Learning Forum

[Juwelmojumder1]

Hi, I'm trying to use the PBM in my nanofluid flow simulation. My fluid flow behaviour is laminar. However, after the complete setup, I run, but the following thread has been appeared. Turbulence must be turned on for population balance modelsnMy enquiry is, does PBM only works in turbulence model ? nThanksnJuwel

[Rob]

A quick check suggests laminar is OK. Check what else you have set in the model. n

[RK]

Hello juwel, nWhat kind of Aggregation model are you using? n

[Juwelmojumder1]

Hello juwel, What kind of Aggregation model are you using?https://forum.ansys.com/discussion/comment/110585#Comment_110585

Hi Rk, nThanks in advance. nUnder the PBM's discrete method, I have only considered the Luo Aggregation Kernel model, as I am expecting some particle's aggregation during flowing. n

[Juwelmojumder1]

A quick check suggests laminar is OK. Check what else you have set in the model.https://forum.ansys.com/discussion/comment/110583#Comment_110583

Hi Rob, nYou are right. I also expected that the model should work for both laminar and turbulent flow. nThe setup are, I used the mixture multiphase model, while only two phases are acting. I have set total of 10bins, the minimum particle diameter as 100nm. The sum of volume fractions in each bin is equal of total volume fraction. However, I have no idea about calculating surface tension, so I kept this as default. nI don’t know what I have been doing wrong.Thanksn

[Rob]

Did you set laminar before or after turning on the Mixture Model and PBM? n

[Juwelmojumder1]

Did you set laminar before or after turning on the Mixture Model and PBM?https://forum.ansys.com/discussion/comment/110608#Comment_110608

Hi Rob,nBy default laminar set up is given even before turning on any of the models. Then, I simply turned on the mixture model first, and the necessary input is given for this model. Then switched to PBM model using TUI command. But after setting the value and models tried for run the simulation. Surprisingly, it requests for turning on the turbulence model. nThanksnJuweln

[Surya Deb]

Hello Juwel, nAggregation and Breakage Kernels can depend on the local liquid-phase turbulent dissipation. You will note in the link below (Equations 19-22 and 19-52), that the breakage and aggregation models, respectively are dependent of epsilon (turbulent dissipation). nAlso check the note just after Equation (19-48) from the link below. nImportant: The breakage and aggregation kernels depend on the nature of the physical application. For example, in gas-liquid dispersion, the kernels are functions of the local liquid-phase turbulent dissipation.nhttps://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_th/flu_popbal_sec_popbal_eqns.html%23flu_popbal_luo_modelnAlthough I was not able to find specifically in the Documentation that Turbulence is needed, but I think the above dependence on turbulence dissipation might be one reason you see the warning. nRegards,nSDnn

[Juwelmojumder1]

Dear SD,nThanks a lot for your time. Yes, you right that applying breakage /aggregation kernels is more feasible in turbulent condition. I'm not sure about Rob's check on implying laminar in PBM. nCould you please clarify a few more set-ups of Discrete method available in PBM?nSuch as the number of bins, and the way of distribution of volume fraction in each bin; this has to manually put in B.C set up (secondary phase>Multi-phase>boundary value). For instance, I considered a volume fraction of 0.0001 (0.01% vol.), which I equally distributed in 10 bins. I'm not sure about the process I maintained. nVolume fraction equations are not converged even in very low convergence criteria (0.001) set-up. nShould I keep the default value of surface tension when the Luo aggregation kernel is activated? nnThanksnJuweln

[Rob]

If you're using the TUI that's an older version of the code, please update to 2021R1. n