytical model and empirical correlations of transonic deviation angle are established near the design point. The model is employed to an in-house through-flow code of streamline curvature method, and the correction method is investigated in the first transonic rotor (R1) of a multi-stage axial compressor. The through-flow predictions agree well with experiment data and CFD results.
  
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  Hybrid-Dimensional Simulation of Gas Turbine Coupled with 17-Stage Compressor Through-Flow Model

  WANG Funing, YANG Chen, ZHANG Xiaoyu, ZHANG Min, WANG Zinan, DU Juan,

  Journal of Engineering Thermophysics. 2024, 45(9): 2612-2621.

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  In order to clarify the characteristics of different zooming strategies, and develop the algorithm of gas turbine hybrid-dimensional simulation for multistage compressor with high pressure ratio. For a split-shaft gas turbine and its 17-stage compressor, the hybrid-dimensional simulation models that coupled zero-dimensional engine model and compressor through-flow model were developed based on the De-coupled approach, conventional iterative coupled approach, fully coupled approach, and the improved iterative coupled approach proposed in this paper respectively. The variations of different zooming strategies were compared and analyzed, the results indicate that the De-coupled approach, iterative coupled approach and fully coupled approach can basically achieve the same simulation accuracy, the maximum relative error between simulation result and experimental data is less than 10%. Moreover, the De-coupled approach tends to converge easily, its simulation accuracy and efficiency are affected by factors such as the quality of characteristic map. Although the conventional iterative coupled approach exhibits high simulation efficiency, its robustness is difficult to guarantee in the zooming of multistage compressor with high pressure ratio. The fully coupled approach has relatively low simulation efficiency and high requirements for both the solving algorithm and the initial value of iterative variables. Meanwhile, the improved iterative coupled approach effectively utilizes the wide pressure ratio range of the 17-stage compressor, exhibiting both high robustness and high simulation efficiency, the effect is optimal.
  
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  Numerical Study on Flow and Heat Transfer Characteristics of Multi-stage Impingement Cooling

  WU Hang, YANG Xing, LIU Zhao, FENG Zhenping

  Journal of Engineering Thermophysics. 2024, 45(9): 2622-2630.

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  This paper investigated the flow and heat transfer characteristics of traditional singlestage and multi-stage impingement cooling structures using numerical simulation methods. The results show that the crossflow in the multi-stage impingement restarts accumulating in each stage of the impingement chamber, which inhibits the development of the crossflow and effectively reduces the detrimental effect of the crossflow on the downstream heat transfer. Under a same Reynolds number condition, the multi-stage impingement structures save substantially on coolant usage, and the two-stage impingement brings an 11% enhancement to comprehensive heat transfer performance, proving that the multi-stage impingement has a significant thermal benefit. Under a same coolant flow rate condition, the multi-stage impingement structures have higher Reynolds numbers, which improves the overall heat transfer effect of the target surface. The two-stage, three-stage, and fourstage impingement structures can bring 1.8, 2.3, and 2.6 times of heat transfer enhancement to the target surface, respectively, but pumping power and total jet inlet pressure are also higher, resulting in a decrease in comprehensive heat transfer performance with an increasing number of stages.
  
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  Aerodynamic Performance Analysis of Supercritical Carbon Dioxide Centrifugal Compressor Based on Non-equilibrium Phase Transition

  HUANG Zhe, Yang Wen, LIANG Tiebo, SHEN Xin, OUYANG Hua, DU Zhaohui

  Journal of Engineering Thermophysics. 2024, 45(9): 2631-2639.

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  As the core power component of the supercritical carbon dioxide (SCO₂) Brayton cycle, accurate analysis of the aerodynamic thermodynamic performance and loss characteristics of the compressor under near-critical conditions is crucial for the efficient operation of the cycle. The compressor is prone to condensation when working near the critical point, and the condensation process is non-equilibrium. In this paper, an SCO₂ non-equilibrium condensation model based on the Euler-Euler source term is established and compared with the equilibrium condensation model to evaluate the impact of the non-equilibrium condensation process on the aero-thermodynamic performance of the SCO₂ centrifugal compressor. The results show that the non-equilibrium condensation model is more accurate in predicting efficiency, and non-equilibrium condensation will cause the compressor to enchance the inlet flowrate and enter near-surge conditions faster.
  
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  Numerical Study of the Torsional Movement of the Discharge Valve of a Rotary Compressor

  ZENG Wang, PAN Xi, XIE Junlong

  Journal of Engineering Thermophysics. 2024, 45(9): 2640-2645.

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  The discharge valve is a key component of the compressor, and the good dynamic characteristics of the valve plate could guarantee the economy and reliability of compressor. In order to investigate the rotary compressor discharge valve motion characteristics, this paper uses the computational fluid dynamics method (CFD) to establish a three-dimensional fluid-solid interaction calculation model. On this basis, the simulation has obtained the pressure contour in rotary compressor, the displacement curve and the impact stress distribution contour of the discharge valve. The results show that the head of valve plate near the oblique incision side impacts lift limiter firstly, but the larger stress appears in the head of valve plate near the cylinder side and the neck of valve plate under the action of the pressure difference and torsional moment, which is easy to bring about the valve plate fracture.
  
