氮化铁磁性流体密封研究

利用磁性流体被磁场吸附的原理，探讨了氮化铁磁性流体密封装置的设计原理和动作过程，分析并通过试验验证了磁性流体密封承压能力，进而成功地研制了氮化铁磁性流体密封安全阀，基于磁性流体密封安全阀开启压力稳定性、可控性和密封性能测试结果，所研制的样机已正常运行10000h。     

Confining effect on the bearing capacity of circular footings on a purely cohesive soilEffet du confinement sur la capacité portante d'une fondation circulaire sur un sol purement cohérent

The bearing capacity of axially symmetrical footings acting on a purely cohesive soil foundation contained by a rigid wall at a finite distance is investigated within the framework of the Yield design theory. Following the same tracks as in a preceding paper devoted to strip footings, the analysis is performed by referring to already existing results concerning the bearing capacity of a circular footing on a soil layer with limited thickness. It comes out that the bearing capacity factor determined by Eason and Shield for a rough circular footing on an unlimited soil foundation is increased by a correction factor that increases when the diameter of the container decreases. Comparison with the results obtained for strip footings acting on a purely cohesive soil in the same conditions shows that the confining effect is significantly lower for a circular footing than for a strip footing. To cite this article: J. Salençon, C. R. Mecanique 330 (2002) 521–525.     

Heat transfer in an oscillating vertical annular liquid column open to atmosphere

The heat transfer from a surface heated with constant heat flux to an oscillating vertical annular liquid column having an interface with the atmosphere is investigated experimentally in the present paper. The analysis is carried out for the case of different oscillation frequencies while the displacement amplitude remains constant. Based on the experimental data a correlation equation is obtained for the cycle-averaged Nusselt number as a function of kinetic Reynolds number.     

Nodeless variable finite element method for heat transfer analysis by means of flux-based formulation and mesh adaptation

Based on flux-based formulation, a nodeless variable element method is developed to analyze two-dimensional steady-state and transient heat transfer problems. The nodeless variable element employs quadratic interpolation functions to provide higher solution accuracy without necessity to actually generate additional nodes. The flux-based formulation is applied to reduce the complexity in deriving the finite element equations as compared to the conventional finite element method. The solution accuracy is further improved by implementing an adaptive meshing technique to generate finite element mesh that can adapt and move along corresponding to the solution behavior. The technique generates small elements in the regions of steep solution gradients to provide accurate solution, and meanwhile it generates larger elements in the other regions where the solution gradients are slight to reduce the computational time and the computer memory. The effectiveness of the combined procedure is demonstrated by heat transfer problems that have exact solutions. These problems are: (a) a steady-state heat conduction analysis in a square plate subjected to a highly localized surface heating, and (b) a transient heat conduction analysis in a long plate subjected to a moving heat source. The English text was polished by Yunming Chen.     

Dynamic dip testing as a method to assess the condensate drainage behavior from the air-side surface of compact heat exchangers

A new method to assess the condensate drainage behavior of the air-side surface of compact heat exchangers—dynamic dip testing—is introduced. The new method is shown to provide highly repeatable data for real-time drainage. Results from experiments with more than 20 flat-tube and round-tube-and-fin heat exchangers are presented, and the data clearly show geometrical effects such as the impact of the tube type on condensate drainage. By comparing the results from dip testing to wind-tunnel experiments for the same heat exchangers, we find dip testing can serve as a powerful tool for assessing the condensate retention behavior. The coils retaining the most and the least condensate in a steady-state wind-tunnel test, likewise held the most and the least in a dip test. However, different amounts of water are retained on the air-side surface during dip tests and wind-tunnel tests. A model based on gravity, surface tension and drag effects is developed to help understand and predict the drainage behavior of heat exchangers. The new model and experimental approach are useful in screening heat exchangers for condensate retention and for assessing off-cycle drainage behavior.     

