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Study of flow Pattern Transition Criterion and Heat Transfer Characteristics in Vertical Rectangular Narrow Channel for Steam Heating

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SSRN 2023年

作者： Gu, Shengjie Tao, Leren Jin, Cheng Ju, Yiwei Zhao, Xiefei School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power and Engineering University of Shanghai for Science and Technology Shanghai200093 China

To clarify the heat transfer characteristics of flow boiling in a narrow vertical rectangular channel at each stage and optimise the performance of the heat exchanger, an experimental study of the flow pattern and local heat transfer characteristics in a narrow vertical rectangular channel of steam heating with dimensions of 1400 mm × 250 mm × 2.75 mm (l × w × s) was carried out using deionized water as the working medium. Based on the mechanical model and the empirical formulas of the researchers, the preliminary derivation of the flow pattern transition criterion in the vertical rectangular narrow channel for steam heating is obtained. The effects of inlet temperature, mass flux and heating power on the local heat transfer characteristics were analyzed in conjunction with the flow patterns, and based on the parametric analysis of the experimental data, a new flow boiling heat transfer correlation formula was obtained which applies to the experimental conditions in this paper. The results show that the increase in inlet temperature has a positive effect on the nucleate boiling section, while the degree of effect on the local heat transfer coefficient is minimal after entering the churn flow phases. The increase in mass flux decreases the local heat transfer coefficient in the nuclear state boiling stage and enhances the local heat transfer coefficient in the evaporation zone of liquid film flow. The peak of the local heat transfer coefficient shows a tendency to shift to the left as the heating power increases. The new heat transfer correlation equation can well predict the local heat transfer coefficient of flow boiling in a vertical rectangular narrow channel heated by steam in this experimental condition. © 2023, The Authors. All rights reserved.

关键词： flow patterns

From Lab to Industry: Scaling-Up Fe-Ni Bimetallic Nano Oxygen Carrier for Mid-Temperature Methane Chemical Looping Reforming

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SSRN 2024年

作者： Tang, Sanli Gai, Zhongrui Li, Yang Liu, Yunlian Liu, Mingkai Pan, Ying Jin, Hongguang Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China University of Chinese Academy of Sciences Beijing100049 China

Chemical looping methane reforming has emerged as a promising avenue to produce blue hydrogen. Currently, the satisfactory CH4 conversion and H2 productivity are usually seen under temperatures above 800 °C. Such temperature requirement poses challenges for industrial reactor design and product gas separation. Investigated widely in chemical looping, bimetallic oxygen carrier has both catalytic and oxygen releasing functions, thus expected to realize both lower reaction temperature and high performance. In this study, we present a nanoscale Fe-Ni bimetallic oxygen carrier for mid-temperature chemical looping methane reforming which can be implemented at large scale. By virtue of a synergy from nanoscale Fe-Ni dispersion, all oxygen carriers from lab-scale to 10-kg scale can operate at 500-600 °C. The lab-scale oxygen carrier was found to convert >90% CH4, produce 3.5 H2 per CH4 molecule with 80-82% overall H2 purity at 575-600 °C. Following the proposed large-scale synthesis workflow, we acquired the 10-kg scale oxygen carrier powder with 70% with 2.8 H2 from per CH4 molecule. The 10-kg powders and beads both persisted phase, morphology and redox stability over 150 cycles. Further explorations revealed the similarity in structure and reaction performance between the lab-scale and 10-kg scale powders, and differences in reaction dynamics between the 10-kg powder and beads. These findings contribute to the mid-temperature chemical looping methane reforming by bridging laboratory practices and industrial application. © 2024, The Authors. All rights reserved.

关键词： Powders

Investigation on the Effect of Hydrothermal Reaction with Cuso4 on Rheological Property of Heavy Oil

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SSRN 2023年

作者： Zhou, Yantao Zhao, Qiuyang Wang, Xuetao Miao, Yan Song, Zhiwei Jin, Hui Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Xinjin Weihua Institute of Clean Energy Research Foshan528216 China

The rheological property is one of important physical properties evaluating heavy oil and asphalt. This work investigated the rheological changes during hydrothermal reaction with CuSO4. The results showed that the addition of CuSO4 at a high reaction temperature had an effect similar to asphalt modifiers, increasing the viscosity and elasticity. Further analysis suggested that the Cu atoms from CuSO4 entered heavy oil molecules, enhancing the interaction attraction between oil molecules. While, at a low reaction temperature, the CuSO4 acted as a catalyst, reducing both viscosity and elasticity. Based on these findings, this work proposed a novel and potential asphalt modification method, which changed the association effect between oil molecules by the chemical reaction to adjust the rheological properties permanently. This method would not fail due to the separation of modifiers and can adjust performance by changing reaction conditions. © 2023, The Authors. All rights reserved.

