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Numerical simulation and structural optimization of spiral finned tube thermal energy storage

International Journal of Advanced Nuclear Reactor Design and Technology 2023年第3期5卷 123-136页

作者： Ma, Yunfei Meng, Yu Li, Jingyu Chen, Weixiong Yang, Xiaohu Li, Shaodan Chong, Daotong Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Wuhan Second Ship Design and Research Institute Wuhan430205 China

Thermal energy storage (TES) has emerged as a promising solution to enhance nuclear safety by passively removing decay heat during reactor shutdown and accidents, thus preventing overheating of the reactor core and protecting the integrity of containment barriers. The research of TES with different structures has broad application prospects and practical significance. In this study, the melting process of phase change material (PCM) in various TES structures was simulated by the numerical simulation method in two and three dimensions. The mechanism of gravity-driven natural convection enhancing heat transfer was revealed. The effects of different TES structures, fin pitch, fin height, and fin thickness on heat transfer performance were studied. The results showed that many vortices formed by liquid PCM are the main reason for enhancing the natural convection. Adding fins could greatly accelerate the heat storage process. The melting time of PCM in annular and spiral finned tube TES was 47.3% and 61.3% less than that in smooth tube TES, respectively. In the present study, the heat transfer effect was enhanced as the spiral fin pitch became small, the fin height increased and the fin thickness increased. Two opposite effects of fin structure on the natural convection were revealed: (1. positive effect provided by heat transfer enhancement and (2) negative effect produced by blockage. © 2023 Xi'an Jiaotong University

关键词： Phase change materials

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The evaporation of nanoscale sodium liquid film on the non-ideal nanostructure surface: A molecular dynamics study

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International Journal of Advanced Nuclear Reactor Design and Technology 2023年第1期5卷 1-8页

作者： Wang, Zetao Ye, Tianzhou Guo, Kailun Tian, Wenxi Qiu, Suizheng Su, Guanghui State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Lab of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi'an Jiaotong University Xi'an710049 China

The nanoscale liquid sodium film inside the microporous wick structure is of great importance to understanding the evaporation mechanism of the sodium heat pipe. The novel optimized wick structure is made of several layers of special screen. The surface of each screen exhibits a nanostructure type. Some non-ideal nanostructures may result from experimental faults or limits. And they will have an effect on the evaporation of film. In the present study, molecular dynamics is adopted to investigate this effect. The simulation system consists of the liquid sodium film and the solid surface. The flat surface is set as the reference. Based on the three non-ideal shapes of deposition, the sinusoidal nanostructures, conical nanostructures, and spherical nanostructures are built. The results indicate that the evaporation is suppressed by the above nanostructure surfaces. The weakening effect is through three forms: the potential gradient of the liquid film is intensified and the evaporation difficulty is increased;the heat transfer in the solid-liquid contact region is impeded;the collision heat transfer inside the liquid film is affected due to the delay of the aggregation variation between liquid atoms. © 2023 Xi'an Jiaotong University

关键词： Heat pipes

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Performance and emission characteristics of a hydrogen-enriched compressed-natural-gas direct-injection spark ignition engine diluted with exhaust gas recirculation

Performance and emission characteristics of a hydrogen-enric...

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作者： Liu, Y.-F. Liu, B. Zeng, K. Huang, Z. Zhou, L. Sun, L. State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Compressed natural gas (CNG) has been widely used in city buses or taxis because of its relatively low price and great abundance. Most of the CNG engines externally mix the natural gas with the intake air and utilize a lean-burn strategy to achieve low nitrogen oxide (NOx) emissions and high fuel economy. However, the well-examined external mixing of gas fuel with the intake air will result in a volumetric efficiency loss at high engine loads and may cause backfire when the natural gas is enriched with hydrogen. Also, the lean-burn technique may not sufficiently satisfy increasingly restricted future legislation. In this paper, the use of the stoichiometric equivalence ratio with exhaust gas recirculation (EGR) was investigated experimentally on a direct-injection spark ignition engine fuelled with hydrogen-natural-gas blends. Attention is focused on the advantages of combining EGR with hydrogen enrichment. The results show that hydrogen enrichment increases the brake mean effective pressure, which dramatically deteriorates under high-level EGR. Optimal efficiencies are achieved with an EGR rate of 5-1. per cent;the NO x emissions can be decreased by about 80per cent with 25 per cent EGR dilution, but the combustion variation increases simultaneously. With hydrogen enrichment, the combustion variation can be controlled under 5per cent, while the NOx, hydrocarbon, and carbon monoxide emissions are kept at a low level. Worse EGR tolerance was exhibited for the late-injection-timing case. © Author 201..

关键词： Efficiency

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Study on ash fusion behaviors and physico-chemical characteristics of semi-coke and its blended fuel with coal 35

Study on ash fusion behaviors and physico-chemical character...