Experimental study on the condensation of supersonic steam jet submerged in quiescent subcooled water: Steam plume shape and heat transfer

The condensation of supersonic steam jet submerged in the quiescent subcooled water was investigated experimentally. The results indicated that the shape of steam plume was controlled by the steam exit pressure and water temperature. Six different shapes of steam plume were observed under the present test conditions. Their distribution as a function of the steam exit pressures and water temperatures was given. As the steam mass velocity and water temperature increase, the measured maximum expansion ratio and dimensionless penetration length of steam plume were in the ranges of 1.08–1.95 and 3.05–13.15, respectively. The average heat transfer coefficient of supersonic steam jet condensation was found to be in the range of 0.63–3.44 MW/m²K. An analytical model of steam plume was found and the correlations to predict the maximum expansion ratio, dimensionless penetration length and average heat transfer coefficient were also investigated.     

Turbulence in cooling channels of rocket engines: Large Eddy Simulations

The aim of this Note is to predict by means of large eddy simulations the three-dimensional structures and secondary mass and heat fluxes which develop within a heated curved duct, for applications to rocket engines cooling channels. We show the existence of unsteady Görtler-type vortices above the concave wall, as well as intense secondary vortices taking the shape of two quasi-steady counter-rotating cells of Ekman type close to the convex wall. These cells control heat exchanges. They induce ejections and sweeps close to the convex wall when it is heated. In this case the Nusselt number undergoes strong transverse fluctuations which might induce material alterations. To cite this article: C. Münch, O. Métais, C. R. Mecanique 333 (2005).     

Two theorems on the steady-state conduction in anisotropic body

In this paper, steady-state plane conduction problems are considered. Two theorems are proven on the conductance of non-homogeneous and anisotropic plane conductors. Here, the conductor is a two-dimensional bounded plane domain with a conducting matter having two seperated boundary terminals and two seperated insulated boundary segments. Known theorems referring to homogeneous and isotropic conductors have been extended to non-homogeneous and anisotropic ones. The results of the paper can be directly used in following fields: heat flow, diffusion, irrotational hydraulic flow, flow of electrical current and anti-plane shear deformation. Application of formulae derived is illustrated in the examples of heat flow and anti-plane elastic shear deformation.     

孔洞形状对围岩极限承载能力影响的分析

为了研究工程岩体的宏观力学性能,采用数值模拟的方法研究了椭圆形孔洞形状对岩块极限承载能力的影响,找出了孔洞形状与极限承载能力之间的关系,同时研究了岩块声发射随着孔洞形状的变化规律。证明了应用数值模拟方法研究岩块的极限承载能力是研究工程岩体宏观力学参数特别是极限承载能力的有效方法。     

An experimental investigation of heat transfer to pulsating pipe air flow with different amplitudes

Heat transfer characteristics to both laminar and turbulent pulsating pipe flows under different conditions of Reynolds number, pulsation frequency, pulsator location and tube diameter were experimentally investigated. The tube wall of uniform heat flux condition was considered for both cases. Reynolds number varied from 750 to 12,320 while the frequency of pulsation ranged from 1 to 10 Hz. With locating the pulsator upstream of the inlet of the test section tube, results showed an increase in heat transfer rate due to pulsation by as much as 30% with flow Reynolds number of 1,643 and pulsation frequency of 1 Hz, depending on the upstream location of the pulsator valve. Closer the valve to the tested section inlet, the better improvement in the heat transfer coefficient is achieved. Upon comparing the heat transfer results of the upstream and the downstream pulsation, at Reynolds number of 1,366 and 1,643, low values of the relative mean Nusselt number were obtained with the upstream pulsation. Comparing the heat transfer results of the two studied test sections tubes for Reynolds number range from 8,000 to 12,000 and pulsation frequency range from 1.0 to 10 Hz showed that more improvement in heat transfer rate was observed with a larger tube diameter. For Reynolds number ranging from 8,000 to 12,000 and pulsation frequency of 10 Hz, an improvement in the relative mean Nusselt number of about 50% was obtained at Reynolds number of 8,000 for the large test section diameter of 50 mm. While, for the small test section diameter of 15 mm, at same conditions of Reynolds number and frequency, a reduction in the relative mean Nusselt number of up to 10% was obtained.