[apisy1]

hello need help urgent
how to plot size distribution curve and breakage rate (1/s) using PBE in fluent ansys?

[apisy1]

hello need help..how to plot size distribution curve and breakage rate (1/s) using PBE in fluent ansys?

[apisy1]

Originally Posted by chittipo

Dear Members,

If you have any specific questions on PBM implementation please post here. I will try to answer them, as I gained some experience in it.

on
- Existing module (or)
- Implementation through UDF

how to plot size distribution curve and breakage rate (1/s) using PBE in fluent ansys?

[masoud.ravan]

Originally Posted by masoud.ravan

Hi everyone

I want to implement Luo breakup frequency by UDF (DEFINE_PB_BREAK_UP_FREQ(name, cell, thread, d_1))but there is no way to calculate number density of ith size bin because we do not know that the d_1 that has been passed to UDF belongs to which size bin. If we find this, we can calculate number density of ith size bin by the relationship between number density and size fraction (C_PB_DISCI).

I would be grateful if you can help me.

I have answered my question in above posts

[apisy1]

Originally Posted by masoud.ravan

I have answered my question in above posts

hi masoud, thanks for replying
there's something that i am still confused of.. eventhough just by turning on the phenomena like aggregation and breakage rate in fluent PBE did not automatically solve it or still need UDF?

my plan is i want to plot a graph for droplet size distribution and breakage rate vs diameter.

I really need help.

[masoud.ravan]

Originally Posted by apisy1

hi masoud, thanks for replying
there's something that i am still confused of.. eventhough just by turning on the phenomena like aggregation and breakage rate in fluent PBE did not automatically solve it or still need UDF?

my plan is i want to plot a graph for droplet size distribution and breakage rate vs diameter.

I really need help.

If you turn on the phenomena and choose one of the FLUENT models, you don't need to write UDF

In order to plot size distribution, follow these steps:
postprocessing-model specific-population balance-number density...
Report type(volume or surface average)
plot type(curve)
Fields(Discrete number denstity)

[apisy1]

Originally Posted by masoud.ravan

If you turn on the phenomena and choose one of the FLUENT models, you don't need to write UDF

In order to plot size distribution, follow these steps:
postprocessing-model specific-population balance-number density...
Report type(volume or surface average)
plot type(curve)
Fields(Discrete number denstity)

thanks again.
this part i found it already. i am using pbe qmom. but regarding the upper diameter limit. how do you choose the best one? the default is 1.5.

and for breakage rate can u tell me where can i plot it in fluent ?

[nhendre]

Originally Posted by masoud.ravan

This part is for finding the index of bin fraction that bubble with size d_1 belongs to.
Here is the other way:
for example, if we have 5 bins with diameters:
Bin-0: 0.0038097
Bin-1: 0.0024
Bin-2: 0.0015119053
Bin-3: 0.00095244
Bin-4: 0.0006
we could find the index and then size fraction by:
if(d<.0007)
{
index=4;
}
else if(d<.001)
{
index=3;
}
else if(d<.002)
{
index=2;
}
else if(d<.003)
{
index=1;
}
else if(d<.004)
{
index=0;
}

size_fraction=C_PB_DISCI(cell, thread, index);

I have written the same way in the udf. But there is showing a parse error. You may check the udf attached herewith.

[apisy1]

Originally Posted by nhendre

I have written the same way in the udf. But there is showing a parse error. You may check the udf attached herewith.

thanks again. i will try it again.

[apisy1]

Originally Posted by nhendre

I have written the same way in the udf. But there is showing a parse error. You may check the udf attached herewith.

hi i try to compile the udf in fluent 2d double precision. but it cannot load.

[apisy1]

Originally Posted by masoud.ravan

If you turn on the phenomena and choose one of the FLUENT models, you don't need to write UDF

In order to plot size distribution, follow these steps:
postprocessing-model specific-population balance-number density...
Report type(volume or surface average)
plot type(curve)
Fields(Discrete number denstity)

hello regarding plotting the plot size distribution. i am choosing the surface average- length number density.
for this one the length number density has high values. the x-axis i put in log scale.
for the length number density if i want to convert it to volume as part of droplet size distribution curve do i need to convert again or what? sorry i am still poor in this area.
by the way i choose pbe-qmom then the size interval i set between 0.1 to 1e-07, at secondary phase i set sautermean diaemeter

looking forward from your reply soon.

[nhendre]

Originally Posted by raju.vadlakonda

Hiii Chittipo,

I am using "Prince and Blanch(1990) coalescence model and Luo & Svendsen(1996) break up model in simulation.

