Conjugate Heat Transfer (CHT) Modeling in Ansys Discovery

Hello, welcome to a presentation by Ozen Engineering. This is Mert Berkman. Today, I would like to talk about ANSYS Discovery, in particular, how to build a conjugate heat transfer model. For this purpose, we’re going to consider a simple electronics cooling problem.

And as you can see, we have an enclosure, which is named “chassis.” If we hide this, what we’re going to see is the insides, where we have a die, which is generating some heat. And on top of it is a heat sink. And then on the bottom, we have a board. And underneath is a PCB.

Obviously, when you start with a CFD type of model, you want to make sure the geometry is correct and it serves the purpose, which is already the case for this particular problem. And as you can see, we’re in the modeling or model mode for ANSYS Discovery.

And we have a lot of control over the geometry. We can change things. We can pull surfaces and manipulate the geometry. But we’re not going to deal with a lot of geometry operations, except what we’re missing is the fluid volume. So you can see four parts for solids. But there’s no air volume.

In order to quickly get that, actually, we could jump to the fluid volume. So we can see the fluid volume. And in order to get that, actually, we could jump to the simulation tab. And if we move on to the explore option, it’s going to bring up the capabilities.

And these are different types of solutions, modeling solutions you can achieve. We’re going to click this internal flow button. And this is a very useful tool in which that it very quickly creates an internal flow. You can see that the flow is very fast. So you can see that the flow is very fast.

If you want to pick the bottom one, external flow, that is going to create an enclosure around the whole geometry. But because we have an internal flow problem, first, we want to mark a surface that kind of defines the inlet. And for the second, we want to click a surface for that bounds the outlet.

We don’t need to cap surfaces because this geometry is already there. And we can see that the flow is very fast. And we can see that the flow is very fast. And this is how we can get the cap when you do inlet and outlet. And as you notice, it generated this volume after clicking those two buttons.

So let’s take a look at the volume. So we go to display and let’s switch to wireframe. And what we do see is the internal details. And if I turn on/off heatsink, die, board, chassis. And we can see the internal details. If I turn on the heatsink, die, board, chassis.

And we can see the internal details. If I turn on/off heatsink, die, board, chassis. You can still see the internals, which is carved out of the fluid volume. And that’s exactly what we want. So I’m going to go back and turn the graphics on to shaded.

And what I’m also going to do now is start putting in some material properties. So let’s go to our volume. One thing I typically like to do is just move this up here. And now we have a little bit of volume. I’m going to turn this off. We have a little bit of value.

So we can see this is the value of the material. Here, and delete this for clarity so we have our five components, and let’s start with the chassis. So the chassis, we don’t want in the simulation; we really don’t need it. So I’m going to keep it this way.

The board, die, and the heat sink, let’s turn these on and make it available for simulation. So starting with the board, I’ll double click on it, and let’s go back to design.

So once I do “board,” it is going to go to this material property, and here you can see that there are so many options for materials. The board is, we want something plastic for a PCB with low conductivity. So I’ll just go to plastic.

Now the board is assigned and it’s also highlighted in orange. Let’s double click on “die” again; it goes to structures (still by default), but this is to be silicon. So I’ll go in the alphabetical order and go assign silicon to our die, and now that’s highlighted in orange.

Let’s do a heat sink; go back there. We want something conductive, some sort of an alloy—aluminum alloy, maybe. We can pick. Now the heat sink is assigned; aluminum alloy. Let’s look at our air volume. The default is water, and let’s change it to air (gas). Now that is also assigned.

Now let’s keep building our physics. So far, what we’ve done is define the fluid flow, and let’s make our inlet five meters per second. So you can quickly change values here.

We’re including gravity, which we can do with the fluid flow, and we can also add some solid thermal boundary conditions, which is all right. It’s not going to play a big role in this problem, but let’s keep it in. What we’re missing is the thermal boundary condition.

So we go back to simulation, and what we’ll do is we want to add some solid thermal boundary conditions, which is going to make this a multi-physics type problem. So here, let’s define some solid conditions.

So I go to “die,” I right-click on the die, and I’ll say “hide others” so that this is only going to show my die. And then I want to add heat because this is a heat-generating component. So the volume is picked, and let’s put 30 watts of total heat to this object.

Now we see this new object, and what it has done is it added our heat and it also very nicely did what it did was found all the external most surfaces and assigned the reasonable (natural convection) boundary condition in this particular case. Actually, we don’t want to use the chassis.

So what I’m going to do is I’m going to go ahead and exclude chassis from the simulation by clicking this button. So notice that that turns off. Now the fluid outer walls have become no-slip walls (default).

Let’s double click on this and let’s see if we can change the boundary condition here. So now it’s wanted to lose heat. So the heat should get out of one domain. So we should put a connection type boundary condition, radiation, and that’s it. It’s done. So we see now that added.

Also, what I do notice is that Discovery has added some connections automatically once I enabled conjugate heat transfer. Essentially, what it did was it looked at all the solids and the fluids and between the solids, it put bonded contacts.

And then between solid-fluid interfaces, it put these kind of pink surfaces highlighted so that the solids and the fluids are coupled to each other where they pass thermal information. So right now, it looks like we have all our setup ready.

And what typically we want to first do is do a simulation in the explore mode, maybe with about the mid-level granularity. So what I’m going to do now is pick that mid-granularity. After that, I go to the bottom arc on the right side and I go to the center and I click the solve button.

What this will do is it will start the iterations for the CFD and thermal solution, and if you turn on any controllers, it has the solution progress as you can actually see the temperatures inside the domain. Any and we’re essentially watching the simulation goal and progress.

If you want to notice, we also tend to produce some of these curves here. We come up side by side and people call them operations. Another indicator that the simulation is underway is this white line kind of traveling in this green border.

And if you leave your mouse in there, it gives you the status. So after about three to five minutes, our solution is converged. So looking at our converged solution, now we see that it’s going to say “complete.” So that’s good. And what we have is a solution.

It essentially shows us that the solution is complete. It shows that the hottest regions are the die, which reaches around 167 degrees C. Then essentially, the heat sink is taking the heat away and putting it out to the cooling air, and then it goes out to the outer bound.

And that essentially concludes our simulation. Thank you. And I would like to note that the simulation was done in the explore mode where we did not use any real mesh.

In the upcoming videos, I’m going to talk about the refine mode, where we can generate the mesh and also see the mesh and get a fairly similar solution. But explore mode is very effective in quickly making design changes and getting solutions.

So I’ll see you in our next video where I’ll talk about some post-processing, refine mode, also some of the settings and options. Thank you.