Coagulation

Question 1

What is the collision surface of a particle with diameter dp?

Answer 1

2dp for a spherical particle.

Question 2

When does the coagulation coefficient depend on particle size?

Answer 2

When the slip correction factor is applicable, i.e. outside of the continuum regime (transition and free molecular)

Question 3

How is the rate of coagulation related to concentration, N?

Answer 3

K is proportional to N^2. i.e. rapid at high N but slows as N is reduced due to coagulation.

Question 4

What is the equation for the rate of condensation (F)?

Answer 4

F = 2*D*(Cinf - Cd)*π*dp
where D = vapour diffusivity
Cinf = bulk vapour conc.
Cd = equilibrium concentration at droplet surface
dp = particle diameter

Question 5

Equation governing growth due to condensation?

Answer 5

ddp/dt = 4*D*(Cinf - Cd)*MW/(ρp *dp)
D = vapour diffusivity
Cinf = bulk vapour conc.
Cd = equilibrium concentration at droplet surface
dp = particle diameter
MW = molecular weight
ρp = particle density

Question 6

When does condensation growth rate depend on size?

Answer 6

Continuum and transition regime.

Question 7

When are the Fuchs, Kelvin and temperature corrections important for estimating particle evaporation?

Answer 7

Fuchs: important for small particles
Kelvin: important for small particles
Temperature: large particles

Question 8

When normalized for size, how do the self preserving size distributions for the continuum, transition and free molecular regimes compare?

Answer 8

Free molecular is quite wide, transition and continuum are similar but transition is slightly narrower.