## Fluids

#### What is Wall Boundary Conditions – Convection: Wall Thickness

• Bran
Subscriber

Hello,

I am new to Fluent and I am doing a simulation of an air conditioning unit supplying cold air to cool down batteries. I am setting boundary conditions for convection, but I was wondering what the significance of the wall thickness is?

What does adding a wall thickness impact? Is it a thickness for the fluid domain to interact with and how can I choose a suitable wall thickness?

Regards

• Rob
Ansys Employee

If you look in the documentation it's explained in some detail.  Very simply Fluent allows us to have infinitely thin walls to divide up geometry (ie a CAD surface can be used to bound a region). If you want to model conduction through the wall you need to give it a thickness and possibly turn on shell conduction.

In most cases the wall between the fluid & solid regions is left alone: also do NOT change anything from "coupled" unless you understand why you're doing it.

• Bran
Subscriber

Hi rwoolhou,

Thanks for your reply. My confusion comes from it being in convection settings, I did take a quick look at the documentation so I was confused whether that thickness was related to conduction.

So in this case, if I have heat generated in a battery, I set a source term of 20 W/m3. I want to cool them with an air conditioner inside a container. I set an inlet velocity and a cold temperature and then I can set a convection heat transfer coefficient in convection settings of the battery walls. If I want the heat generated inside the battery to conduct through the walls then I set a thickness in convection boundary conditions?

Otherwise, it will not take into account conduction, but the heat will still transfer via convection into the air?

Thanks again.

• Rob
Ansys Employee

That's an external wall: you set the convection coefficient for a surface that only has mesh on one side.  The thickness is used to add a "skin" to a system where we don't want to mesh the casing.

Have a look in the tutorials included with the 2019Rx documentation as at least one will have wall thermal conditions set.