电极感应熔化气雾化制粉技术中非限制式喷嘴雾化过程模拟

电极感应熔化气雾化(electrode induction melting gas atomization, EIGA)是一种制备超洁净无夹杂物的先进制粉技术,本文以粉末高温合金的氩气雾化过程为研究示例,对现有用于实际生产的国内某厂家提供的EIGA用非限制式喷嘴进行建模,采用商用计算流体力学软件FLUENT,分布采用欧拉-欧拉VOF(volume of fluid)多相流方法与欧拉-拉格朗日DPM (discrete phase model)离散相方法,对非限制式环缝喷嘴主雾化与二次雾化过程进行了数值模拟.通过对主雾化过程中多相流大涡模拟速度流场,主雾化过程中不同阶段高温熔体云图模拟以及二次雾化过程中TAB (Taylor analogy breakup)模型速度流场及TAB模型粒度分布的模拟研究,实现了对EIGA制粉技术中非限制式喷嘴雾化过程的全过程模拟,并预测了雾化后的粉末粒度分布.在此基础上,采用本文模拟使用的非限制式环缝喷嘴,设定与模拟条件一致(进气压力4 MPa,液流直径约4 mm)的实验条件,制备的粉末大部分颗粒的直径大小在100μm左右,该实验结果与模拟得到的粉末直径D50=100μm大小一致,进一步验证了模拟数据的合理性.该方法也适用于非限制式喷嘴里,其他金属或合金的雾化过的模拟研究.

Computational fluid dynamic investigation of the primary and secondary atomization of the free-fall atomizer in electrode induction melting gas atomization process

Nickel-based superalloy is mainly used for fabricating the important high temperature parts including the turbine disk, turbine baffle, compressor disk, and other critical components. Ceramic inclusions in powder metallurgy (PM) superalloy could promote fatigue crack initiation, and thus accelerating the crack propagation under certain conditions. In this case, the ultra-clean nickel-based superalloy powder is critical for PM superalloy components. Generally, there are two well-known methods of fabricating superalloy powders, i.e., argon gas atomization (AA) and plasma rotating electrode process (PREP). Electrode induction melting gas atomization (EIGA) process is a newly developed method of preparing ultra-clean metal powders. The EIGA process is a completely crucible-free melting and atomization process developed by ALD vacuum technologies. In this process, a slowly rotating prealloyed bar is fed into a conical induction coil. The end of the bar is inductively heated and molten alloys falls into an atomizer where the liquid alloy is atomized with a high-pressure inert gas. The EIGA prepared powders possess the advantages of AA (more fine powders) and PREP (ultra-clean powders) processes. Generally, there are two key issues in EIGA process, and the free-fall gas atomizer design is one of the critical issues for the powder yield and quality. Free-fall gas atomizers are some of the first two fluid atomizer designs to be used for molten metal atomization. In a simple open (unconfined stream) design a melt stream falls from a tundish exit via gravity into the convergence of focused atomization gas jets where it is disintegrated. The gas-melt interaction is complex, and it is difficult to characterize the interaction process directly. To have a good understanding of the atomisation technology, the physical break-up process instead of correlating the gas dynamics with droplet fragmentation indirectly must be able to be examined. And it will be desirable, if we input the atomization parameters, we can obtain the particles' distributions directly. In this work, a computational fluid dynamic approach to simulating the primary and secondary atomization processes is developed by using the volume of fluid method and discrete phase model. By integrating the metal stream break-up (in primary atomization) with the flow field and particles distribution simulation (in second atomization), this numerical simulation method is able to provide the direct assessment for the atomisation process. To verify the method performance, the melt stream is initialized into a 4 mm-diameter stream, which is then injected into the gas flow field for further fragmentation. The experimental results show that the simulated particles' diameter distribution is consistent with the experimental results in the same conditions.