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Discrete element simulation of dry adhesive granular flow in a vertical pipe

POWDER TECHNOLOGY 2025年 460卷

作者： Gao, Xin Parteli, Eric J. R. Fan, Fengxian Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Duisburg Essen Fac Phys Lotharstr 1 D-47057 Duisburg Germany Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The transportation and storage of granular materials with adhesive properties often involves particulate flow through narrow pipes, which is accompanied by still poorly understood dynamic behavior. Due to the difficulty in achieving a quantitative understanding of such flows based solely on experiments, here we perform particle-based numerical simulations of vertical pipe flows of adhesive granular materials using the discrete element method (DEM). Our simulations unveil different regimes of vertical pipe flow depending on the pipe-to-particle diameter ratio and the interparticle adhesive strength. Surprisingly, we find that the particle mass flow rate through the pipe increases substantially with this adhesive strength. This rather counterintuitive result is caused by an enhanced tendency of the particles to form stable agglomerates around the pipe symmetry axis, thus leading to reduced interaction of the particles with the frictional pipe walls. By contrast, incorporation of particle-wall adhesive interactions leads to exactly the opposite behavior, with such interactions dictating the granular dynamics in the pipe and leading to lower mass flow rate values compared to cohesionless flows. Furthermore, we show that the different flow regimes are associated with distinct spatiotemporal patterns of the granular solid fraction along the pipe axis (density waves). Therefore, our results provide theoretical references for future experimental research and application of adhesive granular flows through narrow pipes.

关键词： Granular flow Discrete element method Adhesive particles flow rate

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Theoretical model of electromagnetic flowmeter under annular conductivity distribution based on annular domain weight function

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MEASUREMENT 2025年 253卷

作者： Yang, Yang Yang, Biaohu Wang, Gaoyun Chen, Tianqiu Zhang, Chao Yang, Bin Zhang, Linli 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 Sinopec Shengli Oilfield Co Tech Inspection Ctr Dongying 257000 Peoples R China

Electromagnetic flowmeter has advantages such as non-invasiveness, no moving parts and high reliability. And they are not affected by physical parameters like fluid density, temperature, pressure, and viscosity. However, they can be influenced by non-uniform distribution of medium conductivity. In this paper, the theoretical model of electromagnetic flowmeter under annular conductivity distribution was established based on the fundamental control equation and the annular domain weight function. To verify the effectiveness of the theoretical model, COMSOL Multiphysics numerical simulation and experimental validation study were both conducted. The relative deviations between the theoretical value and the numerical simulation, as well as the experimental result, are +/- 4 % and +/- 1 %, respectively. This study provides a theoretical basis for expanding the application of electromagnetic flowmeter to annular conductivity distribution.

关键词： Electromagnetic flowmeter Annular weight function Annular conductivity distribution Multiphysics coupling

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Experimental study on the relationship between the flow pattern and heat transfer characteristics of flow boiling in a vertical upward rectangular narrow channel

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2025年 242卷

作者： Sun, Chen Dai, Ren Tao, Leren Huang, Lihao Gu, Shengjie Zhang, Yuxin Gu, Zhipan 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 Jiaxing Univ Sch Architecture & Civil Engn Jiaxing 314001 Zhejiang Peoples R China

This study investigated the evolution of flow patterns and heat transfer characteristics of flow boiling within vertical upward rectangular narrow channels. The channel, visualized and heated to simulate compact heat exchangers and the fuel channels of small modular reactors (SMRs), has geometric dimensions of 720 mm x 240 mm x 2.75 mm (l x w x s) and employs deionized water as the working fluid. Experimental conditions include inlet temperature in the range of 50 - 90 degrees C, mass flux between 4.04-24.24 kg/(m2 & sdot;s), and heat flux between 3.32-64.12 kW/m2. Images acquired via high-speed camera are presented to elucidate the flow regime physics. Different types of flow pattern maps were drawn and compared with other researchers' data under adiabatic and steam heating conditions. A new type of dimensionless correlative flow pattern transition criterion for vertical rectangular narrow channels was obtained and showed good accuracy in predicting the critical vapor quality of flow pattern transition. The results indicated that thermo-hydraulic parameters influence the positions and length of flow patterns, and the overall trend of the local heat transfer coefficient (HTC) remains consistent during flow pattern transition. Peak HTC values occurred during the later processes of restricted bubbly flow and annular flow. Critical heat flux (CHF) exhibited a positive correlation with mass flux but showed minimal sensitivity to inlet temperature. Specially, due to the intermittent wetting behavior of the tidal flow, heat transfer deterioration demonstrated a delayed response, and the heat flux of optimal average HTC was higher than the CHF.

