| LI Zun-jia,ZHOU Hong-xia.Numerical Simulation on Effect of Nozzle Downstream Shape on Acceleration Behavior of Cold Spray Particles[J],52(9):451-458 |
| Numerical Simulation on Effect of Nozzle Downstream Shape on Acceleration Behavior of Cold Spray Particles |
| Received:July 27, 2022 Revised:October 26, 2022 |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2023.09.041 |
| KeyWord:cold spraying nozzle downstream shape numerical simulation particle velocity |
| Author | Institution |
| LI Zun-jia |
School of Mechanical Engineering, Qinghai University, Xining , China |
| ZHOU Hong-xia |
School of Mechanical Engineering, Qinghai University, Xining , China |
|
| Hits: |
| Download times: |
| Abstract: |
| 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. |
| Close |
|
|
|