Learning Forum

[Aemon]

 

 

Hello,

I have a heat sink in my system that I cannot trace and I hope that someone can tell me where I might have made a mistake!

The system:

- A solid with a constant heat source (red)
- A "container" with liquid water (blue)
- A solid body with poor thermal conductivity as "insulation" (yellow)

As soon as I activate gravity to obtain natural convection, the heat flow balance is no longer correct (stationary simulation). About 95% of the generated heat goes into the water and does not leave it. The temperature of the water is very low.

- I have defined the density of the water with "Boussinesq" or with my own expression (density graph looks good).
- Boundary conditions: constant temperature (or partial heat flow=0)
- The grid is quite finely resolved in the transitions (>1 million elements)
- Body: A component group in the DesignModeler (seems to be no mesh problems)

The Flux Report confirms that something is wrong:

Where could the error be?

[Rob]

Can you confirm the wall & shadow pair are retained as "coupled" wall (looks that way in the reports) and are you running steady or transient? What's the outer bc on the yellow block (rand-seite and unten as a guess). 

[Aemon]

Hello,

thanks for looking at it!

• wall & shadow are "coupled"
• running steady
• the boundary conditions "rand_seite" and "rand_unten" have two different but constant temperatures (like 10°C)

[Rob]

OK, so the heat ought to leave eventually and reach something near an equilibrium state. Please can you post some images and residual plot. 

[Aemon]

Hello Rob,

when recreating the residuals graphs, I wanted to go a little further down (I still had the termination criterion for the residuals set to "Default", i.e. 0.001).
The large error in the heat flows has decreased massively with smaller residuals. (If the residual of the continuity is 10^(-6), the deviation of the heat flow is only about 0.1%).
Thanks for the suggestion!