Brownian coagulation of polydisperse aerosols in the transition regime

In the event of a core disruptive accident in a sodium cooled fast reactor, the Reactor Containment Building (RCB) is bottled-up with coolant (sodium), fuel and fission product aerosols. The aerosols suspended in the closed environment undergo coagulation and gravitational settling. Sodium aerosols are generated by combustion, while fission product aerosols are generated by vaporization and condensation, with the resulting particles having two flow regimes. It is expected that the mass concentration of sodium aerosols is relatively high, on the order of a few g/m 3 , while that of the fuel and fission products is only a few mg/m 3 . Taking into account the concentration criteria, experiments are carried out by generating sodium aerosols (mono dispersed) with the concentration of 3.0 g/m 3 , and the deposition velocity over time is determined by mass measurements (concentration and flux). Similarly, non-radioactive species of SrO 2 aerosols are generated (mono dispersed) with a number concentration of 10 6 /cm 3 , and their deposition velocity over time is determined by number measurements (concentration and flux). The mass deposition velocity of sodium aerosols was found to be more than two orders of magnitude greater than the number deposition velocity of SrO 2 aerosols. As the SrO 2 aerosols are generated in the free molecular regime, the depletion pattern of the number concentration of suspended aerosols follows a process of simultaneous coagulation and settling. A theoretical formulation for the rate of depletion of the number concentration is developed, and the rate coefficients of coagulation and deposition velocity are determined from the theoretically fitted equation. The experimental and theoretical results are compared and found to be nearly same. The deposition velocity of sodium aerosols is used to predict the deposition time for the suspended aerosol mass concentration inside the RCB. The mass and number deposition velocities are determined by using a state of art Turn Table Instrument fabricated in our lab.

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“…In a confined environment, the decrease in total number concentration N over time t is given in Kim et al (2003) and Kim et al (2000):…”

Section: Assessment Of Simultaneous Coagulation and Settling For Sro mentioning

confidence: 99%

Investigation of Aerosol Mass and Number Deposition Velocity in a Closed Chamber

Misra

Subramanian

Kumar

et al. 2013

Aerosol Air Qual. Res.

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“…A similar model has also been used by Kim et al to investigate rate of diffusion deposition of particles 16 .…”

Section: Particle Loss Mechanismsmentioning

confidence: 99%

Application of bag sampling technique for particle size distribution measurements

2009

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Bag sampling techniques can be used to temporarily store an aerosol and therefore provide sufficient time to utilize sensitive but slow instrumental techniques for recording detailed particle size distributions. Laboratory based assessment of the method were conducted to examine size dependant deposition loss coefficients for aerosols held in Velostat TM bags conforming to a horizontal cylindrical geometry. Deposition losses of NaCl particles in the range of 10 nm to 160 nm were analysed in relation to the bag size, storage time, and sampling flow rate. Results of this study suggest that the bag sampling method is most useful for moderately short sampling periods of about 5 minutes.

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“…Some researchers also conducted experimental works of Brownian coagulation to validate the theory analysis (Wagner and Kerker 1977;Kim et al 2003Kim et al , 2006. Kim et al (2006) obtained the coagulation rate from the change in the total number concentration of polydisperse sodium chloride aerosols in a closed chamber at atmospheric pressure.…”

Section: Particle Coagulationmentioning

confidence: 99%

“…The distance where particle coagulation was apparent and the half-time, which is a crucial indicator in evaluating the degree of particle coagulation, was compared between the study and other researches. Most researchers have focused on particle coagulation in a steadystate environment in which particle dispersion did not occur (Park et al 2002;Kim et al 2003). However, the study examined particle coagulation during the process of dispersion, and a particle dispersion and a coagulation model were combined to determine how the two processes influenced each other.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of particle coagulation in an underground parking lot

Zhao

Kato

Zhao

2015

Environ Sci Pollut Res

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Particles in vehicle exhaust plumes in underground parking lots have adverse health effects due to the enclosed environment in which they are released and the temperature difference between the tailpipe and ambient environment; at the same time, particle coagulation might be obvious near the tailpipe in an underground parking lot. In the present study, airflow and temperature fields were calculated using the Realizable k-ε model, and the Eulerian particle transport model was selected in the numerical simulation of particle concentration dispersion. Polydisperse thermal coagulation due to Brownian collisions was employed to calculate the particle coagulation. The results show that particle coagulation rate and half-time were significant within 1 m from the tailpipe. The variations in the particle coagulation rate and half-time were similar, but their directions were opposite. Air exhaust time was nearly four times longer than averaged half-time and 40 times longer than minimum half-time. The peak particle diameter increased approximately 1.43 times due to coagulation. A double particle concentration at the tailpipe caused the fourfold rise in the particle coagulation rate in the distance ranging less than 1 m from the tailpipe. An increase in exhaust velocity at the tailpipe could shorten the obvious range of particle coagulation along the centerline of the tailpipe from 1 to 0.8 m in the study.

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Brownian coagulation of polydisperse aerosols in the transition regime

Cited by 54 publications

References 14 publications

Investigation of Aerosol Mass and Number Deposition Velocity in a Closed Chamber

Investigation of Aerosol Mass and Number Deposition Velocity in a Closed Chamber

Application of bag sampling technique for particle size distribution measurements

Characteristics of particle coagulation in an underground parking lot

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