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Influence of inlet structure on thermal stratification in a heat storage tank with PCMs: CFD and experimental study

APPLIED THERMAL engineering 2019年 162卷 114151-114151页

作者： Wang, Zilong Zhang, Hua Dou, Binlin Zhang, Guanhua Wu, Weidong Univ Shanghai Sci & Technol Shanghai Key Lab Multiphase Flow & Heat Transfer Sch Energy & Power Engn Shanghai 200093 Peoples R China

heat storage tanks are one of the key components in solar thermal utilisation systems. In this study, the effect of the inlet stratifier on the thermal stratification in a heat storage tank with phase-change materials (PCMs) was investigated. A heat storage tank with a volume of 60 L and aspect ratio of 1.68 was developed based on the phase-change temperature of 331.15 K for sodium acetate trihydrate. The thermodynamic characteristics of the heat storage tank were measured at an initial temperature of 353.15 K and inlet water temperature of 278.15 K. Moreover, a computational fluid dynamics (CFD) model of the heat storage tank was established to simulate the discharge process. In addition, the CFD model was verified with experimental data. The impact of the PCM position on thermal stratification was thoroughly analysed for various flow rates. Furthermore, performance parameters including the Fill Efficiency (FE), Richardson number (Ri), and MIX number were considered. The results show that the equalizer enhances the thermal stratification effectively in the phase-change heat storage tank and stabilises the heat output characteristics of the water tank. Furthermore, in the water discharge process (t* = 0.1-0.7), the distances between the isothermal surfaces (279.15 K) and isothermal surfaces (352.15 K) in PCM4, PCM3, PCM2, and PCM1 increase by 6.56, 7.2, 8.98, and 12.34 cm, respectively. Thus, the mixing of hot and cold water strengthens with higher PCM position, which improves the thermal stratification in a heat storage tank. The half-life of the PCMs (melting rate reaches 50%) is prolonged with increasing inlet flow rate. For an inlet flow rate of 1 L/min, the half-life of PCM4 is t* = 0.5. For an inlet flow rate of 5 L/min, the half-life of PCM4 is t* = 0.95. Moreover, the simulated results of the FE and Ri are slightly higher than the experimental values, whereas the simulated MIX number results are below the experimental values. Finally, the simulated and exper

关键词： Phase-change materials heat storage Thermal stratification Fill Efficiency Water tank

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Aerodynamic design and numerical study for centrifugal turbine with different shapes of volutes

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APPLIED THERMAL engineering 2018年 131卷 472-485页

作者： Wang, Ying Tan, Xin Wang, Naian Huang, Diangui Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

Centrifugal turbine presents good aerodynamic and geometric compatibility. The straight blade can be directly used without significant effect on three dimensional flow field, and therefore the optimum values of the speed ratio and reaction degree can keep constant along the spanwise direction with higher turbine efficiency and simpler manufacturing. Furthermore, the closed impeller which is made by fixing the blade tip using cover band shows larger impeller strength and is suitable for high-speed rotation. In recent years, the centrifugal turbine with many potential advantages is gradually becoming a research hotspot in the field of turbine. In this paper, three kinds of volutes with different cross section shapes were designed for a single-stage centrifugal turbine unit. Based on the CFD simulation in the whole flow passage, the analysis of three-dimensional steady flow for the designed centrifugal turbine was carried out under both of design and off-design conditions, and the following results were obtained: the aerodynamic performance of centrifugal turbines with three kinds of volutes are almost the same under both of design and off-design conditions. Besides, the pear shaped volute shows slightly higher total efficiency, and its overall efficiency, stage internal efficiency and power are 87.36%, 85.79% and 484.88 kW, respectively. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Centrifugal turbine Numerical simulation Aerodynamic design Volute

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Influence of ignition atmosphere on the structural properties of magnetic iron oxides synthesized via solution combustion and the NH3-SCR activity of W/Fe2O3 catalyst

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APPLIED CATALYSIS A-GENERAL 2020年 602卷 117726-117726页

作者： Li, Cheng-xu Xiong, Zhi-bo He, Jun-fei Qu, Xiao-ke Li, Zhen-zhuang Ning, Xing Lu, Wei Wu, Shui-mu Tan, Lu-zhi Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China SPIC Powder Plant Operat Technol Beijing Co Ltd Beijing 102209 Peoples R China Ludong Univ Sch Food Engn Yantai 264000 Peoples R China

