[oliveira1820]

In my simulation I have a container full with 90% liquid water and 10% vapor water ( Steam 2l and Steam 2v material correspondingly), that is, my domain has 2 fluids.

I want to insert a constant volumetric heat source (energy source) in my container that heats the fluids. Like a cylinder of heat that emits the same amount of energy all the time and is motionless.

I created a subdomain that is the fluid domain itslef and I got two options:

- Bulk Source
- Fluid Sources

Wich one should I choose to create the cylindrical energy source right in the middle of the domain, that acts continuously and in the same way in the two fluids regardless of the volume frations variation?

That is, the source must transmit energy in that static volume constantly regardless of the fluids behaviour. Should I choose bulk source or select both fluids in Fluid Sources? Or is it simply not possible?

[ghorrocks]

This is all described in the CFX documentation.

Section 17.2.2: "Select Bulk Sources to specify bulk sources. Bulk sources apply to all fluids in a multiphase simulation."

[oliveira1820]

I read it all but i keep not understanding and why is it different in the end if my container is always 100% full. My source is supposed to be a cylinder static in the middle, that with the fluid flow will have different fluid volume fractions in each instant.

Accordingly with the CFX manual:

Bulk Sources - "Bulk Sources automatically multiply the specified source by volume fraction, ensuring that the source reduces to zero as the fluid volume fraction reduces to zero."

Does this means that, if my container is 90% liquid water and 10% vapour water, and besides the volume fractions change but still add up to 100%, the bulk source is always constant because whatever the fluid it is in a certain position its fraction is never zero?

Fluid Sources - "Fluid sources are used in an Eulerian multiphase simulation to apply volumetric source terms to individual fluids"

Does this means that if I apply the same source to both fluid, the source will be constant volumetrically, because it will be aplied to the position, independently of the fluid in that position, because ther is always or water vapour or liquid?

And considering that my CEL source fucntion is:

Total Source===Sourcefluido

LIBRARY:
CEL:
&replace EXPRESSIONS:

Sourcefluido = dominiofluido* 800[kg m^2 s^-3]

dominiofluido = step((xmaxx-xrms)/unidade)* step((ymaxx-yrms)/unidade)* step((zmaxf-zrms)/unidade)

unity = 1 [m]
xmaxx = 0.0042499 [m]
xrms = sqrt(x^2)
ymaxx = 0.0042499 [m]
zmaxf = 0.006 [m]
zrms = sqrt(z^2)
END
END
END



In the end what is the difference between the sources in my case?

[ghorrocks]

I read the documentation as saying that if the water volume fraction is 0.9 and water vapour is 0.1 then a bulk source will apply 90% of the power to the wafer phase and 10% of the power to the vapour phase.

If you use a fluid specific source then 100% of the power will be applied to whatever phase you choose, regardless of its volume fraction.

Also: Why are you using sqrt(x^2)? Is this to get the absolute value? If so, then just use abs(x).

[oliveira1820]

So the best option to get a constant energy source in a volume, independetly of the fluids volume fractions variations is the fluid specific source. Selecting both fluids and applying my cell source to both fluids, it will apply the same energy to every different position inside my cylinder, right? Because each position is occupied by vapour water or liquid water alternatively.

Thanls, Il use abs instead´.

[ghorrocks]

I do not know what you are trying to do so cannot say what is best. If you are unsure what the options mean then try them both and find out.

[oliveira1820]

I will do it, thank you for everything Ghorrocks.

[oliveira1820]

Just to clearly understand the Fluid Specific Source.

Don´t forget that my cell function applies only to the cylinder with those dimensions. So, inside the cylinder it will be vapour water and liquid water, always changing fractions (phase transfer) and changing position). And I want that my 1000 Energy to be distributed uniformily inside the cylinder, independently of the vapour or liquid quantity or position.

If I activate both fluids, and use the same 1000 W Energy Total Source for both , does it distributes the 1000W energy in both fluids ( inside my cylinder) or does it apply 1000W to each fluid ( to the portion of each indide the cylinder)?



fluido= liquid water
vapour = vapour water

[ghorrocks]

The screen shots you show will apply Sourcefluido [W] of heat to fluid "fluido" and Sourcefluido [W] of heat to fluid "VAP". So there will be a total of 2*Sourcefluido [W] of heat applied to the region.

[oliveira1820]

Just to conclude. I have my fluid domain with water vapour (dispersed) and water liquid (continuous) but the source only applies to a certain part: the cylinder. The fractions keep varying inside.

Instant1 - 80% of the cylinder is Liquid water and 20% is Vapour.

Instant 2 - 60% of the cylinder is Liquid water and 40% is Vapour.

If I select both, it will apply 1000 W on the 80% of liquid water and 1000 W on the 20% Vapour and on instant 2 it will apply 1000 W to the 60% of liquid water and 1000W to the 40% of vapour, is it right?.

If I want to only 1000 W in total inside the cylinder I must estimate the percentage of vapour or liquid water that is inside the cylinder and apply, imagine there is 40% of liquid and 60% of vapour, 400 W to the liquid water and 600 to the vapour?

[ghorrocks]

If I select both, it will apply 1000 W on the 80% of liquid water and 1000 W on the 20% Vapour and on instant 2 it will apply 1000 W to the 60% of liquid water and 1000W to the 40% of vapour, is it right?.

If you use a Fluid specific source then, yes.

If I want to only 1000 W in total inside the cylinder I must estimate the percentage of vapour or liquid water that is inside the cylinder and apply, imagine there is 40% of liquid and 60% of vapour, 400 W to the liquid water and 600 to the vapour?

Or you could just use a bulk source and CFX will do the split based on volume fraction for you.

[oliveira1820]

That´s right, I could I miss that, thanks!!