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Enhancing Vertical-Axis Tidal Turbines with Strategic Superhydrophobic Surfaces for Optimized Aerodynamic and Self-Starting Performances

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SSRN 2024年

作者： Yin, Dawei Sun, Jinjing 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

As observation and research on nature deepen, bionic and hydrophobic surface drag reduction are gaining increasing popularity among researchers. The application of bionic principles and hydrophobic surface technologies in the field of fluid dynamics has opened up new avenues for enhancing the performance of various engineering systems, including vertical-axis tidal turbines (VATTs). By mimicking the natural mechanisms observed in certain species, such as the lotus effect, researchers have been able to develop superhydrophobic surfaces (SHS) that significantly reduce drag in fluid ***, SHS have been applied uniformly across the entire surface of an airfoil. However, this study takes a more nuanced approach by investigating the impact of SHS application at different positions on the airfoil. Through numerical simulations, the study explores how varying the distribution of SHS can influence the power coefficient (Cp), a key performance metric for VATTs . The findings from the study are quite revealing. At a tip speed ratio (TSR) of 1.68, the study observes that applying SHS to 30% of the chord length near the leading edge of the airfoil yields the maximum relative power coefficient benefit, with an increase of up to 34.8%. This suggests that strategic placement of SHS can lead to significant performance improvements without the need for uniform application, which could potentially reduce material costs and maintenance requirements. Moreover, the study also finds that applying SHS only on the inner surface of the VATT can result in a 32% increase in the power coefficient. This indicates that the inner side of the airfoil, which experiences the higher pressure side of the fluid flow, is particularly sensitive to the drag reduction effects of SHS. The leading edge of the airfoil is another critical area where SHS application can have a substantial impact. The leading edge is the first point of contact between the airfoil and the fluid, and any reduc

关键词： Drag reduction

Effect of Mixer Structure on Liquid Film Formation and Nox Conversion Efficiency in Selective Catalytic Reduction System

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SSRN 2022年

作者： Fu, Hang Huang, Zuohua Tang, Chenglong State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Selective Catalytic Reduction as an efficient technology to reduce NOx emission has been widely applied in exhaust aftertreatment system. However, the reductant injection causes inevitable impingement on the exhaust pipe and mixer surface and the liquid film will be generated. In this paper, the simulation of a double-blade mixer (Mixer 1) is verified by a bench test and other three kinds of mixer structures (baffle mixer: Mixer 2, blade-baffle mixer: Mixer 3, and blade mixer: Mixer 4) are simulated. The effect of the mixer structures on the liquid film formation, the pressure drop, the flow and temperature distribution after the mixers and ultimately the NOx conversion efficiency are investigated. Results show that the liquid film is prone to form and accumulate at the connection region between the mixer and exhaust pipe, and liquid film tends to develop with the flow direction. Mixer 2 and Mixer 4 shows smaller liquid film area about 15 cm2. The temperature distribution in four types of mixers shows negligible difference (within 4 °C). NH3 mass fraction distribution uniformity and pressure drop shows a trade-off relationship. For the vertical injection system, it is found Mixer 3 gets the worst NOx conversion efficiency, 57%, and Mixer 2 shows better NOx conversion efficiency, 78%. The paper are supportive to the SCR mixer selection and design. © 2022, The Authors. All rights reserved.

关键词： Computational fluid dynamics

Experimental Study on Frost Crystal Morphologies and Frosting Characteristics Under Different Working Pressures

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SSRN 2022年

作者： Lai, Tianwei Liu, Xue Dong, Xiaojun Qiang, Mingchen Yan, Shaohang Hou, Yu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Frost usually grows on the cooling surface of heat transfer equipment which often operates under different working pressures. In such conditions, one of the fundamental influencing factors of frosting, the diffusion coefficient of water vapor around the cooling surface is different from that in the normal atmosphere pressure. In order to investigate the pressure effect on frosting, a test rig for frosting visualization is designed. The role of working pressure around the cooling surface on the frost crystal morphologies and frost layer characteristics are evaluated under different air parameters and temperatures of cooling surface. The vertical growth and lateral distribution of frost crystals are related strongly to working pressure around the cooling surface. More frost crystal morphologies and faster growth rate of frost layer are presented at a lower pressure. The frost thickness, frost accumulation and density reduce with higher pressure. The dimensionless correlation of frost thickness is proposed considering working pressure around the cooling surface, humid air parameters, and temperature of cooling surface. © 2022, The Authors. All rights reserved.