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  Analysis on Sensitive Parameters of Full-3D Optimization of a Centrifugal Impeller

  ZHANG Xiaotian, JI Cheng, ZHANG Chenqing, XI Guang

  Journal of Engineering Thermophysics. 2024, 45(9): 2646-2655.

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  This paper employs the Sobol sensitivity analysis method to extract aerodynamic performance sensitive parameters under 114 control parameters for centrifugal impellers. By comparing the internal flow fields of the baseline and optimized impellers, this research examines the basis and rationality of the flow mechanism hierarchy for the full three-dimensional optimization results of centrifugal impellers. The findings indicate that the sensitive parameters for blockage flow are located near the throat of the impeller, demonstrating that sensitivity analysis methods can identify key control parameters for specific aerodynamic performance. The sensitive parameters for pressure ratio are distributed at the trailing edge of the blades. Modification of the optimized impeller’s trailing edge shape has improved the uniformity of the relative flow angle at the diffuser inlet without altering the relative pressure distribution along the span at the impeller outlet; The sensitive parameters for efficiency are concentrated at the leading edge of the main blade. The optimized impeller’s control over the convexity and concavity of the blade leading edge has reduced shock and secondary flow losses, achieving an improvement in efficiency. After further research into the high-order interactions of control parameters, sensitivity analysis methods can be used to reduce the number of control parameters and increase the speed of the full three-dimensional optimization approach.
  
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  Influence of Airfoil Profile and Excitation Parameters on Plasma Flow Control

  WANG Dan, WANG Jifei, QIN Ziyang, LIU Suyao

  Journal of Engineering Thermophysics. 2024, 45(9): 2656-2670.

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  Flow control can improve the force state of airfoil and thus improve the aerodynamic characteristics. As an active flow control technology, plasma flow control is one of the hot spots in current research. In this paper, a plasma phenomenological model is adopted, which ignores the influence of plasma excitation on momentum and only considers the influence of energy injection on heat effect. The model is coupled with the flow N-S equation to study the control effect of plasma aerodynamic excitation on airfoil flow separation with different geometric shapes by numerical simulation.The simulation results show that: The application of plasma excitation can improve the aerodynamic characteristics of airfoil by increasing lift and drag, and control the flow separation of airfoil. With the increase of airfoil thickness, the increase of Cl decreases from 147.7% to 72.6%, and the increase of Cl decreases from 147.7% to 19.6% with the increase of bend. The control effect of the excitation flow is weakened and the position of the maximum thickness is near the front or back. In addition, the flow control function is related to the excitation parameters, and changing the excitation voltage peak and frequency will affect the control effect. The research and analysis can provide help for subsequent airfoil selection and better selection of excitation parameters.
  
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  Researches on Solid-liquid Melting Process Based on MRT-LBM Simulation

  CHEN Weiqi, SONG Zhichao, QUAN Dongliang, HE Yurong

  Journal of Engineering Thermophysics. 2024, 45(9): 2671-2677.

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  Due to the characteristics of little temperature/volume change and strong latent heat release/absorption, the solid-liquid melting process is extensively utilized in engineering technologies. In order to better utilize the solid-liquid melting process for energy storage, based on double multiple relaxation time lattice Boltzmann method, the solid-liquid melting process in the square cavity is numerically investigated in this work. The effects of different Rayleigh numbers (Ra) and Stefan numbers (Ste) on the melting process are studied, and the corresponding dimensionless results are presented. The findings show that an increase in Ra number is beneficial for the formation of velocity vortices as well as for causing the convection to begin earlier. The Ste number has no noticeable effect on the formation of velocity vortices, but it can also bring the onset time of convection forward. Additionally, a decrease in Ra or Ste numbers is advantageous for accelerating the melting process.
  
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  Molecular Simulation of Nanodroplet Impact Wetting Carbon Nanotube Arrays

  FENG Xiaoyuan, RAN Jingyu, SHAO Yunlin, HUANG Xin, YANG Tong, SANG Guohua

  Journal of Engineering Thermophysics. 2024, 45(9): 2678-2686.

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  In this paper, molecular dynamics simulations are used to study the wetting characteristics of water nanodroplets on different carbon nanotube arrays. The effects of different structures and surface modified carbon nanotube arrays, and different initial motion states of nanodroplets on the wetting properties were investigated. The results show that the chiral parameters n=30 and m=0 carbon nanotubes have stronger water resistance, and the carbon nanotube arrays arranged in parallelepiped with a spacing of 9 nm are favorable to maintain the droplet morphology and avoid irregular wetting phenomena; the diffusion behavior of nanodroplets on the surface gradually changes from the spreading of droplets to the diffusion of gases during the increase of ambient temperature; the dimensionless wetting radius is the smallest when the nanodroplet We number is 6.74 The minimum, the wetting process is changed from surface tension-dominated to inertia force-dominated; the change of nanodrop motion angle does not affect the final wetting radius of droplets, but irregular wetting phenomenon will occur at small angles, causing the kinetic energy of nanodroplets to be lost in friction and deformation, which has a negative impact on the anti-water performance.
  
