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第五届国际仿生工程学术大会(ICBE2016)

作者： H.X.Chen Y.Y Yan Jinliang Xu Linbin Huang The Beijing Key Laboratory on Multiphase Flow and Heat Transfer North China Electrical Power University Fluids & Thermal Engineering Research Group Faculty of EngineeringUniversity of Nottingham

The wettability of solid surfaces is very important to fundamental research and practical application. Inspired from species in nature a variety of bionic surfaces with super wettability have been fabricated by lithography, templating, plasma treatment and laser methods. Recent years, metal bionic materials used in heat transfer and their enhancement mechanism have been promising topics, for example superhydrophilic surface was used in boiling enhancement [1]dropwise condensation [2]and heat exchangers[3]and so on. But most metal superwettability surfaces used in heat transfer field were uniform while hybrid wetting substrates always were non-metal like silicon wafer. In this paper, the porous metal that involved in the hot applications was chosen as substrate. Superhydrophilic copper mesh(～0 o) and superhydrophobic copper mesh(～150 o) were fabricated by directly oxidation method and functionalization by trichloro(1 H, 1 H, 2 H, 2 H-perfluorooctyl) silane respectively, whose wettability can be interconverted by simple operation. After oxidation a layer of knife-like-flower oxide at thickness of 2μm covered the mesh lines. Closed to the substrate several knife sheets interdigitate together and disperse on the top, the gap between the knife sheets on the top of flowers is 100-200 nm. With functionalization by silane, mesh wettability converted from superhydrophilic into superhydrophobic, while, the knife-like flower layer has littler change but blunt edges. Then, a hybrid wettability mesh with inspired from Stenocara Beetle was prepared, which has circle superhydrophilic spots surrounded by hydrophobic background. The hybrid wettability mesh could be widely used in boiling enhancement, water harvesting, biological medicine and other practical applications.

关键词： copper mesh knife-like-flower hybrid wettability

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Mimicking the Stenocara Beetle——bumpy shell with hybrid wettability to harvest water by modified foam coppers

Mimicking the Stenocara Beetle——bumpy shell with hybrid we...

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第五届国际仿生工程学术大会(ICBE2016)

作者： H.X.Chen Y.Y.Yan The Beijing Key Laboratory on Multiphase Flow and Heat Transfer North China Electrical Power University Fluids & Thermal Engineering Research Group Faculty of EngineeringUniversity of Nottingham

For centuries, water has been a limited resource especially in arid regions, and nature has adapted to provide survival methods for species inhabiting. Stenocara beetles can collect water from morning fog using its bumpy shell, an array of hydrophilic bumps surrounded by hydrophobic background exactly. Dorrer et al, Lee et al and other researches studied kinds of patterned superhydrophobic and superhydrophilc surfaces to prove which bump surface has best water harvesting performance. Obviously, drainage, temperature difference, wind velocity, surface pattern et al are all key factors, but most samples in their studies are solid substrates with a layer microstructure. There are three common grounds:（1） with spraying of fluid almost condensate is blocked on the surface to form a film which weaken the effect of surface pattern to condensation process.（2） draining efficiency of condensate directly determines the performance of next generation, while, condensate mainly relies on gravity and flows away along the substrate surface at a low velocity,（3） more attention is focused on the microstructures on the surface with neglect of cooperation with macro scale of *** this paper, copper foam with the controllable pore structures is chosen to harvest water. After superhydrophilic and superhydrophobic treatments copper foam with hybrid wettability is fabricated with inspiring from the stenocara beetle. As previous reported porous metal with a superhydrophilic wettability could absorb a droplet away instantly, this can be used in the drainage system during water collection. Cooperating multi-layer cooper foams with different wettability and an independent drainage, a novel water collector is designed. When wind blows through the porous structure with less pressure decrease a droplet is generated on the surface of copper foam with certain temperature difference. Meantime, condensate is quickly sucked away by latter superhydrophilica foam then collected. At last, the eff

关键词： harvest water metal foam drainage

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Shock Tube Experimental and Modeling Study of MTHF Ignition Characteristics at High Temperatures

Shock Tube Experimental and Modeling Study of MTHF Ignition ...

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JSAE/SAE 2015 International Powertrains, Fuels and Lubricants Meeting, FFL 2015

作者： Wang, Jingshan Wang, Xibin Fan, Xiangshan Yang, Kangkang State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an710049 China

High temperature ignition delays of 2-methyltetrahydrofuran(MTHF) were measured behind a reflected shock tube under conditions of pressures from 1.2 to 10 atm, temperatures from 1050 to 1800 K, equivalence ratios from 0.5 to 2.0, and fuel concentrations of 0.25%, 0.5% and 1.0% diluted in argon. Results showed that the ignition delay of MTHF decreases with the increase of pressure, temperature, fuel concentration and increases with equivalence ratio. The trend is less notable at higher fuel concentrations and equivalence ratios. Based on sensitivity and pathway analysis at pressure of 10 atm, fuel concentration of 1.0%, equivalence ratio of 1.0 and temperature of 1550K, it was found that the most sensitive reaction of MTHF at high temperature is H+O2=O+OH, and the main consumption way is fuel decomposition instead of H-abstraction. Finally, ignition delays of MTHF were compared with THF both on experimental and kinetic analyses, and MTHF has lower ignition delays than THF. To our knowledge, it is the first time to present the ignition delays of MTHF under these conditions. © 2015 SAE Japan.

