Learning Forum

[farhad]

Hello every one
I’m trying to simulate evaporation of R410a in fluent.
These are some information about my case:
A 2-d axisymmetric smooth tube,
Refrigerant enters to the tube, diameter=9.52mm & length = 3000mm
inlet vapor quality = 0.2
Constant heat flux on the wall = 15 kw/m2
VOF multi-phase model,
turbulence model: k-e standard,
transient method, & time step = 1e-04
I put the liquid and vapor state of R410 in fluent material library. I used DuPont released information of R410.
when I plot temperature in outflow, there is a huge increment in temperature of mixture while the vapor quality is 0.4, it means that before all refrigerant transfer to vapor, the temperature began to increase, & as all we know that is impossible in reality.
Actually I repeated the simulation with water liquid and vapor instead of R410, but the result was same.
Does anyone have any idea why is this happening?
regards

[Rob]

If you're using VOF the inlet flow must be stratified.  Check that (and post images).  

[farhad]

thanks for reply.

i did simulation with all three methods (VOF, Mixture & Eulerian) and in all cases, I put "Mass Flow Inlet" as inlet boundary condition, so base on the vapor quality, an individual mass flow for each phase has set for. 

[DrAmine]

Reformulate your question please.

[DrAmine]

And what is the temperature at inlet ? Do you have any phase transfer model? Provide these info

[farhad]

And what is the temperature at inlet ? Do you have any phase transfer model? Provide these info

hello abenhadj,

thanks for reply.

inlet temperature = 268.15 k = -5 c

i use volume of fluid (VOF) model.

in phase interaction and under "mass" tab i select "evaporation-condensation", and finally put 268.15 (constant) as saturation temperature.

[farhad]

In fact  I think this problem refer to importing R410a in fluent.

whats the best way to import refrigerants like R410a (saturated liquid & vapor) in fluent for multi-phase simulation?

[DrAmine]

In fact  I think this problem refer to importing R410a in fluent.

whats the best way to import refrigerants like R410a (saturated liquid & vapor) in fluent for multi-phase simulation?

Here I recommend using Alternative Energy Treatment, using the Lee Model with PTL table where you import saturation temperature, pressure and Latent Heat. The rest of the material by just changing the material properties.

So you are starting from saturated conditions right? What is now the problem? You might be aware that you are now in your setup neglegting the subgrid effect of boiling at wall. 

[farhad]

In fact  I think this problem refer to importing R410a in fluent.

whats the best way to import refrigerants like R410a (saturated liquid & vapor) in fluent for multi-phase simulation?

Here I recommend using Alternative Energy Treatment, using the Lee Model with PTL table where you import saturation temperature, pressure and Latent Heat. The rest of the material by just changing the material properties.

So you are starting from saturated conditions right? What is now the problem? You might be aware that you are now in your setup neglegting the subgrideffect of boiling at wall.

thanks for reply abenhadj,

at inlet, vapor has the quality of 20%.

my problem is that when there is still some liquid in the tube we don't have to observe any increment in temperature, but in my case the mixture of phases have an increasing in temperature about 20 degrees.

[DrAmine]

What about the superheated steam? If you want to deal with heat resistances then use thermal phase change.

[farhad]

What about the superheated steam? If you want to deal with heat resistances then use thermal phase change.

Thanks for reply Amine.

I'm using VOF model for phase change & "Thermal Phase Change" method could be enabled under "Eulerian" model. this means that you propose to use Eulerian instead of VOF?

[DrAmine]

Steam after being formed will be heated. That explains for me the temperature increase. There is no complete evaporation in your system.

What I proposed is a better model but requires more knowledge and babysitting.

Vof model for homogeneous mixture dims anyhow wrong but okay if you are using first order schemes fir BOF equation. You can use mixture model with SBM to account for subgrid effects.

[farhad]

Here I recommend using Alternative Energy Treatment, using the Lee Model with PTL table where you import saturation temperature, pressure and Latent Heat. The rest of the material by just changing the material properties.

So you are starting from saturated conditions right? What is now the problem? You might be aware that you are now in your setup neglegting the subgrid effect of boiling at wall.

Would you please be more specific about "Alternative Energy Treatment"? I don't know what is "Alternative Energy Treatment" & how i can use it.

Thanks for helping me

[DrAmine]

Search it in the manual. If you still have questions come back again.

[farhad]

Search it in the manual. If you still have questions come back again.

I'm sorry Abenhadj but there is no phrase like "Alternative Energy Treatment" in user manual or even in the web!

[farhad]

Steam after being formed will be heated. That explains for me the temperature increase. There is no complete evaporation in your system. What I proposed is a better model but requires more knowledge and babysitting. Vof model for homogeneous mixture dims anyhow wrong but okay if you are using first order schemes fir BOF equation. You can use mixture model with SBM to account for subgrid effects.

another question: "SBM" & "BOF" are abbreviation of what phrases?

[DrAmine]

Semi mechanistic boiling. with bof I meant vof.