Learning Forum

[ENeo178]

Hi everyone,

I am trying to simulate particles aggregation and deposition using combined CFD-PBM approach. PBM stands for Population Balance Model. However, the deposition function is not found amongst the kernels under phenomena. Does anybody know how to solve for particle deposition using PBM?

[DrAmine]

There are "finialized" PBM UDF macros to describe growth,  nucleation and intra-processes like breakage and coalescence. If you need to model any other process then you probably need to use general purpose functions. 

How is the "deposition" described? 

[ENeo178]

Hello,

The deposition mechanism describes the settling and ahering of particles onto the boundary walls. In other words, it is the zero value return probability density function (PDF) of particles breaking from volume V' to a particle of volume V. For binary breakage,  is symmetric about , (Ansys Fluent Population Balance Module), however, we aim to return this value to zero.

[DrAmine]

 

If it is realizable via a Breakup UDF why not using it? 

From physical point of view why not relying on interfacial momentum and buyoancy for settling?

 

(Your pictures are not clear).

 

[ENeo178]

Hi,

From a physical point of view, deposition occur when particles exit the flow and adhere onto a boundary surface. One way to predict such outcome is to return a zero value for the breakage PDF. And since there is no deposition kernel in ANSYS Fluent Module, I want to ask if there are other methods available using Population balance model to model particles deposition.

[DrAmine]

No there is no dedicated kernel. To be honest deposition on a wall is just due to settling (so buyoancy and drag will affect that) so I still do not understand what you want to achieve. Perhaps you add a reference.

[ENeo178]

Hi,

Okay DrAmine. However, the objective of my study is to model deposition of hydrate particles using a population balance approach. Do you mean the only way to model deposition is through buyoancy and drag?

[DrAmine]

You can still use the PBE approach and settling will be due to interfacial momentum and buyoancy. If you want to incoporate a physic/kernel which I never "used" before and that kernel can be interpreted as breakage kernel then you can use the PBE Macros to do that or just use generaic DEFINE_SOURCE Macros to achieve that: I am not sure what is better as you are here the expert and you know the theorical background behind this "deposition".

[DrAmine]

Please stop relying on non official help websites and use the official website. From there try to compile the example of breakage kernel and report back.

[ENeo178]

Okay will do. Thanks again DrAmine. 

[ENeo178]

I will write back tomorrow. 

[DrAmine]

Great!

[ENeo178]

Hello DrAmine,

You mentioned that deposition on the wall is due to settling and drag efffect, and I have run some simulations to model this effect, but the problem is, the number of particles is not decreasing as a result of settling and drag, and the mass yet still conserved. I have combined PBM to model both the aggreagtion and depostion of sized particles. The objective is for the particles to exit the flow, attach themselves onto the walls and come to inertia. You also mentioned that there is no deposition kernel yet on fluent, but can a UDF mechanism be compiled?

 

[DrAmine]

The volume fraction of the secondar phase should decrease if you a sink source for that. If you do not have that then I expect the mass to be conserved and the number not to change. If you want to eliminate any particles settling at the wall or theier deposition at the wall (and then change the PSD) then you need to write some UDF to model the sink for volume fraction, as well as to model the PSD Size Change you want to achieve.

[ENeo178]

Thank you for your assistance.