Eulerian phase gas diameter
 

Why does Fluent need a particle diameter for a gaseous Eulerian phase. If it does not require one for air if air is primary phase, why is a particle diameter needed if I have air or any other gas as the secondary phase.

The primary phase is the continuous phase - it doesn't need a diameter because it is a continuum.

The secondary phase is a discrete phase - it consists of non-connected particulate entities, whether these are droplets, bubbles or particles - these entities have a certain diameter. This diameter needs to be supplied to calculate interphase forces, such as drag.

Best,
Cees

So, if the secondary phase was water vapor, how do i know what the diameter is. Should i just randomly put on a very very small diameter for a 'gas type' secondary phase?

Thanks

hwet,
it depends on your problem.

if you're modelling gas bubbles in a liquid, then the vapour is the secondary phase.
if you're modelling say, steam condensation, then the liquid is the secondary phase, because you have droplets of liquid suspended in a gas.