目的 超音速喷嘴为冷喷涂技术的核心部件,针对直线型喷嘴难以喷涂转折处、复杂区域或深筒状内壁的难题,其解决办法之一是利用弯管喷嘴,但它在工作时面临喷嘴内部粒子在弯曲段处碰壁及黏结堵塞,同时粒子动能损失至无法正常喷涂等问题。方法 利用磁场探究弯管内流-磁-固多物理场耦合下均匀球形铁粒子的运动轨迹,同时引入磁泳效应。由于铁粒子的相对磁导率远大于载气的相对磁导率,因此在非均匀磁场中微米级粒子在正磁泳效应下偏转到磁场梯度较高处。计算使粒子发生偏转时所需的磁场梯度及粒子在改变运动轨迹的核心点处所受的磁泳力,并建立COMSOL Multiphysics多物理场耦合自定义模块,对喷嘴内部粒子的运动轨迹进行数值模拟。结果 多维度模拟结果显示,针对弯曲角度为90°、60°的2种弯管喷嘴,在施加磁场梯度为780 T/m的磁场时,粒子在喷嘴内部流-磁-固多物理场的影响下皆有效偏转、运动,显著降低了粒子撞击弯曲段内壁的概率。同时,在粒子束的出口速度为600 m/s左右时,满足铁粒子沉积要求。结论 通过在不同弯管喷嘴的弯曲段处搭建线圈,通入相应的电流,以形成合适的磁场梯度,能够有效改变喷嘴内粒子的运动轨迹,降低粒子撞击壁面的概率。可为冷喷涂技术弯管喷嘴领域提供一定的理论基础参考。
Abstract
The key component of cold spraying technology is the supersonic nozzle. Currently, in the field of cold spraying technology, linear nozzles are mostly used, while bent nozzles have received little research. The difficulty with bent nozzles lies in the fact that supersonic particles are prone to collide inside the nozzle, resulting in significant loss of particle kinetic energy and preventing deposition. However, bent nozzles have obvious advantages in engineering applications in special areas, such as the inner walls of cylinders and turning points. There is an urgent need to study cold-sprayed bent nozzles. This article takes iron particles as an example. By using a magnetic field to assist iron particles in deflection within supersonic nozzles, it can reduce the impact of disorders of iron particle within the nozzles, thereby meeting the deposition requirements.
To study the collision of iron particles in the bent nozzle of cold spray, a coil is applied to the bent nozzle to form a non-uniform magnetic field, which makes the iron particles deflect angularly under the action of the magnetic field. The trajectory of the particles is corrected in combination with the turbulent gas field in the nozzle to reduce the collision probability of iron particles in the bent nozzle and reduce the kinetic energy loss of particles. The velocity, pressure, temperature, and particle trajectory of the gas flow field in the bent nozzle with 90° and 60° bending angles are simulated numerically by constructing a Comsol Multi-Physics coupling module. Because the continuous phase gas selected is helium, its flow field characteristics are not affected by the magnetic field. However, due to the geometric structure of the bend, the vortex flow field forms above the bend section and interacts with the incoming flow, making the airflow show a trend of decreasing velocity, increasing pressure, and increasing temperature in the expansion section. Meanwhile, the airflow velocity at the central axis is the fastest and decreases to the upper and lower walls. Without magnetic field coupling, the particles in the bend hit the wall one after another, resulting in a particle velocity of only about 400 m/s at the exit. At the same time, the particles released at the same time have a large time difference when they reach the outlet, which makes the spraying process unstable. Under the background of the inhomogeneous magnetic field, the relative permeability of iron particles is much larger than that of helium, so the micron particles are deflected to a higher magnetic field gradient by the positive magnetophoresis effect in an inhomogeneous magnetic field. The five particles in the two bends realize effective deflection motion, and the particles arrive at the exit at adjacent time nodes. Except for some particles in the bend of 90°, which were restrained by the magnetic field and appeared a transient stall phenomenon, the rest particles have no collision trajectory, and their velocity reaches the critical velocity required for deposition.
Under the conditions of magnetic field and flow field, supersonic iron particles have obtained superior movement trajectories in the cold-sprayed bent nozzle, providing a theoretical reference for the field of bent nozzles, a core component of cold spraying technology.
关键词
冷喷涂 /
COMSOL Multiphysics /
流磁固耦合 /
正磁泳
Key words
cold spray /
COMSOL Mulitphysics /
fluid-magnetic-solid coupling /
positive magnetophores
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基金
江西省教育厅科学技术项目（GJJ2202721）; 南昌理工学院高层次人才科研启动基金
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