I want to simulate an evaporation model in a horizontal smooth tube. Currently I m using r22 as primary n secondary phase and I put the properties from REFPROP for saturation temp 278 deg K. My problems are...where should I put the corresponding saturation pressure ...inlet or outlet or operating pressure? I am using inlet velocity, outlet pressure and wall temperature (283k plus) as boundary conditions. Which multiphase model do u prefer for that?...now I m using mixture model. Thnx in advance Is it possible to simulate phase change (evaporation/condensation) phenomena in FLUENT?
Use this forum cfd.online it may be helpful for your topic. Good luck.
Thank you samad.
I am using already that.
But my problem is ....setting of saturation pressure.
Where should I set the saturation pressure of r-22 corresponding to 5deg celcius?
But sat temp should b changed with a change of sat pressure.
How fluent will count this???
Thats y, I think we must put sat pressure accurately.
Does ur model run correctly? Have u found pressure drop n heat transfer as expected?
Thank you samad.
I think it is very difficult to get an accurate solution, because when we come into the state with varying quality factor x we also have to introduce a diffusion factor into the phase change. Please notice that for instance the program REFPROG is for steady state condition.
Thank you @Ivar, so far I know evaporation condensation model in the mass transfer tab is a fit model to calculate the diffusion(mass transfer). Is there any necessity to develop any UDF for heat n mass transfer during phase change?
I have used REFPROP only for using material properties of r22 liquid nd r22 vapor to defined material. Since the varying parameter is pressure I observed that there is a small change of material properties(sat temp, density, cp etc) due to a large pressure drop.
For this reason I have taken the properties constant further more the mixture model also gives us the mixture properties at diffrent qualities or volume fraction.
I believe its necessary to specify Phase change conditions using UDF codes, because Fluent can't evaluate it easily by default
Thank you @abimbola...Do u hve any idea abt this code for phase change??
You can do so by applying the energy equation modified specifically for the modelled problem. It will depend on the problem geometry to setup appropriate boundary conditions.
I hve attached the geometry image.
its a horizontal smooth tube of dia 6.4mm and length 1.62m. The inlet is velocity inlet of liquid velocity 8cm/s and outlet is pressure outlet. I set the saturation temp at 278K where as I put a UDF for the wall.
#include
DEFINE_PROFILE(unsteady_temperature,thread,position)
{
real x[ND_ND];
real z;
face_t f;
begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
z=x[2];
F_PROFILE(f,thread,position)=283.0+5.6*z;
}
end_f_loop(f,thread)
}
According to theory, so far I know the temp of the liq-vapor mixture will not change until it a complete vapor or liquid. But it does change its temp during simulation where as the vapor fraction is abt 0.5. I didnt expect any sensible heat transfer but it happened n dissapointed me.
Any support will be highly appreciated.
Heat transfer has to take place as long as there is vapor involved from the reaction mixture. You need to use continuity equation for the vapor emission coupled with energy (heat) equation for heat transit modeling. In short, Navier-Stokes equation are used to model reaction in mixtures.
Dear solomon thank you for ur answer.
But will there actually be any reaction? the materials are r22 liquid and r22 vapor. So, How does reaction take place?
One more thing, If I want to use Navier-Stokes equation then what Should I do?
I thought its an in built equation for continuty in cfd solver and thats y I considered its being used to solve continuity problems.
Please help me if possible.
Actually, Navier-Stokes equations are used in fluid dynamics. In your case there is no mixture, but vapor and heat are products of the system and need to be mathematically modeled.
Dear Shaon
its better to use Eulerian Multiphase method instead of mixture. the mixture model is tuned for the flow with low stokes number. in a boiling/evaporating problem the stokes number is not very small and the secondary phase is deviate in momentum from primary phase obviously. in the material dialog box you should modify standard enthalpy. in addition in mixture model the mass average of velocity and volume average of other property is used in the equations and this is maybe the source of your problem(i.e. raising temperature in saturation mode )
It sounds lika a good idea to use liquid and gas separately. As is said REFPROP tells us the overall condition.
- Badges
- Science topic