李尊甲,周红霞.喷嘴下游形状对冷喷涂粒子加速行为影响的数值模拟研究[J].表面技术,2023,52(9):451-458.
LI Zun-jia,ZHOU Hong-xia.Numerical Simulation on Effect of Nozzle Downstream Shape on Acceleration Behavior of Cold Spray Particles[J].Surface Technology,2023,52(9):451-458 |
| 喷嘴下游形状对冷喷涂粒子加速行为影响的数值模拟研究 |
| Numerical Simulation on Effect of Nozzle Downstream Shape on Acceleration Behavior of Cold Spray Particles |
| 投稿时间：2022-07-27 修订日期：2022-10-26 |
| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.041 |
| 中文关键词: 冷喷涂 喷嘴下游形状 数值模拟 粒子速度 |
| 英文关键词:cold spraying nozzle downstream shape numerical simulation particle velocity |
| 基金项目:国家自然科学基金(52001180) |
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| 中文摘要: |
| 目的 冷喷涂过程中喷嘴内流道关键尺寸是影响粒子加速的重要因素。虽然喷嘴下游长度与扩张比是喷嘴的2个最重要参量，但目前对喷嘴优化设计的研究仍有深入空间，比如喷嘴下游形状。方法 本文利用计算流体动力学的软件ANSYS/Fluent进行数值模拟研究，在与传统锥形下游相比较后，设计了钟形下游与喇叭形下游喷嘴。同时研究了喷嘴下游形状对气流与粒子加速行为的影响。结果 对于钟形下游喷嘴，其气流速度在过喉部后迅速增加到较高数值，随后变化缓慢;对于喇叭形下游喷嘴，其气流速度在过喉部后先增加缓慢，直至截面积开始快速增加时，气流速度迅速增加;喷嘴下游形状对粒子撞击基板时的速度有一定影响，且随着喷嘴下游长度和粉末粒度的变化而改变。对于Cu粉，当为下游100 mm短喷嘴时，锥形下游喷嘴对10~20 μm的粒子加速效果最好。当粉末在20 μm以上时，喇叭形下游喷嘴的加速效果最好。对于下游220 mm长喷嘴，钟形下游喷嘴对10~30 μm的粒子加速效果最好。当粉末在30 μm以上时，锥形下游喷嘴的加速效果最好。对于Al粉，当为下游220 mm长喷嘴时，钟形下游喷嘴对10~50 μm的粒子加速效果最好，喇叭形下游喷嘴加速效果最差。结论 冷喷涂喷嘴下游形状对气体与粒子加速有显著的影响。 |
| 英文摘要: |
| The particle impact velocity is one of the most important and crucial factors which determine the deposition process and coating quality in cold spraying. When the gas conditions (gas type, pressure, temperature) and powder parameters (particle morphology, particle size and distribution) are selected, the dimensions of the spray nozzle inside are important for the particle acceleration. Although it has been known that the nozzle downstream length and expansion ratio (the cross-sectional area of exit divided by that of the throat) are two very significant parameters that influence the particle velocity, the nozzle dimension optimization is still necessary for some aspects, such as nozzle upstream length and downstream shape. Taking into the great difficulty to manufacture the nozzles with a curved inner wall, this study tried to examine the effect of nozzle downstream shape by the numerical simulation method with the commercial software ANSYS/Fluent. A two dimensional axisymmetric model was employed as used before. The flow gas was taken as the ideal gas and the standard k-ε turbulence model was used to solve the equations. Besides the conventional cone shaped downstream, bell shaped and horn shaped downstream nozzles were also considered, while the other dimensions such as inlet diameter, throat diameter, exit diameter, and upstream length were fixed. In addition, two downstream lengths were also used to investigate the interaction of downstream length and shape. The standoff distance was fixed as 30 mm. The main driving gas and powder carrier gas were both nitrogen (N2) with an inlet pressure of 3 MPa and temperature of 600 ℃. The discrete phase model was used to solve the particle acceleration and the interaction between the particles and gas flow was omitted in this study based on previous experience. The spherical Cu powder was used with the particle size of 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm. The initial velocity of particles was 10 m/s and they were fed at room temperature. The results showed that all different nozzles presented a similar gas flow behavior, i.e., the gas velocity increased greatly after the nozzle throat until the nozzle exit. But there was some obvious difference. For the bell shaped nozzle, the gas expanded more quickly after the throat and then shortly its velocity increased slowly until near the nozzle exit; while for the horn shaped nozzle, the gas expanded slowly after throat until somewhere near the exit and then it expanded quickly to a higher velocity before it impinged the substrate. The particle impact velocity also changed with the nozzle downstream shape and particle size. When the Cu powder was used, for the short downstream length nozzle (i.e. 100 mm), the conventional cone shaped nozzle showed a better particle impact velocity when the particle size was in the range of 10-20 μm; while when the particle size was larger than 20 μm, the horn shaped nozzle showed a better acceleration. For the long downstream length nozzle (i.e. 220 mm), the bell shaped nozzle showed a better particle impact velocity when the particle size was in the range of 10-30 μm; while when the particle size was larger than 30 μm, the conventional cone shaped nozzle was better. When the 10~50 μm Al powder was used, for the long downstream length nozzle (i.e. 220 mm), the bell shaped nozzle showed the highest particle impact velocity and the horn shaped nozzle showed the worst acceleration. Therefore, based on the above results, the nozzle downstream shape and length have interaction for different particle size ranges. Since the nozzle downstream shape has a significant effect on particle acceleration, a comprehensive design method should be paid more attention to in future nozzle optimization. |
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