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  Parameter Measurement and Flow Pattern Study on Gas-Liquid Two-Phase Flow in Vertical Helically Coiled Tube

  LI Xi, CHEN Kexin, ZHU Yanlin, WANG Hengyuan, LI Huixiong

  Journal of Engineering Thermophysics. 2024, 45(9): 2687-2695.

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  Due to the more complex flow pattern distribution and transition characteristics in the gas-liquid two-phase flow in a helically coiled tube steam generator (HCT-SG) compared to a straight tube, accurately measuring the flow pattern distribution and predicting its transition rules are of great importance for the design and operational safety of HCT-SGs. In the present study, a two-sensor conductivity probe measurement system for measuring two-phase flow parameters in HCTs was developed. By using the conductivity probe, flow parameters of gas-liquid two-phase flow in a vertically HCT with an inner diameter of 8 mm were measured on a water-air two-phase flow experimental system. A high-speed camera was used to record the typical phase distribution characteristics of each flow pattern. The features and transition processes of two-phase flow patterns in the helical tubes were analyzed by combining the two-phase flow parameters obtained from probe with high-speed photographic images. Based on the measurement data from the conductivity probe, the effects of the superficial velocities of the gas and liquid phases on the void fraction, bubble velocity, and bubble length were analyzed, and the correspondence between bubble length, void fraction, highspeed photographic characteristics, electrical signals, and flow patterns was established. It was found that in the range of the present experiment, the flow regimes of gas-liquid two-phase flow in HCT could be divided into four types: plug flow, slug flow, bubble flow, and slug-annular flow. Among them, the two-phase flow parameters distribution range corresponding to the slug-annular flow is the widest, and the range of parameters for this flow pattern is larger than that reported in the
  literature.
  
  
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  Evaluating and Correcting Laser Diffraction Particle Size Measurement Errors at Different Obscurations

  SU Geyi, SUN Cunjin, DENG Fei, SU Mingxu

  Journal of Engineering Thermophysics. 2024, 45(9): 2696-2701.

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  Multiple scattering effects can result in an underestimation of the particle size. To investigate the light scattering characteristics of high-obscuration particles, a Monte Carlo methodbased Mie model has been developed. A constructed system was utilized to conduct a series of experiments on two standard particles at different concentrations, measuring both scattered light energy distribution and obscuration simultaneously. The results show that the Monte Carlo model agrees well with the traditional model. When multiple scattering was taken into account, as the obscuration increased, the scattered light energy curves gradually shifted, and the inversion error gradually became larger. For an obscuration range of 0.15∼0.20, the inversion error is within 5%. However, for an obscuration range of 0.55∼0.60, the inversion error escalated beyond 13%. Moreover, by utilizing inversion correction on experimental spectra for 2.6 μm, the error was successfully reduced to ≤3%. The model allows for the accurate inversion of particle size in the presence of high obscuration.
  
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  Study on Pressure-based Numerical Simulation Algorithm of Hydraulic Slug

  SHI Guoyun, GONG Jing

  Journal of Engineering Thermophysics. 2024, 45(9): 2702-2706.

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  A pressure-based algorithm is proposed to simulate the initialization and development process of hydraulic slug. Firstly, the algorithm combines the two-fluid model and the appropriate closed relationship to construct a mathematical model suitable for hydraulic slugs. Secondly, in order to solve the singular problem of the equations caused by the absence of gas in the slug head, a pressure-based solution algorithm that can simultaneously deal with the coupling of the singlephase and two-phase between the slug body and the liquid film region is proposed. The results show that the algorithm can automatically initialize the hydraulic slug and simulate the conversion process of stratified flow to hydraulic slug flow, which is consistent with the common flow pattern conversion diagram. At the same time, the slug frequency and length are random, and the statistics are consistent with the empirical relationship.
  
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  Heat Transfer Characteristics of Passive Solar Porous Thermal Storage Wall with Heat Absorption and Storage

  LI Wei, LING Xiang, ZENG Min

  Journal of Engineering Thermophysics. 2024, 45(9): 2707-2713.

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  This work investigates the heat transfer performance of a porous thermal storage wall (PTSW) based on a composite sorbent of hydrates for the solar energy direct storage and conversion process under dynamic variations in solar irradiance and ambient temperature. The results indicate that during the charging phase with solar irradiation, the temperature of the PTSW and the outlet air temperature of the channel first increase and then decrease, reaching their maximum values at 14:30, approximately 67.5°C and 47.9°C, respectively. Before 20:00, the outlet temperature remains above 30°C, and the desorption conversion rate at this time is 0.82. During the discharging phase, the temperature initially increases and then stabilizes. The adsorption conversion rate at 09:00 the next day is approximately 0.75, and the outlet temperature during the stable period is around 39.7°C. This PTSW enables the efficient utilization of solar heat with extended heating periods.
  