Two kinds of magnetic iron oxides (Fe2O3-PO and Fe2O3-AO) are synthesized via the solution combustion coupled with the chemical oxidization of hydrogen peroxide. The magnetic carbon-containing Fe2O3-AO obtained at the absence of air presents the main gamma-Fe2O3 crystal with smaller crystallite size and larger BET surface area, but not the aggregated and sintered alpha-Fe2O3 crystal of Fe2O3-PO. The doping of tungsten has no effect on the growth of alpha-Fe(2)O(3)in Fe2O3-PO during the annealing process at 400 degrees C. However, the doping of tungsten effectively restrains the irreversible transformation of gamma-Fe2O3 into alpha-Fe2O3 crystal and enhances the anti-collapse of the pore structure of Fe2O3-AO under the same annealing process at 400 degrees C by inducing a stronger interaction between tungsten species and gamma-Fe2O3 crystal. In addition, the doping of tungsten improves the ratio of surface adsorbed oxygen, the Fe2+/(Fe2++Fe3+) ratio and the surface acidity of Fe2O3-PO-400 and Fe2O3-AO-400. Therefore, the doping of tungsten promotes the catalytic performance of Fe2O3-PO-400, especially its high-temperature activity, but exhibits a better promotional effect on the low-temperature activity of Fe2O3-AO400. Magnetic 5W/Fe2O3-AO-400 shows the highest BET surface area, the largest Fe2+/(Fe2++Fe3+) ratio, the strongest surface acidity and the appropriate redox ability compared with the other tested catalysts, thus exhibits the highest low-temperature NH3-SCR activity and better resistance to SO2 and H2O than 5W/Fe2O3-PO-400. The formation of low crystallinity and high dispersive gamma-Fe2O3 is an important reason on the good catalytic performance of magnetic 5W/Fe2O3-AO-400, which is also confirmed by the influence of annealing temperature. Furthermore, the results of steady-state kinetic experiments demonstrate that the 5W/Fe2O3-AO-400 catalyst mainly follows the Eley-Rideal mechanism.

关键词： De-nitrogen Selective catalytic reduction Magnetic iron oxide Tungsten doping Solution combustion Ignition atmosphere

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The composite Chebyshev integration method for radiative integral transfer equations in rectangular enclosures

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INTERNATIONAL JOURNAL OF THERMAL SCIENCES 2021年 170卷 107141-107141页

作者： Zhou, Rui-Rui Sun, Ya-Song Li, Ben-Wen Ma, Jing Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Northwestern Polytech Univ Sch Power & Energy Shaanxi Key Lab Thermal Sci Aeroengine Syst Xian 710072 Peoples R China NPU Ctr Computat Phys & Energy Sci Yangtze River Delta Res Inst Taicang 215400 Peoples R China Dalian Univ Technol Sch Energy & Power Engn Key Lab Ocean Energy Utilizat & Energy Conservat Minist Educ Dalian 116024 Peoples R China Changan Univ Sch Automobile Key Lab Shaanxi Prov Dev & Applicat New Transport Xian 710064 Peoples R China

Recently, the Chebyshev integration method was developed to solve the radiative integral transfer equations (RITEs) after singularity removing (IJTS, 149 (2020) 106,158), and shown fourth order convergence accuracy. This superior property makes the Chebyshev integration method attractive to produce results with quite high accuracy to be benchmark solutions. However, the Chebyshev integration method, which is a global method, is only suitable for problems with smooth parameters and temperature distribution. To overcome this drawback, in this paper, the composite Chebyshev integration method is proposed. The computational domain is divided into several subdomains, and then the Chebyshev quadrature is applied in each subdomain. Several benchmark problems in the rectangular medium with continuous/stepwise-change scattering albedo and emissions are solved. Increasing the grid number with fixed subdomains, one can observe that the composite Chebyshev integration method still has the high order convergence accuracy. Besides, the solutions rounded to seven significant digits are given in tabular form for convenience. They are also used as benchmark solutions to assess the collocation spectral method (CSM) and its modified version for radiative transfer equation (RTE). The results indicate that the CSM suffers from severe ray effect when the discontinuities appear in the scattering albedo and temperature distribution. Though the modified CSM can avoid the ray effect due to stepwise-change emissions, it requires heavier computational load but produces less accurate results than the composite Chebyshev integration method for RITEs under the same spatial grid system. Compared with the CSM or modified CSM to solve the RTE, the composite Chebyshev integration method for RITEs can achieve much higher accuracy with acceptable computational time, thus could also be a good alternative for thermal radiation calculations in simple geometry.

