Ballistic particle separator

A device for the physical separation of particles from a gas stream consisting of a two-dimensional flow unit in which the flow is accelerated to the throat and then diffused so that the particles are inertially urged to the core and to the trap. It is unique in that a telescope two-stage nozzle-diffuser arrangement is used to obtain a compact, low pressure loss unit. The design is such that all inertal forces including the Magnus force within the boundary layer act in the direction of particle separation towards the core and a sharp particle size cutoff is obtained down to 2 micron.

This invention relates to a device for separating a substance of a greater 
density from another substance, and more particularly to a device for 
separating solid particles from a flow of gas. 
Devices for separating substances of different densities in response to 
inertia forces have commonly been of the centrifugal or cyclone-type of 
separator. Cyclone separators remove solid particles such as dust from a 
flow of air or other gas by subjecting the flow to a spiral-like motion 
during which centrifugal force urges the denser particles to move outward 
with respect to the gas in which they are suspended. Openings adjacent the 
outer portion of the cyclone separator remove the outer portion of the 
flow into which the denser particles have been concentrated. Because of 
the necessity of forcing the flow through a spiral path, cyclone 
separators are devices which inherently require a large space envelope and 
consequently they frequently penalize applications where space or weight 
is a prime consideration. 
Equipment such as internal combustion engines must be operated with a flow 
of air that is relatively free from dust and other solid particles. In 
reciprocating engines, dust can become deposited in the lubricating oil 
and cause rapid wear. The passage of dust through gas turbine engines can 
erode the blades. In addition, the long and tortuous flow paths through 
cyclone generators can result in a substantial pressure drop across the 
separator which results in a power loss in the internal combustion engine 
connected to the separator. This is especially true in the case of gas 
turbine engines in which the performance is radically affected by changes 
in pressure and temperature at the air inlet to the engine. 
It is an object of the invention to provide a device which can separate a 
substance of greater density from the flow of another substance and which 
is comparatively compact in relation to the quantity of flow of the 
substances through the device. 
Another object of the invention is to provide a device for separating a 
substance of greater density from the flow of another substance with the 
minimum of pressure drop occurring during the flow of the substances 
through the device. 
A further object of the invention is to provide a relatively compact device 
for separating dust particles from a flow of air flow with a minimum of 
pressure drop across the separating device. 
In the embodiment of the invention, the device for separating the particles 
consists of concentric tubular or rectangular members which cause the main 
air flow to modulate and separate from the particles which are scavenged 
out together with a small amount of scavenge air.

Referring to FIG. 1 the particle-laden gas enters the separator and 
particles are quickly accelerated at the inlet section 52 to almost air 
velocity. Particle inertia of the larger particles causes them to leave 
the streamline at the throat 53 and enter the trap 54. The main or primary 
air flow travels through passages 55 and 56. Additional oversize particles 
are separated in the air streamline undulation between 55 and 56, these 
particles entering trap 57 which leads to a common manifold 58 with trap 
54 and from there the particles are scavenged out. The test data on this 
concentric geometry have shown that practically 100% of all particles 
above a size as low as about 2 micron can be efficiently removed. 
Another version of the element geometry of FIG. 1 is shown in FIG. 3 
wherein the passages are rectangular in cross section, as shown by FIG. 4, 
rather than tubular.