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  Molecular Dynamics Simulation of the Deposition Characteristics of Composite Fouling on Rough Surfaces

  WANG Jingtao, YANG Jialin, SUN Hongjian, JIA Yuting, WANG Bingbing, XU Zhiming

  Journal of Engineering Thermophysics. 2024, 45(9): 2714-2723.

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  To explore the deposition characteristics of composite fouling on rough surfaces, this study takes the mixed system composed of MgO particle and calcium carbonate solution as the research object. The molecular dynamics simulation method was used to analyze the deposition mechanism of composite fouling on different rough surfaces and under motion states. The results show that in a static state, Ca²⁺ and CO₃²⁻  in the mixed system are adsorbed on the surface of MgO particle and the wall to form calcium carbonate clusters, and MgO particle are indirectly adsorbed on the wall through calcium carbonate clusters. The interaction energy between ions and particles with wall surface increases with increasing wall roughness coefficient, and more Ca²⁺ and CO₃²⁻  were adsorbed. Under motion conditions, the deposition process of composite fouling exhibits similar patterns as in a static state. The action of shear forces prolongs the deposition time of composite fouling, and the roughness significantly affects the deposition of composite fouling. The deposition of MgO particle on the wall surface is related to the number of adhesion points of Ca²⁺ and CO₃²⁻  on the surface of MgO particle and the bond strength between calcium carbonate clusters and the wall. Moreover, Ca²⁺ and CO₃²⁻  are more likely to deposit on the top surface and edges near the rough structure of the wall.
  
  
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  Study on Convective Heat Transfer Coefficient of Porous Foam Interface Based on Single Cell Pore Structure

  LI Wenhao, FAN Rongrong

  Journal of Engineering Thermophysics. 2024, 45(9): 2724-2731.

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  The interfacial convective heat transfer coefficient is a key parameter in the study of the flow and heat transfer process of porous foam using the local thermal non-equilibrium model. In this paper, the body center tangent sphere method is used to construct the cell pore structure of porous foam to simulate the real physical structure of porous foam. The numerical simulation of the flow and heat transfer process under the pore structure is carried out to calculate the convective heat transfer coefficient, and the Nusselt number obtained from the experimental research in the literature is compared to verify the accuracy of the numerical simulation. Then, the flow and heat transfer process of porous foam with different pore structures is numerically simulated, The criterion correlation of interfacial convection heat transfer coefficient is established by data fitting. Based on the established correlation of the interfacial convection heat transfer coefficient criterion, the macro numerical simulation of the flow and heat transfer process of porous foam under the two assumptions of local heat balance and local heat non-equilibrium was carried out and compared with the experimental values in the literature. The accuracy of the established correlation was further verified, indicating that the method of obtaining the interfacial convection heat transfer coefficient based on the structure of single cell pores was effective. It is also verified that the local thermal non-equilibrium model can more accurately describe the flow and heat transfer process of porous foam.
  
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  VO₂/GST Photonic Structure Combined with ANN for Multi-level Dynamic Spectral Selectivity

  SONG Kuilong, XIE Ming, AI Qing

  Journal of Engineering Thermophysics. 2024, 45(9): 2732-2735.

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  Photonic structure with selective absorption performance and emission control ability are widely applied in many fields. In this work, a design of multilayer photonic structure including two phase-changing materials is presented. Firstly, the spectral reflectivity of the structure is calculated by FEM method, and a dataset is established to train a ANN model. Finally, the multi-level dynamic spectral selectivity of the photonic structure combined with phase-changing material VO₂ and GST is demonstrated. The results show that when the structural parameters are d₁=0.1 μm and d₂=0.3 μm, the calculation time of the ANN model is 1.5 s, which saves the calculation time. The four modes of this photonic structure exhibit different spectral selective absorption. This work provides an idea of multi-level dynamic control for spectral selectivity.
  
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  Experimental Investigation on Heat Transfer Performance of R32 Oscillating Heat Pipe

  LI Yadong, JI Yulong, YU Chunrong, WU Mengke, YANG Xin, LIU Zhang, FENG Yanmin

  Journal of Engineering Thermophysics. 2024, 45(9): 2736-2741.

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  To investigate the working fluid of the oscillating heat pipe with high heat transfer efficiency, an experimental investigation was conducted to study the heat transfer performance of R32 oscillating heat pipe with filling ratios of 30% to 70%, operating angles of 90°, 45°, and 0°, heating powers ranging from 10 W to 250 W, and diameters of 1 mm and 2 mm. The results show that oscillating heat pipe exhibits minimal thermal resistance at low filling rates. Within the range of operating angles from 90° to 45°, the heat transfer performance is insignificantly influenced by the operating angle. When the operating angle is 0°, oscillating heat pipe cannot start. With the increase of heating power, the thermal resistance of the oscillating heat pipe initially decreases and then increases when the filling ratio is below 50%, when the filling ratio is greater than 50%, the thermal resistance decreases initially and then stabilizes. The oscillating heat pipe with a diameter of 2 mm has the best heat transfer performance, with a minimum thermal resistance of 0.12 °C·W⁻¹. 
  
