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Acoustic Agglomeration to aid fine aerosol particulate collection

Description:

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber

 

OBJECTIVE: Organically develop or modify commercially available electroacoustic agglomerator for air pretreatment in an aerosol collection system similar to the

Radionuclide Airborne Particulate Sampler Analyzer (RASA).

 

DESCRIPTION: DTRA supports the Comprehensive Nuclear Test Ban Treaty (CTBT) via the Nuclear Arms Control Technologies Program (NACT).  The CTBT is strategically important to the United States (US) by banning nuclear testing for participating countries and allowing US access to 337 stations and laboratories worldwide. The NACT supports the US contribution to the CTBT with 37 stations and laboratories.  Part of the CTBT monitoring regimen is radionuclide aerosol (RN) monitoring. The US accomplishes its CTBT RN monitoring via a system called the RASA. The required collection efficiency and Minimum Detectable Concentration (MDC) for RN collection as specified in the CTBT operational manuals are:

For filter: ≥ 80% at Ø = 0.2 μm

Globalᵈ: ≥ 60% at Ø = 10 μm

MDC  ≤ 10 to 30 Bq/m3 for Ba-140

 

The current RASA system minimally meets these requirements.

 

The efficiency of particle capture on a filter is related to the intake air velocity, particle size, filter pore size and other variables such as humidity, wind speed, duct shape, etc.. A filter’s efficiency is rated as a Minimum Efficiency Reporting Value (MERV), which measures a filter's ability to capture particles between 0.3 and 10 microns (µm). Most Penetrating Particle Size (MPPS) refers to the size of the particles that most easily pass through a filter. A high-efficiency particulate air (HEPA) filter can remove 99.97% of particles down to 0.3 Micron. An MPPS of 0.2 to 0.3 microns is difficult; many filters are effective at capturing particles smaller or larger than this, but 0.2 to 0.3 micron particles regularly gets by basic filtration. Using 0.3 microns as the MPPS measures the worst-case efficacy of the filter.

 

The fact that collection efficiency of 0.2 to 0.3 microns particles is worse than for smaller particles might seem counterintuitive, however the combined effect of the various filter collection mechanisms (interception, intertial effect, diffusion effect, gravitational effect, and electrostatic effect) as they relate to particles size causes a dip in the collection efficiency in the 0.2 to 0.3 micron

 

Ultrasonic sound can cause submicron particles to agglomerate and larger particles to disassociate. Literature varies with respect to the effectiveness; one study  showed that mean particle size increased from sub-micron to five micron, and another study  reduced the number concentration of micron &

sub-micron by seventy and thirty percent respectively. Ultrasonic agglomeration studies, might not be comparable as the number and positioning of sound transducers, sound energy and frequency, shape and turbulence of the collection piping and chamber, humidity, etc./, varied from study to study. These

variables have an effect on agglomeration effectiveness, however, in every study ultrasonic agglomeration increases particle size distribution from sub-micron to micron or greater. Collection efficiency greatly increases when particle size becomes 3 micron or greater. Furthermore, when

combined with other collection mechanisms such as electrostatic charging  or the addition of humidity or water droplets  the collection efficiency may be substantially increased from any mechanisms acting alone. Successful application of this technology to the future RASA 2.0 system would allow for greater collection efficiency, reducing the Minimum Detectable Concentration (MDC) of targeted Radionuclides and improving the detection likelihood of a clandestine nuclear test.

 

PHASE I: Conduct extensive document research to determine state of the art with respect to aerosol collection via acoustic agglomeration aided with electrostatic charging and agglomerates such as water droplets. Design and model a system that could interface with the RASA 2.0 intake system for particle collection. Conduct trade-off studies for the system.

 

PHASE II: Based on the knowledge and determination of feasibility obtained in Phase I, construct a working prototype of the system designed in Phase I.

 

PHASE III DUAL USE APPLICATIONS: Provision of an aerosol agglomeration system that could interface with other aerosol collection or air purification systems such as the Senya Snow White.

 

REFERENCES:

  1. de Sarabia E, Gallego-JuaÂrez JA. Ultrasonic agglomeration of micron aerosols understanding wave conditions. J Sound Vib. 1986; 110: 413±427. https://doi.org/10.1016/S0022-460X(86)80144-4 
  2. 99/02815 Pilot scale acoustic preconditioning of coal combustion fumes to enhance electrostatic precipitator performance. Fuel and Energy Abstracts (1999, July). , 40(4), 293.https://doi.org/10.1016/S0140-6701(99)98584-3
  3.   Ng BF, Xiong JW, Wan MP (2017) Application of acoustic agglomeration to enhance air filtration efficiency in air-conditioning and mechanical ventilation (ACMV) systems. Table 2 Summary of relevant experimental works in acoustic agglomeration with reported performances.https://journals.plos.org/plosone/article/figure?id=10.1371/journal.pone.0178851.t002
  4. Daolai CHENG, Meng CAI, Fang ZHAO, Huimin Hu, Junfeng YAO (2015), The Study on the Removal of Ultrafine Particles, International Conference on Advances in Energy and Environmental Science (ICAEES 2015).https://doi.org/10.2991/icaees-15.2015.120
  5. Zhongyang Luo, Hao Chen, Tao Wang, Dong Zhou, Mengshi Lu, Mingchun He, Mengxiang Fang, Kefa Cen, Agglomeration and capture of fine particles in the coupling effect of pulsed corona discharge and acoustic wave enhanced by spray droplets, Powder Technology,Volume 312, 2017, Pages 21-28, ISSN 0032-5910,https://doi.org/10.1016/j.powtec.2017.02.025
  6. Li, F.; Cao, H.; Jia, Y.; Guo,Y.; Qiu, J. Interaction between Strong SoundWaves and Aerosol Droplets: Numerical Simulation. Water 2022,14, 1661.https://doi.org/10.3390/w14101661

 

KEYWORDS: particulate, aerosol, radionuclide, agglomeration

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