The Digital Particle Image Velocimetry (DPIV) is an efficient method for measuring the internal flow field of a low-speed cooling fan. This paper studied the velocity field by means of PIV technology for a leading edge swept axial-flow fan without casing, and the tip vortex phenomenon was observed. Time-averaged velocity measurements were taken near the pressure surface, the suction surface and the tip of blade, etc. Moreover, the flow characteristics were visualized using numerical techniques. Experimental results showed that this tip vortex existed at the leading edge of the blade. The generating, developing and dissipating evolvement process of the tip vortex from the blade leading edge to downstream were discussed in detail. In addition, by comparing DPIV results and numerical results, a good agreement between them indicated a possibility to predict flow field using CFD tools. The experimental data provided in this paper are reliable for improving the aerodynamic characteristics of the open axial fan.
A spherical Fe matrix composite powder containing a high volume fraction(82vol%) of fine TiC reinforcement was produced using a novel process combining in situ synthesis and plasma techniques. The composite powder exhibited good sphericity and a dense structure, and the fine sub-micron TiC particles were homogeneously distributed in the α-Fe matrix. A TiC –Fe cermet was prepared from the as-prepared spherical composite powder using powder metallurgy at a low sintering temperature; the product exhibited a hardness of HRA 88.5 and a flexural strength of 1360 MPa. The grain size of the fine-grained TiC and special surface structure of the spherical powder played the key roles in the fabrication process.
The influences of the heating rate,annealing temperature and soaking time during continuous annealing on the microstructure evolution and bake hardening behavior of the low carbon steel were investigated.After 2% prestraining,bake treatment(180 ℃×20 min)was carried out to measure BH(bake hardening)values.The results showed that,with the increase of the annealing temperature,the grain size increased except for annealing in the intercritical region.Furthermore,the BH value increased and the mean grain size reduced with increasing the heating rate from 5to 80 ℃/s.The BH value was very low before complete recrystallization.After a significant decrease from 630 to 720 ℃,the BH value enhanced when the steel was annealed at 750℃.With the increase of the soaking time from 20 to 100s,the BH value reduced linearly due to the segregation of solute C atoms.
A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature,and it was found that the higher this temperature is,the coarser the grains are. After rolling at 400 ℃ ,well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation,with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging,while the final grain size approaches several millimeters. Finally,a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed,and verified by experiments.
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