How to... define quasi porous material in Transient Thermal (material combination)

 A very interesting option in newer versions of Ansys Workbench is defining materials consisting of several components.  It is especially useful because the program automatically updates the physical and thermal properties of the new defined mixture.  It is possible to create, for example, porous materials consisting of a solid and a fluid.

Also thanks to this option it is possible to model the material resistances between multiple layers of solids.  Of course, the mixture may not only consist of two materials.  The amount of ingredients can be created from a large amount so that we can create a quasi-composite.

Below, I will show you step by step how to define the simplest two-component material mix.  It will consist of air and structural steel.  All operations to perform such material modeling may take a few minutes at most.

First of all, select the materials folder in the tree.  Then click Insert and select the Material Combination functions.  After pressing this function, we have to choose the type of materials that our mixture will consist of.  Remember to select the materials you are interested in the program library before defining the mixture in the Ansys Workbench schema block. 

After selecting the materials, you need to set the proportions of our mixture.  We define the proportions as a percentage (red frame).  Once our new material is precisely defined, Ansys will automatically calibrate its physical (density) and thermal properties (conductivity and heat capacity).  If we were to define such a combination in the Structural Module, the program would also calibrate parameters such as Young's modulus, Poisson's ratio, etc.

All changes can be followed in the remaining selected frames in the photo above.

Today, as I mentioned before, I showed you an example of a combination of steel and air to define a quasi-porous material that I modeled as a thin layer (1mm thick) adhering to a solid made of steel.  In this way, I wanted to determine the longitudinal thermal resistances in a material where the porosity of the contact zone with the heat flux was taken into account.  In this way, you can also model the surface roughness of the contact zones, which also significantly affects the resistance between materials.

In the next posts, I want to show you how anisotropic materials are defined in Ansys Fluent.  This is an extremely important method of simplifying models.  We often deal with a solid body that consists of many layers.  In such cases, the mesh of finite elements is very complex and in some cases impossible to produce.  Therefore, in such cases it is worth defining the anisotropic material.  Fluent offers a very rich library of definitions of such materials.  Look for this type of tutorials in the next blog entries.