关键词： Shock tubes

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Specific Heat Ratio of High Methane Fraction Natural Gas/Air in Confined Vessel

Specific Heat Ratio of High Methane Fraction Natural Gas/Air...

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SAE 2015 World Congress and Exhibition

作者： Tang, Chenglong Si, Zhanbo Zhang, Shuang Huang, Zuohua Pan, Shiyi Wang, Jinhua Gong, Jing Xi'An Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xi'an710049 China

The specific heat ratio used in heat release calculation plays an important role and the mass fraction burned is also a crucial parameter in thermodynamics analysis for engine combustion. A research of high methane fraction natural gas was investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of the initial pressure, the specific heat ratio is decreased, and the time of the mixture burned up is postponed, while the peak heat release ratio is increased. With the increase of the methane fraction, the parameters have the opposite behavior. With the increase of the initial temperature, the specific heat ratio is decreased, and the time when the mixture is burned up is accelerated, and the peak heat release ratio has no obviously difference. With the increase of the dilution ratio or the CO2/N2 ratio, the specific heat ratio is decreased, and the peak heat release heat ratio is decreased. Meanwhile, the time of mixture burned up is postponed with the increase of dilute ratio or CO2/ N2 ratio. Copyright © 2015 SAE International.

关键词： Specific heat

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Burning velocity and flamelet structure of turbulent premixed CH4/H2/air flames with CO2 dilution 10

Burning velocity and flamelet structure of turbulent premixe...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Wang, Jinhua Yu, Senbin Zhang, Meng Jin, Wu Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Turbulent burning velocity and statistical flame front structure parameters of turbulent premixed CH4/H2/air flames diluted with CO2 were measured with OH-PLIF technique. Hydrogen fractions are up to 0.2 and CO2 dilution ratios are up to 0.1. The instantaneous flame front structure was detected using the OH-PLIF technique on a turbulent premixed Bunsen burner. Through image processing and statistic analysis, turbulent burning velocity ST and statistic quantitative parameters, i.e. flame surface density Σ and flame brush thickness δT were obtained. Results show that turbulent burning velocity ST normalized by laminar burning velocity SL decreases with CO2 dilution. Increased Markstein number LM and flame intrinsic instability li with CO2 dilution leads to the passive response of flame to turbulence wrinkling which resulting in less wrinkled flame front, smaller Σ, lower local burning velocity and ST/SL. Convex structure is more frequent than that of concave ones at normal pressure and the bias distribution is much weaker comparing to that of high pressure. The positive structure decreases while the negative structure increases slightly with CO2 dilution. This would be one of the mechanisms leading to the decrease of the effective contact surface between reaction zone and unburned mixture which resulting in the decrease of ST/SL with CO2 dilution.

关键词： Carbon dioxide

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Investigation on the matching performance of a small cryogenic air turboexpander 24

Investigation on the matching performance of a small cryogen...

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24th IIR International Congress of Refrigeration, ICR 2015

作者： Yang, Shanju Li, Bowen Liu, Guoqing Hou, Yu Chen, Shuangtao State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9782362150128

The matching performance of a turboexpander is essential for a small reverse Brayton air refrigerator, especially when it works under varied operation parameters. Generally, an appropriate brake pressure is required when the turboexpander works under different operation parameters. In this paper, the matching performance of a turboexpander supported by a bump journal foil bearing and a pressurized thrust gas bearing is studied. A centrifugal blower is used as a brake. The performance curve is analyzed through a numerical simulation using CFX. The matching calculations were carried out with different brake blowers under both room temperature and low temperature. A brake pressure feedback control is applied in the experimental study. A thermal performance of the refrigerator is tested. The results indicated that the appropriate brake blower and brake pressure facilitate the system thermal performance under both room and low temperature. The simulation agrees well with the experimental results.

关键词： Temperature

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"Thermal-mechanical" coupled model based on porous media characteristics of EPDM insulator char layer 52

"Thermal-mechanical" coupled model based on porous media cha...

