Hi, just a quick question. I am modelling a bubble column using a descretized population balance method.

In order to compute the gaz liquid interaction i have to calculate a new diameter which is gonna depend on the distribution size of the bubble in the each cells.

Many authors propose to use the sauter mean diameter but my some quick calculations i have done show that the mean diameter give me a better results in term of hydrodynamics and also calculation of the bubble surace area needed for transfert.

Can anyone help me to undertsand the motivations of the authors who propose to use the sauter diameter ?

if the answer needs a to be discussed just leave your number on my e-mail box, I would be happy to make the call.

Hope someone will help me, Thomas

The Sauter mean diameter is the equivalent spherical diameter by surface area per unit volume to the full distribution. In other words the particle diameter that has the same specific surface (area per volume) as that of the full distribution. It is always skewed towards the finer end of the distribution.

The SMD should be giving you the proper surface area for phase transport. Are you sure you're calculating it correctly?

Jeff

Thanks for your answer, Yes I am sure to calculate the right Sauter mean diameter. But i am still have a doubt on what you say ''The SMD should be giving you the proper surface area for phase transport''. Let say that the main momemtum exchange between gas & liquid is the drag force. The formulation of the drag force is not based on the surface area but the projected area in the flow direction. The calculation of the projected area using the SMD seems to be overestimated while a simple mean diameter (based on density number) seems to give better results.

Could you let me know your feeling about it ! Thanks Thomas

[rajasekaran.raam]

Hi Thomas,
Since you are solving population balance, i am having some questions.
In population balance model, bubble diameter fraction(bin size fraction) at gas inlet is to be specified as boundary condition.Bubble diameter at inlet can be calculated using buoyancy and surface tension force balance.
bubble diameter at gas outlet(pressure outlet or top of bubble column) is zero because in gas domain,bubbles will not be there.
so in the domain between liquid surface and outlet(usually in bubble column,some distance will be maintained to avoid liquid leaving column),how bubble diameter will be calculated in this region?
How to get contour plot sauter mean diamter in fluent? whether it is inbuilt function or we have to write UDF?

Thanks in advance.

Originally Posted by thomas
;68882

Hi, just a quick question. I am modelling a bubble column using a descretized population balance method.

In order to compute the gaz liquid interaction i have to calculate a new diameter which is gonna depend on the distribution size of the bubble in the each cells.

Many authors propose to use the sauter mean diameter but my some quick calculations i have done show that the mean diameter give me a better results in term of hydrodynamics and also calculation of the bubble surace area needed for transfert.

Can anyone help me to undertsand the motivations of the authors who propose to use the sauter diameter ?

if the answer needs a to be discussed just leave your number on my e-mail box, I would be happy to make the call.

Hope someone will help me, Thomas