关键词： flow boiling Narrow channel flow pattern CHF Two-phase flow heat transfer

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An improved model on the evaporation kinetics of the single aerosol droplet and its application for the droplet composed of ammonium sulfate or sucrose solution

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POWDER TECHNOLOGY 2025年 453卷

作者： Zhang, Chao Lu, Miaoran Bao, Han Ma, Nan Yu, Dandan Yang, Yang Wang, Yueshe Wiedensohler, Alfred 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 Jinan Univ Inst Environm & Climate Res Guangzhou 511443 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Leibniz Inst Tropospher Res D-04318 Leipzig Germany

An improved model is proposed to investigate effects of gas phase temperature, relative humidity and initial solute concentration on the evaporation rate of the aerosol droplet consisted of ammonium sulfate (AS) or sucrose (SC) solution and the water diffusion coefficient in bulk phase. Results show that the new model is more accurate than the traditional model ignoring the bulk phase mass diffusion. Effect of the bulk phase mass diffusion on the evaporation rate of the AS-water droplet is almost unaffected by factors studied here due to the predominance of the mass transfer in gas phase and gas-droplet interface. However, effect of the bulk phase mass diffusion on the evaporation rate of the SC-water droplet is negatively correlated with the gas phase temperature and the relative humidity, but it is positively correlated with the initial solute concentration. Furthermore, influence mechanisms of the water diffusion coefficient in AS (SC)-water droplets are revealed.

关键词： Aerosol droplets Evaporation Theoretical model Mass diffusion

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Experimental investigation on flow boiling heat transfer of R1233zd(E) in parallel microchannel heat sink with variable channel widths

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2025年 244卷

作者： Jiang, Chen-han Lu, Di Yu, Wen-long Fang, Yi-dong Zhao, Jia-yi Yang, Hui-nan Chen, Shuo 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 Tongji Univ Sch Aerosp Engn & Appl Mech Shanghai 200092 Peoples R China

In this study, a novel parallel microchannel heat sink with variable channel widths was proposed to confront the issue of flow maldistribution. With R1233zd(E) as the working fluid, subcooled flow boiling experiments were conducted in the microchannel heat sink with variable and uniform widths under the inlet subcooling of 5-8 degrees C and the mass flux and heat flux ranges of 500-2000 kg/m2 s, 0-180 kW/m2, respectively. The results indicated that the two-phase flow pattern in the microchannel with variable channel widths (VWMC) showed a better distribution uniformity than the one with uniform channel width (CWMC). The boiling curve in the two test sections showed that the onset of nucleate boiling (ONB) is incipient earlier in VWMC due to the improved flow uniformity, meanwhile it had lower wall superheat with the increase of heat flux. The deviation of boiling curves at local positions was also smaller in VWMC. Furthermore, the overall heat transfer coefficients (HTCs) in VWMC were consistently higher than those in CWMC across all operating conditions, with a maximum improvement of up to 60%. The improvements of HTC were also observed at various locations in different channels of VWMC along the flow direction. The pressure drop of VWMC, however, was generally higher than that in the CWMC, with the maximum penalty of 39%. Meanwhile, the pressure drop fluctuations maintained at a low level of +/- 0.6 kPa under most conditions, presenting optimal two-phase flow stability.

关键词： flow boiling Parallel microchannel Variable channel widths flow pattern heat transfer

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Experimental and numerical investigation of rectifier designs for enhancing energy separation efficiency in vortex tubes

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APPLIED THERMAL engineering 2025年 272卷

作者： Hu, Zhuohuan Zheng, Xiaohua Gao, Fan Wu, Hongwei Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanghai Univ Polit Sci & Law Shanghai Peoples R China Univ Hertfordshire Sch Phys Engn & Comp Sci Hatfield AL10 9AB England

