# Is stoke's number same as inertial impaction parameter?

1. Dec 2, 2007

### jay234

Is stoke's number same as inertial impaction parameter??

thx a lot

2. Dec 3, 2007

### Astronuc

Staff Emeritus
Welcome to PF Jay. Please do not multi-post in the forums.

K. Su and Shi-Chune Yao, Numerical Studies Of Sprays Impacting Normally On An Infinite Plate,
Atomization and Sprays, Volume 9, Issue 4, 1999
http://www.edata-center.com/journals/6a7c7e10642258cc,05bf4e953090d651,19ab9f946f278b77.html

An inertial impaction parameter K for impacting sprays is defined in terms of the momentum conservation to reveal the relation between spray transportation and aerodynamic conditions.

http://www.epa.gov/NCEA/pdfs/partmatt/April1996/app_10a.pdf
This document defines inertial impact parameter as the product dae2 $\dot{V}$, where dae is the aerodynamic particle diameter (in µm), and $\dot{V}$ is the volumetric flow rate (in cm3/s).

More generally the inertial impact parameter is defined by

$$\psi\,=\,C_f{\rho_p}v(d_p)^2/18{d_d}\mu$$, where

$C_f$ = Cunningham correction factor,
$\rho_d$ = particle density, 1/ft{sup]3[/sup]
$v$ = particle velocity, ft/s
$d_p$ = particle diameter,ft
$d_d$ = droplet diameter, ft
$\mu$ = gas viscosity, lb/ft-s

Ref: Handbook of Environmental Engineering Calculations
C. C. Lee, Shun Dar Lin, McGraw-Hill Professional, 2000

This form relates to the use of the inertial impact parameter in the Johnstone equation which describes the collection efficiency of a liquid Venturi scrubber.

It appears to be different from the Stokes number
http://en.wikipedia.org/wiki/Stokes_number

3. Dec 3, 2007

### jay234

sorry for making 2 thread b4, cos after i created thread in here, i found that it should be more suitable for the thread created in the other forum and i am unable to delete the thread myself

I ve read some articles and found that ppl used either of the equation to describe the same thing. (anderson cascade impactor)
I just wanna know whats the difference between or how they are derived from each other.

here is my question come from

as both of the equation is similar, ive tried to proved that inertial impaction parameter is same as stoke number
i converted the particle physical diameter dp in equation on LHS from the pic attached into aerodyanmic diameter, da.
But still, the equation is not the same as on RHS.

or did i missed out sth
im so confused

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Last edited: Dec 3, 2007