Supersonic Virtual Impactor for Separating Small Particles from Gases

本研究开发了一种分离小颗粒（10>m）的新方法。（在直径和更小的）气体流中的粒子。在这种方法中，气流被安排成射流，并被迫撞击锥形撞击器表面。锥表面的尖端，只有一小部分（称为少数流）实际上通过孔径移动。少数流中颗粒的平均尺寸远大于主流流中颗粒的平均尺寸，这是由于动量较大的大颗粒无法通过转弯跟随小颗粒进入孔径。孔径连接在两个同心管上。所述外管具有实心壁，所述内管在其末端附近具有与实心板连接的短距离多孔壁。气体在高压下供应到管之间的环形空间，并通过管的多孔部分进入孔径后面的空间，形成逆流。最后在孔径下游的内管中施加吸力。通过多孔管的吸力和流动的结合产生了一个零流平面，将从内管底部流出的气体和从小孔流出的气体分开。穿过小孔的粒子必须逆着逆流前进。它们的动量足够大，可以让它们穿过逆流，最终重新加入锥上的主流。通过调节逆流压力，可以移动零流平面，从而对下游端收集的粒度分布提供一定的控制。这项研究将改进这种设计，使影响锥的喷射气流以超音速移动。超音速允许大颗粒速度，并允许小颗粒通过零流平面并被收集。

This study develops a new method for the separation of small (10>m. in diameter and smaller) particles from a gas stream. In this method, the gas stream is arranged to flow as a jet, and forced to impinge upon a conically shaped impactor surface. The tip of the cone surface, and only a small fraction (termed the minority flow) actually moves through the aperture. The average size of the particles in the minority flow is much larger than that in the mainstream which passes over the particles because the larger particles, with greater momentum, cannot negotiate the turn and follow the small particles into the aperture. The aperture is joined to two concentric tubes. The outer tube has a solid wall, and the inner tube a porous wall for a short distance near its end joining the solid plate. Gas is supplied at high pressure to the annular space between the tubes, and passes through the porous part of the tube into the space behind the aperture creating a counterflow. Finally suction is applied in the inner tube, downstream from the aperture. The combination of suction and flow through the porous tube creates a plane of zero flow which separates gas flowing out of the bottom of the inner tube and gas flowing out of the aperture. Particles that have traveled through the aperture must progress against the counterflow. The ones large enough that their momentum can allow them to pass through the counterflow and eventually rejoin the majority flow over the cone. By adjusting the counterflow pressure the plane of zero flow can be moved, and this provides some control of the particle size distribution collected at the downstream end. The study will improve on this design by causing the jet gas stream impacting on the cone to move at supersonic speeds. Supersonic speeds allow large particle velocities, and permits smaller particles to pass through the plane of zero flow and be collected.