关键词： Working pressure

Study on the Safety Characteristics of Fluoride-Salt-Cooled High-Temperature Advanced Reactor

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SSRN 2023年

作者： Lv, Xindi Zhang, Dalin Li, Xinyu Zhou, Xingguang Jiang, Dianqiang Su, Guanghui Tian, Wenxi Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China

FuSTAR is a small, modular fluoride-salt-cooled high-temperature advanced reactor, proposed by Xi'an Jiaotong University (XJTU), aiming at fulfilling the requirements of Gen IV nuclear system and meanwhile ensuring the inherent safety and economics. In order to evaluate the safety performance of FuSTAR, five typical design basis accidents are selected for safety analysis with different initial events. The sensitivity analysis is also performed. The results of transient accidents indicate that safety of FuSTAR has been guaranteed in URIA and ULOF. Meanwhile, the maximum limit of external parameters causing ULOHS and UOC are obtained by sensitivity analysis. In the ULOF and ULOHS, the peak of fuel temperature, cladding surface temperature and core outlet temperature of coolant are below their safety limits. Therefore, FuSTAR exhibits acceptable safety under design basis accidents. This study will provide supports in verifying the rationality of the design and the subsequent optimization of FuSTAR. © 2023, The Authors. All rights reserved.

关键词： Sensitivity analysis

Numerical Investigation on the Radiation Performance of a Crisscross Liquid Droplet Radiator in Space Under Different Operating Conditions

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SSRN 2022年

作者： Zhu, Maoguo Sha, Zhaoyang Zhao, Quanbin Chong, Daotong Chen, Weixiong Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China

Crisscross liquid droplet radiator (LDR) is a promising solution for the heat dissipation of large-power space structures. In this study, a three-dimensional steady numerical simulation of the radiation performance of crisscross LDR in space under different operating conditions was conducted. Significantly, the radiation interaction between adjacent droplet planes was introduced into the radiation model to accurately compute the energy radiated by the crisscross droplet sheet. Simulation results indicated the radiation performance of crisscross droplet sheet deteriorated with an increase in the nonuniformity of droplet planes arrangement and hence droplet planes uniformly arranged were required for a good crisscross LDR. Moreover, there existed a critical droplet sheet angle of 72° where the pressure disturbance frequency almost had no influence on the radiation performance of crisscross LDR. For certain pressure disturbance frequency, decreasing the droplet sheet angle can expand the available operational pressure difference range. The radiation performance of crisscross LDR with high initial droplet temperature was more sensitive to the changes in droplet sheet angle than that with low initial droplet temperature. Finally, the optimal working medium collocation scheme and droplet sheet configuration for crisscross liquid metal LDR were proposed. Given the lightweight and efficiency of crisscross liquid metal LDR, the collocation scheme of working medium including tin and lithium can be adopted and the droplet sheet angle should be designed as 15°. The present work can provide significant guidance for selecting suitable operating conditions for droplet generators to optimize the thermal design of a crisscross LDR. © 2022, The Authors. All rights reserved.

关键词： Drops

Improving sampling depth of laser speckle imaging by topical optical clearing:A theoretical and in vivo study

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Journal of Innovative Optical Health Sciences 2020年第2期13卷 33-43页

作者： D.Li Y.Zhang B.Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049P.R.China

The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A double-layer skin tissue model embedded with a single blood vessel was established,and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent.808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the e®ect of optical clearing agents(OCAs)on photon deposition in *** show that the photon energy deposition density in the epidermis increases with the amount of tissue°uid replaced by *** with glucose solution,polyethylene glycol 400(PEG 400)and glycerol can considerably increase the average penetration depth of photons in the skin tissue,thereby raising the sampling depth of the *** the action of glycerol,PEG 400,and glucose,the average photon penetration depth is increased by 51.78%,51.06%,and 21.51%for 808nm,68.93%,67.94%,and 26.67%for 632.8 nm lasers,*** vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood°ow rate,whereas PEG 400 can signicantly improve the capability of light penetration without a®ecting blood velocity,which exhibits considerable potential in the monitoring of blood°ow in skin tissues.