In this article, a comprehensive experimental investigation was conducted on several rectifier-incorporated vortex tube to quantify key thermal performance metrics, including cold-end temperature difference, hot-end temperature difference, and coefficients of performance (COP), under the same operational conditions. Among the tested configurations, the vortex tube with a double-ring rectifier exhibited the highest energy separation efficiency, achieving a cold-end temperature difference up to 8.6 K higher than that of the prototype. Furthermore, this configuration attained the highest COP value of 0.104, representing a 43.2 % improvement over the prototype. A temperature-entropy analysis revealed that the rectifier effectively reduced irreversible losses during the energy separation process, thereby mitigating thermodynamic irreversibility associated with turbulent dissipation. Additionally, numerical simulations were performed on both the vortex tube prototype and the vortex tube with a double-ring rectifier. The numerical results demonstrated that the double-ring rectifier enhanced fluid rotational intensity and established distinct stratified flow regimes between the core and peripheral regions. Moreover, contour analysis identified a larger velocity gradient in the flow field near the rectifier, which disrupted the thermal boundary layer between the inner and peripheral fluid. This disruption facilitated greater heat transfer to both the peripheral fluid and the tube wall, thereby enhancing the vortex tube's energy separation performance. Overall, the combined experimental and numerical findings confirm that rectifier-induced flow field optimization significantly enhances vortex tube energy separation efficiency.

关键词： Vortex Tube Rectifier Energy Separation Coefficient of Performance Experimental

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Numerical study on shell-side shear flow and heat transfer in a spiral wound heat exchanger under onshore/offshore conditions

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APPLIED THERMAL engineering 2025年 267卷

作者： Ren, Yan Guo, Yixin Cai, Weihua Jiang, Yiqiang Wu, Weidong Yang, Yingying Chen, Jie Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai Peoples R China Norhteast Elect Power Univ Sch Energy & Power Engn Jilin Peoples R China Harbin Inst Technol Dept Bldg Thermal Energy Engn Harbin Peoples R China CNOOC Gas & Power Grp Beijing Peoples R China

Given that studies on shell-side shear flow and heat transfer characteristics in spiral wound heat exchangers (SWHEs) used in floating liquefied natural gas (FLNG) systems are still scarce, a mathematical-physical model was established based on the two-fluid thermal phase change model, incorporating a modified mean diameter of the dispersed phase. According to the results under onshore conditions with operating pressure ranging from 0.2 to 0.6 MPa, mass flux ranging from 40 to 100 kg/(m2 & sdot;s), heat flux ranging from 2,000 to 8,000 W/m2, and vapor quality ranging from 0.3 to 0.9, respectively, the shell-side frictional pressure drop gradient increased with decreasing operating pressure and increasing mass flux and vapor quality. The effect of the heat flux was negligible and could be ignored. The offshore conditions significantly increased the proportion of shear flow on the SWHE shell side. Therefore, the effects of the rolling and operating parameters on the shear flow were investigated with rolling amplitudes and periods of 5-15 degrees and 5-15 s, respectively. Consequently, the flow and heat transfer characteristics of the shell-side shear flow exhibited sinusoidal periodic fluctuations owing to the influence of the rolling motion, and their fluctuation periods were approximately equal to the rolling period. Within the allowable operating range, a higher mass flux could not only effectively resist the influence of the rolling motion but also maintain the heat exchanger performance at a higher level while delaying the adverse drying of the heat exchange tube wall. Additionally, Aunan's correlation was proven to exhibit good adaptability for calculating the frictional pressure drop gradient of shear flow under both onshore and offshore conditions. These results provide guidance for the design and operation of FLNG SWHEs.

关键词： Shear flow Thermal phase change model flow and heat transfer Shell side FLNG

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Numerical study on the performance of an interventional microaxial blood pump with superhydrophobic surface

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PHYSICS OF FLUIDS 2025年第1期37卷

作者： Geng, Xuesong Li, Chengcheng Ma, Jianying Qiu, Huihe Cui, Guomin Wang, Ying Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200039 Peoples R China Fudan Univ Zhongshan Hosp Shanghai Inst Cardiovasc Dis Dept Cardiol Shanghai 200032 Peoples R China Hong Kong Univ Sci & Technol Guangzhou Thrust Sustainable Energy & Environm Guangzhou Peoples R China

