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作者： Gu, Xiao-Jun Emerson, David R. Tang, Gui-Hua Computational Science and Engineering Department STFC Daresbury Laboratory Warrington WA4 4AD United Kingdom School of Energy and Power Engineering State Key Lab of Multiphase Flow Xi'An Jiaotong University Xi'an 710049 China

A set of linearized 26 moment equations, along with their wall boundary conditions, are derived and used to study low-speed gas flows dominated by Knudsen layers. Analytical solutions are obtained for Kramers' defect velocity and the velocity-slip coefficient. These results are compared to the numerical solution of the BGK kinetic equation. From the analysis, a new effective viscosity model for the Navier-Stokes equations is proposed. In addition, an analytical expression for the velocity field in planar pressure-driven Poiseuille flow is derived. The mass flow rate obtained from integrating the velocity profile shows good agreement with the results from the numerical solution of the linearized Boltzmann equation. These results are good for Knudsen numbers up to 3 and for a wide range of accommodation coefficients. The Knudsen minimum phenomenon is also well captured by the present linearized 26-moment equations. © 2009 Springer-Verlag.

关键词： Method of moments

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Numerical studies on natural circulation precooling loop of cryogenic liquid rocket engine

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Hangkong Dongli Xuebao/Journal of Aerospace Power 2009年第3期24卷 698-704页

作者： Chen, Er-Feng Li, Yan-Zhong Cheng, Xiang-Hua School of Energy and Power Engineering Xi'an Jiaotong University Xi'an 710049 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

One set of one-dimensional unsteady homogenous mathematic models for flow and heat process of natural circulation precooling loop of cryogenic liquid rocket engine was established, whilst both inverted annular model and dispersed model were introduced for the prediction of filming boiling region. The results indicate the unstable characteristics of circulation flow rate in precooling process is caused by the unstable characteristics of natural circulation driving force, that is, the heat flux transferred to the cryogenic liquid from the natural circulation precooling loop. Moreover, about 80% of wall temperature drop takes place in filming boiling region, and the inverted temperature distribution law of the return pipe is well interpreted by introducing the two filming boiling models mentioned above.

关键词： Rockets

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Comparative analysis of single droplet evaporation models in Cryogen Spray Cooling

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Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics 2009年第4期30卷 653-656页

作者： Xin, Hui Zhou, Zhi-Fu Chen, Bin Wang, Guo-Xiang Wang, Yue-She State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Department of Mechanical Engineering University of Akron Akron OH 44325 United States

Cryogen Spray Cooling is used for cooling human skin during selected laser treatment of Port Wine Stain. Transient state cryogen spray involves intricate droplets evaporation, intense heat convection and mass transfer. In present paper, mass transfer equation of single droplet evaporation model for cryogen spray equilibrium evaporation stage was improved and the effect of seven gas phase models on single droplet evaporation characteristic in R-134a cryogen spray is compared. It is pointed out that the gas phase model which takes the effect of superheat into account was most coincidence with experiment data. A parametric study of the influences of initial diameter and velocity on the droplet evaporation is then carried out by this gas phase model.

关键词： Heat convection

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Evaporation characteristics of single R404a droplet in laser treatment of PWS in conjunction with cryogen spray cooling

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Zhongguo Jiguang/Chinese Journal of Lasers 2009年第10期36卷 2691-2695页

作者： Xin, Hui Zhou, Zhifu Wang, Guoxiang Chen, Bin Wang, Yueshe State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China Department of Mechanical Engineering University of Akron Akron OH 44325 United States

Cryogen spray is an effective cooling technique for the laser treatment of port wine stain (PWS), which can protect the epidermis from the thermal injuries safely. However, cryogen R134a cannot supply enough cooling capacity for the laser surgery in patients with darker skin because of the absorption of laser energy by melanin. Cryogen R404a are expected to protect the darker skin well because of its lower boiling point. A theoretical model is proposed to describe the evaporation process of single droplet and its validation is confirmed by the agreement between numerical simulation with experimental result. With this model, the cooling effect of R404a droplet is compared with R134a droplet and it is found that R404a droplet can reach lower temperature. Then the influences of initial diameter and ambient mass faction of cryogen on the evaporation characteristics of R404a droplet are analyzed and the result is useful to guide the cryogen spray cooling for laser therapy of PWS patients with darker skin.

关键词： Drops

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PIV measurement of turbulent bubbly mixing layer flow with polymer additives

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Journal of Physics: Conference Series 2009年第1期147卷

作者： Ning, T. Guo, F. Chen, B. Zhang, X. State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an 710049 China

Based on experimental investigation of single-phase turbulent mixing layer flow with polymer additives, bubbly mixing layer was experimentally investigated by PIV. The velocity ratio between high and low speed is 4:1 and the Reynolds number based on the velocity difference of two steams and hydraulic diameter of the channel ranges is 73333. Gas bubbles with about 0.5% gas fraction were injected into pure water mixing layer with/without polymer additives from three different parts at the end of the splitter plate. The comparison between single phase and bubbly mixing layer shows clearly that the dynamic development of mixing layer is great influenced by the bubble injection. Similar with single phase, the Reynolds stress and vorticity still concentrate in a coniform area of central mixing flow field part and the width will increase with increasing the Reynolds number. Mean Reynolds stress will decrease with bubble injection in high Reynolds numbers and the decreasing of Reynolds stress with polymer additives is much more than pure water case. © 2009 IOP Publishing Ltd.

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Comparison of modeling options for delayed neutron precursor movement in a molten salt reactor

Comparison of modeling options for delayed neutron precursor...

