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Experimental study of a rectangular microchannel printed circuit heat exchanger using supercritical carbon dioxide and water cooling

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APPLIED THERMAL engineering 2025年 262卷

作者： Ren, Yan Jiang, Ruowen Wang, Peidong Wu, Weidong Yang, Yingying Yang, Qiguo 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 Shanghai Elect Power Generat Equipment Co Ltd Turb Shanghai 200240 Peoples R China

Printed circuit heat exchangers with rectangular microchannels (RM-PCHEs) have attracted interest in recent years owing to their excellent heat-transfer performance and efficient and convenient processing methods. However, experimental studies on RM-PCHE using supercritical carbon dioxide (SCO2) and cooling water as working fluids are still scarce. This study established an experimental system to investigate the flow and heattransfer characteristics of an RM-PCHE. The experiment considered inlet temperature ranges of 343.13-371.1 K for SCO2 and 283.13-293.13 K for the cooling water. The results showed that the SCO2 inlet temperature had the most significant effect on the heat-transfer performance. With a 1 % increase in the SCO2 inlet temperature, the test sample Qave increased by 2.18 %, and thermal performance decreased by 2.62 %. Decreasing the SCO2 inlet temperature or increasing the cooling-water inlet temperature improved the hot-side flow performance. The cold-side pressure drop and effectiveness were most significantly affected by the cooling-water mass flow rate and minimally affected by the cooling-water inlet temperature. The effectiveness increased to 96.9 % with an increase in the cooling-water mass flow rate to 1500 kg & sdot;h- 1. These results provide theoretical and data support for the structural design and performance optimization of SCO2 microchannel water coolers.

关键词： Printed circuit heat exchanger Supercritical carbon dioxide Cooling water flow and heat-transfer characteristics Rectangular microchannel

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Numerical study on the wake characteristics of a square cylinder in linearly stratified flow at a Reynolds number of 200

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PHYSICS OF FLUIDS 2025年第3期37卷

作者： Wei, Na Shi, Liuliu Chen, Eryun 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 Shanghai Jiao Tong Univ Key Lab Power Machinery Engn Minist Educ Shanghai 200240 Peoples R China

In this study, the flow structures and hydrodynamic forces acting on a square cylinder in a linearly stratified flow at a fixed Reynolds number of Re = 200 are analyzed using large eddy simulation across a Froude number range of 0.2 <= Fr <= infinity. This study examines the effects of stratification on flow structures and associated hydrodynamic coefficients, employing both qualitative and quantitative analysis. The findings indicate that the flow patterns can be categorized into two primary types: the V pattern and the W pattern. In the V pattern (2 <= Fr <= 10), the wake is characterized by large-scale vortices shed from the separated shear layers. In contrast, the W pattern (0.2 <= Fr <= 1) shows a complete absence of vortex shedding. In this case, internal waves are the primary factor influencing the flow field. A transition between these two patterns is observed at a Froude number of 1. Furthermore, as the strength of stratification increases, the size of the recirculation zone progressively diminishes, signifying a gradual suppression of vertical motion. The analysis of drag and lift coefficients, Strouhal number, and pressure coefficient reveals a dependence on the Froude number, with the transition at Fr = 1 serving to further validate the classification of the flow patterns.

关键词： Hydrodynamics

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Quantitative description of surface tension for nanodroplets containing ammonium sulfate and its application to the particle hygroscopicity prediction

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PHYSICS OF FLUIDS 2025年第1期37卷

作者： Zhang, Chao Lin, Haoyang Zhang, Zhichao Yang, Yang Pan, Jinxiong 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 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

Surface tension is critically important in the hygroscopicity prediction of nano-aerosols, but experimental measurements of suspended nanodroplet surface tension are currently unattainable. In this study, effect of size and solute concentration on the surface tension of aqueous ammonium sulfate (AS) droplet smaller than 10 nm is investigated based on molecular dynamics simulations. A surface tension formula is proposed and applied in the theoretical model for particle hygroscopicity, and the prediction is compared with models using traditional methods of surface tension description. Results show that with the increase in AS concentration, surface tension decreases first and then increases, and the correlation between surface tension and droplet size changes from positive to negative. Compared to the surface tension model considering only the AS concentration effect, the surface tension formula including both AS concentration and size corrections enables the particle hygroscopicity model to obtain a smaller hygroscopic growth factor, which is closer to the experimental results. The improvement effect of the new formula on the model accuracy increases with the decreasing particle size. Additionally, the new surface tension formula leads to an increase in the critical supersaturation for particles smaller than 5 nm but a decrease for larger particles. The present study highlights the importance of the molecular dynamics investigation for nanodroplets comprising of complex ingredients.

关键词： Surface tension

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Simple synthesis of AgInS2/ZnS core/shell quantum dots with wide tunable emission wavelength for white light-emitting diodes

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OPTICS COMMUNICATIONS 2025年 575卷

作者： Ma, Qing Yang, Bin Yan, Fengrui Sun, Yanzi Yuan, Jiandi Li, Qingping Huang, Lanting Zhang, Tingting Li, Qinghua Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Lingnan Normal Univ Sch Phys Sci & Technol Zhanjiang 524048 Peoples R China

Phosphor with efficient and broad range emission is necessary for lighting applications. I-III-VI group quantum dots (QDs) have the advantages of non-toxic composition and large adjustable spectrum range, and have potential applications in the field of lighting. However, the efficient luminescence of these QDs at shorter wavelengths still needs further study, which is crucial for the development of high color rendering index white light LED devices (WLEDs). In this work, wide visible range emitting AgInS2/ZnS QDs with broad band and high luminous efficiency were obtained by altering the Ag/In ratios and Zn2+ inter-diffusion with cation of AgInS2. Photo-luminescent (PL) wavelength range of the obtained core-shell structured AgInS2/ZnS extended from 703 nm to 524 nm with high PL quantum yield (QY) and stability. The champion device based on the optimized AgInS2/ZnS QDs exhibits warm white light (correlated color temperature = 3652 K) characteristics with high color rendering index (CRI Ra) of 92.85 while maintaining excellent color stability under different driving currents. These properties are far superior to those of WLEDs with YAG phosphor.