关键词： Radiative heat transfer Ray effect Rectangular medium Singularity subtraction method Chebyshev polynomials

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Effects of mixed surfactants on heat transfer performance of pulsed spray cooling

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2019年 144卷 118593-000页

作者： Liu, Ni Yu, Zhixiang Liang, Yong Zhang, Hua Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai Peoples R China

Pulsed spray cooling is a new type of cooling technique which can make full use of working medium and achieve better heat transfer effect. In this study, the effects of surfactants on pulsed spray cooling were investigated experimentally in a closed pulsed spray cooling system. The optimal pulsed spray parameters were determined to be 450 ms spray cycle and 60% duty cycle. Under this condition, the heat transfer performance of surfactant FS-31 was studied. The results show that the mean surface temperature and the heat transfer coefficient of FS-31 are 50.01 degrees C and 1.55 W/cm(2).K at the concentration of 100 ppm. Furthermore, the effects of mixed surfactants of AOS-FS-31, CTAB-FS-31 and CTAB-AOS on the heat transfer performance of pulsed spray cooling were studied. The results show that the mixed surfactants of AOS-FS-31 has a significant enhancement on the heat transfer performance of pulsed spray cooling due to the synergistic effect between anionic and nonionic. The mean surface temperature and the heat transfer coefficient can reach 48.03 degrees C and 1.75 W/cm(2).K. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Pulsed spray cooling Duty cycle Spray cycle Mixed surfactants

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Statistical characterization of gas-liquid flow in swirl vane separator with image processing technique 18

Statistical characterization of gas-liquid flow in swirl van...

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18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019

作者： Liu, Li Bai, Bofeng School of Nuclear Science and Engineering Shanghai Jiao Tong University Shanghai200240 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi710049 China

Swirl vane separator is not only used in SG for separating more than 80% of liquid water from steam-water mixture to feed qualified steam to dryers and turbines, but also applied in the thorium molten salt reactor to remove dilute dispersed bubbles from reactor coolant. The proper design and operation of swirl vane separator requires a fundamental understanding of the gas-liquid flow pattern in the system, since the mass, momentum, and energy transfer rates and processes are quite sensitive to the distribution of the phases within the flow. This paper presents a comprehensive experimental study aimed at classifying flow patterns in the condition of swirling gas-liquid flow in a downscale swirl vane separator. While a large amount of work has been done on conventional, non-swirling, two-phase flow in small pipes, investigations on swirling flow regime classification are still scarce. Here, optical and image processing techniques are used to measure gas and liquid holdup in the system through time. Detailed qualitative description of the flow regimes observed in the experiment is provided. The temporal statistics of liquid holdup (PDF and CPDF) are also analyzed to characterize and distinguish the various swirling flow regimes objectively. Based on this study, the influence of centrifugal force on phase distribution of gas-liquid flow was clarified and the general relationship between swirling gas-liquid flow and non-swirling gas-liquid flow was gained. © 2019 American Nuclear Society. All rights reserved.

关键词： Image processing

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Numerical simulation of the bubble dynamics in a bifurcated micro-channel using the lattice Boltzmann method

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JOURNAL OF APPLIED PHYSICS 2019年第3期126卷 034301-034301页

作者： Lou, Qin Li, Tao Yang, Mo Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

The dynamics behavior of a bubble passing through a bifurcated microchannel is studied numerically by using the lattice Boltzmann model. The effects of channel wettability, the viscosity ratio, the capillary number (Ca), the initial bubble size, and the flow flux ratio on the interface dynamic behavior, breakup mechanism, and residual mass of the bubble through the bifurcated microchannel are studied systematically. The simulation result indicates that these factors have significant influence on the bubble motion behavior. The bubble splits into two sub-bubbles and flow out of the channel completely when the channel surface is hydrophilic. However, some mass residuals of the bubble are observed when the channel surface is hydrophobic and the residual mass increases with the contact angle. On the other hand, as the viscous ratio of gas-liquid increases, the bubble is more likely to break up and to flow out of the channel. In addition, for the case of low capillary number and small bubble size, the bubble cannot break up, so it finally strands in the main channel. Besides, as capillary number increases, the flow flux ratio required for the bubble to flow out of subchannels increases. Eventually, we establish the relation for the critical flow flux ratio Qc as Qc =0.604 e 13.44 C a and Qc = 1.985 e 5.53 C a to describe whether the bubble breaks up or not for different bubble radii.