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35th Annual International Pittsburgh Coal Conference, PCC 201.

作者： Yuan, Maobo Wang, Chang'an Wang, Pengqian Tao, Zichen Du, Yongbo Zhao, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

ISBN: (纸本)1890977357

With the rapid development of coal chemical industry in China, a large number of low-volatile carbon-based fuels such as semi-coke are in urgent need of combustion and utilization, and the co-combustion with high-volatile coal shows the potential to realize the large-scale utilization of semi-coke in coal-fired power plant. Because the blending coal can hardly match the design coal, it is easy to aggravate the degree of deposition and slagging on the heating surface and affect the operation of the boiler. However, the melting behavior of ash produced by blended coal with semi-coke combustion needs further study. In this paper, the ash melting behavior and physico-chemical characteristics of semi-coke and its blended fuel with coal were experimentally studied. Firstly, the relation of ash composition and ash melting behavior was observed by comparing the ash composition and ash fusion point of semi-coke and raw coal. Secondly, the influence of blending ratio and blending mode on the ash melting behavior of semi-coke blended fuel was studied by micro-computer ash melting point meter. Finally, the microstructure and physico-chemical properties of the melted ash at the softening temperature were evaluated by scanning electron microscope (SEM) technique with X-ray spectrometer (EDS) and X-ray diffractometer (XRD) technique. The experimental results showed that the mineral composition and oxide content in the semi-coke were different from the raw coal, which led to the change of coal ash fusibility. Meanwhile, the ash fusion point of semi-coke blended fuel could not be expressed linearly by the ash fusion point of its raw coal, and the influence of blending mode including in-furnace blending and out-furnace blending on the ash fusion point could be neglected. While the microstructure and physico-chemical properties were affected by the blending mode. Compared to the in-furnace blending, the carbon content was lower in out-furnace blending. Furthermore, the blending mode h

关键词： Coal

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Study of low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames

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Chinese Science Bulletin 2009年第9期54卷 1477-1486页

作者： YU Wu WEI LiXia MA ZhiHao HUANG ZuoHua YUAN Tao TIAN ZhenYu LI YuYang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei 230029 China

Low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 1.%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experimental results provide detailed data in understanding the combustion of n-heptane and n-heptane/propane blends in engine. They are also helpful in establishing and verifying the kinetic models.

关键词：正庚烷火焰丙烷混层低压氮氧真空紫外

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Numerical investigation on the dryout point of annular flow in the upward narrow annuli with bilateral heating

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中国高等学校学术文摘·能源与动力工程 2007年第3期1卷 264-272页

作者： SU Guanghui DUAN Feng QIU Suizheng XIAO Zejun HUANG Yanping State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China National Key Laboratory of Bubble and Natural Circulation Nuclear Power Insitute of ChinaChengdu 610041China

Based on the fundamental conservation principles-the mass,momentum,and energy conservation equtions of liquid films and the momentum conservation equation of vapor core,a theoretical three-fluid model has been developed to predict the dryout point of upward annular flow in vertical narrow annuli with bilateral *** range of the parameters are:pressure from 0.5 to 5.0 MPa;mass flow Through numerically solving the model,the relationships among the parameters of the critical quality (Xc),critical heat flux (QCHF),mass flow rate,system pressure,and the ratio of heat flux on the inner wall of the outer tube to that on the outer wall of the inner tube (qo/qi) are obtained and *** predicted results accurately match with the experimental *** a fixed qo,Xc will increase with the decreases in the gap size and the tube curvature when the dryout point occurs on the outer wall of the inner ***,for a fixed qi,when the dryout point occurs on the inner wall of the outer tube,the parametric trend is *** the dryout point on the inner and outer walls occurs simultaneously,Xc reaches a peak value,and the ratio of qo/qi at this position changes with the gap size and the tube curvature.

关键词： critical heat flux critical quality annular flow dryout numerical simulation

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Exhaust recovery of vehicle gasoline engine based on organic rankine cycle

Exhaust recovery of vehicle gasoline engine based on organic...

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SAE 201. World Congress and Exhibition

作者： Zhang, Xinxin Zeng, Ke Bai, Sujuan Zhang, Ying He, Maogang State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an Shaanxi 710049 China

