Learning Forum

[Masooma_Qizilbash12]

hello friends,

i am simulating particle size distribution via discrete model population balance model and i want to assign population balance boundary condition in all bins but when i open the boundary conditions task page the multiphase option is off how can i enable it. From thep hase dropdown list i selected secondary phase . please help me thank you very much

masooma 

[Rob]

Looks OK, can you double check the settings? 

[Masooma_Qizilbash12]

Hi Rob,

Thank you for your answer.... i have a simple geometry not a complex one... a turrax agitator in a mixing tank having PVA solution 1% and adding through syringe the PEI 33%...i want to determine particle size distribution of PEI. i am trying different settings to see which model ran in less time can you guide me basic infromation that what kind of settings are you talking about to activate the multiphase in the boundary task page .... kindly help.

i shall be thankful to you 

regards,

Masooma 

 

[Rob]

I switched on Eulerian multiphase, applied and then turned on the Discrete PBM option, applied and checked the phase-2 diameter was "sauter-mean". The phase option was then available as per the image. Check whether your model is steady/transient in case that is a factor. 

[Masooma_Qizilbash12]

Hi Rob,

I am also using the same settings but multiphase option is still off. here is the picture of what i am getting .It would be a great help if you solve my problem. i am stuck in this point. Also please guide that is it necessary to have inlets?because in this model i am not having any BC named as inlet.

thank you so much for the coordination.

kind regards,

masooma.

 

 

[Masooma_Qizilbash12]

my case is transient. speed of the impeller is 5000 rpm.

[Rob]

That's a wall so there is no phase setting. 

If there are no flow boundaries you need to set the population balance via the Phase panel and then Initialise the initial size distribution. If there is no flow inlet you don't have any mass to add so it can't have a size distribution. 

Have you run the model single and/or multiphase without the PBM set? It's not a model I'd recommend for a new user, and is a model I treat with some caution. 

[Masooma_Qizilbash12]

ok...

yes Rob i ran the model without using PBM but my focus was just to see weather case runs or not and it ran properly so i enable the population balance model put in values but facing problem in setting population balance boundary conditions step.

so Rob please guide me what do you mean by phase panel? ... should i remodel starting from geometry and introduce inlets?

thank you for guidance

regards

masooma

[Rob]

You don't have inlets so there is no boundary to set for the initial bucket size. However, if you look at the initialisation and patch options you'll find you can set those. The size distribution when then evolve from those initial settings. 

[Masooma_Qizilbash12]

Rob 

you mean i dont need to set the population balance boundary conditions... 

please help

thank you

regards,

masooma

 

[Rob]

As you have no flow boundaries there are no population balance bc's to set. The model is reliant on you setting sensible initial conditions for the initial size distribution. 

[Masooma_Qizilbash12]

ok Rob,

Thank you so much .

Rob i want to ask some more questions regarding the setting should I use this same thread or i should find another relevant thread to have help from ansys forum...like my questions are:

1. I used Eulerian phase discrete PBM, k-épsilon when i run the program it is taking too long to converge and residual of bin-fractions don´t converge under 1e+2 what does that mean i used the following setting 
2. 
3. 
4. I shall be extremely thankful for the help

kind regards,

Masooma 

[Rob]

Courant Number may be a little optimistic, but the system is very likely showing some transient behaviour. How do the monitors look? 

[Masooma_Qizilbash12]

yes, I used the transient settings because the speed of the impeller is 5000 RPM. Just changed the settings a little by putting turbulent Kinetic Energy and dissipation rate from 0.9 to 0.5 and pressure =1,  Bin 0,1,2,3,4,5. All bins have 0 value except for bin 3. bin 3=1. The trend is the same here in the monitors. Also attached is the population balance model settings used.

thank you for the help

regards,

masooma.

[Rob]

5000rpm? In a mixer? What tip speed is that giving you? The results look like you've chopped everything up so that it's in the smallest bin. 

[Masooma_Qizilbash12]

yes 5000. It is an open beaker having PVA and there is a turrax agitator inside attached is the picture of my experimental setup. I varied the speed of the agitator. and added PEI with the help of syninge at 0.333 ml/min.

I want to determine the particle sizes of PEI.

I didn't calculated TSR.

what settings should i use ?

i shall be thankful for your time 

kind regards,

Masooma