topic Re: Thermal Conduction Heat Flux Wall Calculator help in CFD Forum

Thermal Conduction Heat Flux Wall Calculator help

Anonymous — Wed, 17 Jul 2019 13:37:50 GMT

Hi,

I am studying thermal conduction on a wall.

Using the "wall calculator", I get 55W of heat flux, which I also get by hand calculation.

However, I'm confused when adding air volume

I would like to justify the Heat Flux = 6.97348 W on the internal surface of the wall.

To get the outside heat flux, I assumed the following calculation:

Can someone help?

Re: Thermal Conduction Heat Flux Wall Calculator help

KKizildemir — Wed, 17 Jul 2019 14:55:12 GMT

Hi @Anonymous

The temperature gradient of the wall edges adjacent to the air block tells us that there is something wrong with Boundary ID3. Did you turned off 24°C BC on that face? Or can you please send the simulation files? So we can see all the BCs you've create.

Re: Thermal Conduction Heat Flux Wall Calculator help

Anonymous — Wed, 17 Jul 2019 15:12:13 GMT

https://we.tl/t-Xz11ixxLEa

Re: Thermal Conduction Heat Flux Wall Calculator help

Anonymous — Wed, 17 Jul 2019 16:04:39 GMT

Re: Thermal Conduction Heat Flux Wall Calculator help

marwan_azzam — Wed, 17 Jul 2019 17:43:18 GMT

That last image looks more like what I get when I recreated the model.

The delta temperature through the solid part is pretty small. It varies from 35 C to 34.944 C.

Marwan

Re: Thermal Conduction Heat Flux Wall Calculator help

Anonymous — Wed, 17 Jul 2019 19:04:12 GMT

The 6,... heat flux should be the heat going into the airbox. And that beautiful gradient because of the airbox walls with boundary condition set are touching the concret wall, and affects to the heat flux.

I'm a noob, so... some noob opinions 😉

1. Keep the model as simple as possible

2. If you want the air being affected by temperature, set air material as variable, and when solving activate flow, and set gravity air as Earth (0,0,-1)

3. The mesh is very important, it changes temperatures and heat flux values, as Marwan showed me here https://forums.autodesk.com/t5/cfd-forum/simple-air-box/td-p/8907562

Re: Thermal Conduction Heat Flux Wall Calculator help

marwan_azzam — Wed, 17 Jul 2019 19:23:36 GMT

CFD predicts the heat flux going into and out of the system of 0.28 Watts.

Hand calculations produce a heat flux of 0.28 Watts as well.

Marwan

Re: Thermal Conduction Heat Flux Wall Calculator help

Anonymous — Wed, 17 Jul 2019 20:56:36 GMT

Yes, I assumed that the first image has more surfaces with BC 24º, the second only 1, which is agree with manual calculations, but... (always a "but")

at the contact surface (boundary 3), CFD gives you 0 W? I get some residual value 0.093...