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-   -   nucleate boiling (http://www.cfd-online.com/Forums/openfoam/65737-nucleate-boiling.html)

 isabel June 24, 2009 11:50

nucleate boiling

Hello everybody,

I want to calculate a growing bubble with interFoam. The bubble grow by adding a
masssource term within the bubble.

In principle that would be done by adding a
source term to the continuity equation:

div(U)= mass_source

Unfortunatly the continuity is not solved that way in interFoam.

 sega June 24, 2009 13:28

If you are talking about nucleate boiling, than your bubble is growing on some heater surface (and from within a nucleation site)?

Do you want to simulate the actual evaporation or just the growth of the bubble?

 isabel June 25, 2009 03:08

I only want to solve the growth of the bubble.

The continuity equation is:

div(U)=mass_source

The gamma equation is also affected by the source.

The problem is that the interFoam solver doesn't solve the continuity equation in that way. Which is better, use the pEqn of the interFoam solver or delete it and define a new equation div(U)=mass_source ?

 sega June 26, 2009 08:42

If you only want to simulate the growing bubble on a heater surface I can suggest you have a look into the work of Gerlach et al. from 2007.

http://therealsega.th.funpic.de/open...ch/gerlach.jpg

He uses an approach in which the 'evaporated mass' is simply flowing into the computational domain through an orifice at the bottom.

Here is an image of the used computational domain, to make this more clear:

http://therealsega.th.funpic.de/open...lachDomain.jpg

In this case you don't have to solve the energy equation as the actual evaporation is not modelled at all and no temperature is needed.
You even can use the interFoam solver, without altering it.

I have done these calculations with interFoam in my bachelor thesis, so I don't know if this is challenging enough for your PhD thesis?!

 isabel June 26, 2009 09:39

I want to calculate a bubble in a heated wall. Due to the heating, the bubble grows.
The heat transfered by conduction is: q = k*grad(T)
The mass evaporated is: k*grad(T)/L calling L the vaporization latent heat.

To do that, I need to add a source to the mass equation.

 sega June 26, 2009 10:29

Quote:
 Originally Posted by isabel (Post 220621) I want to calculate a bubble in a heated wall. Due to the heating, the bubble grows. The heat transfered by conduction is: q = k*grad(T) The mass evaporated is: k*grad(T)/L calling L the vaporization latent heat. To do that, I need to add a source to the mass equation.
As you have allready read in the thread Phase change with VOF this is far more than interFoam can do as it's an isothermal solver.
Read carefully the suggestions by H. Weller and espacially H. Jasak.

Maybe you should consider contacting B. Shu who started the thread and just finished typing his PhD on this subject. By the way he was my mentor during my bachelor thesis.

Good luck.

 vishal July 9, 2009 07:21

Hi,

I am trying to simulate boiling of water. i have supplied one surface of the damain as hot surface. however water enters the donmain at room temp and atmosheric pressure. However it should leave the system as waterand watervapour mixture.

I am using interPhaseChangeFoam for this case. but, as i tried to analise the code I didn't find that it solved energy equation. and i also noticed that no tempreture is need to be specified at with initial boundary conditions.

Please let me know where i am goin wrong and suggest me the right procedure.......:rolleyes::rolleyes::rolleyes:

Thanks,

Vishal

 isabel July 10, 2009 12:19

Hi vishal.
You have to add the energy equation to the interPĥaseChangeFoam
By curiosity, żare you using level set method?

 isabel July 13, 2009 04:20

Hi again, vishal,

In this link you have information about adding the energy equation to a solver. It is to icoFoam, but to interFoam the process is similar:

http://openfoamwiki.net/index.php/Ho...ure_to_icoFoam

 Edy September 16, 2010 10:21

Hi Isabel,

One year later, i hope that you have solved the problem. If not, my objective is gonna be challenging.

My configuration is a turbulent flow flowing in an uniformly heated channel at intermediate pressure (45bars).