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  Failure Characteristics and Mechanism of External Short-circuit Thermal Runaway of Lithium-ion Battery

  AN Zhoujian, AN Xian, DU Xiaoze, ZHAO Yabing, SHI Tianlu, ZHANG Dong

  Journal of Engineering Thermophysics. 2024, 45(9): 2742-2749.

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  In this paper, the electrothermal characteristics and failure mechanism of lithium-ion batteries during external short circuit were analyzed, and the performance of batteries without thermal runaway in subsequent use and the potential thermal runaway risk were explored. The results indicated that the temperature and voltage changes of the battery during external short circuits were related to the internal resistance which changes with SOC and short-circuit current. Further external short-circuit batteries were accompanied by phenomena such as electrolyte evaporation, lithium metal deposition, electrode particle rupture, and membrane closure, which affect the internal Li⁺ transport process. The battery without Thermal runaway was tested in the cycle. The battery capacity was recovered in the cycle, and the polarization internal resistance was reduced to the initial level, but the ohmic internal resistance was higher than the initial value. The potential risk of Thermal runaway inside such batteries was analyzed through the secondary short circuit.
  
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  Study on Transient Heat Transfer Characteristics of Gear Pump Based on Machine Learning

  YANG Shiyu, LIN Yuanfang, XU Xianghua, LIANG Xingang

  Journal of Engineering Thermophysics. 2024, 45(9): 2750-2758.

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  In order to study the transient heat transfer characteristics of gear pump, a transient heat transfer model of gear pump was developed by multiple linear regression algorithm and the corresponding temperature prediction model was proposed to avoid the complicated modeling process. The step and cosine responses of the pump outlet temperature with a specific time interval were predicted. The results indicated that the average relative error between the simulation results and the experimental results is only 0.74%∼1.67%. The heat transfer characteristics of the pump under the coupling change of temperature and flow were predicted and the error is less than 2.68%. The temperature step responses at different time intervals were predicted. The results showed that the model could predict the pump outlet temperature at each time well within a certain range. The method presented in this paper can improve the computational efficiency of heat transfer of drive components in thermal management system and provide some technical support for the actual engineering applications.
  
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  Method for Simultaneous Measurement of Temperature-Dependent Thermal Conductivity of Solid-Liquid Phase of Phase Change Materials

  XIAO He, ZHOU Tian, XU Zhangnan, SHI Lei, SUN Zhiqiang

  Journal of Engineering Thermophysics. 2024, 45(9): 2759-2766.

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  A method to simultaneously measure the temperature-dependent thermal conductivity of solid- and liquid- phase of phase change materials has been proved in this study. The theoretical basis is to discretize the temperature region of phase transition into several temperature intervals with very small temperature ranges on a time scale and calculate the thermal conductivity that is changed with temperature by using inverse problem method. Designed an experimental equipment to satisfy the boundary conditions of the theoretical model, including phase change vessel, temperature control system and data acquisition system. The temperature-dependent thermal conductivity of n-eicosane was measured at 70∼10°C and 60∼15°C, the measurement results were compared with the temperature-dependent thermal conductivity of n-eicosane that mentioned in the literature. The experimental results show that the measurement results of the two-phase temperature-dependent thermal conductivity measured by this method are reliable. Compared with the traditional method, the method in this study can realize the simultaneous measurement of the temperature-dependent thermal conductivity of solid and liquid phase in once experiment. This method has a good application prospect.
  
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  Study on Plasmonic Nanoparticles-based Photothermal Films for Transparent Anti/de-icing

  YAO Peng, YANG Rui, PU Jinhuan, DU Mu, SUN Qie, LIU Xiaoyan, TANG Guihua

  Journal of Engineering Thermophysics. 2024, 45(9): 2767-2772.

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  Currently, the utilization of solar energy based on the plasmon resonance effect is one of the economical, effective, and environmentally friendly ways to resolve issues of anti/de-icing. This study proposes a new transparent photothermal film based on plasmonic particles. The apparent radiation characteristics of the film are simulated via the combination of the Discrete Dipole Approximation method, Mie theory, and Monte Carlo method. The results show that the transparent photothermal film selectively transmits visible light and absorbs ultraviolet, blue-violet, and infrared light. It achieves a non-visible light absorbance of 82.2%, a blue light transmittance of 91.8%, and a non-blue light transmittance of 78.2%. With different surface wettabilities, the Monte Carlo ray tracing method is employed to simulate the light transfer through the ice droplets. The results show that the super-hydrophilic surfaces have a minimal impact on transmittance and haze, and the transmittance of hydrophobic surfaces is the lowest. This work provides a new option for transparent photothermal anti/de-icing materials.
  
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  Molecular Mechanism of Enhanced Water Evaporation on Hybrid Nanostructure

  WANG Zequn, AN Meng, SUN Xuhui, CHEN Dongsheng, SHI Junwen, YUAN Yuejin

  Journal of Engineering Thermophysics. 2024, 45(9): 2773-2778.

