DPM-Rosin Rammler- Spread Parameter

Fabio · May 1, 2009, 03:19

Hi all, from the data collected in an experiment i got a districution with 49 diameters, following the FLUENT manual i've tried to fit a RR distribution. All till the calculus of the various $Y_{d}$ , then i would like to get the spread parameter from anaverage, but for some of my diamters i got a negative value of that.
It's ok, or something went wrong during my fitting of the data?
Thank in advance.

visagant · March 15, 2012, 08:16

Hi have you solve this problem.I too get a negetive value .
Please confirm

ghost82 · March 15, 2012, 09:20

Hi,
if your data doesn't fit wel the R-R distribution you can set different injection points/surfaces, each one with its diameter.

Daniele

visagant · March 15, 2012, 09:51

im using surface injection with min and max diameter, But spread parameters i get a negetive value.
Im simulating a nozzle flow so i think point injection is not a correct choice.May be im wrong.

I have a problem with stream formation. its splitting to half in the midair. is it something to do with Particle parameters.

Fabio · March 15, 2012, 10:07

Hello negative values are correct in this fitting process, like the poster above said be sure that R-R is the distribution that fit your case.

About your problem it depends if are the particles beign splitted (breakup) that under some condition should be correct, or if you see an anomaly in their trajectories, unfortunately DPM involves a wide variety of parametres and for sure is not the more famous model of fluent thus is difficult find someone with a sound knowledge of it.

Fabio

visagant · March 15, 2012, 10:22

Thanks for the reply fabio and daniele

In my case particle dont split it think, its in micro meter range.
I have a multiphase(water and air) with mixture model(water+particles). And the fluid flow With k-e(RNG) trubulence.

http://imageshack.us/photo/my-images...jetstream.jpg/

I think im making a mistake in patching(volume fraction).
I tried everything still cant solve this problem.

If you can give me any advice it will be great.

Fabio · March 16, 2012, 04:35

Hello, thinkihg about your problem, i would check the forces acting on your particles, modeling a spray in the proper way is quite chellenging.
Forces due to secondary effects (like temperature gradients for example) are negligible or not in correlation with the velocity magnitude and also the size of your particle and thus disturbing the trajectories of your particles.

May 1, 2009, 03:19	DPM-Rosin Rammler- Spread Parameter	#1
Fabio Member Join Date: Mar 2009 Posts: 39 Rep Power: 17	Hi all, from the data collected in an experiment i got a districution with 49 diameters, following the FLUENT manual i've tried to fit a RR distribution. All till the calculus of the various $Y_{d}$ , then i would like to get the spread parameter from anaverage, but for some of my diamters i got a negative value of that. It's ok, or something went wrong during my fitting of the data? Thank in advance.

March 15, 2012, 10:07		#5
Fabio Member Join Date: Mar 2009 Posts: 39 Rep Power: 17	Hello negative values are correct in this fitting process, like the poster above said be sure that R-R is the distribution that fit your case. About your problem it depends if are the particles beign splitted (breakup) that under some condition should be correct, or if you see an anomaly in their trajectories, unfortunately DPM involves a wide variety of parametres and for sure is not the more famous model of fluent thus is difficult find someone with a sound knowledge of it. Fabio Last edited by Fabio; March 15, 2012 at 10:13. Reason: Added comment.

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March 15, 2012, 08:16		#2
visagant New Member Join Date: Oct 2010 Posts: 9 Rep Power: 15	Hi have you solve this problem.I too get a negetive value . Please confirm

March 15, 2012, 09:20		#3
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Hi, if your data doesn't fit wel the R-R distribution you can set different injection points/surfaces, each one with its diameter. Daniele

March 15, 2012, 09:51		#4
visagant New Member Join Date: Oct 2010 Posts: 9 Rep Power: 15	im using surface injection with min and max diameter, But spread parameters i get a negetive value. Im simulating a nozzle flow so i think point injection is not a correct choice.May be im wrong. I have a problem with stream formation. its splitting to half in the midair. is it something to do with Particle parameters.

March 15, 2012, 10:22		#6
visagant New Member Join Date: Oct 2010 Posts: 9 Rep Power: 15	Thanks for the reply fabio and daniele In my case particle dont split it think, its in micro meter range. I have a multiphase(water and air) with mixture model(water+particles). And the fluid flow With k-e(RNG) trubulence. http://imageshack.us/photo/my-images...jetstream.jpg/ I think im making a mistake in patching(volume fraction). I tried everything still cant solve this problem. If you can give me any advice it will be great.

March 16, 2012, 04:35		#7
Fabio Member Join Date: Mar 2009 Posts: 39 Rep Power: 17	Hello, thinkihg about your problem, i would check the forces acting on your particles, modeling a spray in the proper way is quite chellenging. Forces due to secondary effects (like temperature gradients for example) are negligible or not in correlation with the velocity magnitude and also the size of your particle and thus disturbing the trajectories of your particles.