I have to model subcooled nucleate boiling in OpenFOAM as well. The model i want to implement is a rather simple one based on Kurul & Podowski's research. This model studies the growth and lift-off of bubbles. The main idea is that the wall heat flux can be partitioned in 3 components:
- evaporation: heat given to superheated water that evaporates and leads to bubble growth
- quenching: heat given to subcooled water that has just replaced the site previously occupied by a leaving bubble
- single-phase convection: where no bubble appears, the heat transfer is basic single phase heat convection

Correlations exist for these terms and they can be expressed as a function of the subcooling.

So i wanted to have your opinion about the way to do it. From which solver should i start? How did you solve your problems?

Any tips/advices welcome!

Thanks a lot!

 Edy September 16, 2010 10:23

I am brand new on this forum, in OpenFOAM and in CFD in general... :)
So please detail (just a bit) your answers.

Thanks :)

 isabel September 22, 2010 04:22

Hi Edy,

One year later, I have solved the problem. I simulated the growth and detaching of a bubble from a heated wall and I tried two ways:

- Employing “VOF method”
- Employing “level-set method”

Both ways were successful. My reference solver was interFoam, but I had to program a lot of changes.

About the turbulence, my problem is laminar, and about evaporation, quenching and single-phase I have not considered those. I only considered that the heat at the interface is transfered by conduction, i.e. q = k*grad(T) and the mass evaporated is: k*grad(T)/L calling L the vaporization latent heat.

 Edy September 24, 2010 05:29

Hi Isabel,

Thanks for your answer and sorry for the delay, I will try something different, solving conservation equations (mass, momentum, energy) for both phases. Using closure relationships should enable me to avoid these interface tracking methods and calculate void fraction for each cell.
Hoping this will work...

Thanks

 ovie October 2, 2010 20:29

Quote:
 Originally Posted by isabel (Post 276102) Hi Edy, One year later, I have solved the problem. I simulated the growth and detaching of a bubble from a heated wall and I tried two ways: - Employing “VOF method” - Employing “level-set method” Both ways were successful. My reference solver was interFoam, but I had to program a lot of changes. About the turbulence, my problem is laminar, and about evaporation, quenching and single-phase I have not considered those. I only considered that the heat at the interface is transfered by conduction, i.e. q = k*grad(T) and the mass evaporated is: k*grad(T)/L calling L the vaporization latent heat.
Hi Isabel,

Please kindly provide some insight into how you were able to pull this off. I am using interFoam and I am having some challenges incorporating the source terms into the equations. Could you please help? In my case I am simulating falling film evaporation of a liquid on a heated vertical surface and for now I am considering laminar flow.

Thanks.

 isabel October 4, 2010 02:35

Hello ovie.
Are you going to use "VOF" or "level set"?

 ovie October 4, 2010 02:47

Thanks Isabel for your response..

I am using VOF with interFoam modified to include an energy equation.

Thanks

 isabel October 4, 2010 03:39

Hello ovie,

These are the steps I did to interFoam:
- First of all, I added the energy equation
- Secondly, I programmed a source to the pdEqn
- Finally, I programmed a source to the gammaEqn

 ovie October 4, 2010 13:03

Quote:
 Originally Posted by isabel (Post 277617) Hello ovie, These are the steps I did to interFoam: - First of all, I added the energy equation - Secondly, I programmed a source to the pdEqn - Finally, I programmed a source to the gammaEqn
Thanks for your response.

But could you please be more elaborate on how to program the source terms? That is what I am grappling with at the moment.

Thanks

 isabel October 5, 2010 04:06

p { margin-bottom: 0.21cm; } In the pdEqn, if the equation is grad(U) = source, I have programmed:

fvScalarMatrix pdEqn
(
fvm::laplacian(rUAf, pd) - fvc::div(phi) - sourcepd
);

In the gammaEqn, the same. I have programmed:

fvScalarMatrix gammaEqn
(
fvm::ddt(gamma) + fvm::div(phi,gamma) - sourcegamma
);

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