关键词： Gas liquid interfaces Computer simulation Bubble breakup Bubble dynamics Lattice Boltzmann methods Microfluidics

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Facile synthesis of Au nanoparticles with different shapes in a soluble starch-hydroquinone system and their SERS activity

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MATERIALS LETTERS 2019年 255卷 126502-126502页

作者： Sun, Li Zhu, Jiacheng Zhang, Hua Dou, Binlin Su, Wenxian Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Jun Gong Rd 516 Shanghai 200093 Peoples R China

A simple soluble starch-hydroquinone system was explored, in which flower-like and star-like gold nanoparticles (Au NPs) could be individually synthesized only by adjusting the injection rate of the precursor solution. Meanwhile, their size could be easily tuned just by changing the molar ratio of Au3+ ions and Au seeds in the precursor solution. As-prepared samples were proved to be polycrystalline, pure and stable Au NPs by means of various characterization techniques. Clearly, the novel and facile method to control the shape (morphology and size) can provide a unique perspective for the shape control of other metal NPs. In addition, obtained Au NPs showed distinct shape-determined surface-enhanced Raman scattering (SERS) activity towards Rhodamine 6G molecules, implying their potential for applications in SERS-based detections and analysis. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Gold Nanoparticles Shape Controllable synthesis Raman

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Numerical simulation on the forced oscillation of rigid riser with helical strakes in different section shapes

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OCEAN engineering 2019年 190卷 106439-000页

作者： Liu, Qingsong Hao, Winxing Li, Chun Miao, Weipao Ding Qinwei Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

In order to study the helical strakes' suppression effects on the vibration riser, triangle and circular sections helical strakes are proposed. With the technology of dynamic mesh, forced oscillation in steady flow of the riser with helical strakes in different cross-section shapes at low Reynolds number are numerically simulated. The analysis is focused on the lock-in range, as well as the force status and trailing vortex structure under different values of amplitude (A) and oscillation frequency (f(e)), and draw comparisons to the bare riser's results. Research shows the lock-in range will increase with the increase of amplitude ratio (A/D), the riser with all three different shaped helical strakes have larger lock-in range than bare riser. Before entering into the lock-in region, riser with different shaped helical strakes all have good effects on suppressing the vibrations of riser. Within and after lock-in region, riser with triangle and circular sections helical strakes have smaller lift force than that with rectangular section, which reduced lift coefficient by 65.83% and 83.53%. The trailing vortex structures of the riser with helical strakes are in strength three-dimensional character. Inside the lock-in region, riser with triangle and circular sections have better suppression effect than that with rectangular section. Outside the lock-in region, riser with triangle section helical strakes has the best vortex suppression effect, of which the influence on the flow field is greatest and the vortex-induced force is least.

关键词： Helical strakes Forced oscillation Lock-in Vortex-induced vibrations Suppression

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Numerical simulation on the thermal performance enhancement of energy storage tank with phase change materials

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JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 2019年第2期14卷

作者： Tian, Yang Zhao, Ming Univ Shanghai Sci & Technol Coll Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

The model of the energy storage tank based on multiple tubes with phase change material was established. The influence of the tube circle diameter and the inner annulus temperature on the heat storage performance of the tube bundle in the concentric circle was studied by numerical simulation. The results show that the increase of the tube circle diameter (Phi) can significantly improve the heat storage efficiency, and the increase in inner wall temperature (T-w) can make the heat storage time significantly shorter, but with the tube circle diameter (F) increases, the effect of T-w on shortening the heat storage time is gradually weakened. In addition, the dimensionless criterion equation of the liquid fraction function (f) at different tube circle diameters is presented too. Furthermore, based on the variation of the mean Nu with Fo, the heat transfer mechanism of the melting process of the PCM can be divided into four stages: (1) heat conduction dominates stage;(2) natural convection dominates stage;(3) natural convection begins to transform into heat conduction stage;and (4) heat conduction dominates again.

关键词： Numerical simulation Latent thermal energy storage Tube circle Wall temperature Fitting

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