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2009 ANS Annual Meeting and Embedded Topical Meeting: Nuclear and Emerging Technologies for Space, NETS 2009

作者： Zhang, Dalin Rineiski, Andrei Qiu, Suizheng State Key Laboratory Multiphase Flow in Power Engineering School of Nuclear Science and Technology Xi'an Jiaotong University 28 West Xian ning Road Xi'an 710049 China Institute for Nuclear and Energy Technologies Forschungszentrum Karlsruhe Hermann-von-Helmholtz-Platz 1 Eggenstein-Leopoldshafen D-76344 Germany

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Investigation on surface wettability and surface structure of PTFE after remote oxygen plasma treatment

Investigation on surface wettability and surface structure o...

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IEEE International Conference on Plasma Science (ICOPS)

作者： H. X. Liu H. J. Zhang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an China Department of Environmental Engineering Xi'an Jiaotong University Xi'an China

Summary form only given. In this paper, the surface wettability and surface structure of poly(tetrafluoroethylene) (PTFE) treated with remote oxygen plasma are studied. The contact angles of the samples are measured and the critical surface tensions (gamma c ) are determined on the basis of the Zisman's plots. Then the variation of contact angle to water (thetas H2O ) and the gamma c are as the functions of the sample positions, which are at the different distance from the center of oxygen plasma active discharge zone. Since the better surface wettability can be obtained at 0 cm and 40 cm from the center of oxygen plasma active discharge zone, respectively, the variation of thetas H2O and are farther as the functions of the plasma treatment time. Furthermore, the values of dispersion force gamma s d , dipole force gamma s p and hydrogen bonding force gamma s h to the surface free energy gamma s of treated PTFE are evaluated by the extended Fowkes equation. The analysis is carried out between the distribution of reactive species in remote oxygen plasma and the surface free energy as well as surface wettability. All the results show that the surface wettability of PTFE treated with oxygen plasma is only determined by the value of polar force (gamma s p + gamma s h ), especially the gamma s h . A mixed atmosphere constituted by all reactive species or super pure and high free radicals concentration in remote oxygen plasma are both propitious to the increasing of polar force (gamma s p + gamma s h ), but the surface free energy is influenced mainly by the concentration of charged particles. X-ray photoelectron spectroscopy (XPS) indicates that the C-F bonds on the PTFE surface are broken by the oxygen plasma treatment, and then the polar functional groups of C-O and C=0 are introduced effectively, the surface wettability increases.

关键词： Surface treatment Surface structures Plasma measurements Water Plasma x-ray sources Surface tension Surface discharges Hydrogen Bonding forces Equations

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Experimental study on the performance of an aircraft environmental control system

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Applied Thermal Engineering 2009年第16期29卷 3284-3288页

作者： Hongli Zhao Yu Hou Yongfeng Zhu Liang Chen Shuangtao Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 PR China The First Aircraft Institute of AVIC1 Xi’an 710089 PR China

In this paper, the experimental study on the off-design performance and dynamic response of an aircraft environmental control system (ECS) was presented. A bootstrap air cycle refrigeration system with high-pressure water separation was employed in the ECS. Both the static test and the dynamic test were conducted on the ECS. The performance of the key components including precooler, recuperator, compressor, and turbine was investigated. The test results show the performance of the tested ECS can meet the requirements of design. However, some parameters including outlet pressure, turbine efficiency, and rotational speed might vary obviously when the operation conditions changed. The outlet humidity ratio and outlet temperature might also fluctuate largely during the start-up process. It is necessary to take into account the off-design performance and the transient performance in the design of ECS.

关键词： Environmental control system Off-design performance Dynamic response Brayton cycle

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Dynamic stability experiments of compliant foil thrust bearing with viscoelastic support

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Tribology International 2009年第5期42卷 662-665页

作者： Quan Zhou Yu Hou Chunzheng Chen School of Energy and Power Engineering Xi’an Jiaotong University Xi’an 710049 PR China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 PR China

In order to reduce the complexity of machine construction and improve the mechanical efficiency, high speed rotation machineries usually implement self-acting gas bearings to substitute the traditional oil-lubricated bearings. This paper presents test results of a gas thrust bearing with viscoelastic support which is designed for high speed turbo-machinery. The gas bearing, which belongs to compliant foil bearings, consists of a top thin metal foil and a bottom thin rubber foil. Static and stability experiments are conducted on a high speed gas turbine test rig. The static results indicate that the structural stiffness of test bearing generally increases with the increase in axial load and the decrease in thickness of bottom foil. In the rotation tests, rotor runs stably with small vibration amplitude, which is dominant in waterfall plot during whole speed up procedure. It shows that test bearing has preferable stability characteristics for high speed gas turbines.

关键词： Foil thrust bearing Structural stiffness Bearing stability

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Characteristics of heat transfer for narrow gap on horizontal heated surface with porous media

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Yuanzineng Kexue Jishu/Atomic Energy Science and Technology 2009年第5期43卷 431-434页

作者： Hu, Ben-Xue Xu, Yan-Feng Su, Guang-Hui Qiu, Sui-Zheng Zhao, Da-Wei Wu, Ying-Wei State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China School of Nuclear Science and Technology Xi'an Jiaotong University Xi'an 710049 China Nuclear Power Institute of China Chengdu 610041 China

Experiments were carried out to study the characteristics of heat transfer on a downward-facing heated surface with porous media in narrow horizontal gap at atmosphere pressure using water as working fluid. The boiling curves were obtained under different conditions. The heat transfer increases significantly with porous media in the gap especially under boiling condition. The heat transfer in narrow horizontal gap can be enhanced by increasing the gap size and by using porous media with high thermal conductivity and appropriate porosity. Based on the mechanism of heat transfer in porous media, the correlations for natural convection and nucleate boiling were proposed to predict the heat transfer under the present condition.

关键词： Facings

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