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  The molecular-scale influential mechanisms of hydrophilic-hydrophobic hybrid nanostructured surfaces on water evaporation utilizing molecular dynamics simulations were investigated. The MD simulation results demonstrated that the wettability of hybrid nanostructured surfaces can effectively enhance the water evaporation rate. By analyzing the interactions among water molecules and the nanostructured surfaces, it was found that hybrid nanostructured surfaces can regulate the evaporation barrier of water molecules. This study contributes to understanding molecular-scale water evaporation mechanism and provides valuable insights for designing efficient interfacial evaporation surfaces.
  
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  Heat Transport Properties of Stable Carbon Honeycomb Structures

  ZHAO Donglei, ZHANG Xiaowei, BAI Hao, LIU Xiaochuang, ZHANG Tengfei, LIU Hangbing, HAN Yang

  Journal of Engineering Thermophysics. 2024, 45(9): 2779-2784.

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  In recent years, carbon honeycomb structures synthesized by experiments have been widely concerned by the scientific community because of their high mechanical strength, high thermal conductivity and light weight. In this work, we investigate the heat transport properties of a recently proposed stable carbon honeycomb structure (hC28) using non-equilibrium molecular dynamics methods. The results show that the thermal conductivity along the honeycomb axis is much higher than that perpendicular to the honeycomb axis, showing anisotropy. In addition, with the increase of temperature, the scattering between higher order phonons is enhanced, and the thermal conductivity of the model decreases gradually. The research results of this paper have a certain guiding significance for the development of carbon honeycomb structure as a heat conduction device.
  
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  Performance of Electrosynthesis of H₂O₂ by Maltose-derived Oxygen Self-doped Electrocatalysts

  CHEN Jinhong, YE Dingding, ZHU Xun, YANG Yang, WANG Shaolong, CHEN Rong, LIAO Qiang

  Journal of Engineering Thermophysics. 2024, 45(9): 2785-2793.

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  In situ electrosynthesis of H₂O₂ by two-electron oxygen reduction reaction is a promising method for energy storage and H₂O₂ production. Maltose-derived oxygen self-doping electrocatalysts were obtained by one-step carbonation method for the electrosynthesis of H₂O₂. The carbonization temperature would change the types of surface functional groups and the degree of defects of the catalyst, thus affecting the H₂O₂ selectivity. The results show that the catalyst carbonized at 800°C has the optimal selectivity, using oxygenic functional groups and defects as reaction sites, and the pore structure dominated by micropores can promote uniform distribution of reaction sites and mass transfer. Under the applied current density of 100 mA·cm⁻², the H₂O₂ yield of the air-breathing cathode loaded with the catalyst achieves 39.88 mg·h⁻¹·cm⁻², which is close to the requirement of industrial sustainable production of H₂O₂.
  
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  Design of Ca/Co-based Composites for Thermochemical Energy Storage Based on First Principle

  GUO Sijia, TIAN Xikun, YAN Jun, ZHAO Changying

  Journal of Engineering Thermophysics. 2024, 45(9): 2794-2801.

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  Given the urgent need to enhance the cyclic stability and optical absorption of CaCO₃/CaO thermochemical energy storage (TCES) systems for solar utilization, this paper proposes an advanced TCES material composed of calcium carbonates and cobalt oxides. The optical properties of Ca/Co composites are theoretically calculated using first principles, and the modification mechanism for improving optical absorption is revealed from the perspective of electronic structure, which can facilitate the active design of TCES materials. In experiments, the key factor contributing to the improved optical properties of the best-performing materials prepared by the sol-gel method is the formation of a Ca₃Co_2−xMn_xO₆ (x=0/0.5/1) multiphase solid solution. With materials’ optical absorbance increasing from 9.53% to 79.3%, and the conversion rate in the 30th cycle increasing from 20% to 53.4%, the proposed TCSE materials exhibit promising application prospects.
  
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  Study on Thermal Radiation Transfer Characteristics of Single Droplet

  TU Maoping, ZHANG Dan, YUAN Yang, HAN Wei, WANG Yixiao

  Journal of Engineering Thermophysics. 2024, 45(9): 2802-2813.

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  Atomization evaporation was a high-energy consumption process widely used in industrial fields such as energy storage, carbon capture, and wastewater treatment. Using thermal radiation to heat droplets can not only achieve volumetric rapid heating, but also easily combine solar energy to achieve green production. In order to achieve efficient and fast heating of droplets in the fog field by thermal radiation, this paper conducted research on the radiation transfer performance of a single droplet. Firstly, a systematic model, including reflection, absorption and transmission under different condition of external radiations, droplet shapes and radiation properties was set up according to Zone Method. Secondly, the analyses of radiation transfer characteristics were carried out with projection angle between 0 and 180°, droplet length-width ratio between 1 and 10, equivalent diameter between 0.1 and 1.0mm, absorption coefficient between10 and 15000 m⁻¹, refractive index between 1.2 and 2 The results indicate that in the reflection process, the overall reflectivity of droplet is independent of their equivalent diameter and absorption coefficient; In the absorption process, droplet has two absorption modes for radiation: surface absorption and volumetric absorption. When the optical thickness of the droplet is less than 1, volumetric absorption dominates. At this time, increasing the absorption coefficient or refractive index can enable the droplet to achieve uniform and rapid heating; The larger the aspect ratio, the greater the heating rate, and the stronger the selectivity to external projection orientation; The overall absorption rate of droplets decreases with a decrease in equivalent diameter or an increase in aspect ratio, and remains almost unchanged with the direction of projection; In the transmission process, as the equivalent diameter decreases or the aspect ratio increases, the directional radiation intensity of the transmission radiation located on the opposite side of the projection direction to the long axis rapidly increases, and the overall transmittance of the droplet monotonically increases. The research results of this article can provide reference for the design and regulation of process links such as thermal radiation heating droplets.
  
