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Difference between "droplet Particle" and "Particle Mixture"

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Old   October 18, 2011, 21:19
Default Difference between "droplet Particle" and "Particle Mixture"
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Mohsin Mukhtar
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Hello

What is the difference between "droplet particle" and "particle Mixture" in Materials panel of FLUENT. This comes when I use "multicomponent" particle type in DPM model.

Please assist
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Old   October 31, 2011, 06:51
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In "droplet particles" You can spray only pure substance. If You want to spray mixture You need to switch to "multicomponent". Then in Materials you will see droplet particles and mixture particles. Now You can create your own mixtures from pure materials. You need to read or create material species to droplet particles and then in properties of mixture droplet you can choose your mixture components.
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Old   October 31, 2011, 08:40
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Thank you for your reply
Regarding multi-component model in DPM, could you guide in the following:

1. In the Materials panel, how can u specify whether the mixture is "dissolved mixture" "undissolved mixture", "suspension" , "emulsion" etc?

2. In the Materials panel, a "mixture" tab appears under "fluent droplet materials" which asks whether the fluid particle is "mixture" or "NONE". What does it mean? if i specify "NONE" then, does it mean it will consider the fluid as separate entity and not as a mixture?

3. In "dpm model" panel if i use multi-component model, then "component" tab is activated where there is an option of "non-vaporizing". if i specify the component of a mixture as "non vaporizing" then does it mean it will not vaporize? even if i specify its "volatile fraction" in the materials panel?

Thanks for your consideration
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Old   October 31, 2011, 09:52
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I don't know exactly answer for your 1 question. But what I thing is that Fluent know what kind of mixture You have from the properties of component. For DPM I thing it's doesn't matter. If You want to simulate emulsions and emulsification process You should use VOF model.

2- it's doesn't matter if there is NONE or Mixture. If you select None You just add new species to your case. And then You need to add this species to your mixture as e component. If You select Mixture this substance should be automatically add to you mixture. But it's better to do it by yourself.

3- in multicomponent there is no available evaporating law. If you choose "vaporizing" in "component" tab after simulation starting You will receive error. You need to write UDF with heat and mass transfer process. It is Fluent "help" in macros topic. Only if you use udf u can solve problem of evaporating from multicomponent droplet. Udf recognize which species is evaporating so this option "volatile fraction" for multicomponent droplet is not taken into account.
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Old   October 31, 2011, 22:18
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Jaskull, Thank you very much for your time.

[/QUOTE] in multicomponent there is no available evaporating law. If you choose "vaporizing" in "component" tab after simulation starting You will receive error. You need to write UDF with heat and mass transfer process. It is Fluent "help" in macros topic. Only if you use udf u can solve problem of evaporating from multicomponent droplet.[/QUOTE]

You are right. As I started simulation there was no vapor generation from the liquid in the multicomponent mixture. However, I am a little puzzled by the following:

1. In FLuent user guide (picture shown, untitled) it is mentioned that "Multi-component" model uses "Law 7" to calculate radiation, convection and vaporization by using one equation. Also, If it cannot calculate vaporization then what was the reaso/purpose of "Non-vapoizing" and "evaporating species" tab under "component" in DPM injections (Picture-untitled 2).

2. Could you recommend some tutorials on a similar problem using UDF's (other than UDF mfluent manual) or could you give me any guideline/procedure for writing a UDF and hooking in FLUENT for this kind of problem. For instance, should i write a UDF for only vaporization (LAW 2)? Do I have to use DPM injection's Cutsome laws for this purpose? But the "custom law" has only 2 options i-e "inactive" or "multi-component". How would you incorporate UDF into this.

Your valuable suggestions would help me to move forward on this issue. Regards
Mohsin
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Old   November 1, 2011, 03:19
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Hi Moshin

I'm PhD student from Poland. Mostly I focus on spray drying of detergent. It's very difficult to find any usful information on Internet about writing UDF. I also not very good in this case. But what I already do its write udf which describe heat and mass transfer between particle and continuous phase. You can find it in Fluent help. In part UDFs then define macros and dpm macros. Its called DPM_HEAT_MASS or something like this. You need to compile this macro to .dll library. How to do that is describe in FAQ of this forum. But be careful when you want to copy this code from help. Sometimes something can disappear.

[/QUOTE]
In FLuent user guide (picture shown, untitled) it is mentioned that "Multi-component" model uses "Law 7" to calculate radiation, convection and vaporization by using one equation. Also, If it cannot calculate vaporization then what was the reaso/purpose of "Non-vapoizing" and "evaporating species" tab under "component" in DPM injections (Picture-untitled 2). [/QUOTE]

It's kinda strange but there is reason. In UDF you will be automatically recognize which species is volatile. So You need to choose vaporizing species from component tab. It can be one or more UDF will automatically calculate as many species as you selected.

It's strange that they don't put this code inside Fluent but force users to add it by yourself. Maybe 14th version will be different.
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Old   November 1, 2011, 07:24
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[QUOTE=Jaskull;330268]Hi Moshin

what I already do its write udf which describe heat and mass transfer between particle and continuous phase. You can find it in Fluent help. In part UDFs then define macros and dpm macros. Its called DPM_HEAT_MASS or something like this. You need to compile this macro to .dll library. How to do that is describe in FAQ of this forum. But be careful when you want to copy this code from help. Sometimes something can disappear.
[QUOTE=Jaskull;330268]

Perhaps you are referring to this FLUENT UDF Macro and the exapmple:
https://www.sharcnet.ca/Software/Flu...udf/node64.htm

I would study UDF and this example and hooking procedure and would get back for any querry. Thanks alot.

