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 Herold October 13, 2007 03:11

Total Energy -thermal energy

Hello, I have a problem. I am not sure if I have to use the thermal energy or the total energy model for my Fluid. I am using water from the IAPWS library. I have high pressure and water with 200 °C with low density and I am injecting water with 25 °C and higher density in a pipe. Because of the density difference do I have to use compressible flow with the total energy model or is it OK to use the thermal energy?

 Chirag October 15, 2007 03:16

Re: Total Energy -thermal energy

Of course you get to model compressible flow if density difference is significant and/or you want to capture change in density.

Best luck, Chirag

 hectagomp January 26, 2012 11:43

Models for Greenhouse. Help me please.

In the case of a greenhouse. What models use? I have radiation, also compressible fluid and air currents to 12 m / s.

Free convection, radiation and turbulence effects. Help me? Thank you.

greetings.

 ghorrocks January 26, 2012 17:25

Can you describe what you are trying to learn from your model? That determines what physics you are interested in.

Air is compressible but it is unlikely that is significant in a greenhouse. You can probably use incompressible air with bousinesq buoyancy.

 hectagomp January 26, 2012 17:56

Do you know the solar chimney system?
solar collector, as a greenhouse
A chimney.

I was thinking it could disregard the compressibility of air. The speeds are not high. I hope a speed of 12 to 20 m / s.

I have doubts about how to place the boundary conditions for the radiation. Also that use models. I thought about Total energy model if I take the compressible air or in the opposite case of a thermal energy model. Do you combine it with the K-e standard?

Thanks, I'm just starting on this.

 ghorrocks January 26, 2012 18:05

Yes, I know of solar chimneys. What is the range of densities you would expect in this system?

Whether you model radiation directly or just apply it as a heat source depends on what you are trying to achieve.

You can use any turbulence model. The choice of turbulence model is independent of the heat source. I would recommend using SST as the normal default choice unless you have a good reason to do otherwise.

 hectagomp June 20, 2012 15:11

Hello ghorrocks.

I tested differents models, but I don't feel happy with my model.

I found velocities approximate of other research, but I don't Know if is casuality.

I explain: The diferential of temperature expected is 17.5 degrees, therefore I couldn't use the bousinessq buoyancy, or yes?

I read that it's not advisable use approximation of boussinessq with diferential of temperature over 10 degrees.

I want measure the velocities and mass flow. Also the temperature for stablish relations with the power.

Therefore I set the model so:

a) Fluid: Gas ideal: default set

Bouyancy Activated: g=9.81, Bouy. reference
density: 1.185

b) thermal Model: Thermal energy (I need change the thermal model for total energy model?)

c) Turbulence Model: SST

d) Bouyance Turbulence: None

f)The boundary conditions are:

Absortion in the soil

Generation of heat in the cover the greenhouse.

In and out: Opening with pressure value and temperature.

you can given me suggestions??

Best Regards. Thank you for you help

 ghorrocks June 20, 2012 18:36

Quote:
 The diferential of temperature expected is 17.5 degrees, therefore I couldn't use the bousinessq buoyancy, or yes?
It depends on how accurate you want to be. You are starting to get into the range where material property changes make a few % difference.

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