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13th International Conference on Liquid Atomization and Spray Systems, ICLASS 2015

作者： Wang, R. Zhou, Z.F. Chen, B. Bai, F.L. Wang, G.X. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University China

Cryogen spray cooling has been applied to protect epidermis from thermal damage in laser dermatology. However, present cryogen R134a shows insufficient cooling capacity on minimizing the laser energy absorption by the melanin in darkly pigmented human skins. With lower boiling point, R404A has potential to improve the cooling capacity. This paper presents an experimental study on the temporal and spatial variation in surface temperature and heat flux during spray cooling using R404A by a straight tube nozzle with expansion chamber, which significantly improves the atomization effect. The experimental results indicate that the temporal and spatial conditions strongly influence the uniformity of surface heat transfer. There exists a sub-region of uniform cooling with radius of 2 mm around spray center with high transient heat flux above 400 kW/m2, which is conducive for physicians to control the therapy area precisely with enhanced laser energy. © 2015 International Conference on Liquid Atomization and Spray Systems. All rights reserved.

关键词： Laser surgery

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Influence of Geometrical Structure on Inertial Focusing of Particle in the Microchannel

Influence of Geometrical Structure on Inertial Focusing of P...

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2016年大连国际微流控和芯片实验室大会

作者： Liang-Liang Fan Hong Zhao Qing Yan Jing Guo Liang Zhao Jiang Zhe Fuli School of Food Equipment Engineering and Science(FEES) Xi'an Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Department of Mechanical Engineering University of Akron

Particles subjected to the inertial lift force will be focused in several equilibrium positions in *** to now,most research on inertial focusing of particles have been focused on the microchannel with a constant cross-section,such as the straight *** study the influence of variable cross-section on the inertial focusing of particles in microchannel,three kinds of microchannels with different cross-sections including the gradually constricted,the constant,and the gradually expanded were designed and fabricated,where inertial focusing behavior of particles was investigated by *** result shows,in comparison with the microchannels with the constant and the gradually constricted cross-sections,7.32 um particles are focused in two symmetric streams with narrower bandwidth in the microchannel with the gradually expanded cross-section,indicating the gradually expanded geometrical structure is more efficient for the inertial focusing of ***,smaller secondary flow was generated at outlet of the microchannel with the gradually expanded cross-section,which is helpful for keeping the focused particle streams in a narrow *** further investigate the influence of the arrangement of the gradually expanded cross-section on the inertial focusing of particles,a series of gradually expanded geometrical structures arranged on one side,symmetrically arranged on two sides,and asymmetrically arranged on two sides of the microchannel were designed,*** on inertial focusing of particles were conducted using7.32 um and 9.9um particles,showing particles are focused in one or two streams in the microchannels with gradually expanded geometrical structures arranged on one side or symmetrically arranged on two sides while particles are focused in two or three streams in the microchannel with gradually expanded geometrical structures asymmetrically arranged on two *** it can be obtained that to achieve one-stream inert

关键词： Influence of Geometrical Structure on Inertial Focusing of Particle in the Microchannel

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Numerical simukation of nitrogen condensation flow in acryogeni nozzle 24

Numerical simukation of nitrogen condensation flow in acryog...

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24th IIR International Congress of Refrigeration, ICR 2015

作者： Wan, Sun Guoqing, Liu Lu, Niu Shuangtao, Chen Yu, Hou State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University 710049 China

ISBN: (纸本)9782362150128

2-D numerical simulations on the nitrogen expansion flow with spontaneous condensation in a nozzle were conducted based on the equilibrium model and the non-equilibrium model respectively. In the equilibrium model, the mass transfer between the liquid and vapor is determined by the saturation enthalpies of the liquid and vapor phases. The pressure distribution of the nozzle could be influenced slightly by the condensation process. In the non-equilibrium model, the classical nucleation model is used for the droplets formation. The flow is heated by the latent heat and consequently the decrease of pressure and the increase of Mach number are delayed. Meanwhile, due to the requirement of a certain supercooling level, the condensation onset point is pushed away from the nozzle inlet, and the nozzle outlet wetness fraction becomes smaller. Then, the influence of the nozzle inlet temperature and inlet pressure on gas supercooling, nucleation rate and wetness are analyzed.

关键词： Nucleation

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Fabrication of hybrid super-wettability copper mesh with knife-likeflowers

Fabrication of hybrid super-wettability copper mesh with kni...

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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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Energy efficiency evaluation method for plate heat exchanger

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Kexue Tongbao/Chinese Science Bulletin 2016年第8期61卷 802-808页

作者： Zhang, Yanfeng Jiang, Chen Shou, Binan Zhou, Wenxue Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Technology Service Center CO. LTD Beijing100011 China LanZhou Guanyu Heat Transfer and Energy Saving Engineering and Technology Research CO. LTD Lanzhou730050 China

In heat exchangers, heat transfer between the cold and the hot fluid consumes pumping power. Evaluating the energy efficiency of this process scientifically and quantitatively is an urgent issue for both academic research and industrial applications, and has important significance to energy saving and emission reduction. We comprehensively analyzed the flow and heat transfer characteristics of water-water heat transfer process without phase-change in a heat exchanger, and proposed the energy efficiency index (=k/pn, k is overall heat transfer coefficient and p is flow pressure gradient). EEI reflects the inherent energy efficiency properties of a heat exchanger, which represents the overall heat transfer coefficient per equivalent flow pressure drop consumption. At a given temperature difference and fluid flow rate, for the heat exchangers with the same heat transfer area and fluid flow length, bigger EEI means a lager heat transfer rate per equivalent pumping power consumption. EEI is independent on the heat transfer area;no dependence or weak dependence on the flow velocity can be achieved by choosing the index n reasonably, indicating a good stability of EEI. Evaluation result based on national standard of heat exchanger performance test measured could represent the energy efficiency of the heat exchanger. Combined with the water-water heat transfer process without phase-change flow and heat transfer performance database of the plate heat exchangers, the value of index n and the overall EEI distribution of plate heat exchangers in industry are obtained, providing a basis for the classification of the energy efficiency of plate heat exchangers. © 2016, Science Press. All right reserved.

关键词： Heat exchangers

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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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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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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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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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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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