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With the use of RNG k-e turbulence model, SIMPLEC algorithm and CFD software, the turbulent flow in an axial flow impeller was numerically simulated in the clear water (single-phase) and the sandy water (solid-liquid two-phase) conditions. The distributions of solid concentration, velocity and pressure on the impeller of an axial flow pump were analyzed at the same particle diameter but different volume concentrations in sandy water. And these distributions were comparatively analyzed under the clear water and the sandy water conditions. According to the simulation results, the axial pump impeller will be damaged more easily and quickly in sandy water than in clear water. And the area more prone to damage on the axial flow impeller is predicated. The predicted vulnerable parts in an axial flow impeller are consistent with that in actual projects. This study shows that the numerical simulation results are the same as the actual situation, and it has guiding significance for the wear design of the axial flow pump.DOI: http://dx.doi.org/10.5755/j01.mech.24.3.13854

The very poor hot workability of high-alloyed GH4742 superalloy is represented in the aspects of very narrow available deformation temperature range, high deformation-resistant force and poor ductility. In this paper, a special heat treatment to change the ingot microstructure is proposed to improve the hot workability of the GH4742 superalloy. The' phase with a appropriate size and morphology and tortuous grain boundary were obtained by slow cooling in the ' two phases region after solution treatment. Modified microstructure induces that the hot deformation flow stress of GH4742 superalloy was decreased effectively and hot deformation plasticity was increased obviously.

As the key component of a hydroelectric power generation system, hydraulic turbine plays a decisive role in the overall performance of the system. There are many sandy rivers in the world, and turbines working in these rivers are seriously damaged. Therefore, the research of flow in sandy water has great theoretical significance and practical value. Based on the specific hydrological conditions of a hydropower station, the solid–liquid two-phase flow in the whole flow passage of a Francis turbine with splitter blades in sandy water was numerically studied. A geometric model of the whole flow passage of the Francis turbine was established on the basis of given design parameters. The solid–liquid two-phase turbulent flows in Francis turbine runner under three different loads were numerically analyzed by using this model. The three different loads are as follows: Condition 1: single unit with 1/4 load, Condition 2: single unit with 1/2 load, and Condition 3: single unit with full load. The distributions of pressure and sand concentration on the leading side and the suction side of the runner blades, as well as the velocity vector distribution of water and sand on the horizontal section of the runner, were obtained under different load conditions. Therefore, the damages to various flow passage components by sand can be qualitatively predicated under various conditions. To guarantee the safety and stability of the unit, the adverse conditions shall be avoided, which can provide certain reference for plant operation.

Mechanochemical process was employed to prepare Fe/MgO and Fe/NaCl nanocomposites. The carbon nanostructures (nanotubes and carbon-encapsulated Fe nanoparticles) were successfully synthesized using two nanocomposites as the catalyst. Our wok revealed that the morphology of Fe nanoparticles in the Fe/MgO nanocomposites depended on the distribution and particle size of iron oxides in the precursors. The size of Fe nanoparticles greatly affected their catalytic properties and the morphologies of carbon nanotubes. The successful carbon encapsulation of Fe nanoparticles was achieved by using the mechanochemically derived Fe/NaCl catalyst.

Mechanical milling was employed to prepare the nanocomposite precursors for the catalytic growth of carbon nanostructures. For alumina substrates, our study showed that mechanical-millingderived catalyst precursors possessed high hydrogen reduction efficiency that in turn enabled the high yield of CNTs. The alloying effects presented by the mechanical milling could accelerate the substitutional reactions between the parent oxides and thus the quality of CNTs was apparently improved. In addition, by using water-soluble substrates such as NaCl, we realized large-scale formation of carbon-encapsulated metal nanoparticles (CEMNs) that can be completely separated by a simple washing process. It was found that the morphologies of as-obtained carbon nanostructures were strongly dependent on the substrate effects. By selecting different salt substrates, we can strategically change the morphologies of the as-obtained nanostructures, from CNTs to CEMNs and the intermediate state between CNTs and CEMNs, such as quasi-nanocages.

This paper presents the true stress - strain curves and data analyses of a Ni-containing TiAl and its reference alloy based on the isothermal compression tests at 1000°C and 0.01 - 1.0s-1strain rates. The results show that the minor Ni addition makes the flow softening coming sooner and therefore significantly lowers the peak stress. Those effects, in addition with a better balance between the work hardening and flow softening during hot deformation, improve the steady state flow behavior of TiAl. The Ni-influence mechanisms are also suggested based on the TEM observation of dislocation configurations and lamellar breakdown during the deformation.