P.S. I am working as a Researcher in South Korea. I am working on Spray drying of multicomponent mixture. I also have some Polish friends here. hope to be in contact with you. Thanks again.

Mohsin Mukhtar
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Old   November 8, 2011, 01:17
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Hi

I have a basic knowledge of C++ and it would be my first experience to deal with UDFs. To develop this type of code, I've started to learn C++ and UDF's, its compiling and hooking in fluent etc. In particular, for the above problem, I am trying to understand all the concepts related with the above example of multicomponent evaporation. (At first, I used the same code, given in the above example, but after "build" command in FLUENT it gave a compile error. Hence, it was imperative to study UDF and C++ for the proper implementation of this code)

I am reading the book "The C programming language B.Kernighan and D.Ritchie" and "FLUENT UDF's user guide" but I wanted to ask you, do you have some other relavant
preperation materials, videos, training links, documents, lectures etc on our drying issue. I'll be glad.

Last edited by Mohsin; November 8, 2011 at 02:07.
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Old   November 8, 2011, 05:39
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Hello again.

Just like I promise I send You article title: "CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer" authors: Meng Wai Woo, Wan Ramil Wan Duad, Arun Mujumdar. Article describe well mechanism of 2 step drying in very simple way ti implement to Fluent.
However, I have grieved you that the best way to learn Fluent is method of trials and errors and unfortunately user guide. But I have some .pdf files from Ansys company that can be helpful If You send me Your mail address I can send You those materials.

Maciek
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Old   November 8, 2011, 05:53
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Thank you Maciek

Actually, I have already read this article. As you said, it is very well written. He uses 2 approaces REA and drying curve approach. By the help of UDF's he simulated the problem. I have also read most of the papers by Professor Mujumdar.

I dont have access to pdf files from ANSYS company, I'll be very much grateful if you could send me on my following email.

mohsinmukhtar85@gmail.com
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Old   November 10, 2011, 21:06
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Hello Maciek
Thank you for sending me some files. It's so nice of you.

I have some querries, I'll be grateful for your insight into this.

1. Fluent has its own in built macros where it has already defined "structs", "functions" and "constants" etc. You can access that in Fluent...>"src" in .h files. In the "DEFINE_DPM_HEAT_MASS" macro example, it has used some structs and functions which it is taking from somewhere in the header files. But I am unable to find its whereabouts. Could you tell me where to find them? such as:

Material
TP_N_COMPONENTS

2. The aforementioned example calculates particle temperature K/s, particle component mass (kg/s), gas phase enthalpy (J/s) and gas phase species mass (kg/s). However, I wanted to calculate species mass fraction. Do i have to incorporate separate code to calculate particle species mass fraction?
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Old   November 15, 2011, 08:05
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Dear Mukhtar
I am conducting some simulations using Fluent, and I am studying UDF too. Could u please send me the ".pdf files from Ansys company" to my email address: forwardyang1984@hotmail.com
Thank you very much!
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Old   November 15, 2011, 21:31
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Dear forwardyang

The pdf files of Ansys company (which I could gather) consists of couple of ppt slides covering some udf concepts, turbulence and heat transfer concepts, however these concepts are already covered in FLUENT's UDF Manual and FLUENT's manual. I think reading manuals would be more effective. nevertheless, I will send you the files on ur address.
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Old   November 15, 2011, 22:45
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Thank you Mukhtar
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Old   November 22, 2011, 23:53
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Dear Maciej Jaskulski

I am solving 3D Spray Dryer's drying kinetics, with steady state, Realizable KE, Non equilibrium Wall functions, Energy Equation, Species transport, high swirl, PRESTO, 2nd order upwind and lower under-relaxation than default. I got the following errors while using DPM multi-component UDF example:

1. In DPM model, when I use the option “interaction with continuous phase after every 20 iterations”, then on 20th iteration, when DPM particle tracks are being calculated, I get the following error:
Floating point exception; Divergence detected in AMG solver.


2. To counteract the first problem, I solved the flow without DPM first and then when steady flow field was calculated, I used "DPM particle tracks" to see the summary of the trajectory. However, it showed no vaporization from the droplet, in other words, vaporization is not initiated and I get mass fraction species=0 all over the domain.

Could you please put some light on this issue or tell me some steps, by your experience, how to avoid these issues. Thank you very much.

Mohsin Mukhtar

Last edited by Mohsin; November 23, 2011 at 00:28.
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Old   November 23, 2011, 03:26
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Could you also see these points:

1. In the DPM injection panels, under the multi-component tab, What does the "evaporating species" option mean??? Is it the specie in which the evaporating species will evaporate. For instance, N2?

2. After incorporating UDF code into FLUENt for multi-component evaporation, is it necessary to click on the "custom" options and activate multi-component laws?

Last edited by Mohsin; November 23, 2011 at 04:54.
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