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Numerical simulation on characteristics of hydrodynamics, interphase and wall to bed heat transfer in a pseudo 2D spouted bed using supercritical CO_(2) as fluidizing agent

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Particuology 2025年第1期96卷 106-125页

作者： Kun Jiang Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

By employing the Eulerian-Eulerian Two Fluid Model, the effect of different particle size, supercritical CO_(2) (scCO_(2)) velocity at slit jet (U_(jet)) and initial bed height on the macroscopic characteristics (i.e., fountain morphology, profiles of particle velocity, momentum transfer characteristics among particles, transient temperature evolutions of particles, interphase heat transfer coefficient and wall to bed heat transfer characteristics) in the pseudo 2D rectangular spouted bed using scCO_(2) as fluidizing agent is numerically studied in detail herein. Considering there are currently no relevant visualized experiments reported using scCO_(2) as a fluidized agent due to the extreme operating pressure of CO_(2) (25 MPa in this paper) under supercritical conditions, present numerical model was validated with experimental data by using air as the fluidizing agent, confirming simulated instantaneous volume fraction distribution of air and transient temperature evolutions of particles basically consistent with the experiments. Numerical results reveal some of the internal relations among hydrodynamics characteristics in bed, momentum transfer characteristics among particles and relevant heat transfer behaviours. Results show larger Ujet and smaller particle size will accelerate the particles' translational motion in spout, spout core and fountain core zone. Larger particle concentration will promote inter-particle collisions while suppress the kinetic motion of particles in above zones. Decrease the particle size will enhance interphase convective heat transfer coefficient, while increasing U_(jet) results insignificant impacts. Finally, we also observe the transition zone between annular and periphery zone has a certain enhancing effect on the wall to bed heat transfer coefficient.

关键词： Spouted bed Two fluid model Kinetic theory of granular flow Supercritical CO_(2) Hydrodynamics Heat transfer

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Specific Heat Capacity and Coordination Number of Nano-Confined Transcritical Water

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Journal of Thermal Science 2025年第2期34卷 498-509页

作者： ZHANG Bowei JIANG Kun ZHANG Jie JIN Hui State Key Laboratory of Multiphase Flow in Power Engineering(SKLMF) Xi’an Jiaotong UniversityXi’an710049China

In the field of nano energy,investigating the specific heat capacity and coordination number of nano-confined water is highly significant for gaining a better understanding of the energy and microstructure of confined *** this work,we employed the method of molecular dynamics(MD)simulation to calculate the specific heat capacity at constant volume and coordination number of water molecules confined in carbon nanotubes(CNTs)under different conditions(T=600-700 K,P=21.776 and 25 MPa,CNT diameter=0.949-5.017nm).The results showed that near the critical point,the specific heat capacity at constant volume of confined water was lower than that of bulk water,and the energy fluctuation showed a trend of first increasing and then remaining unchanged with the increase of temperature and CNT *** them,the saturation point of temperature is 650 K(reduced pressure P_(r)=1)and 660 K(P_(r)=1.15),and the saturation point of CNT diameter is 2.034 ***,the pseudo-critical temperature of confined water was the same as bulk water,and it increased with the increase of critical ***,with the increase of CNT diameter,the coordination number of confined water increased rapidly,and reaches the saturation state when the CNT diameter is 2.034 *** investigation revealed the mass and energy characteristics of nano-confined water near the critical point,which could provide guidance for the critical phase transition of nano-confined water.

关键词： molecular dynamics nano-confined transcritical water specific heat capacity at constant volume coordination number

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Effect of ignition timing on the combustion characteristics of liquid ammonia spray in a lean premixed H2/Air

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COMBUSTION AND FLAME 2025年 274卷

作者： Ge, Ruihan Yin, Geyuan Hu, Erjiang Shen, Shujie Zhan, Haochen Tang, Chenglong Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian Peoples R China

Combustion of ammonia has recently been emerging as a promising approach for carbon mitigation. However, monitoring ignition of ammonia is a technique challenge due to its low reactivity. This work experimentally investigates the ignition and combustion behaviors of ammonia spray injected into a lean hydrogen air mixture, with emphasis on the ignition timing effect on the ignition and flame evolution behaviors as well as the pressure evolution and heat release. Results show that the ignition timing leads to profound alteration of the ammonia spray ignition and flame evolution due to the mixture status induced by different spray evolution time. Specifically, the flame is the most significantly affected by spray injection at ignition timings close to the start and end of injection and the heat loss is reduced, compared with the premixed fuel due to the lower heat release from evaporation and incomplete combustion. Additionally, for 10 ms pre-ignition timing, at the instant when the spray reaches the flame, the unburned gas assists in the evaporation and diffusion of the liquid ammonia, leading to a sudden increase in flame speed and a higher pressure of combustion. While, finally, for the 10 ms postignition timing case, the stratified fuel concentration distribution leads to accelerated heat release rate and a reduced overall combustion duration. The special spray characteristics of liquid ammonia and the high latent heat of evaporation are the main factors leading to the reduction of the combustion efficiency of liquid ammonia spray, which can be effectively solved by precombustion heating or homogeneous mixing. This study is believed to be beneficial for organizing better combustion for this zero-carbon fuel in SI engines.

