Particle Impactor and Indexing Media Filter: Advanced Filtration Methods for Long-Duration Space Applications
Logan J. Larson
Purdue University, NASA Glenn Space Academy 2011
Juan Agui, Ph.D.
NASA Glenn Research Center
Lunar regolith has proven to be a major hindrance in previous NASA missions to the lunar surface. The small, sharp, and sticky submicron dust gets in many adverse places, causing both problems within the lunar module and potential health issues for the astronauts. Current filtration methods for mitigating dust and other unwanted particles are insufficient for future long-duration space applications due to their long-term inability to maintain their original efficiencies without many necessary man-hours spent replacing the filtration systems. For this reason several advanced filtration methods were tested on a parabolic flight rig to better understand their capabilities and efficiencies in a zero G environment. These two systems, an inertial particle impactor and an indexing media filter, should necessitate less maintenance to preserve their initial efficiencies. The inertial particle impactor utilizes the idea that larger particles contain greater inertia. This inertia does not allow the particles to follow the air streamlines, causing the particles to collide into an impactor plate. The indexing media filter is similar to current filtration methods, but rather than needing to be replaced often, the filter is indexed, allowing a “fresh” portion of the filter to be utilized at all times. Results prove that both filtration systems maintain near predicted filtration efficiencies over most particle sizes, though anomalies for small particle efficiencies occur for particle impactors and for all particles while only testing the indexing media. Pressure drops across each component for given flow rates correlate well with what was predicted.
In order to support the exploration of future planetary surfaces for long-duration missions, advanced filtration systems will need to be developed. Currently, there is priority for a filtration system which will remove and dispose of surface dust and particulate matter. To meet the necessary requirements of manned modules within these planetary atmospheres, lightweight, highly efficient, and low power alternatives are required. It is also desired that this system have a long-term removal capacity and produce little noise.
Current filtration methods require extensive manual maintenance and repeated replacement to be effective for long-duration missions. Besides this obvious drawback, these systems also require manual servicing[j1] . Electrostatic Precipitation (EP) is a particulate collection device that has been utilized in industry as an efficient filtration system for over a century for various applications. EP involves adding a positive or negative charge to air particles through the use of an electrostatic corona discharge and high voltage collecting electrodes of the opposite polarity. While these systems utilize little energy and effectively filter their surrounds, they also have the possibility of producing threatening ozone.
A superior variation of EP is electro-spray filtration. This technique replaces the threatening corona discharge with a small, highly-charged mist produced by electro-spray ionization. This method appears to have all the advantages of EP, yet mitigates the downfalls by producing no ozone. If this – or other state-of-the-art and developmental systems and technologies that are currently being investigated at the NASA Glenn Research Center – can be developed, a better alternative to the current method of filtration can be obtained.
Primary Goals of the Research Associate
The primary goal of my project will be to test an electro-spray filter by implementing it within the GRC’s lunar dust filtration testing facility. The lunar dust filtration testing facility is a 6 inch diameter by 8 foot long closed flow filtration loop which also includes internal particle generation, optical particle counters, particle image velocimetry, and flow and pressure sensors. In addition, optical and SEM microscopy is available for analysis of filter test samples. Under the guidance of Juan Agui and several research associates, multiple tests have previously been performed using this testing facility, including the use of various filters.
Currently, an electro-spray filter has been provided by an outside contractor and has been designed to fit within the structure of the testing facility. In order to understand any alterations that must be made to the electro-spray filtration system and to confirm its effectiveness, initial testing to the electro-spray filter unconnected to the testing facility needs to be conducted. For example, any leaks in the filter must be sealed in order to achieve similar results to those obtained with different, previously tested electro-spray filters. Also, table-top tests can be used to demonstrate droplet breakup and ejection performance and to determine the droplet generation rate.
Once these modifications are completed, tests can begin with the electro-spray filter connected to the testing facility. The eventual goal is to test the filtration system under very controlled conditions and compare the results to the contractor’s data. In particular, the filter system will be tested for:
- Filtration performance and efficiency with lunar simulant dust
- The effective handling and operation of safe materials
- Level of consumable materials penalties
- Pressure drop compared to conventional filtration systems
Further alterations to the testing facility hoped to be made in order to be able to perform tests at pressures similar to those found in a Martian atmosphere. [j2]
Secondary Goals of the Research Associate
Besides working on an electro-spray filtrations project, I will also be performing supporting tasks towards the completion of several other projects including the modification of a flight rig set to fly an Indexing Media Filtration System and the testing of the NASA Centaur digger hardware.
The test rig for the Indexing Media Filtration System will support the investigation of filtration systems in a zero g environment while testing of NASA’s Centaur digger will aid in future explorations of celestial bodies.