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Numerical simulation on flow boiling heat transfer characteristics of R513A in the horizontal microfin tubes

APPLIED THERMAL engineering 2025年 260卷

作者： Zhang, Suhan Tao, Leren Huang, Lihao Jin, Cheng Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

To address the growing demand for high-efficiency heat exchangers in refrigeration, air conditioning, and heat pump systems, this study investigates the boiling heat transfer performance of R513A (an environmentally friendly azeotropic refrigerant) in horizontal microfin and smooth tubes with a 5.89 mm ID. Using 3D transient simulations, the tubes were analyzed under operating conditions of a mass flux of 50 kg/(m2 center dot s) and a saturation temperature of 5 degrees C. The simulation results were validated against experimental data within a +/- 10 % error margin, confirming the reliability of model. At the constant mass flux, both the microfin and smooth tubes exhibited predominantly wavy-stratified flow, where surface tension dominated bubble flow. Gravity effects became more pronounced in slug, plug, and wavy-stratified flows. Structural parameters of microfin tubes, such as helical angle, fin height and number of fins, significantly affected flow boiling heat transfer. Increasing the helical angle had limited effect on enhancing boiling heat transfer performance. Microfin tube 4# (helical angle of 28 degrees) exhibited an 11.27 % reduction in the boiling heat transfer coefficient compared to microfin tube 2#, due to the uneven distribution of liquid droplets in the vapor phase further reduced liquid film continuity and thickness. Microfin tube 5# (fin height of 0.30 mm) achieved an average mainstream velocity 1.36 times that of tube 2# (fin height of 0.17 mm), enhancing heat transfer. Conversely, microfin tube 6# with 54 fins showed local drying, negatively impacting its heat transfer efficiency. In summary, microfin tube 5# exhibited the optimal heat transfer characteristics.

关键词： CFD Simulation R513A flow boiling Geometric structure Two phase flow flow pattern

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Study on the Destruction of PCDD/Fs and Synergistic Solidification of Heavy Metals in Fly Ash by Low-Temperature Pyrolysis with the Assistant of N-Doped Hierarchical Porous Carbon

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PROCESSES 2025年第4期13卷 1202-1202页

作者： Yue, Mingqi Wang, Qiulin Wang, Haonan Wang, Xiaoyiran Jin, Jing Liu, Dunyu Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Highlights What are the main findings? The low-temperature destruction of PCDD/Fs during FA pyrolysis is enhanced by NHPC. More lower-chlorinated PCDD/Fs can be decomposed in the presence of NHPC. The heavy metals in fly ash are synergistically solidified with the aid of NHPC. What is the implication of the main finding? NHPC regulates the structure properties and the chemical environment of fly ash. The addition of NHPC provides a novel research approach for the synergistic disposal of PCDD/Fs and heavy metals in fly *** What are the main findings? The low-temperature destruction of PCDD/Fs during FA pyrolysis is enhanced by NHPC. More lower-chlorinated PCDD/Fs can be decomposed in the presence of NHPC. The heavy metals in fly ash are synergistically solidified with the aid of NHPC. What is the implication of the main finding? NHPC regulates the structure properties and the chemical environment of fly ash. The addition of NHPC provides a novel research approach for the synergistic disposal of PCDD/Fs and heavy metals in fly *** There is an urgent need for energy-efficient disposal and resource utilization of the fly ashes from municipal solid waste incineration (MSWI). The low-energy pyrolysis-based detoxification of is a prerequisite for the harmless treatment and sustainable utilization of the fly ashes. In this study, the nitrogen-doped hierarchical porous carbon (NHPC) was prepared from the biomass-derived corn cobs and used to enhance the low-temperature destruction of PCDD/Fs in the MSWI fly ash. On thermal treatment in pure nitrogen (referring to pyrolysis in) at 350 degrees C for 30 min, the removal efficiencies of PCDD/Fs in fly ash based on mass (eta mass) and TEQ (eta TEQ) are 87.4% and 76.2%, respectively. After 5 wt.% NHPC is added in fly ash, the eta mass and eta TEQ values can be increased to 94.9% and 90.2%. The NHPC can enhance the decomposition and inhibit the regeneration of PCDD/Fs in fly ash, for the NHPC can regulate the st

