Learning Forum

[ilardimichael26]

Hello, 

I am creating a simple heat transfer simulation in ANSYS FLUENT. 

My Model is a 10'x10'x10' box with 1 inch wall thickness. The inside was made hollow, and then filled in DesignModeler.

I did simple meshing, and created named selections for the fluid body inside the box and the box itself.

Then in FLUENT, I set the boundary condition wall between the fluid and the box to coupled.

I am trying to set the box (aluminum default) to 320K and the inside fluid (air default) to 300k, and have simple heat transfer between the two bodies. 

 

How would I go about setting these initial conditions and successfully simulate the heat transfer?

 

Thanks

[peteroznewman]

What boundary condition will you use on the six outside faces of the box?  If you do nothing, FLUENT will assume a zero heat flux = adiabatic = insulated condition.  In that case, the heat in the walls will, over time, be transferred to the air inside the box.

If you set the Operating Temperature to 300 K, that will be used to set the temperature of the air during initialization. Then you PATCH the box to be 320 K in the Initialization stage before you start calculations.

Do you want the Steady State solution or do you want a Transient solution and watch the change over time? The steady state solution will be the air and walls at some value between 300 and 320 K.

 

[ilardimichael26]

Thank you for the reply,

For the 6 outside faces i am not setting any conditiona because i am only concerned about the heat transfer to the air inside the box. I want a steady state solution. I think my issue lies in the boundary conditions or initial conditions. Im using the density based solver because i have no inlet or outlet , thus the only calculation is the energy equation for the heat transfer.

If this all sounds right, how do i go about setting the initial conditions or this patch? I have tried using the boundary conditions amd cell zone conditions to set constant temperatures but it hasn't been working.

[Rob]

Are you looking at buoyancy effects? 

For initial conditions you just patch the two temperatures. However, the steady state solution will be a uniform temperature somewhere between 300K & 320K. 

[peteroznewman]

Did you do a hand calculation using the mass of air, mass of aluminum and the specific heat capacities of each material?

Note: below is an example. I have not calculated the mass of air or aluminum, I just made up some numbers to illustrate the heat balance equation. The specific heat capacity values might not be correct. You can do your own calculation.

[ilardimichael26]

Yes I can do the calculations, the steady state temperature will definitely be between 300 and 320. However the purpose of this model I am doing is for demonstration and teaching for a group project. I am making instructions on how to make a FLUENT model, set boundary conditions, patches if needed, and get some results. So although the solution to my simple model is easy to calculate, I still need to get FLUENT to solve it for me.

Unfortunately, I do not have any training or anyone to train me, but have figure out a decent amount from videos online. Now that I know I need to create a patch for the two regions (wall and fluid domain) to set these initial temperatures, how exactly do I do this? When I go to standard initialization. The option to patch is grayed out.

Thanks

[Rob]

You need to initialise the solution before you can patch.

If you're teaching a course I strongly advise getting access to the ANSYS Learning Hub (training courses) so you're further up the learning curve than the students. They'll be asking questions on here too!