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-   -   DPM - Why do the particles not vanish? (http://www.cfd-online.com/Forums/fluent/45149-dpm-why-do-particles-not-vanish.html)

Johannes June 25, 2007 02:43

DPM - Why do the particles not vanish?
 
Hi there,

when simulating the injection of fuel into a combustion chamber, I've got a problem. The particles mass and diameter do not reach zero. The particles size was about 25E-06 m and only reaches about 2.5E-06m. Why is this so? The temperature is high enough and the length of the computational domain should be big enough to let all particles to evaporate. There seems only to happen evaporation at the beginning and then it stops. Another problem is, that the particles minimum temperature does not match my initialization temperature. I initialize the particles with a temperature of 293.15 K into hot air of about 800K. Nevertheless the lowest temperature of the particles in the particle tracking modus are about 370 K. I would be glad, if someone can help me.

Greetings, Johannes.

sanjay patel June 25, 2007 11:51

Re: DPM - Why do the particles not vanish?
 
sir could u just describe me ur whole work....i'm very much interested in the simulation of fuel injection system for combution in an engine. i'm a student at iit roorkee (India)

Johannes June 26, 2007 03:15

Re: DPM - Why do the particles not vanish?
 
Sorry, I'm not allowed to describe my work in detail, but I'm simulating the vaporization of fuel (293.15K) injected into hot air at about 870K. The temperatures of the particles rise at a reasonable rate. First till the niveau of vaporization and then further on. But I don't get it, that the particles don't evaporate till they are gone, because the time is more than enough. But after decreasing their diameter till about one tenth of their starting size, they seem to stop vaporizing.

Johannes June 26, 2007 03:26

Re: DPM - Why do the particles not vanish?
 
Just some more information:

mixture material: fuel-oil-air droplet material: fuel-oil-liquid

steady Discrete Phase Calculation no breackup model

rana June 26, 2007 07:22

Re: DPM - Why do the particles not vanish?
 
i am getting lots of particles as ABORT can anyone tell me what is the cause of this and what can be the probable remedy ?


ritmat June 26, 2007 09:01

Re: DPM - Why do the particles not vanish?
 
i know that lost means something wrong with geometry but never see (yet) abort. sorry

rana June 26, 2007 16:32

Re: DPM - Why do the particles not vanish?
 
yes, thats my problem..dont know why i am getting so much abort did u take ur fluid as water or air ? are u doing unsteady tracjking or steady ?


ritmat June 27, 2007 03:00

Re: DPM - Why do the particles not vanish?
 
my gas is flue gaz so gas from combustion of wood so it is not totally air. My tracking is steady and i am working in steady flow as well. Did you try to increase number of step in the tracking parameters? Are you sure as well that the solution for your flow are converged before to inject your particules? Is your particules are interfering with your flow?

rana June 27, 2007 05:40

Re: DPM - Why do the particles not vanish?
 
>> Are you sure as well that the solution for your flow are converged before to inject your particules? how do we do that ? just gas/continuos phase we have and solve in single phase eulerian & check for the convergence right ? i did that.. if there's anythign else, do tell me also: in the inlet boundary condition, there is one option for velocity. this velocity refers to which phase (conntious or the tracking phase) ?

in the point properties under injection, what are the values u r giving for 'velocity' and 'total flow rate' ?

please do reply..


ritmat June 27, 2007 05:46

Re: DPM - Why do the particles not vanish?
 
to check convergence you should use residual as well as if your mass flow and temperature are the outlet become stable. inlet boudary condition are for the flow. The inlet velocity for particule has to be applied in your injection. i dont get why you need exactly my value just try any value

sanghals June 27, 2007 14:54

Re: DPM - Why do the particles not vanish?
 
HELLO

i am working in a big company base in greece, we try to test the code some years ago for buying it and we had the same problem.... we never solve that....

if you tell me what is not working then it would be good for me....

best regards

ritmat June 29, 2007 08:32

Re: DPM - Why do the particles not vanish?
 
hi rana I got some abort particule as well. I track some of my particules and actually i saw that for me it appeared in some region closed to walls in dead zone where particules was probably in equilibrium. So the residence time is too big and so that the solver cannot resolve it it is why they become abort. To resolve you have to check your particule by tracking them and maybe change the DPM boundary conditions at this level. Hope its help

R. July 6, 2007 11:19

Re: DPM - Why do the particles not vanish?
 
The DPM material's volatility needs to be 1.0 (100%) for the entire droplet to evaporate. (Materials panel, DPM phase)

If its 0.9, then 10% of the injected mass does not evaporate, and the particle is tracked until it escapes, is trapped, or reaches the limit of steps defined in the DPM model panel.

To fudge it, you need to set the volatility to 1.0, and adjust the mass injected accordingly.

R.



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