I unable to write UDF terms for number density for bubble.Is there any terms to represent number density ??

Thank you,

Dear Raju,
I am also trying the same. HAve you got the solution for your UDF in getting number density.
Kindly reply.

[nhendre]

Originally Posted by raju.vadlakonda

Hiii Chittipo,

I am using "Prince and Blanch(1990) coalescence model and Luo & Svendsen(1996) break up model in simulation.

I unable to write UDF terms for number density for bubble.Is there any terms to represent number density ??

Thank you,

Did you get the solution for defining ni and nj?

[apisy1]

hello can somebody please guide me how to plot the breakage rates in fluent?

[nhendre]

Originally Posted by apisy1

hello can somebody please guide me how to plot the breakage rates in fluent?

Have you written udf for coalescence rate? Previously, there you had few queries regarding ni and nj.

[masoud.ravan]

Dear Members,
Do you know why FLUENT uses the Hagesather or Ramkrishna method for breakage formulation? Couldn't we use the Luo formulation directly?
Thanks in Advance,

[shaham]

Thank you for mentioning the important point. Yes for the models that only have Ni and Nj in the model you do not need to find these values. but there are some models that either are defined independent from NI NJ or some other cases. As I remember I was trying a few cases of coalescence and breakage models just to check the results I faced that type of models. So still it might be needed.

I first used a case file, then found the for loop a better idea. I wanted to make the code read the bin values from a file! but I left PBM for DPM later and threw PBM into the garbage

Regarding your question for the bins, I remember in the help it mentioned that for every interval it uses the lower boundary for calculation. Basically, for a bins 1mm,2mm,3mm, the code add any particle with diameter of 1-2mm for bin 1mm. You can check it in the help if I am right. In that case I think PBM uses the lower value of each bin for any other calculations

Originally Posted by obscureed

Hi All,

I think Shaham has pointed out something important: the UDF is intended to return the value of the kernel (which is effectively a rate constant), not the aggregation rate. (This is fairly clear in the documentation, and you have to ignore the fact that the UDF type's name ends in "_RATE".)

So, you do not need the factor of "*n1*n2". You do not need to look up which intervals d_1 and d_2 fall into. In fact, your UDF should not need to know anything about the size intervals -- it is defining the size behaviour of the aggregation phenomenon. You definitely should not need to hard-code the bin sizes into your UDF (either by a fixed array "double dbin[11]={..." or nested inside lots of "if" statements) -- this would be difficult to maintain.

OK, this structure makes some assumptions about the nature of the aggregation phenomenon -- for example, it assumes that there are no effects that are second-order in concentration, etc. Within those assumptions, this is a much cleaner way to define the UDF interface.

By the way, for the sake of my sanity, please do not use two different approximations to pi -- you should find that M_PI will work (without the need for any extra #include statements).

I have to admit that I once tried to reconstruct the fine detail of how Fluent's discrete-PB model treats size distributions: exactly what mean size is used inside each interval? does it assume constant length-based number density, or constant volume-based number density, or some other approximation of the distribution inside each interval? These are very small details, but I wanted to get them right. I did not finish this in the time available. If you make any solid conclusions about what Fluent is doing under the hood, please post them here.

Good luck!
Ed

[shaham]

1) I learned C in fluent, so that's the only way I found to compare two real values (convert them to integers and then compare)

2) What I wrote was for breakage I think. For coalescence you can get the bin number for d2 by adding another if-statement in the loop for d2

You are welcome

Originally Posted by nhendre

Dear Shaham,
1) Can you please explain the loop:
'if (ROUND(1e10*d_1)==ROUND(1e10*dbin[i]))'
2) Also is it required to write second 'for' loop for calculating number density of second particle?
Thanks

[nhendre]

Originally Posted by masoud.ravan

Dear Members,
Do you know why FLUENT uses the Hagesather or Ramkrishna method for breakage formulation? Couldn't we use the Luo formulation directly?
Thanks in Advance,

We can choose any one of them. The point is Hagesather formulation requires minimum number of integral points and lower computational power. The accuracy is also comparable with that of Ramakrishna formulation.

[masoud.ravan]

Originally Posted by nhendre

We can choose any one of them. The point is Hagesather formulation requires minimum number of integral points and lower computational power. The accuracy is also comparable with that of Ramakrishna formulation.

Thanks,
but my question is why should we choose one of them?
Are they two methods of discretization of PBM or another thing..?