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52nd AIAA/SAE/ASEE Joint Propulsion Conference, 2016

作者： Liu, Yang Pei, Jing-Qiu Guan, Yi-Wen Hui, Kun Li, Jiang Li, Zong-Yan Science and Technology on Combustion Internal Flow and Thermal-structure Laboratory Department of Aerospace Propulsion Technology Xi’anShaanxi710072 China State Key laboratory of clean energy utilization Zhejiang University College of mechanical engineering Zhejiang university Hangzhou310027 China

ISBN: (数字)9781624104060

ISBN: (纸本)9781624104060

Based on the porous characteristics of char layer after ablation of EPDM insulator, the model is in full consideration of char layer strengthen model and particles impact principles with char layer. With analysis of char layer’s porous construction generated in the process of ablation and utilizing the theory of cellular solids structure and properties, the relation for EPDM formula between char layer mechanical parameters (elastic modulus, fracture toughness and hardness) and char layer’s porosity is established. The model of particle erosion for char layer is established utilizing the theory of elastic/plastic indentation fracture. Coupling of particle erosion and chemical ablation mode was completed and applied to EPDM insulation prediction. Some conclusion could be drawn as follows: (1) According to the relation between char layer mechanical parameters and porosity, the elastic modulus, fracture toughness and hardness of char layer trend downward as porosity increases. (2) Char layer with different porosity will be eroded and merely indicates difference in erosion rate under the same intense particle erosion condition, which indicates that there is no threshold of porosity when particle erosion occurs. (3) Numerical computation for a certain EPDM insulation was carried out. The max error of between experiment and numerical results is less than 12%, and the accuracy of the model of particle erosion is acceptable. It indicates that particle erosion model in this paper can be used to predict the ablation rate of EPDM formula in SRM. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Porosity

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Numerical investigation of granular flow similarity in rotating drums

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Particuology 2015年第5期13卷 119-127页

作者： Huabiao Qi Ji Xu Guangzheng Zhou Feiguo Chen Wei Ge Jinghai Li State Key Laboratory of Multiphase Complex Systems Institute of Process EngineeringChinese Academy of Sciences University of Chinese Academy of Sciences

The theory of flow similarity has not been well established for granular flows, in contrast to the case for conventional fluids, owing to a lack of reliable and general constitutive laws for their continuum descrip- tion. A rigorous investigation of the similarity of velocity fields in different granular systems would he valuable to theoretical studies. However, experimental measurements face technological and physical problems. Numerical simulations that employ the discrete element method （DEM） may be an alterna- tive to experiments by providing similar results, where quantitative analysis could be implemented with virtually no limitation. In this study, the similarity of velocity fields is investigated for the rolling regime of rotating drums by conducting simulations based on the DEM and using graphics processing units. For a constant Froude number, it is found that the particle-to-drum size ratio plays a dominant role in the determination of the velocity field, while the velocity field is much more sensitive to some material properties than to others. The implications of these findings are discussed in terms of establishing theoretical similarity laws for granular flows.

关键词： Discrete element method Granular flow Similarity Rotating drum Scale up Graphics processing unit

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Interfacial stability in vertical swirling annular two-phase flow 16

Interfacial stability in vertical swirling annular two-phase...

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16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2015

作者： Liu, Li Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

ISBN: (纸本)9781510811843

The linear stability of liquid film flowing upward the inner surface of vertical cylinder under the action of the swirling gas core flow is investigated taking exactly the centrifugal force and curvature of the cylinder into account. Swirl has been considered by superposing a circular movement on the annular flow. The theoretical model of the stability of interface to small perturbation is established by analyzing the normal force balance condition at the wavy interface. The characteristic equation is solved and the stability criterion is obtained. The stability characteristics of neutral, growing and damped modes are presented showing the influences of swirl intensity, relative motion of gas-liquid flow, and the surface tension force. The modeling results indicate that the swirling of the gas phase stabilizes the film flow while the curvature of the cylinder destabilizes it. For strong swirling annular flow, it is found that there is a small influence of surface tension on the stability of interface because the stabilizing centrifugal force is dominant on this condition. The neutral wavelength is found to be very sensitive to the values of swirl intensity and cylinder radius when gas-liquid relative movement is small. However, when gas flow rate is large enough, there is no significant difference in its value.

关键词： Stability criteria

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Cellular instability of syngas/air mixtures with H2O dilution 10

Cellular instability of syngas/air mixtures with H2O dilutio...

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10th Asia-Pacific Conference on Combustion, ASPACC 2015

作者： Xie, Yongliang Wang, Jinhua Cai, Xiao Nie, Yaohui Peng, Cheng Yu, Qianqian Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

A study on effects of CO/H2 ratio, H2O dilution and pressures on the cellular structure of moist syngas flame was conducted using spherically expanding flames. Experimental conditions for the CO/H2/H2O/air mixtures are the pressures from 0.1 to 0.3 MPa, initial temperature of 373K and H2O dilution ratios are from 0 to 0.15. Results show cellular instability is promoted at atmospheric pressure and suppressed at elevated pressure when H2O is added into the mixture. In addition, critical radius increases with the increase of H2O dilution ratio for the mixture with CO/H2 ratio of 50/50 and changes little when CO/H2 ratio is 20/80. Critical Peclet number decreases with the addition of H2O and increases with the decrease of CO/H2 ratio.

关键词： Dilution

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