关键词： Transition metals

Dynamics of two-dimensional water flow in angstrom-scale mono and hybrid channels

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Physical Review Fluids 2024年第12期9卷 124201-124201页

作者： Chengzhen Sun Qiyuan Wang Mehdi Neek-Amal Runfeng Zhou Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China Department of Physics Shahid Rajaee Teacher Training University 16875-163 Lavizan Tehran Iran Departement Fysica Universiteit Antwerpen Groenenborgerlaan 171 B-2020 Antwerpen Belgium

We investigate the dynamics of two-dimensional (2D) water flow within angstrom-scale channels (ASCs), a domain scarcely explored in nanofluidics. Our study focuses on the transformation of monolayer water through hybrid channels made of graphene and MoS2, as well as channels where both walls are made of either graphene or MoS2, with sizes ranging from 6 to 8 Å. We find that the transport of monolayer water through ASCs is significantly hindered under low-pressure conditions at nanoscale timescales. To comprehensively explore the flow dynamics, we introduce a refined extension of the Hagen-Poiseuille equation that accounts for frictional slippage dynamics. Our results indicate that hybrid channels exhibit lower flux compared to monochannels. These findings provide valuable insights into the 2D flow mechanisms of monolayer water molecules, highlighting their distinctive interactions with channel walls and unique structural properties.

关键词： flow confinement Nanofluidics Molecular dynamics Navier-Stokes equation

Numerical Investigation of Vibrational and Misalignment Effects on Atomization Characteristics of Impinging Jets

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SSRN 2023年

作者： Dai, Qingwen Yang, Jianwen Yang, Bin Wang, Ying School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai200093 China Xi’an Aerospace Propulsion Institute Xi’an710100 China

To explore the influence of vibration, misalignment and their combined effects on the atomization characteristics of the impingement process, this paper utilizes the polyhedral mesh adaptive refinement algorithm and VOF-to-DPM multiphase flow model to simulate the atomization process of impinging jets atomization. Additionally, compared the results with experimental data to ensure accurate calculations. The whole process of liquid film broke into liquid filaments and further atomized into droplets under different working conditions are analyzed in this paper. The results show that the proposed algorithm and model can better simulate the two impinging liquid jets atomization. Vibrations cause fluctuations in mass flow, which will lead to the offset of the impingement point by the impinging jets atomization. With the increase of vibration frequency, the performance of atomization become worse. When the vibration frequency is 1000 Hz, the back splash phenomenon becomes more apparent. When the misaligned degree is small, low-amplitude, high frequency vibrations can weaken the influence of misaligned impingement, resulting in improved atomization performance. However, when the degree of misalignment is large, a larger deflection angle of the liquid film results in a smaller broken length of the liquid film and a worse atomization quality. At this time, the vibrations lead to vortices in the atomization field and have an entrainment effect on the atomization field. Therefore, the vibrations have adverse effects on engine thermal protection. © 2023, The Authors. All rights reserved.

关键词： Atomization

Comprehensive Parameter Analyses on Steam-Air Condensation at Equal- Height-Difference Natural Circulation Loop Under Large Air Mass Fraction

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SSRN 2024年

作者： Chen, Weixiong Wang, Han Li, Sinian Kai, Hui Zhao, Quanbin Li, Shaodan Wang, Jinshi State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Missile Engineering College Rocket Force University of Engineering 710025 China Science and Technology on Thermal Energy and Power Laboratory Wuhan 2nd Ship Design and Research Institute Wuhan430205 China

With the development of small-sized reactors, a passive containment cooling system (PCCS) named equal-height difference natural circulation loop (EHDNCS) has been developed. Experiments were conducted at higher air mass fractions to evaluate the condensation heat transfer coefficient (HTC) as a function of steam-air mixture pressure, air mass fraction, and wall subcooling. The results indicate that the condensation HTC decreases with increasing air mass fraction and increases with increasing steam-air mixture pressure in the containment. The relationship between condensation HTC and air mass fraction gradually transitions from non-linear to linear as the steam-air mixture pressure increases. The condensation HTC increases with increasing wall subcooling;However, for air mass fractions greater than 75%, the condensation HTC remains nearly constant with changes in wall subcooling. A quantitative relationship between the condensation HTC and the height of the PCCS (sum of riser height and 0.5 times heat exchanger height) has been derived by calculating the cooling water flow driving force and resistance in the natural circulation loop. The applicable conditions for optimizing the riser height and the initial ratio of the riser to heat exchanger height to enhance the heat transfer power of the PCCS were proposed. Based on the experimental results, an empirical correlation equation for predicting the condensation HTC for PCCS with EHDNCS is established, with a prediction deviation within ±31%. © 2024, The Authors. All rights reserved.

