Particle seeding is a key diagnostic component of filter testing and flow imaging techniques. Typical particle generators rely on pressurized air or gas sources to propel the particles into the flow field. Other techniques involve liquid droplet atomizers. These conventional techniques have drawbacks that include challenging access to the flow field, flow and pressure disturbances to the investigated flow, and they are prohibitive in high-temperature, non-standard, extreme, and closed-system flow conditions and environments.
In this concept, the particles are supplied directly within a flow environment. A particle sample cartridge containing the particles is positioned somewhere inside the flow field. The particles are ejected into the flow by mechanical brush/wiper feeding and sieving that takes place within the cartridge chamber. Some aspects of this concept are based on established material handling techniques, but they have not been used previously in the current configuration, in combination with flow seeding concepts, and in the current operational mode. Unlike other particle generation methods, this concept has control over the particle size range ejected, breaks up agglomerates, and is gravity-independent. This makes this device useful for testing in microgravity environments.
Before any particles can be generated in the flow, the cartridge chamber is filled with the solid particles of choice. A programmable mechanical motor providing a range of rotational motion is used to drive a helical brush (or wiper) inside the chamber. Due to the action of the brush, the particles are dragged across the length of the internal chamber, particularly along the surface of the fine mesh screen, causing the particles to pass through the screen. The flow around the cylindrical body of the cartridge then entrains the ejected particles into the flow stream. System components consist of: a motor, flange supports for mounting and sealing the internal chamber volume, a drive shaft and tube conduit, a particle sample cartridge, a helical wire brush or wiper, a fine mesh screen, and screws (see figure). An optional aerodynamic leading edge can be used to streamline or stabilize the flow around the cartridge body, and to decrease flow effects as the particles are entrained in the flow. Alternately, a turbulence generating element can be used to accelerate the spreading angle of the particle flow, as a result of turbulent mixing, for more complete particle coverage throughout the flow stream.
The concept provides the additional advantages of unlimited choice of solid particles, including somewhat sharp and abrasive particles; no need for an outside pressurized gas feed source; complete containment and enclosure of the flow environment; and the ability to be used in non-standard (temperature and pressure) environments and closed systems. Additionally, the rate of particle flux and the upper cut size of particles delivered to the flow can be controlled. The particles can also be released and distributed over a broad cross-section of the flow duct/pipe.
This work was done by Juan H. Agui of Glenn Research Center, and R. Vijayakumar of Aerfil.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-18837-1