Learning Forum

[Alex Chiella]

Hi! I have got an elbow pipe with a stream at -100°C, surrounding atmosphere is air at 20°C.

I'd like to know how to make the wall adiabatic.
If I set the heat transfer boundary condition to 0 I get this:

The're a gradient on the outside.
There's no material flow through the wall:

 

Now, the adiabatic hypothesis is quite strong and I might even take this "smoothing" as it is without posing question, but I have two issues:

1. Here, it looks like the pipe is behaving more like an ideal heat source at T=Twall_cell. Which might be useful, but it really is not anything I have ever been taught as adiabatic
2. The main one: it gives me some issues with residuals and convergence

Where am I messing up? At some point I'll hopefully have the time to properly initialize the wall heat transfer, but till then I'd much rather shut off any heat flow there.

[Saurabh R Patil]

Hi,

You can define an adiabatic wall by setting a zero heat flux condition. This is the default condition for all walls.

Thank you.

[Alex Chiella]

 

Hi SRP, thanks for reaching out!!
The problem is that it looks like it’s not working. This is set way I initialized all my walls:

Yet, I do see an air Temperature gradient right at the wall, with no other temperature differences or heat sources available. What did I get wrong?

P.S. I just noticed that multi-editing didn't quite work and that some walls were automatically initialised as coupled. I'm checking that out right now

[Rob]

A coupled wall should have heat passing through it - it's the boundary between the fluid and whatever is containing it. So, wall & wall:shadow which represent the "wet" and "dry" sides, but not necessarily respectively.