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  Reconstruction of Pollutant Gel and Analysis of Its Heat and Mass Transfer and Pollution Characteristics

  WANG Qi, ZHANG Lizhi

  Journal of Engineering Thermophysics. 2024, 45(9): 2814-2821.

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  Gel fouling is a key problem in membrane desalination. In this study, gel contaminants generated under the actual operating conditions of seawater desalination were reconstructed by a chemical crosslinking method, and the various physical and chemical properties of the gel were tested and characterized. The reconstruction not only solves the disadvantage of requiring long operation in real seawater experiments, but also optimizes the problem that the real characteristics of gel contamination cannot be effectively explained in experiments with simple synthetic seawater. The results show that the mass transfer resistance of the water-producing system was not only caused by the dense structure of gel, but also the decrease of the temperature difference on both sides of the membrane caused by the low heat conduction of the gel layer. The gel contaminant exhibited hydrophilic and viscoelastic properties, which confer strong tensile strength, compressive stress, and anti-scouring ability. The characteristics of gel make it easy to adhere to the membrane surface. The model constructed by coarse-grained simulation can reflect some real parameters of gel and could be used for subsequent calculation.
  
  
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  Structure of the High-temperature in Premixed Turbulent Flames of Hydrogen-rich Gaseous Fuels

  ZOU Jun, SUN Guozhen, ZHANG Yang, ZHANG Hai, LÜ Junfu

  Journal of Engineering Thermophysics. 2024, 45(9): 2822-2830.

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  In this paper, the high-temperature structure in stretched turbulent flames of hydrogenrich gaseous fuel are studied. The Laser Tomographic Visualization (LTV) and numerical simulation methods are used to quantitatively characterize the structural changes in the high-temperature region in laminar and turbulent cases. The results show that the thickness of the high temperature zone in the flame increases with the increase of equivalent ratio. With the increase of the outlet flow rate, the strain rate of the flame is increase, and the thickness of the high temperature zone decreases. The laminar flame is relatively stable, so the position and shape of boundaries of the high temperature region are relatively steady. The turbulent vortexes will destroy the structure of the high temperature region, resulting in drastic fluctuations and bends of the high temperature boundary. With the increase of turbulence intensity, the thickness of flame high temperature zone also increases. Compared with the changing trend of flame high temperature zone boundary in high turbulence intensity and the energy spectrum analysis results, the results show that flame enters the Thin Reaction Zone (TRZ) combustion mode. 
  
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  Experimental Study on Flame Height and Oscillation Behavior of Linear-source Buoyant Turbulent Diffusion Jet Flame Under Sub-atmospheric Pressures

  YUAN Yilin, ZHANG Xiaolei, HU Longhua

  Journal of Engineering Thermophysics. 2024, 45(9): 2831-2838.

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  In this paper, experiments of linear buoyant turbulent propane jet fire at various subatmospheric pressures were carried out, and different aspect ratios of burners were considered. The evolutions of flame height and flame oscillation frequency with the burner aspect ratio, ambient pressure and heat release rate are studied. The experimental results show that the flame height decreases with the increase of burner aspect ratio or pressure, and it increases with the increase of heat release rate. However, the flame oscillation frequency decreases with the increase of burner aspect ratio and increases with the increase of pressure, and heat release rate has no significant effect on the flame oscillation frequency. Based on the analysis of air entrainment mechanism and the dimensionless relationship between Strouhal number (St) and Froude number (Fr), non-dimensional models of flame height and flame oscillation frequency of linear source jet flames coupled with the ambient pressure effect are established.
  
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  Study on the Pyrolysis Characteristics of Glycidyl Azide Polymer (GAP)

  ZHOU Yintao, CHU Qingzhao, LIAO Lijuan, MAO Qian, SHI Baolu

  Journal of Engineering Thermophysics. 2024, 45(9): 2839-2846.

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  Understanding the pyrolysis characteristics of glycidyl azide polymer (GAP) in hightemperature atmosphere is of great significance to improve the energy release level of solid propellants. This study employed the ReaxFF molecular dynamics simulations to investigate atomic-level thermal decomposition processes of GAP. The kinetic parameters in high temperature and high pressure were obtained. In addition, two main reaction pathways in the formation of the gas-phase products were discovered through atomic tracking techniques. It was found that N₂, CO, CH₂O and HCN were mainly obtained through stepwise decomposition reactions. However, most of the H₂O and NH₃ were produced by the binding reactions between H, OH and NH_x radicals which were generated by the decomposition of GAP. The results of GAP pyrolysis at different densities showed that the higher the initial density, the binding reactions were preferred compared the decomposition reactions. 
  