关键词： White light-emitting diodes AgInS2/ZnS Tunable emission Color rendering index

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Bio-inspired asymmetric airfoil design based on the wind energy quality and flow field spatio-temporal on the vertical axis wind turbine rotor plane

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RENEWABLE ENERGY 2025年 248卷

作者： Huang, Shengxian Li, Chun Ng, Eddie Y. K. Wang, Ying 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 Nanyang Technol Univ Sch Mech & Aerosp Engn Singapore 639798 Singapore

Significant progress has been made in optimizing the energy efficiency of vertical-axis wind turbines (VAWTs). However, most optimization studies overlooked the variation in wind energy quality between the upwind and downwind regions. This oversight may hinder further improvement in wind energy utilization. Adopting a typical H-type VAWT, this study evaluates the wind energy quality in the VAWT rotor plane. Lagrangian coherent structure and dynamic mode decomposition are employed to investigate the attenuation principle of wind energy quality. Inspired by the superior hydrodynamic performance of Dall's porpoise, a novel asymmetric airfoil design method is proposed. Unlike previous bio-inspired airfoil designs, the geometric morphometric-based outline method and the average morphological of multiple Dall's porpoise samples is applied. The results indicate that: (1) Wind energy quality in the upwind region is higher than that in the downwind region. At the tip speed ratio (TSR) of 1.2, the downwind wind speed is 55.8 % of the upwind speed. (2) The asymmetric bio-inspired airfoil demonstrates a higher power coefficient compared to the NACA 0018 airfoil. (3) At TSR = 0.5, the bio-inspired airfoil achieves a 42.3 % improvement in wind energy utilization. The proposed design methodology for asymmetric bio-inspired airfoil offers valuable insights into blade and airfoil optimization.

关键词： VAWT Wind energy quality LCS DMD Asymmetric bio-inspired airfoil

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Numerical and experimental investigations on the effect of skeleton shapes and heat transfer directions on water freezing in porous media

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2025年 236卷

作者： Yang, Qingyu Yang, Tao Yang, Yingying Shen, Jun Beijing Inst Technol Sch Mech Engn Beijing 100081 Peoples R China 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

Incorporating porous skeletons into PCMs is an effective strategy for enhancing their thermal properties. However, this approach increases the complexity of the heat transfer process and poses a challenge to accurate modeling. This study investigates the water freezing process in porous skeletons with various shapes and heat transfer directions through experiments and numerical simulations. The model employs the hybrid finite element method with mesh adaptation to optimize numerical solutions. The experimental and simulation results are in good agreement, which validates the accuracy of this model. The study aims to reveal the evolution mechanisms of the phase interface, temperature field, and freezing rate of water in various porous skeletons, enhancing the theoretical foundation and offering insights for practical applications. Results show that the square steel skeleton exhibits the highest freezing rate among the tested skeleton shapes, while the rhombus resin skeleton demonstrates the slowest. Furthermore, the square skeleton shows the smallest interface deflection before and after the pores, while the rhombus skeleton presents the largest. Additionally, vertical heat transfer from bottom to top increases the freezing rate by 38.97% compared to horizontal heat transfer from left to right.

关键词： Solid-liquid phase change Numerical simulation Porous skeletons heat transfer characteristics

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Research on flow characteristics of dual-outlet centrifugal disk blood pumps

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Shengwu Yixue Gongchengxue Zazhi/Journal of Biomedical engineering 2025年第2期42卷 374-381页

作者： Lian, Qilong Xiao, Yuan Xiao, Yiping Cao, Zhanshuo Cui, Guomin Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China

Tesla blood pumps demonstrate a reduced propensity for hemolysis and thrombosis compared with vane blood pumps. Considering the restricted driving force within the secondary flow channel of vane blood pumps, along with the low hydraulic efficiency of conventional Tesla blood pumps and their internal flow characteristics that significantly contribute to hemolysis and thrombosis, this study introduces a set of vanes atop the rotor of the Tesla blood pump. This forms a dual-fluid domain rotor, and an axial dual-outlet volute shell structure is adopted to realize the separation of the fluid domains. Through numerical simulations of the new structure, a comparative analysis was conducted in this study on the internal flow characteristics of double-outlet and single-outlet volute shells, and symmetric and asymmetric cross-sections of the same rotor. The results indicate that the flow field distribution is more uniform under the double-outlet volute shell structure, and overall energy dissipation is decreased. After implementing the double-outlet design, in the asymmetric cross-section, compared with the symmetric cross-section, the fluid velocity gradient and turbulent kinetic energy at the tongue of the septum are reduced, and the fluid velocity gradient at the convergence of the diffuser tube outlets are also decreased. The maximum scalar stress is lower, and the decline in head and efficiency is mitigated. Moreover, compared with the single-outlet volute shell, the hemolysis index in the asymmetric cross-section is reduced. In summary, this paper proposes a novel dual-outlet centrifugal disk blood pumps, which can provide a reference for the structural design and performance optimization of magnetically levitated centrifugal blood pumps. © 2025 West China Hospital, Sichuan Institute of Biomedical engineering. All rights reserved.

关键词： Shells (structures)

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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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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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