Unlike traditional blood pumps, interventional microaxial blood pumps are characterized by their small size, high rotational speed, and narrow gap between the impeller rim and pump housing. These features result in an unstable flow field within the pump, leading to high shear stress regions that can cause hemolysis. To improve the hydraulic efficiency of the blood pump and mitigate blood damage, this paper proposes an interventional microaxial blood pump with a superhydrophobic surface. The finite element method was used to model the axial blood pump and arterial flow field, with Navier slip boundary conditions applied to the impeller and outflow structure walls, simulating a slip length of 50 mu m to represent the superhydrophobic surface characteristics. A combination of numerical simulations and hydraulic experiments was employed to evaluate the effects of the superhydrophobic surface on the pump's hydraulic performance and hemolysis characteristics. The results indicated that the designed interventional microaxial blood pump model demonstrated good blood compatibility. The superhydrophobic surface significantly reduced shear stress at the design point, with wall shear stress in the impeller and outflow structure regions decreasing by approximately 8.09%. Hydraulic efficiency increased by approximately 12.16%, and the hemolysis index decreased by about 12.60%. These findings provide valuable support for further optimization of microaxial blood pumps.

关键词： Shear stress

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The influence of peak wave-channel clearance on performance characteristics of traveling wave pump

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Energy 2025年 325卷

作者： Li, Gucheng Zhu, Qianming Gu, Qingqing School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer Shanghai200093 China

Pumped storage plays a significant role in addressing the intermittency associated with solar and wind energy. The research on pumped storage is vital for sustainable development, with the pump serving as a key component. Achieving efficient energy conversion necessitates advancements in pumped storage technology, specifically through the development of novel pump designs that overcome limitations such as cavitation and vibration associated with conventional pumps. This study introduces a traveling wave pump that utilizes a traveling wave motion mechanism within a vertical rectangular flow channel to lift water to higher elevations. A simplified two-dimensional traveling wave plate model is employed to examine the influence of peak wave-channel clearance on pump performance using numerical simulations. The findings indicate that reducing the clearance causes a linear increase in time-averaged efficiency and a corresponding decrease in volumetric loss. Under high head conditions, pump performance is particularly sensitive to variations in clearance. A reduction in clearance accelerates high-speed fluid flow above the contraction point while reducing the low-speed zone below it. Furthermore, it weakens the intensity of the high-speed vortex at the leading edge of the traveling wave plate and the leakage vortex beneath the contraction point. © 2025 Elsevier Ltd

关键词： Vortex flow

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Enhanced electronic cooling with guest NCG microbubbles

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APPLIED THERMAL engineering 2025年 272卷

作者： Luo, Peng Tong, Wei Wei, Lichuan Zhang, Jie Zhao, Yugang Zhang, Hua Cheng, Ping Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shenzhen Envicool Technol Co Ltd Shenzhen 518129 Peoples R China China Aerodynam Res & Dev Ctr Key Lab Icing & Anti Deicing Mianyang 621000 Sichuan Peoples R China Shanghai Jiao Tong Univ Sch Mech Engn Key Lab Power Machinery & Engn MOE Shanghai 200240 Peoples R China

Electrical and electronic devices are producing a higher density of heat along with their elevated performance to meet the booming needs of industrials and human activities, and in response, more effective cooling technologies are always in demand. Liquid immersion is one of the most popular cooling methods developed due to its thermal efficiency and operational feasibility. However, conventional single-phase immersion cooling exhibits relatively lower thermal efficiency and heat capacity, and dual-phase immersion cooling occurs only when the heating surface temperature exceeds the liquid boiling point, constraining the selection of suitable coolants. This work presents a cooling method using guest noncondensable gas (NCG) microbubbles to enhance heat transfer in immersion cooling. Direct experimental results show that the heat transfer rate increases drastically, and surface superheating is suppressed or even eliminated. NCG microbubbles can disturb the thermal boundary layer, serve as evaporation/boiling nuclei, and collide with existing bubbles to facilitate their departure. This cooling method performs better at a large degree of pool subcooling, while the effect of bubble size is relatively minor. The fundamental understanding of bubble dynamics upon impinging onto the heating surface in subcooled liquid has promising applications in thermal management systems, such as microelectronic chips, nuclear reactors, steam generators, and among others.

关键词： Noncondensable gas Microbubbles Immersion cooling heat transfer enhancement

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