When the global energy consumption continues to increase, the research hotspot in the field of internal combustion engine (ICE) is how to improve the fuel utilization efficiency to achieve the energy saving. But as far as the engine efficiency is concerned, it has been very difficult to improve the fuel utilization efficiency after the Gasoline Direct-Injection (GDI) and Homogeneous Charge Compression Ignition (HCCI) technology were adopted. In this study, the exothermic distribution of fuel was studied detailedly when a TOYOTA 8A-FE gasoline engine operated at different working conditions through conducting steady-state experiment. Only one third of fuel's chemical energy is converted into effective work by engine, the rest is released to the environment in the form of waste heat generated from cooling and exhaust gas. But except the waste heat that has to be released to the environment according to the second law of thermodynamics, the rest can be theoretically utilized. If the waste heat of the vehicle engine can be recovered, the engine efficiency will be evidently improved. Results on the exergy analysis show that the exergy in the exhaust gas is about 45-70% and it will evidently increase with the increase of engine load and revolution. So it will have a good effect on exhaust recovery when the engine has a heavy load. Considering the character of exhaust gas, the Organic Rankine Cycle(ORC) is adopted to recover the waste heat of engine's exhaust gas. The thermodynamic performances of the cycle were analyzed and R1.3 was determined to be the working fluid. The experimental exhaust gas recovery system used to testify the aforementioned theoretical calculation was designed and established. The system consists of exhaust gas simulation device, expander, condenser, dynamometer, pump and data acquisition and processing system. In experiment, the performance parameter and {1. output of the Organic Rankine Cycle were measured. The expander show a high isentropic ef

关键词： Recovery

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A two-phase non-isothermal mass transport model for direct methanol fuel cells

A two-phase non-isothermal mass transport model for direct m...

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2009 US-EU-China Thermophysics Conference - Renewable Energy, UECTC'09

作者： Miao, Zheng He, Ya-Ling Li, Xiao-Yue Zou, Jin-Qiang State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an Shaanxi China

ISBN: (纸本)9780791802908

A two-dimensional two-phase non-isothermal mass transport model for liquid feed direct methanol fuel cells (DMFCs) is presented in this paper. The heat and mass transfer across the membrane electrode assembly (MEA) is formulated based on the classical multiphase {1. theory in the porous media. The effects of methanol crossover and non-equilibrium evaporation/condensation of methanol and water at the gas-liquid interface on the cell performance are considered. Results of this model show that the methanol feeding concentration and cell operation temperature have great effects on the cell performance. The distribution of cell temperature is non-uniform and the highest temperature appears in the cathode catalyst layer (CL). The effects of open-ratio of the {1. field plate and the thermal conductivity of diffusion layers, catalyst layers and membrane are also investigated in this work. Copyright © 2009 by ASME.

关键词： Methanol

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Eosin Y-sensitized ZnO/TiO2 for efficient visible light photocatalytic hydrogen evolution

Eosin Y-sensitized ZnO/TiO2 for efficient visible light phot...

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201. MRS Spring Meeting

作者： Liu, Haipei Jing, Dengwei Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an 710049 China

ISBN: (纸本)9781618395238

In this work a series of Eosin Y-ZnO(x%)/TiO2 were prepared. ZnO well dispersed on the surface of TiO2, which improves the adsorption of Eosin Y and the excited electron to transfer to the conduction band of TiO2. Therefore the visible light activity of 0.2%Pt-Eosin Y-ZnO(x%)/TiO2 is much higher than that of the 0.2%Pt-Eosin Y-TiO2 and 0.2%Pt-Eosin Y-ZnO. The 0.2%Pt-Eosin Y-ZnO(1.5%)/TiO 2 has the highest visible light activity among the catalysts coupled with various ZnO amount, whose activity is increased by a factor of 3.5 compared to that of 0.2%Pt-Eosin Y-TiO2. It is proposed that, 0.2%Pt-Eosin Y-ZnO(1.5%)/TiO2 has the optimal trapping sites of carriers and thickness of the space-charge layer on the TiO2 particle surface, so these factors result a more efficient charge separation, an increased lifetime of the charge carriers, and the enhanced of hydrogen production. © 201. Materials Research Society.

关键词： Titanium dioxide

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Catalytic combustion of ventilation air methane in a reverse-flow reactor

Catalytic combustion of ventilation air methane in a reverse...

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作者： Wang, Yikun Man, Chengbo Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xian Jiaotong University Xian 710049 China

This paper describes an experimental study on the catalytic combustion of ventilation air methane in a vertical reactor. The mixture of natural gas and compressed air was used in the experiments, and the combustion products were analyzed by the Fourier transform infrared (FTIR) gas analyzer. The effects of the initial temperature, cycle time, feed gas concentration, and space velocity were studied. The experimental results show that the reactor could run under a wide range of operating conditions with self-sustaining operation and high methane conversion. Besides, it could even run with a feed gas concentration as low as 0.1. vol % without generation of CO and NOx, which has not been achieved in previous studies. The optimization of operating parameter combination increases the stability and efficiency of combustion. Different from the previous studies, the present research shows that the temperature profile of the cyclic steady state is not affected by the initial temperature. In addition, the methane conversion and reaction zone change during the process of the reaction. Thus, there is a limitation about the employment of a gas chromatograph (GC) to measure the methane concentration. Moreover, the presence of natural convection makes the temperature profiles of the cycle steady state asymmetrical. © 201. American Chemical Society.

关键词： Compressed air

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