关键词： energy-efficient pyrolysis fly ash PCDD/Fs heavy metals N-doped hierarchical porous carbon

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Numerical simulation on the condensation heat transfer and flow characteristics outside smooth and enhanced tubes

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APPLIED THERMAL engineering 2025年 258卷

作者： Cheng, Jian Tao, Leren Li, Meng Jin, Cheng Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Most of the current studies only conducts two-dimensional simulations of condensation heat transfer and flow outside enhanced tubes, which cannot accurately reflect the flow and heat transfer characteristics of liquid film outside enhanced tubes. In order to provide theoretical support for the design optimization of enhanced tubes, this study adopts the VOF multiphase model and Lee condensation model to simulate the condensation heat transfer(HTC) of refrigerants outside smooth and enhanced tubes. The instantaneous film flow characteristics of the liquid film outside the horizontal smooth and enhanced tubes are analyzed, and the thickness of the liquid film and the relationship with the condensation heat transfer coefficient of the smooth and enhanced tubes under different working conditions are calculated. The refrigerants are compared under the same working conditions, and the results are shown: The simulation results are in good agreement with the experimental data and the Nusselt analytical solution, and the error is all within 15%;the distribution of liquid film is highly sensitive to the magnitude of local condensation heat transfer coefficients, and the condensation HTC outside the enhanced tube is approximately six times of that of smooth tube. Combining the distribution of the liquid film and the thermophysical properties of the refrigerants, it was determined that R410A has the highest HTC, while R1234yf has the lowest HTC.

关键词： Condensation heat transfer coefficient CFD VOF Liquid film

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Numerical study on the wake structures of a sphere in linearly stratified flow

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JOURNAL OF VISUALIZATION 2025年第1期28卷 97-113页

作者： Shi, Liu Liu Wei, Na Chen, Er Yun Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

In this study, numerical simulations have been carried out to evaluate the influence of internal Froude number (Fr) on the wake characteristics of a sphere in linearly stratified flow. Five models with different levels of Fr (Fr = 0.05, 0.2,0.25,0.5 and 1) at a Reynolds number of Re = 3700 have been selected for comparative study. UDF (User Defined Function) is employed to establish linear density stratification. The influences of stratification on wake characteristics are studied by analyzing the wake patterns, vortical structures, velocity distributions, and lee waves. The results of the study demonstrate that reduced Fr values lead to heightened vertical suppression of the near wake, while increased stratification prompts a transformation of the wake's three-dimensional coherent structures towards quasi-two-dimensionality. Furthermore, the presence of stratification notably impacts the length and amplitude of the lee wave.

关键词： Linearly stratified flow Internal Froude number Wake Lee wave

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Evaporation of Non-Isothermal Wall Microlayer Based on the Lattice Boltzmann Method

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PROCESSES 2025年第3期13卷 872-872页

作者： Dang, Mengyuan Gao, Ming Yang, Jianhua Dong, Wuhan Zhang, Lixin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China South China Univ Technol Sch Chem & Chem Engn Key Lab Enhanced Heat Transfer & Energy Conservat Educ Minist Guangzhou 510640 Peoples R China

In the process of boiling heat transfer, the microlayer is not only a crucial medium for enhancing heat transfer but also directly determines the heat flux distribution, dry zone expansion, and overall heat transfer efficiency through its morphological evolution and evaporation behavior. Building on this, this study employs the Lattice Boltzmann Method (LBM) with a single-component multiphase model to numerically simulate the evaporation process of microlayers on non-isothermal walls. The results show that, due to the uneven velocity distribution in the flow field, the microlayer exhibits significant contraction behavior during evaporation, particularly at the three-phase contact point, where velocity differences lead to fluid accumulation and the formation of a "cap-like" structure. The initial growth of the dry zone follows a linear trend, but its growth rate gradually decreases as the microlayer thickness increases, while near-wall density effects result in residual thickness within the dry zone. Additionally, the microlayer height first increases and then decreases over time, accompanied by a noticeable time lag. heat flux analysis reveals that, during the formation of the dry spot, the lowest heat flux occurs at the three-phase contact point, followed by a sudden increase. A cold air ring forms above the dry zone, expanding and splitting as it moves with the dry spot. Higher temperatures promote microlayer evaporation, with the evaporation volume exhibiting nearly linear growth and the total fluid mass decreasing linearly.