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  Numerical Study of the Effect of Taylor Dispersion on Flames in Semi-Open Narrow Channels

  CHEN Canruo, VALIEV DAMIR

  Journal of Engineering Thermophysics. 2024, 45(9): 2847-2852.

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  Effects of Taylor dispersion on the propagation of a premixed flame ignited at a closed end of a semi-open narrow channel are investigated within a range of Peclet numbers (representing a non-dimensional channel diameter), thermal expansion coefficients, Lewis numbers, and Zel’dovich numbers. The unconventional nonmonotonic dependence of burning rate on channel diameter is identified and attributed to the competition between Taylor dispersion mechanism and flame elongation effects. Furthermore, a domain, in terms of Peclet number and thermal expansion coefficient, in which the flame speed is significantly influenced by Taylor dispersion, is established. The influences of Lewis number and Zel’dovich number on the burning rate and structure of reaction zone are found to be negligible in narrow channels due to thickened and undistorted flame caused by Taylor dispersion mechanism.
  
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  The Influences of Thermal History on Product Characteristics During Microwave-assistant Pyrolysis of Biomass

  SUN Daoguang, LI Fangzhou, YANG Ke, ZHANG Huiyan

  Journal of Engineering Thermophysics. 2024, 45(9): 2853-2860.

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  The complex energy and heat conversion processes in microwave-assisted biomass pyrolysis have important effects on product properties. In this study, the thermal history and product distribution characteristics of microwave-assisted biomass pyrolysis under different operating conditions were investigated. To detect the mechanism, a numerical model coupled pyrolysis reaction kinetics and the equations of electromagnetic wave and heat transfer for the microwave-assisted biomass pyrolysis was established. The results indicate that, in comparison to conventional pyrolysis, the distinctive thermal profile of microwave-assisted pyrolysis results in a 0.71 to 7.43 times increase in the synthesis gas yield (CO+H₂) in the pyrolysis gas, along with a 4.87% to 18.8% rise in the selectivity of aromatic hydrocarbon components in bio-oil. By altering the dielectric properties and addition ratio of the microwave absorber, as well as the microwave power, we achieve a certain degree of directional control over the product composition by regulating the heat history during microwave-assistant pyrolysis of biomass.
  
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  A Combustion Kinetic Model Reduction Method based on Particle Swarm Optimization (PSO)

  LIN Shengqiang, ZHANG Xianfa, WU You, ZHU Jinjiao, YI Ting, XIONG Yonglian, LI Chunsheng, SUN Yan, YANG Bin

  Journal of Engineering Thermophysics. 2024, 45(9): 2861-2866.

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  To reduce the instability and uncertainty of current linear methods for combustion kinetic model reduction, a new nonlinear method based on artificial intelligence algorithm is proposed to simplify chemical models. This method is applied to reduce the USC-Mech II and JetSurF 2.0 mechanisms, so that the reduced mechanisms can accurately predict the ignition delay time of ethylene and n-decane respectively. The results show that the new reduction method based on particle swarm optimization (PSO) can obtain more compact reduced models. The 22-species ethylene mechanism and the 45-species n-decane combustion mechanism are obtained, which are more compact than those obtained by other reduction methods under similar operating conditions. 
  
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  Extinction Limits and Chemical Kinetics Analysis of Counterflow Diffusion Flames of Dimethyl Ether/Ammonia

  SONG Yu, ZHANG Zunhua, ZHOU Mengni, XU Shuang, LI Gesheng

  Journal of Engineering Thermophysics. 2024, 45(9): 2867-2875.

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  Ammonia has recently received much attention as a novel clean energy with broad application prospects. The paper focuses on the extinction limits of dimethyl ether/ammonia mixtures cool and hot diffusion flames by an atmospheric counterflow burner. The low and high temperature chemical kinetics of dimethyl ether/ammonia are analyzed. The results show that the extinction limits of dimethyl ether/ammonia mixtures cool and hot diffusion flames decrease with the increase of the ammonia blend ratios. For dimethyl ether/ammonia cool flames, the low temperature reactivity of dimethyl ether is inhibited mainly through three aspects: ammonia and dimethyl ether vie OH, DME + NO ⇐⇒ R + HNO and RO₂ + NO ⇐⇒ RO + NO₂. For dimethyl ether/ammonia diffusion hot flame, the high temperature reactivity of dimethyl ether is improved by the reaction of OH, H and O radicals generated by ammonia with dimethyl ether and the reaction of HCCO + NO ⇐⇒ HCNO + CO and HCCO + NO ⇐⇒ HCN + CO₂. Moreover, this research shows that the main oxynitrides in dimethyl ether/ammonia cold flame and hot flame are NO₂ and NO respectively.