modeling iso kinetic

8/9/2019 Modeling Iso Kinetic

1/13

Comparison ofIsokinetic Stack Sampler Models

Under a Variety of Sampling

Conditions

S. A. COLBY

May 2009


2/13

Washington State Radiation Protection Code Requires

Radionuclide Potential Emissions Meet Applicable TechnologyStandards.

Includes the ANSI N13.1 Sampling and Monitoring Releases ofAirborne Radioactive Substances from Stacks.

ANSI N13.1 Requires Modeling of Stack Sampling Performance.

-- Which is the subject of this paper --

S. A. COLBY

May 2009

The Big Picture


3/13

Models Stack Sampling Variations

1. Aerosol Particle Size

2. Turbulent Flow

3. Variance Between a Stack and a Samplers Flow Velocity

(i.e., Anisokinetic Conditions)

S. A. COLBY

May 2009


4/13

Compares Two Isokinetic Sampler Models

1. DEPO Freeware by McFarland et al., 2001a.

2. Handbook Aerosol Sampling; Science, Standards, Instrumentation,

and Applications, by Vincent et al., 2007.

S. A. COLBY

May 2009


5/13

Isokinetic Sampler Design

7.5 mm

LT = 300 mm

Stack Velocity (VT)= 10 m/s

dT =

Particle Diameter (dP)= 10E-6 m

Gravity (g)= 9.8 m/s2

Air Density (pa)= 1.2E3 g/m3

Air Viscosity (ua)= 0.018 g/m-s

Particle Density (pp)= 1.0E6 g/m3

S. A. COLBY

May 2009


6/13

Vincent Isokinetic Equations(10 40 um Liquid Aerosol)

1. Settling Velocity (Vs):

Vs = gdp2pp

18ua

4. Gravitational Deposition (GT):GT = (LT/dT)(Vs/VT)

3. Reynolds Number (Re):

Re = VTdTpa

ua

2. Stokes Number (ST):

ST = dp2ppVT

18uadT

5. Empirical Dimensional Argument (KT):

KT = ST0.5

GT0.5

Re

0.25

6. Aerosol Penetration Through a Tube (PVincent):

PVincent = exp(-4.7KT0.75)

S. A. COLBY

May 2009


7/13

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

0 2 4 6 8 10 12 14 16 18 20

Aerosol Aerodynamic Diameter (micron)

AerosolPenetra

tion(%)

Vincent

DEPO

S. A. COLBY

May 2009

DEPO Model Predicts Substantially LessAerosol Penetration Compared to Vincent

Nre = 5000


8/13

40%

50%

60%

70%

80%

90%

100%

2500 3000 3500 4000 4500 5000 5500

Reynolds Number

AerosolPenetratio

n(%)

DEPO

Vincent

DEPO Predicts Substantial Aerosol LossDuring Turbulent Flow

S. A. COLBY

May 2009

dp = 10 um

Vs = 0.003


9/13

Vincent Anisokinetic Equations(25-70 um Silica Aerosol)

1. Stack Velocity/Sampler velocity (R):

R= V/Vs

2. Ratio Coefficient (G):

G = 2 + 0.62/R09R0.1

3. Impaction Efficiency (B):

B = 1-(1/(1+STG))

S. A. COLBY

May 2009

4. Anisotropic Aspiration through Nozzle (Aaspiration):

Aaspiration =B(R-1)+1

5. Aerosol Penetration Through a Nozzle & Tube (PVincent):

PVincent = (Aaspiration)(PVincent)


10/13

Models Predict Similar Affects FromAnisokinetic Sample Velocity Variations

S. A. COLBY

May 2009

Nre = 5000

40%

50%

60%

70%

80%

90%

100%

0 2 4 6 8 10 12 14 16 18 20

Aerosol Aerodynamic Diameter (micron)

AnisokineticAspiration

Efficiency

DEPO

Superisokinetic Ratio = 0.8

DEPO

Isokinetic

Ratio = 1.0

DEPO

Subisokinetic

Ratio = 1.2

Vincent

Subisokinetic

Ratio = 1.2

Vincent

Isokinetic

Ratio = 1.0

Vincent

SuperIsokinetic

Ratio = 0.8


11/13

S. A. COLBY

May 2009

Both Models Have Limitations

1. Liquid Particles vs. Solid Particles

2. Based on Quasi-Steady State

3. Large Model Extrapolations

4. Compounding Conservatism


12/13

Practical Considerations

1. Upstream Rust

- Settle In Sample Tube

2. Filter Paper Limited Flowrate- Size Limited to 47 mm


13/13

Recommend ANSI N13.1 RevisedTo Keep It Simple

S. A. COLBY

May 2009

For Example Provide Probe Design Standards:

1. 1/4 Inch Nozzle diameter.

3. Nozzle Reynolds Number 2000.5. 5R Transport Tube Bends.

7. Electrically Grounded.

8. Conducting Materials of Construction.

9. Periodic Inspection Criteria.

modeling iso kinetic

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