Characteristics of Argon Laminar DC Plasma Jet at Atmospheric Pressure

利用特殊设计的等离子体发生器,选择等离子体产生的工艺参数,实现工艺过程的精确控制,在大气压环境下获得了性能稳定的氖气直流层流等离子体射流。与湍流等离子体射流长度较短、径向尺寸较大、工作噪音高等特点相比,层流等离于体射流长度可达到550mm,而且沿整个射流长度其径向尺寸维持不变,工作噪音很小。当气流量为120cm~3/s、弧电流在70-200A的范围时,射流长度随弧电流的增加而增加,热效率起初略有降低然后维持平稳。随气流量的增加,层流等离子体射流的热效率也增加,在弧电流为200A时,可以达到40%。实验中测

Computation of Viscous Incompressible Flow using Pressure Correction Method on Unstructured Chimera Grid

In this paper, a pressure correction algorithm for computing incompressible flows is modified and implemented on unstructured Chimera grid. Schwarz method is used to couple the solutions of different sub-domains. A new interpolation to ensure consistency between primary variables and auxiliary variables is proposed. Other important issues such as global mass conservation and order of accuracy in the interpolations are also discussed. Two numerical simulations are successfully performed. They include one steady case, the lid-driven cavity and one unsteady case, the flow around a circular cylinder. The results demonstrate a very good performance of the proposed scheme on unstructured Chimera grids. It prevents the decoupling of pressure field in the overlapping region and requires only little modification to the existing unstructured Navier–Stokes (NS) solver. The numerical experiments show the reliability and potential of this method in applying to practical problems.

Experimental Study of Pore Pressure and Deformation of Suction Bucket Foundations Under Horizontal Dynamic Loading

Centrifuge experiments are carried out to investigate the responses of suction bucket foundations under horizontal dynamic loading. The effects of loading amplitude, the size of the bucket and the structural weight on the dynamic responses are investigated. It is shown that, when the loading amplitude is over a critical value, the sand at the upper part around the bucket softens or even liquefies. The liquefactio...

Influential Factors of Loess Liquefaction and Pore Pressure Development

The liquefaction of loess under dynamic loading is studied experimentally with a dynamic triaxial test system. The effects of over-consolidation ratio (OCR), saturation degree and the frequency of dynamic loading upon loess liquefaction are investigated. The development of pore pressure within loess samples is also discussed. Based on the experimental results, the empirical relationship between pore pressure ratio and loading cycle number ratio is established for normal consolidated saturated loess.

Spherical nanometer-sized diamond obtained from detonation

Ultrafine diamond (UFD) was synthesized under high pressure and high temperatures generated by explosive detonation. The structure, composition, surface and thermal stability of UFD were studied by use of XRD, TEM, Raman Spectroscopy, FTIR, etc. The influences of the synthesis conditions and purification conditions on the properties of UFD were analyzed. The UFD had an average size of 4-6 nm, commonly exhibiting a spherical shape. The highest yield was of up to 10 mass% of the explosive. Attempts were made to use UFD as an additive to metal-diamond sintering and as crystallite seeds of CVD diamond films. The results show that UFD can decrease the coefficient of friction of the composite by 30%, and raise the nucleation density in CVD diamond films by 2-3 times.

Experimental study on pore pressure in rock-soil slope during reservoir water level fluctuation

A test system was developed for measuring the pore pressure in porous media, and a new model was devised for the pore pressure testing in both saturated and unsaturated rock-soil. Laboratory experiments were carried out to determine the pore pressure during water level fluctuation. The variations of transient pore pressure vs. time at different locations of the simulated rock-soil system were acquired and processed, and meanwhile the deformation and failure of the model are observed. The experiment results show that whether the porous media are saturated or not, the transient pore pressure is mainly dependent on the water level fluctuation, and coupled with the variation of the stress field.

Flow Characteristics and Its Friction Coefficient of Laminar Near-Wall Boundary Layer in Dusty Atmosphere

采用双向耦合的双流体模型,研究了大气悬浮沙尘的存在对大气边界层中层流底层流动特性及摩阻系数的影响,计算并讨论了不同沙尘含量下含尘大气相对于无尘大气摩阻系数的变化。结果表明：摩阻系数的变化取决于悬浮沙尘的初始运动状态和质量载荷率。

Experimental Study on the Thermal Argon Plasma Generation and Jet Length Change Characteristics at Atmospheric Pressure

The generation, jet length and flow-regime change characteristics of argon plasma issuing into ambient air have been experimentally examined. Different torch structures have been used in the tests. Laminar plasma jets can be generated within a rather wide range of working-gas flow rates, and an unsteady transitional flow state exists between the laminar and turbulent flow regimes. The high-temperature region length of the laminar plasma jet can be over an order longer than that of the turbulent plasma jet and increases with increasing argon flow rate or arc current, while the jet length of the turbulent plasma is less influenced by the generating parameters. The flow field of the plasma jet has very high radial gradients of plasma parameters, and a Reynolds number alone calculated in the ordinary manner may not adequately serve as a criterion for transition. The laminar plasma jet can have a higher velocity than that of an unsteady or turbulent jet. The long laminar plasma jet has good stiffness to withstand the impact of laterally injected cold gas and particulate matter. It could be used as a rather ideal object for fundamental studies and be applied to novel materials processing due to its attractive stable and adjustable properties.

Preliminary Investigations on Low-Pressure Laminar Plasma Spray Processing

The usual plasma spraying methods often involve entrainment of the surrounding air into the turbulent plasma core and result in coated materials having relatively high porosity and low adhesive strength. Therefore, exploration of new plasma spraying methods for fabricating high quality coatings to meet the requirement of special applications will be quite important. In this study, an alternative plasma spraying method, i.e. the low-pressure laminar plasma spraying process, is investigated and used in an attempt for spraying thermal barrier coatings (TBCs). Investigations on the characteristics of the laminar plasma jets, feeding methods for the ceramic powder and the formation process of the individual quenched splats have been carried out. The properties of the TBCs sprayed by laminar plasma jet process, such as the adhesive strength at the interface of the ceramic coating/bond coat, the surface roughness and microstructure, are examined by tensile tests and scanning electron microscope (SEM) observations.

Graphite intercalation compounds under pressure

Motivated by recent experimental work, we use first-principles density functional theory methods to conduct an extensive search for low enthalpy structures of C$_6$Ca under pressure. As well as a range of buckled structures, which are energetically competitive over an intermediate range of pressures, we show that the high pressure system ($\gtrsim 18$ GPa) is unstable towards the formation of a novel class of layered structures, with the most stable compound involving carbon sheets containing five- and eight-membered rings. As well as discussing the energetics of the different classes of low enthalpy structures, we comment on the electronic structure of the high pressure compound and its implications for superconductivity.