关键词： microlayer three-phase contact point heat flux evaporation rate Marangoni effect

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Temperature distribution measurement of solid propellant combustion based on dual-wavelength imaging method

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MEASUREMENT 2025年 247卷

作者： Yang, Bin Cao, Huayu Li, Lingfeng Fan, Rong Wang, Zhixin Yang, Yang Shi, Zhiquan Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanghai Space Prop Technol Res Inst Shanghai 201109 Peoples R China

The combustion temperature is an important parameter that characterizes the combustion behavior and energy of solid propellants. It can provide data support for the research of solid propellant combustion mechanisms and the establishment of combustion models. However, the combustion of solid propellants involves hightemperature and multiphase physical and chemical processes, which pose difficulties for thermometry. Therefore, this study selected the 680 nm and 760 nm wavelengths through mathematical simulation and designed a dual wavelength radiation image measurement system for spectral splitting. The temperature distributions of HTPB propellant with different formulas were obtained using this system. The combustion temperatures of three different formulas of propellants are 2045.3K, 1915.5K, and 1855K, respectively;The uncertainties are +/- 29.8K, +/- 33.9K, and +/- 31.8K, respectively. The measurement results show that aluminum content is an important factor affecting the combustion characteristics of HTPB solid propellants. As the aluminum content increases, the combustion temperature and rate will also increase, and the flame shape will also change accordingly. It provides effective measurement methods for the analysis of combustion performance and formulation optimization of solid propellants.

关键词： Combustion diagnostics Temperature measurement method Solid propellant Dual-wavelength temperature measurement method Radiation imaging method

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The heat transfer enhancement mechanism for composite phase change material based on variable heating power and pore density

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JOURNAL OF ENERGY STORAGE 2025年 115卷

作者： Wang, Zilong Zhu, Hua Gui, Jintao Zhang, Hua Wu, Weidong Li, Ying Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Sch Mat & Chem Shanghai 200093 Peoples R China

Adding foam metal materials is one of the key methods to enhance the thermal conductivity of phase change materials (PCMs). To investigate the heat transfer mechanism of PCMs under different heat source powers and foam metal pore densities, a visualized thermal energy storage device was designed and constructed in this study. The effects of heat source power and the pore density of copper foam metal on the thermal properties of the composite PCMs, including internal temperature differences, equivalent thermal conductivity, comprehensive heat transfer coefficient, and heat storage performance during the melting process, were thoroughly analyzed. An empirical correlation for calculating the Nusselt number (Nu) of the composite PCMs was also derived. The research results indicate that the rate of temperature rise in the internal temperature difference of the composite PCMs increased with the rise in heat source power, while the melting time shortened accordingly. When the heat source power was increased from 30 W to 90 W, for composite PCMs with copper foam, the pore density of copper foam increased from 5PPI to 25PPI, and the rate of temperature rise in the internal temperature difference during the melting process enhanced from 176.9 % to 183.5 %, while the reduction in melting time enhanced from 61.9 % to 62.5 %. The comprehensive heat transfer coefficient of the composite PCMs is directly proportional to the heating power and inversely proportional to the pore density. When the heating power is increased from 30 W to 90 W, the comprehensive heat transfer coefficient of the composite PCM with a pore density of 5PPI is increased by 61 %, while that of 25PPI is increased by 59 %. Additionally, based on the structural parameters of copper foam metal, an empirical correlation for the Nu during the melting process of the composite PCM was derived, the error between the experimental value and the calculated value is +/- 5 %. In addition, the dimensionless heat-storage rat

关键词： Phase change material heating power Pore density Enhanced heat transfer Foam meta

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Pore-scale study of coupled charge, gas, and liquid water transport in the catalyst layer of PEM fuel cells

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FUEL 2025年 380卷

作者： Dou, Shaojun Hao, Liang Wang, Yuanhui Wang, Qianqian Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Yanshan Univ Sch Vehicle & Energy Qinhuangdao 066004 Peoples R China

