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Performance analysis of feeding device of port pneumatic grain unloader in CFD GUO Liwei1, a, LIU Bo2,b 1, 2 College of mechanism and electron engineering, Central South University, Changsha ,Hunan ,China 410075 alevisguo@qq.com, b liuboyh@126.com, Keywords: CFD; Port pneumatic grain unloader; Feeding nozzle; Secondary air.
Feeding noozle of port pneumatic grain unloader is vital to the whole system, CFD is used to simulate the flow field and optimize the geometry of the vacuum nozzle.
Vacuum nozzle is one of the largest power consumption device components of the port pneumatic grain unloader, the resulting pressure loss account for 1 /3 of the entire system.
There are mainly two types of feeding nozzle in the vacuum device, single tube nozzle which is generally used on small grain suction machine, and large, multi-use twin tube suction nozzle used on medium-grain suction machine.
Numerical simulation of nozzle flow field analysis based on CFD software is a fast, intuitive design approach can significantly improve the efficiency and accuracy of the test study, shorten product development cycles and reduce the number of product trial.

The grain size on the rolling surface after cold rolling slightly increases, accompanied a certain stretch, but microstructure on the cross section formed fibrous feature, and the greater of the deformation implemented, the fuzzier of the grain boundaries and more slender of the grain become.
However, a large number of lath martensite appeared after the heating temperature went to 850°C, and the microstructure was found to be fully martensite after the sample was quenched from 950℃.
However, the austenitic grain size decreases when the sample was reheated after double cold rolling, and the austenitic grain size decreases with the increase of deformation degree, but the austenite grain refinement comes to be indistinctive when the deformation amount increases to a certain extent.
Ultra-refinement of austenitic grains in low-carbon structural steel [J].
Method of Prior Austenite Grain Refining Using Induction Hardening[J].

The influence of the number of passes and the type of processing routes (A or C) on the mechanical properties of Armco Iron after ECAP processing is presented in Fig. 2 [3].
This grain size is usually obtained after a few passes and is a result of the equilibrium between grain refinement and grain growth.
Thin sheets with just one or few crystal grains in thickness direction exhibit material flowing difficulties compared to sheets with many grains.
Smaller crystal grains have fewer atoms inside the grain compared to bigger grains and therefore have more surface atoms.
(a) Cylinders machined from the samples upset in various numbers of passes (b) Cracked cylinder specimen machined from the sample upset in eight passes [14] The results of the study showed that material formability was kept high even after a high number of SPD upsetting passes (Fig. 5).

Stress induced macroscopic separation of the material along the grain boundaries is mostly attributed to grain boundary weakening due to intergranular precipitation and/or impurity segregation [1,2].
The composition of grain boundaries was studied by Auger electron spectroscopy (AES) using a Microlab 310F VG.
It consists of twinned austenite grains separated by straight boundaries.
(5) Owing to a number of measured and theoretically assessed quantities of various uncertainty levels, a possible deviation ∆ i γcoh = ∆ i γcoh (∆f, ∆ktd , ∆kmd, ∆k * , ∆RS) of the intergranular fracture energy was determined following the standard error analysis.
The former mechanism was observed in ASS due to grain boundary precipitation of carbide particles.

Specimens with different grain sizes were obtained via severe plastic deformation, as severe plastic deformation can result in grain growth for materials with very small initial grain sizes [25,26].
It is clear that with increasing grain size the number of grains containing twins first decreased and then increased, which indicates an obvious grain-size effect on twin density.
It is noted that the grains containing twins in the 5-revolution specimen are of grain size smaller than 35 nm, and no twins were observed in larger grains.
However, the grains containing twins in the 10-revolution specimen are of grain size larger than 45 nm, and no twins were observed in smaller grains.
The height of these steps is equal to the number of the accumulated partials multiplied by the {111} inter-planar distance [29,30].