关键词： Heat exchangers

Investigation of the Solar-Driven Chemical Looping Methane Dry Reforming on Rh-Doped LaCeO3.5 Oxygen Carrier

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SSRN 2024年

作者： Li, Peng Gai, Zhongrui Zhang, Jinrui Rao, Qiong Tang, Sanli Shen, Yuanhui Pan, Ying Jin, Hongguang Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China University of Chinese Academy of Sciences Beijing100049 China

The feasibility of a solar-driven chemical looping dry reforming of methane (DRM) process, which converts solar energy and methane into syngas via a looping material oxygen carrier is investigated experimentally. Thermogravimetric analysis (TGA) experiments were firstly carried out to verify the effect of the Rh-doped LaCeO3.5 which were synthesized via modified Pechini method and incipient wetness method and the result shows that Rh greatly improved the reaction kinetics. Photo-TGA experiments were conducted to evaluate the light effect in chemical looping DRM. Under the light condition, the Rh-doped LaCeO3.5 shows higher methane conversion, oxygen extraction rate and CO selectivity compared with the undoped one, decreasing the apparent activation energy of the reaction at the same time. Insights obtained from the UV-Vis spectroscopy verified that the surface Rh under the light could promote the activation of surface methane species and increase the light absorbance. Meanwhile, the FEM methods were used to obtain the distributions of the temperature fields of the photo-TGA reactor through the calculation of the coupling of the fluid, reaction and temperature fields. In this way, the conversion mechanism of the solar, heating and chemical energy was illustrated and furthermore, the calculated surface reaction rate and the variation tendency of the outlet-gas were consistent with the experimental results. Through the integration of solar energy, a high methane to solar fuel conversion efficiency could be achieved. The proposed process has the potential to produce solar fuels at high efficiency with reduced carbon footprint. © 2024, The Authors. All rights reserved.

关键词： Methane

Investigation of Thermal Radiative Transfer Characteristics of Single Water Droplet

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SSRN 2023年

作者： Zhang, Dan Tu, Maoping Yuan, Yang Han, Wei State Key Laboratory of Multiphase Flow in Power Engineering School of Energy & Power Engineering Xi'an Jiaotong University Shaanxi Xi’an710049 China Xi'an Thermal Power Research Institute Co. Ltd Shaanxi Xi’an710054 China

Directly heat water droplet by thermal radiation was the key process of coupling solar energy to achieve green production in many industrial applications, such as desalination, carbon capture, energy storage, and so on. The radiative transfer of single water droplet for given irradiation, including reflection, absorption, transmission and their dependences on external irradiation, droplet geometry and radiative properties were investigated through a calculation model set up according to zone method. In current study, the ranges of equivalent diameter and length-width ratio of droplet were 0.1-1.0 mm, 1-10 respectively, its absorption coefficient was 10-15000 m-1 and refractive index was 1.2-2.0. Results suggested that, (1) the absorption mode of droplet could be classified into surface absorption (SA) and volumetric absorption (VA) depending on whether its optical thickness was greater than 1. In VA, droplet could get uniform and fast temperature increasing, and its absorptivity and mean temperature increase rate could be simultaneously improved by increasing absorption coefficient. (2) Scattering included reflection and transmission. Compared with incident irradiation, reflection distributed mainly on the same side of droplet's long axis, while transmission mainly on the opposite side. The overall reflectivity increased with rising refractive index, but was independent on droplet size. While its transmissivity increased with enlarging length-width ratio or reducing equivalent diameter. (3) In VA, at least 40% of incident irradiation was scattered out. The total quantity of scattering could be adjusted by changing absorption coefficient in VA or refractive index in SA. The proportion of transmission in scattering could always be increased by reducing refractive index. © 2023, The Authors. All rights reserved.

关键词： Drops

Thermal Characteristics and Structural Parameters Optimization of Apg/Cu/Pcm Integrated Architecture

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SSRN 2024年

作者： Su, Lizheng Zhang, Tianning Li, Xiaoyang Li, Dong Jiang, Xinyu Xie, Zhongnan Xi'an Electronic Engineering Research Institute Xi’an710100 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China State Key Laboratory of Nonferrous Metals and Processes GRINM Group Co. Ltd. Beijing100088 China

The challenges faced by radar seeker primarily stem from inadequate heat dissipation in chips and excessive weight. To address these issues, this study introduces a novel integrated phase-change heat sink architecture, composed of a copper alloy matrix, annealed pyrolytic graphite (APG), and phase-change materials (PCMs) serving as heat conduction reinforcements. The numerical analysis of the heat dissipation performance of this architecture is conducted using Fluent software. The study evaluates the impact of APG anisotropy, APG/Cu interface thermal resistance, APG thickness, and surface area on the heat conduction efficiency. Results demonstrate that APG facilitates a uniform in-plane temperature distribution, allowing PCMs to absorb heat more evenly. Consequently, APG proves effective in enhancing heat dissipation and safeguarding chips from high temperatures. In comparison to a pure copper component, the APG/Cu/PCM structure reduces chip temperature by a substantial 56.27%. Furthermore, increasing the surface area of APG generally contributes to an enhanced heat transfer capability of entire architecture. The paper presents a quantitative relationship between APG surface area and optimal thickness. Importantly, APG satisfies the lightweight requirement, further emphasizing its suitability for addressing the thermal challenges in radar seeker structures. © 2024, The Authors. All rights reserved.

关键词： Phase change materials