Understanding the catalyst layer (CL) structure-process-performance relationship is essential for optimizing proton-exchange membrane fuel cells. This study stochastically reconstructs a high-resolution porous CL with a full thickness of 8 mu m. The liquid water distribution within CL is simulated by a capillary condensation model, and a pore-scale model coupling oxygen and proton transport with electrochemical reaction is developed to investigate the CL structure-performance relationship under different operating conditions. Results indicate that CL exhibits better performance at higher humidities, up to the flooding threshold at the water saturation of 0.41, as the benefits of increased electrochemical surface area, enhanced proton conductivity, and improved oxygen permeability through the ionomer film significantly outweigh the increased transport resistances through both the pores and the water film. Under the flooding condition at water saturation of 0.41, CL performance starts to decline due to the sharply increased pore resistance. Proper perforation of CL is suggested to alleviate the pore resistance in flooded electrodes. Additionally, reducing the Pt-to-C mass ratio is found to achieve better Pt dispersion in low Pt-loaded electrodes, thereby lowering the local oxygen resistance, and the bilayer CL design with higher Pt content on the membrane side is shown to further mitigate the performance degradation.

关键词： Polymer electrolyte membrane fuel cell Liquid water Pore-scale model Catalyst layer

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Research on vorticity driven reward for active flow control over airfoil based on deep reinforcement learning

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JOURNAL OF HYDRODYNAMICS 2025年第1期37卷 124-137页

作者： Dong, Xiang-rui You, Sun-yu Wang, Qi Zhu, Jia-hao Jin, Zhi-hao Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

An intelligent flow control on the flow separation over an airfoil under weak turbulent conditions is investigated and solved by deep reinforcement learning (DRL) method. Both single and synthetic jet control at the airfoil angles of attack of 10 degrees, 13 degrees, 15 degrees are compared by training a neural network for closed-loop active flow control strategy based on the soft actor-critic (SAC) algorithm. The training results demonstrate the effectiveness of the deep reinforcement learning-based active flow control method in suppressing the flow separation at high angles of attack, validating its potential in complex flow environments. To improve the stability of the shedding vortex alley over airfoil, a novel reward function considering the vorticity statistics in terms of both vortex and asymmetric shear intensity is first proposed in this work. This vorticity driven reward is demonstrated to perform better in suppressing the rotation and shear intensity and the aerodynamic optimization than the traditional one. Moreover, it can accelerate the convergence speed during the exploration phase. Moreover, it can accelerate the convergence speed during the exploration phase. This study provides valuable insights for future applications of DRL in active flow control under more complex flow conditions.

关键词： Fluid mechanics flow control deep reinforcement learning (DRL) multiple attack angle synthetic jet

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Depth from defocus technique with convolutional neural networks for high particle concentrations

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EXPERIMENTS IN FLUIDS 2025年第1期66卷 1-11页

作者： Xu, Rixin Huang, Zuojie Zhou, Wu Tropea, Cameron Cai, Tianyi Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai Peoples R China Tech Univ Darmstadt Inst Fluid Mech & Aerodynam Darmstadt Germany

Recent advantages in the depth from defocus technique for the size and location determination of particles in dispersed two-phase flows have enabled the technique to detect and analyze spherical particle images in flow systems with high number concentrations. In the present study, the use of convolutional neural networks for this task will be explored, with comparisons to the conventional analyses in terms of accuracy, tolerable concentration limits and computational speed. This approach requires a large teaching dataset of images, which is only practical and feasible if the dataset can be synthetically generated. Thus, the first development to be presented is an image generation procedure for out-of-focus neighboring spherical particles resulting in a known blurred image overlap. This image generation procedure is validated using laboratory images of known particle size distribution, position and image overlap, before creating a teaching dataset. The trained processing scheme is then applied to both synthetic datasets and to experimental data. The synthetic datasets allow limits of image overlap and tolerable volume concentration limits of the technique to be evaluated as a function of particle size distribution.(https://***/xu200911/Generate-overlapping-out-of-focus-particles)

关键词： Convolutional neural networks

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