Study on the classification of nano-size fine particles in ultarasonic flow field

1)超音速开口障碍物绕流场的数值分析及其分级特性，同时考虑质量守恒、动量守恒和能量守恒，计算了不同开口形状和大小的障碍物在不同马赫数、吸力流量和喷嘴出口与障碍物间隙组合下的流场。得到了它们对颗粒的分离效率。结果表明，在较小的吸气流量下，障碍物周围的驻波形状是相似的，因此对于无开口的障碍物也可以得到类似的特性。2)单分散的溴化亚锡颗粒在20~1000 nm范围内，具有相同喷嘴宽度4 mm、不同形状和不同间隙的四个超声冲击器的分离效率。首先用蒸发和冷凝法产生多分散状态下的测试粒子，然后用差示迁移率分析仪将其分类为单分散粒子。由这笔赠款购买的光散射粉尘计数器监测了入口和出口颗粒物浓度的稳定性。3)实验得到的分离效率曲线与常规冲击器相比，分离效率曲线有很大的提高，分离出的颗粒比常规冲击器更小、更锐利。然而，分离性能强烈地依赖于喷嘴的形状和喷嘴出口与障碍物之间的间隙。最后，利用修正的斯托克斯数同时考虑了这些影响，对其进行了总结。

In this research, followings were studied to develope a novel scheme classifying nano-size ultrafine particle in an ultrasonic flow field.1)Numerical analysises of supersonic flow field around an obstracle with openning and its classification characteristics ; The flow field around an obstacle with different shape and size of openning has been calculated for various combinations of Mach number and suction flow rate and gaps between nozzle outlet and obstacle taking account of conservations of mass, momentum and energy, simultaneously. Then their separation efficiency of particles has been obtained. As a result, shape of standing shock wave around an obstacle was found to be similar for small sucktion flow rate and thus it can be expected to obtain similar characteristics for the case of obstacle without openning.2)Separation efficiency of four ultrasonic impactor with same nozzle outlet width of 4mm but different shapes and different gap distances using monodisperse Stannous Bromide particles ranging 20 to 1000nm. Test particles were first generated in polydisperse state by evaporation and condensation method, and then classified to monodisperse particles by a differential electric mobility analyzer. Stability of inlet and outlet particle concentrations have been monitored by a light scattering dust counter purchased by this grant. Coarse and fine fractions of test particles were determined quantitatively by a liquid ion chromalography.3)Experimentally obtained separation efficiency curve increase very steeply and they separate much smaller and sharper cut performance than a conventional impactor. However, separation performance was found to depend strongly on the nozzle shape and gap between nozzle outlet and obstacle. Fanally it was summarized by using modified Stokes number taking account of those effects simultaneously.