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## Simulation CFD

Active Member
Posts: 10
Registered: ‎04-03-2012

# where should I places the film coefficient?

304 Views, 4 Replies
05-07-2012 01:00 PM

where should I places the film coefficient?

I have a greenhouse which I have the indoor temperature and air flow, now I want a film coefficient places. but where should I put this?

on the inside where the film coefficient touches the indoor air or the exterior side?

greeting
mark

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Employee
Posts: 60
Registered: ‎04-06-2011

# Re: where should I places the film coefficient?

05-07-2012 02:03 PM in reply to: markkolk

assuming you are modeling the "wall" of the greenhouse as a 3D solid to account for the conductivity, you should apply the fim coeff on the exterior surface of the wall.

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Active Member
Posts: 10
Registered: ‎04-03-2012

# Re: where should I places the film coefficient?

05-07-2012 10:40 PM in reply to: markkolk

Hi derrek,

the model is not a 3d solid, but is made with walls in revit architecteur. because there are several areas on 1 surface. with different coefficients.

If I solve this with heat transfeur what should I use for convection. natural or forced?

mark

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Member
Posts: 5
Registered: ‎04-06-2014

# Re: where should I places the film coefficient?

04-09-2014 02:20 PM in reply to: markkolk

What coefficient would you use?

Is that 0.024 for air?

Say I was modelling an internal flow of water, in say a radiator, but wanted to simulate conduction to the external flow, how would I go about doing it? Would I need both an internal and external flow coefficient?

Cheers

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Product Support
Posts: 704
Registered: ‎08-25-2011

# Re: where should I places the film coefficient?

04-10-2014 01:24 AM in reply to: markkolk

Lots of questions here:

1. Boundary conditions are just that, conditions which should only go on the external surface of your model. So, if you do not have the external air modelled, you should apply a film coeff to the external walls. If you have the external air modelled, CFD will calculate the film coeff for you based on the local air temperatures and material properties. You can apply volumetric heat loads internally, that is the exception to the rule
2. I think there is some confusion over the natural/forced convection. I am going to assume you do not have anything other than the temperature differential to drive the flow, so your flow will be natural. To take this into account, you will need air_variable, flow on, heat transfer on and gravity (as earth) with a value of 1 in your downward direction. This is all in the user guide.
3. esukjf, I think I have answered your question also

Thanks.

Jon

Jon Wilde
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