关键词： Liquid ammonia Spray combustion Hydrogen Ignition timing

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Enhancing the performance of proton-exchange membrane fuel cell by optimizing the hydrophobicity and porosity of cathode catalyst layer

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Science China(Technological Sciences) 2025年第3期68卷 72-81页

作者： Yan ZHANG Puping JIA Suyi YANG Jinzhan SU Liejin GUO International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power EngineeringSchool of Energy&Power EngineeringXi’an Jiaotong UniversityXi’an710049China

Appropriate hydrophobicity and porosity of the proton-exchange membrane fuel cell(PEMFC)cathode catalyst layer(CCL)are essential for efficient charge and mass *** this study,the effects of the CCL hydrophobicity and porosity on PEMFC performance were comprehensively *** to a normal CCL,a cathode hydrophobic duallayer catalyst structure(with a 2:1 Pt loading ratio between the inner and outer layers and 9.3%polytetrafluoroethylene(PTFE)in the outer layer)exhibited a 29.8%increase in power *** the tested pore-forming agents,ammonium bicarbonate(NH_4HCO_(3))was the most suitable because of its low pyrolysis *** maximum power density of the CCL with a porous structure(prepared with a Pt/C:NH_4HCO_(3)mass ratio of 1:3)was 38.3%higher than that of the normal *** simultaneously optimizing the pore structure and hydrophobicity of the CCL,the maximum power density of the cathode hydrophobic dual-layer CCL(DCL)with pores showed a 44.7%increase compared to that of the normal *** study demonstrates for the first time that simultaneously optimizing cathode porosity and hydrophobicity can enhance PEMFC performance.

关键词： proton-exchange membrane fuel cell cathode catalyst layer membrane electrode assemblies polytetrafluoroethylene pore-forming agent

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Investigation on intermittent flow characteristics in horizontal pipe by visualization measurement method

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EXPERIMENTAL THERMAL AND FLUID SCIENCE 2025年 160卷

作者： Huang, Bo Xu, Qiang Cao, Yeqi Yu, Haiyang Li, Yuwen Chang, Yingjie Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Accurate measurement and prediction of the intermittent flow characteristics in horizontal pipes is important for constructing multiphase flow models and ensuring pipe flow safety. In this paper, a quantitative image post- processing technique for intermittent flow characteristics based on gray histogram image similarity is proposed, which can realize the measurement of slug frequency. In addition, the technique also has the ability to classify a large number of images, and can quickly find the elongated bubble head, liquid film area and liquid slug area of intermittent flow. On the basis of this technique, combined with image post-processing methods such as gas-liquid interface feature analysis, a set of intermittent flow image processing technique with perfect route is formed. Based on this post-processing technique, the similarity image oscillation trajectories of plug flow and slug flow are obtained. There are differences in the similarity image oscillation trajectories of the two intermittent sub-flow patterns, and the similarity image of the plug flow has an obvious platform period and trailing rising line, which can be used as a basis for the classification of the two intermittent sub-flow patterns. A correlation for predicting the slug frequency of intermittent sub-flow patterns is developed. The accuracy of this slug frequency prediction correlation can be improved by about 10% compared to not dividing the sub-flow patterns. When the mixture Froude number Frm m is less than 5.0, the radial position of the elongated bubble head decreases linearly as the Frm m increases. When the Frm m is greater than 5.0, the elongated bubble head oscillates near the middle of the pipe. Prediction correlations for the radial position of the elongated bubble head and the slug velocity are established separately, and the maximum error is +/- 10 %. The modified mixed Froude number is proposed, and based on this, a new prediction model for the transition from plug flow to slug f

关键词： Intermittent flow flow visualization Quantitative image processing flow characteristics flow pattern transition

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Three-dimensional dynamic multi-physics modeling and long-term degradation performance analysis of solid oxide fuel cell considering carbon deposition

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JOURNAL OF power SOURCES 2025年 631卷

作者： Li, Bohan Wang, Chaoyang Liu, Chang Liu, Ming Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Carbon deposition is a critical issue in solid oxide fuel cell (SOFC) operations. In this study, a 3D dynamic model of SOFC considering carbon deposition is established and validated to investigate the effects of key operating conditions (i.e., output voltage, operating temperature, and fuel composition) on the long-term power degradation of the cell. Additionally, the total working lifecycle power generation (Ptot) of the cell is calculated for methane molar fractions in the feeding fuel (XCH4) ranging from 0.1 to 0.4, output voltages (U) from 0.6 V to 0.8 V, and operating temperatures (T) from 1003 K to 1043 K. The results indicate that the long-term SOFC operating voltage should exceed the voltage for maximum steady-state power output to achieve higher Ptot. When the power degradation threshold (PDT) equals 0.75, Ptot reaches 2880 kW h/m2 at U = 0.75V, approximately twice that at U = 0.55V. The power degradation process of the cell can be divided into two stages: a rapid degradation stage and a slow degradation stage. Decreasing the operating temperature or reducing XCH4 to regulate PDT to the slow degradation stage can significantly enhance the cell's total working lifecycle power generation. A distinct boundary in X CH4 is observed between high and low P tot . When X CH4 exceeds the boundary value (0.25), the cell's P tot decreases by over 70 %.

