mass transfer coefficient for boundary condition
 

I'm struggling with the boundary condition for the oxygen mass transfer in a model for char particle combustion.

There is a boundary condition at the edge of the particle of the form:
D*(dYO2/dr) = km*[YO2,surroundings-YO2,edge]

In which D is the diffusion coefficient, km the mass transfer coefficient and YO2 the oxygen mass fraction.


I wonder how you calculate the mass transfer coefficient and what the value of this mass transfer coefficient is approximately.

I ask this because in my model, the reaction is limited due to a lack of oxygen. The amount of oxygen is that low, since the mass transfer of oxygen through the boundary is very limited. I use a mass transfer coefficient of 0.04 [m/sec] for a spherical particle with a diameter of 1 mm.

I hope you can answer my question or knows where I can find more information.

Thanks!
Niek