﻿ 两阶段悬浮液超音速火焰喷涂多相流模拟研究
 上海理工大学学报  2023, Vol. 45 Issue (6): 591-601 PDF

Multiphase flow simulation of two-stage suspension high-velocity oxygen fuel spraying
HE Dai, JIAO Jianliang, SHAN Yanguang
School of Energy and Power Engineer, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: In order to study the flow field distribution and droplet/particle behavior in two-stage suspension high-velocity oxygen fuel spraying, three-dimensional Euler-Lagrange coupling modeling method was used to simulate the flow field and the process of suspension fragmentation atomization, motion heat transfer, evaporative diffusion and finally being captured by substrate. The suspension properties are compiled by an experiment-based fitting function and the influence of droplet shape changes is considered. The results show that: By adjusting the mass flow rate of nitrogen, the flame flow temperature can be adjusted without affecting the flame flow velocity, so as to meet the technological requirements of coating preparation of different temperature-sensitive materials. By adjusting the volume flow rate of suspension, the suspension can reach the center of flame flow and be heated and accelerated sufficiently. Appropriately reducing the volume flow rate of suspension is helpful to improve the temperature and velocity of particles captured by substrate, appropriately increasing or decreasing the particle concentration of suspension can increase the particle output per unit time or reduce the particle size without affecting the velocity of particles captured by substrate, which can be adjusted according to different process requirements.
Key words: suspension; high-velocity oxygen fuel spraying     numerical simulation     multi-phase flow     TiO2

1 数学模型 1.1 连续相模型

 $\frac{\partial }{{\partial {x_i}}}\left( {\rho {u_i}} \right) = 0$ (1)
 $\frac{\partial }{{\partial {x_i}}}\left( {\rho {u_i}{u_j}} \right) = - \frac{{\partial P}}{{\partial {x_i}}} + \frac{{\partial {\tau _{ij}}}}{{\partial {x_i}}}$ (2)
 $\frac{{\partial \rho e{u_i}}}{{\partial {x_i}}} = - \frac{{\partial p{u_i}}}{{\partial {x_i}}} + \frac{{\partial \left( {{u_{ij}}{\tau _{ij}} - {q_i}} \right)}}{{\partial {x_i}}}$ (3)
 $\rho = - \frac{{{P_0} + P}}{{\left( {{R \mathord{\left/ {\vphantom {R {{M_{\text{w}}}}}} \right. } {{M_{\text{w}}}}}} \right)T}}$ (4)

 图 2 液滴形状变化示意图 Fig. 2 Schematic diagram of droplet shape change

 ${C}_{{\rm{d}}\text{，}{\rm{sphere}}}\left\{\begin{array}{cc}0.424& {{R}}{e} > 1\;000\\ \dfrac{24}{{{R}{e}}}\left(1+\dfrac{1}{6}{{{R}{e}}}^{2/3}\right)& {{R}}{e}\leqslant 1\;000\end{array}\right.$ (17)
 ${C}_{{\rm{d}}}={C}_{{\rm{d}}\text{，}{\rm{sphere}}}(1+2.632y)$ (18)

1.3 数值计算方法 1.3.1 计算区域

 图 3 两阶段悬浮液超音速火焰喷涂计算域示意图 Fig. 3 Schematic diagram of computing domain of two-stage SHVOF
1.3.2 边界条件

1.3.3 网格划分

 图 4 计算域结构化网格 Fig. 4 Structured grid of computing domain
1.3.4 数值方法

2 结果与讨论

 图 5 实验与模拟燃烧室压力和枪管出口温度对比图 Fig. 5 Comparison of experimental and simulated combustor pressure and barrel exit temperature
2.1 流场分析

 图 6 流场中心沿轴线方向压力、温度与速度变化 Fig. 6 Changes of pressure, temperature and velocity in the center of flow field along the axis

2.2 悬浮液体积流量分析

 图 7 不同距离液滴/颗粒温度分布 Fig. 7 Droplet/particle temperature distribution at different distances

 图 8 不同距离液滴/颗粒速度分布 Fig. 8 Droplet/particle velocity distribution at different distances

 图 9 流场中心沿轴线方向压力、温度与速度变化 Fig. 9 Changes of pressure, temperature and velocity in the center of flow field along the axis

 图 10 液滴/颗粒平均温度与速度变化 Fig. 10 Droplet/particle average temperature and velocity variation

2.3 悬浮液颗粒体积分数分析

 图 11 流场中心沿轴线方向压力、温度与速度变化 Fig. 11 Changes of pressure, temperature and velocity in the center of flow field along the axis

 图 12 液滴/颗粒平均温度与速度变化 Fig. 12 Droplet/particle average temperature and velocity variation

 图 13 颗粒被基板捕捉时的粒径分布 Fig. 13 Diameter distribution of particles captured by substrate

 图 14 颗粒被基板捕捉时的温度分布 Fig. 14 Temperature distribution of particles captured by substrate

 图 15 颗粒被基板捕捉时的速度分布 Fig. 15 Velocity distribution of particles captured by substrate
3 结　论

a. 随着注入混合室N2质量流量的增加，枪管出口的温度逐渐降低，而速度几乎没有变化。在不影响焰流速度的前提下，调节N2质量流量可以调节焰流温度，进而影响颗粒温度，以满足不同温敏材料涂层制备的工艺要求。

b. 在悬浮液注入口直径确定的情况下，调节悬浮液的体积流量，使其能够迅速到达焰流中心被充分加热和加速。在悬浮液能够到达焰流中心的前提下，适当降低悬浮液的体积流量有助于提高颗粒被基板捕捉时的温度与速度，从而提高涂层的结构致密度与结合强度。

c. 在悬浮液能够立即到达焰流中心的情况下，适当提高或降低悬浮液颗粒体积分数可以在不影响颗粒被基板捕捉时，提高单位时间内的颗粒输出量或降低颗粒粒径，从而提高涂层的沉积效率或提高涂层的结构精细度，具体调整可根据不同的工艺要求进行。

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