Commonly, the multidirectional forging to a strain of about 0.4 leads to the appearance of a large number of the strain-induced subboundaries with low-angle misorientations (q < 15°), which appear as deformation microbands (DMBs) and/or dense dislocation walls (DDWs) crossing over the original grains (Fig. 2).
The new grains are characterized by nearly equiaxed shape, with a mean grain size below 1 mm.
The formation of the new ultrafine grains occurs nearby the initial grain boundaries as well as along several DMBs/DDWs.
Such grains include the great number strain-induced boundaries with low-angle misorientations.
The corresponding grain size distributions are characterized by sharp peaks for the grains with sizes less than 2 mm (Fig. 3), which can be considered as DRX grains.

This phenomenon is known from alloying element segregation to grain boundaries.
Here the hardening effect interferes with grain size strengthening.
The high-resolution capability of such analytical tools makes it possible to study small scale mechanical properties of individual grains, across grain boundaries and of selected areas, like precipitates and strongly deformed grains.
Twinning, as a form of plastic deformation, increases the number of interfaces (twin boundaries) and causes strain hardening, which leads to a hardness increase; see the value of 2.01 GPa in Table 3.
Although the extruded material is very fine grained, the scale of the indentation at the point where the first pop-in occurs is still smaller than the grain size.

Hence it can be considered that the number of potential barrier, which is inversely proportional to the grain diameter, eventually changes with the amount of aluminum addition.
Tilt angle of the grains, that is angle made by the [ 0011 ] of the both grains, is ranged between 13 and 16.5° in this grain boundary.
In addition, segregation of aluminum at grain boundary was also observed at incoherent grain boundary as shown in Fig.3.
(1) Here, e is the electric charge, Ns density of trap at grain boundary, ε relative dielectric constant, ε0 the dielectric constant in vacuum, n carrier concentration in grain, vn thermal velocity of the electron, L length of specimen, V applied voltage to the specimen, ng the number of grain boundary along L, k the Boltzmann constant, and T absolute temperature [7].
Because the grain boundary plays an important role in the variation in mobility, grain boundary structure was modified via magnetic texturing which enabled to align c-axes of grains highly.

Introduction Grain boundaries act generally as diffusion short circuits; consequently, the major part of material transport will occur by grain-boundary diffusion in nanomaterials where a large amount of atoms can lie on grain or interphase boundaries (50% for a grain size equal to 5 nm; 20% for a grain size equal to 10 nm).
It is well known from classical treatments of grain or interface diffusion that there are three different grain-boundary diffusion regimes in coarse grained crystals: type A, B and C.
We will see that there is an increasing number of new experimental evidences that the above diffusion coefficients agree very well with each other, i.e. in most of the cases the structures of relaxed grain-boundaries in nanocrystalline and polycrystalline samples are very similar.
-In A kinetic regime (Dv t)1/2 >> d), the different diffusion zones overlap each other resulting in a macroscopic homogeneous diffusing distribution which appears to obey Fick's laws as for a homogeneous system with an effective diffusion coefficient (Deff) equal to an average of Dv and Db weighted in the ratio of the number of diffusing atoms in the grains to that in GB [6]: Deff = g Db + (1-g) Dv, (2) 4 Title of Publication (to be inserted by the publisher) where g is the grain-boundary volume fraction (g � �/d; the factor of proportionality depends on the grain shape, but is in the order of unity).
In effect, owing to the number of GBs and the synthesis conducted under UHV conditions, the grain boundaries must be purer in the first type of materials if one excepts the contamination during the preparation (specially by oxygen) and supersaturated metastable nanocrystalline solid solutions.

The preliminary observations data show complex temporal and seasonal variation in estuarine flocculation of fine-grained sediment.
Introduction Approximately 90 percents of the suspended sediment load transported from the Yangtze River to its estuarine and coastal areas consists of fine-grained particles with dispersed medium grain size of smaller than 32 μm.
Flocculation processes change physical characteristics such as original size, density and settling velocity of fine-grained sediment [1].
In other words, below the critical τ, the increased τ could promote the suspended sediment re-flocculation to large flocs by increase number of particle collisions per unit time, and lead large suspended sediment flocs break-up to small ones above the critical τ.
Estuarine macroflocs and their role in fine-grained sediment transport [D].