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Another Relatively Simple Natural Convection Problem....

Posted Mar 10, 2015, 2:11 p.m. EDT Heat Transfer & Phase Change Version 4.4 3 Replies

Brian Simonds
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Hello,

I have been trying to model a very simple problem of natural heat convection, onto which I would like to eventually add some complexity. Unfortunately, I've been unable to make the simple system work. My simple system is a suspended piece of glass in air with a heat source applied to one side in 2D. I would like to see the convective heat flow from the heated surface.

The error messages I get make me believe that the problem is with defining boundary conditions, but for the life of me I cannot figure out the problem. I've looked at every model and discussion of this problem, but to no avail. I'm hoping the community can show me the way! The model is attached.
3 Replies Last Post Mar 13, 2015, 3:31 a.m. EDT
Julien Givernaud
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Posted: 10 years ago Mar 11, 2015, 12:33 p.m. EDT
Hello Brian,

You can try the Boussinesq approximation
rho(T)=rho(T0)*(1-alpha[1/K]*(T-T0) as volume force (Fy=-rho(T)*g_const [N/m^3])

With a time dependent solver it's easier, you can have an initial condition for a stationnary solution.
I attach your model with my modifications in 5.0.

Julien
Hello Brian, You can try the Boussinesq approximation rho(T)=rho(T0)*(1-alpha[1/K]*(T-T0) as volume force (Fy=-rho(T)*g_const [N/m^3]) With a time dependent solver it's easier, you can have an initial condition for a stationnary solution. I attach your model with my modifications in 5.0. Julien
Brian Simonds
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Posted: 10 years ago Mar 12, 2015, 1:41 p.m. EDT
Hey Julien,

Thanks for taking a look and making some changes. I was able to make some headway by doing continuation studies and inching the viscosity and input power towards what I want them to be. I would like to look at your changes, but unfortunately I cannot open the 5.0 version in 4.4. Is there anyway for you to make the program back-compatible with previous versions?

Thanks,
Brian
Hey Julien, Thanks for taking a look and making some changes. I was able to make some headway by doing continuation studies and inching the viscosity and input power towards what I want them to be. I would like to look at your changes, but unfortunately I cannot open the 5.0 version in 4.4. Is there anyway for you to make the program back-compatible with previous versions? Thanks, Brian
Julien Givernaud
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Posted: 10 years ago Mar 13, 2015, 3:31 a.m. EDT
Hi Brian,

Yes, your solution is a good one.
I am sorry but I have uninstalled previous versions..
Boussinesq is easier to converge, if you have time you can compare the 2 methods in accurary term if you have some experimental results.
I have only defined a variable named rho_T and its value is what I write in my previous post. Put it in volume force * g_const, nothing to change in material properties.

Hope it helps

Julien
Hi Brian, Yes, your solution is a good one. I am sorry but I have uninstalled previous versions.. Boussinesq is easier to converge, if you have time you can compare the 2 methods in accurary term if you have some experimental results. I have only defined a variable named rho_T and its value is what I write in my previous post. Put it in volume force * g_const, nothing to change in material properties. Hope it helps Julien

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