Thermal Analysis of baffles in Ansys Fluent

In today's post, I would like to show you a tutorial on heat transfer through partitions. Thanks to such an analysis, we are able to determine the insulation performance of a building or device. We are also able to determine the size of thermal bridges in the analyzed geometry.

Thermal analysis of baffles model in Ansys Fluent

In the first stage, we need to define the boundary conditions of our geometry. We are dealing here with four layers. Two of them are the most important: the thickest one on the left is made of polystyrene and the third layer in the order from the left, defined as a space filled with air. Two thin layers can be defined as any solid material. The bc_out condition is the temperature outside the building, while bc_in is the thermal condition inside the room. A detailed description of these above conditions will be presented below.

Boundary conditions of analyzed model

In the next step, we define the type of analysis as Steady State. We also define gravity to take into account hydrostatic forces in the gas domain. Due to the fact that our model is two-dimensional, we have an additional 2D Planar option turned on. This option is available only in Fluent. At CFX, unfortunately, we cannot analyze typically two-dimensional models.

Type of simulation and type of geometric model (2D)

There are three physical models in our analysis. We turn on heat transport (Energy - ON) and set the turbulence (viscous) model for laminar flow. We also define the radiation model between the walls that border the gas domain and the bc_in / bc_out conditions. In our case, we deal with the radiation of surfaces affecting each other, so we choose the Surface to Surface (S2S) type. We cannot forget to initiate interaction coefficients between model objects by pressing the (Compute / Write / Read) button. It is important to specify all radiation conditions in the program. We do this only when our model is S2S.

Surface to Surface Radiation Model (S2S) in Ansys Fluent

We define three solid domains in which we use two wood materials (red and blue frame) and for the thickest layer we use polystyrene (black frame).

Material Definition in Ansys Fluent

As I mentioned before, any material can be assigned to solid domains. We just have to stick to the definition for the thickest layer (polystyrene) and the domain where the gas will be (the second, the thickest).

Cell Zone Definition in Ansys Fluent

To describe the conditions inside the room and the conditions outside the building as accurately as possible, we use the MIXED boundary condition in the Thermal tab. Thanks to this kind of boundary condition, we can precisely define the convection and radiation conditions for our bc_in and bc_out.

BC's of IN and OUT conditions for our geometry

As for the solver settings, we choose Coupled due to the fact that we are dealing with a simplified (laminar) analysis of the Steady State type. We set the Energy and Momentum solvers to Quick because for our analysis we do not need increased accuracy of the calculations - the most important thing is the calculation time. Due to the undisturbed flow, we set the Courant number at the level of 2. We define 240 iterations (black frame).

Solver Settings in Ansys Fluent

Below we can see the temperature distribution on the model for each defined layer. As you can see, the distribution is not uniform (gas domain) due to the action of hydrostatic forces - warm air moves up due to gravity and low flow rates.