Learning Forum

[Himanshu]

Hello,

I am working on single slope solar still simulation. I have made geometry by design modeler. For meshing, I have used fluent with meshing. If i use unstructed and hexa mesh then i got floating point error after some iterations.

I am using following models:

1. Multiphase VOF model: Implicit, 2-phase (Phase-1:- Air-vapor mixture and Phase-2:- Water-liquid), Lee model for evaporation and condensation.
2. Species Transport: To make mixture phase only.
3. Viscous model: Laminar
4. Radiation model (Discrete Ordinates and Solar ray tracing): Solar calculator

Boundary conditions: Glass cover: Mixed (Thermal), Semi-transparent (Radiation)      Bottom plate: Adiabatic (Thermal), opeque-yes (Radiation)   Other walls and collector: Adiabatic (Thermal), Opeque-No (Radiation).

Solution methods: SIMPLE Scheme

Total time of simulation is 11 hours (50400 sec).

Issues:

1. From the close domain, mass of water is getting zero while vapor is not generated during simuation.

                                                           at t = 0 sec                                                                                                                      at t = 3215 sec

i have tried with 3 phase also (air, vapor and water) by keeping all parameters same, still i got same issues.

[Rob]

If the domain is sealed what gas phase density option are you using? If you focus on the first second or so what's going on in the model?

[Himanshu]

 

I am using default setting.

 

 

 

[Rob]

If liquid evaporates into vapour where does it go? 

[Himanshu]

First thing, water vapor is not generated during the simulation and water-liquid volume fraction was reduing with flow time. Water-liquid volume fraction is having range 0-1 before the simulation and 0-9.92e-5 after 3451 sec (Flow time) and after that 0-0.

where the water is going from the close domain, i don't konw.

[Rob]

And does the temperature increase during the simulation? Look at the vapour density option and tell me where the expaned vapour goes. 

[Himanshu]

Temperature is incresing during the simulation. I didn't understand the meaning of expaned vapor.

[Rob]

You have a fixed volume. You have expansion of the vapour phase as temperature rises. Where does the excess volume go? 

[Himanshu]

I already mentioned vapor was not generated during the simulation.

[Himanshu]

Sir, can you help me in this project?

[Rob]

But vapour does expand? 

[Himanshu]

How can i ensure, whether vapor is expending or not?

Can you tell me something to verify it?

[Rob]

You're using incompressible ideal gas so it's got to expand if the domain is warming up. Given that, where does the excess volume go? 

[Himanshu]

Temperature of water is increasing during the dimulation but vapor is not generated. I used 2-phase due to mixture of air and water vapor, so generated vapor will be prasent with air.

[Rob]

Yes, which means the gas is expanding. So, where is the gas going? 

[Himanshu]

gas is inside the close domain only. In the domain, neither inlet nor outlet is provided.

[Rob]

Yes, and if the gas expands as it gets warm in a sealed domain where does the excess go? 

[Himanshu]

Gas in the domain is not expanding.

[Rob]

What is the gas density model?