Development of New Gas Atomizer Nozzle System for the Production of Fine Metal Powder used in Power Metallurgy

在气体雾化方法中，熔融金属通过超音速自由射流雾化。然而，熔融金属液滴的破碎过程尚不清楚，工业雾化器系统是通过经验考虑设计的。本研究的目的是用基于激光的新诊断方法阐明破碎过程，开发具有特殊出口形状的超声速喷嘴，并建立数值预测超声速射流详细结构的方法。获得了以下结果。(1)为了观察水滴的破碎过程，发展了一种新的方法。这使用了Nd：YAG激光器的THG（波长355 nm）。利用该紫外激光器构建了同轴激光全息系统，并对已知直径的标准粒子进行了测试，获得了10%的精度。(2)为了检查超声孔的出口形状对水滴的“破碎”的影响，将孔制成具有在孔的直径方向上拉伸的50微米线。全息测量发现，这种有线孔板产生的水颗粒直径比普通孔板小10 ~ 20%。从这个实验中，我们相信液滴的大小是可控的，通过改变出口形状的孔或喷嘴。(3)为了研究超音速自由射流的详细结构，本文采用TVD格式求解Euler方程，并计算了滞止比为1500的超音速自由射流。为了提高计算精度，将该格式推广到边界拟合网格上进行计算.还提出了三维计算方案。

In the gas atomization method, the molten metal is atomized by supersonic free jets. However, the breakup process of the melted metal droplet is not known and the industrial atomizer system is designed through the empirical consideration. The aims of the present research are to clarify the breakup process with the laser-based new diagnostic method, to develop the supersonic nozzle with a special exit shape and also to establish the method for numerically predicting the detailed structure of supersonic jets. The following results are obtained.(1) To observe the breakup process of the water droplet, the novel method is developed. This uses the THG of the Nd : YAG laser (wavelength 355 nm). The inline laser holography system with this ultraviolet laser is constructed and tested with the standard particle with known diameter, and the accuracy of 10% is obtained.(2) To check the effect of the exit shape of a supersonic orifice on the breakup' of a water droplet, the orifice is made that has 50 micron-wire stretched over the diametrical direction of the orifice. It is found from the holography measurements that this wired-orifice produces water particles with the diameter 10 to 20% smaller than the normal orifice. We believe from this experiment that the droplet size is controllable by changing the exit shape of the orifice or nozzle.(3) To clarify the detailed structure of the supersonic free jets, the TVD scheme is developed for solving the Euler equations, and the jets with the ratio of stagnation to ambient pressure of up to 1500 are calculated. This scheme is extended to calculated with the boundary fitted grid to increase the accuracy. The three-dimensional calculation scheme is also developed.