Investigation on target jet mill based on the entrainment of the annular supersonic flow
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摘要: 气流磨作为生产超精细粉末的设备在工业界得到了广泛应用。通过数值模拟和试验验证，提出了一种超声速靶式气流磨。该气流磨采用环状超声速气流引射颗粒流，使其达到超声速状态并获得极大动能，以颗粒束形式维持于气流中心，准确碰撞靶头，实现超声速粉碎。对颗粒速度和运动轨迹的两相流数值模拟结果表明：在总压1.5 MPa、马赫数3.0的超声速气流引射作用下，粒径为25~1 μm的颗粒可加速至440~530 m/s，并精准地碰撞靶头。在此基础上，设计制造了超声速靶式气流磨并进行了铁粉粉碎试验和靶头侵蚀试验，结果表明：颗粒具有极大的碰撞能量，且与靶头发生了聚焦式碰撞。Abstract: The jet mill widely used in many industrial fields is a kind of apparatus to produce superfine powder. A new supersonic jet mill, whose design is based on numerical simulations and collision experiments, is presented and manufactured. In our design an annular supersonic flow produced by an annular converging-diverging nozzle is used to entrain the central subsonic flow with particles. After the supersonic flow's entrainment, the particle beam concentrated in the flow center impacts on the target accurately with a great kinetic energy. The multiphase numerical studies show that the collision speed of particles of 25 μm to 1 μm in diameter can reach 440 m/s to 530 m/s approximately in the entrainment of the supersonic flow with the Mach number of 3.0 and the total pressure of 1.5 MPa, and particles can precisely collide on the target. The collision experiments implemented in the new-made jet mill manifest the huge collision energy and the precise supersonic collision in the jet mill by the target erosion and the iron particles size reduction.
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Key words:
- target jet mill /
- supersonic annular flow /
- entrainment /
- supersonic collision /
- multi-phases flow
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图 2 装置中速度场的数值模拟结果
Figure 2. The velocity field in the jet mill by numerical simulation
图 3 不同粒径的颗粒的轴向速度在中轴线上的加速过程
Figure 3. The accelerating process of the streamwise velocity of particles with different diameters along the axis
图 4 采用DPM两相流模拟的不同粒径颗粒的运动轨迹
Figure 4. The motion trajectories of particles with different diameters numerically simulated by the discrete phases model
图 6 铁粉粉碎试验中靶头的侵蚀效果
Figure 6. The targets' erosion photographs of the iron particle size-reduction tests
表 1 超声速气流磨的参数
Table 1. The parameters of supersonic jet mill
几何参数 热力学参数 动力学参数 环状喷管 Athr=15.7 mm2
Aex=66.5 mm2p0=1.5 MPa
T0=300 K
pex=40.8 kPa
Tex=107 KMa=3.0
uex=622 m/s
加料管 A=7.07 mm2
L=0.1 mpatm=0.1 MPa
Tatm=300 Kuex=317 m/s
加速段 L=0.4 m
Φin=10.02 mm
Φex=14.00 mm碰撞室 β=3° pout=0.1 MPa
T0，out=300 K靶头 Φ=4.00 mm 壁面 χ=0.03 
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表 2 超声速气流磨流场验证试验结果
Table 2. The validation test of the jet mill supersonic field
p0 /MPa p/MPa Ma v/(m·s-1) Kinetic energy/(J·g-1) 0.5 0.091 1.77 481 115 1.0 0.082 2.29 555 154 1.5 0.058 2.77 604 182 2.0 0.053 3.02 623 194
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表 3 铁粉的统计粒径
Table 3. The statistic radius of iron particles size distributions
d10/μm d50/μm d90/μm Before 28.2 64.3 150.8 After 2.6 7.8 29.9
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