关键词： Laser speckle image topical optical clearing imaging depth Monte-Carlo simulation dorsal skin experiment

Experimental Investigation on Separation Characteristics of Gas-Liquid Two-Phase flow Around the Perforated Tube

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SSRN 2022年

作者： Wang, Jinzhi Xie, Xiangdong Wang, Yechun Xu, Qiang Wang, Jiang Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

The flow around cylinder is widely used in industrial applications. In this study, the separation characteristics of gas-liquid two-phase flow around a perforated tube are investigated experimentally. The interface fluctuation process of the gas pocket and liquid slug periodic separation around the perforated tube is presented intuitively using a high-speed camera. The mean value and standard deviation of the void fraction in the wake region are independent of the inlet liquid flow rate. When the flow pattern is plug flow, the air separation efficiency first decreases and then increases with an increase in the inlet void fraction;the separation efficiency increases monotonically when the flow pattern is slug flow. The separation purity and total pressure drop increase with increasing inlet void fraction. Based on the principle of minimum kinetic energy, methods for predicting the void fraction in the wake region, separation purity, air separation efficiency and pressure drop have been developed. The new correlations are based on the Weber number and liquid-phase Reynolds number that are also controlling dimensionless group in determining the void fraction, separation efficiency and pressure drop. The prediction accuracies of the void fraction and separation purity are within ±10% and the prediction accuracies of the separation efficiency and pressure drop are within ±20%, which provides an accurate prediction of the separated flow around the perforated tube. © 2022, The Authors. All rights reserved.

关键词： Void fraction

Transient Thermoelectric Characteristics of the Principle Prototype for the Heat Pipe Cooled Nuclear Silent Themoelectirc Reactor (Nuster)

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SSRN 2023年

作者： Guo, Kailun Zhang, Yin Lin, Xingyang Huang, Jinlu Wang, Chenglong Qiu, Suizheng Tian, Wenxi Su, Guanghui School of Nuclear Science and Technology Shaanxi Key Laboratory of Advanced Nuclear Energy And Technology State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

This paper proposes an optimized design for the Heat Pipe ThermoElectric Generator(HPTEG) principle prototype. The refined scheme adopts high-temperature sodium heat pipes as heat transfer elements to enhance the overall operating temperature of the device. It adopts Half-Hessler(HH) alloy ThermoElectric Generator(TEG) arranged on the upper and lower sides of the heat exchanger to enhance the thermoelectric conversion efficiency of the device. A heat pipe dynamic conduction model is established to simulate the start-up process of the sodium heat pipe. A TEG model is developed, which is able to simulate the three-dimensional thermoelectric properties of the TEG. The numerical simulation platform is used to analyze the steady-state and transient thermoelectric properties of the refined HPTEG prototype. This study provides data support for the subsequent design modification of the future HPTEG principle prototype and provides ideas for the 3D transient calculations of the solid-state heat pipe reactors. © 2023, The Authors. All rights reserved.

关键词： Heat pipes

Thermodynamic Performance of Cacl2 Absorption Heat Pump Thermal Energy Storage System with Triple Storage Tanks

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SSRN 2023年

作者： Chen, Jinsen Zhou, Yuan Liu, Jiping Zhao, Yongliang Zhang, Shunqi Yan, Junjie MOE Key Laboratory of Thermal Fluid Science Engineering Xi'an Jiaotong University Xi’an710049 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China

Absorption thermal energy storage has the characteristics of high thermal energy storage density (ESD) and low heat loss for long-term storage. To solve the coal-fired combined heat and power plant heat-power-coupling problem, in this work, an absorption heat pump thermal energy storage system (AHPTES) using CaCl2-water solution as the working fluid is proposed. A steady-state thermodynamic model of the system was constructed using Aspen Plus. Under the design conditions, the AHPTES system requires a tank volume of 464.61 m3 for one hour of operation, an ESD of 29.81 kW·h/m3, a thermal energy storage ratio of 46.50%, and a heating ratio of 53.54%. Compared to the dual-tank thermal energy storage system with H2O and CaCl2-water solutions as working fluids, the AHPTES system has 1.43 and 1.25 times higher ESD and 0.7 and 0.8 times lower tank volume, respectively. Then, the effects of CaCl2 mass fraction, driving pressure, evaporator outlet temperature, preheating temperature, and condensing temperature on the system performance are simulated. Improving the CaCl2 mass fraction, lowering the evaporator outlet temperature, and raising the condensing temperature and preheating temperature can boost the system's performance. At the optimal system performance, the required tank volume for one hour of system operation is 439.56m3, ESD can reach up to 37.39 kW·h/m3, heating ratio to 44.83%, and the energy storage ratio to 55.17%. Besides, raising the mass fraction of CaCl2 to 52% and decreasing the evaporator outlet temperature to 30 °C at 50% mass fraction resulted in crystallization of the system. © 2023, The Authors. All rights reserved.

关键词： Thermal energy