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particle time step size, number of time steps in DPMPM

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Old   April 22, 2014, 08:21
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Hi Amir sir

In my heat sink cooling problem actually I want relative humidity of 15% at the exit of the sink but I am getting it 7.42% , I tried with different combinitions of particle time step size and number of time steps. In this particular process I have given mass flow rate of 4.22e-7 and stop time of injection as 100s for every combinition, But still my rate of evaporation and hence RH is not increasing. (In my problem the relative reynolds number is 0, air velocity is 1 m/s). Can you suggest me a way to resolve the problem?

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Old   July 3, 2014, 13:34
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Hi amir sir

Actually I am able to validate results of one of paper by using DPM in FLUENT. I drawn geometry with symmetry boundary condition, but I was giving total mass flow rate through duct. But that mass flow rate must be half. So with excess mass my sink was getting overcooled. Because of your previous quick replies, I was able to understand various terms in fluent physically. Thanks a lot.
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Old   July 29, 2016, 13:03
Default Particle status for DPM iteration
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I have read the Fluent User guide and also have read the posts regarding this but I am not able to comprehend the unsteady particle tracking of Fluent. I am running unsteady simulations for continuous phase and also want to have unsteady particle tracking. In the particle treatment I choose unsteady and I also choose to inject particles with fluid flow time step. Till here its good but now it starts to get messy.
Firstly, if I want to inject particles at fluid flow time step why does it still asks about particle time step size and what is this parameter exactly?
Secondly, the time step size of my continuous phase is 1e-5 and I keep my particle time step size as 0.0001. When I run the simulation, Fluent recognizes the number of parcels but the status for the parcels it prints on the console is wierd.
Updating solution at time level N... done.
Injecting 31360 particle parcels with mass 5.375e-09 at t = 0

DPM Iteration ....
number tracked = 31360, escaped = 0, aborted = 0, trapped = 0, evaporated = 0, incomplete = 0, incomplete_parallel = 0

My question why the status of the particle is zero?

When I try to reduce the time step size of the continuous phase to 1e-4, the same 31360 particle parcels are tracked and gives proper status (in my case they are droplets and should evaporate).
The mass flow rate of the DPM phase is 0.5375 g/s and I inject 31360 particle parcels from injection file.
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Old   November 2, 2016, 03:12
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Originally Posted by Amir View Post
No! The DPM equations are solved in unsteady fashion, but they can be considered in steady or unsteady flow fields. These two are different.

Nope. In each numerical analysis, you should assure the iterations are quite enough and increasing them any further wouldn't change the results. I don't see any proportion ....
You can take a look at any text book in this field; aerosols. For instance, this one:
"Aerosol Technology, William C. Hinds"


Dear Amir,

I want to inject a fluid in my flow inside a nozzle that has gas in it, I used plain atomizer model. I am not sure about the diameter. What diameter should I choose?
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