关键词： Solid oxide fuel cell 3D dynamic model Direct internal reforming Carbon deposition

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Numerical simulation of closed-cycle R410A flash spray cooling with multiple nozzles on a large heat exchange surface

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APPLIED THERMAL engineering 2025年 268卷

作者： Yang, Wenbo Sang, Xuehao Chen, Bin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

To address the heat dissipation of high-power chips with large heat exchange surfaces, a mathematical model of a multi-nozzle R410A closed flash evaporation spray cooling system was established based on the Euler-Lagrange method to investigate the effects of nozzle number, nozzle distance, spray angle, refrigerant mass flow rate, and spray distance on heat transfer efficiency. In the single-phase stage and two-phase stage, the optimal numbers of nozzle are 2 and 4, respectively. The optimal values for nozzle distance, spray angle, refrigerant mass flow rate, and spray distance are 7.5 mm, 30 degrees, 6 g/s, and 25 mm, respectively, with an average heat exchange surface temperature of 318.6 K. The dimensionless number Sw is proposed to describe the relationship between nozzle spacing, spray distance, and heat exchange area, with an optimal value of 1.0.

关键词： Spray cooling Multi-nozzle optimization Numerical calculation R410A Heat flux density

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Experimental study on water boiling heat transfer characteristics of microchannel surface in distributed jet array impingement with effusion slots

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INTERNATIONAL JOURNAL OF HEAT AND FLUID flow 2025年 112卷

作者： Tang, Xiaoyu Xu, Qiang Yu, Haoyuan Pei, Chenyu Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Distributed jet array impingement can improve the uneven temperature distribution and achieve high heat flux cooling. This paper experimentally investigated the two-phase heat transfer and pressure drop characteristics in a distributed jet array impingement on the microchannel surface. The test operating conditions were mass flux of 100 200 kg/m2s, subcooling degree of 20 40 K, jet-to-target spacing of 2 4 mm, and atmospheric pressure at the outlet. The experimental results show that lowering subcooling from 40 K to 20 K enhances the heat transfer coefficient between 45.4 % and 57.2 % and a growth in the average pressure drop of 25.5 %. Increasing mass flux causes inlet and outlet pressure to fluctuate more sharply due to enhanced condensation. The pressure drop of single-phase forced convection and that of two-phase nucleated boiling display an opposite trend as mass flux increases. Reducing jet-to-target spacing to 2 mm exhibits a noticeable enhancement in pressure drop of more than 2.5 times, and the standard deviation of inlet pressure declines instead, indicating that decreasing jet- to-target spacing can attenuate flow instability. The coefficient of performance can be raised by increasing subcooling and jet-to-target spacing and reducing mass flux in the whole heat flux range. Expanding jet-to-target spacing from 2 mm to 4 mm can produce 105.5 % to 141.7 % higher the average coefficient of performance.

关键词： Distributed jet array impingement Microchannel surface Heat transfer Jet-to-target spacing Coefficient of performance

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System design and thermo-economic analysis of a novel gas turbine combined cycle co-driven by methanol and solar energy

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APPLIED ENERGY 2025年 380卷

作者： Zhang, Peiye Liu, Ming Hu, Wenting Chong, Daotong Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Methanol, known as "liquid sunshine", is a versatile and low-carbon alternative to traditional fossil fuels. To effectively utilize methanol and solar energy, a novel gas turbine combined cycle (GTCC) integrated with a solardriven methanol decomposition reaction (Solar MDR) process is proposed in this study. Based on the cascade utilization of chemical energy, methanol is first decomposed into syngas in the parabolic trough solar receiverreactor (PTSRR) field, followed by the conversion of chemical energy into power through combustion. The methanol preheating process is comprehensively considered by integrating methanol evaporator into heat recovery steam generator (HRSG) and utilizing waste heat from the PTSRR to drive the methanol preheater and superheater. Thermodynamic analysis is conducted to evaluate the impact of solar integration on irreversibility and power output in the methanol-fueled GTCC system. The results indicate that the system co-driven by methanol and solar energy improves the methanol power generation rate from 3.17 kWh kg- 1 to 3.75 kWh kg- 1. The exergy efficiency of the system slightly decreases from 51.05 % to 50.42 % due to the integrated system incurring an additional 106.28 MW of loss and destruction, with solar integration contributing an extra 34.9 MW of exergy loss and 66.7 MW of destruction in the PTSRR field. The proposed system achieves a solar-to-electric efficiency of 43.93 % and a solar levelized cost of electricity (LCOE) of $75.7 MWh- 1, offering a competitive advantage over other solar thermal power technologies from thermo-economic perspectives.

关键词： Solar energy Methanol utilization Gas turbine combined cycle Thermo-economic Solar-to-electric efficiency

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Size Effects on Bubble Dynamics during Photoelectrochemical Water Splitting

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ACS NANO 2025年第8期19卷 8200-8211页

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

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

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

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