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-   -   FloEFD.V5 - Problems with Heat Source (http://www.cfd-online.com/Forums/floefd-floworks-flotherm/69347-floefd-v5-problems-heat-source.html)

 CP85 October 20, 2009 09:13

FloEFD.V5 - Problems with Heat Source

Hello!

I am trying to simulate a simplified cylinder of a small engine with FloEFD.V5.

Therefore I set up an internal analysis. The cylinder ist put in a rectangular room with a constant volume flow of air (for cooling). Exclude cavities without flow conditions is activatet. (so the inner air-volume of the cylinder is not modelled).
Heat conduction in Solids is activatet and I am running a stationary analysis.
The default material is aluminium, the rectangular box is an insulator.

Some facts I know from reality:
The volume flow arround the cylinder (~218 m³/h)
The material of the cylinder (aluminium)
The heat generation of the engine (~7kW)
In reality this leads to surfacetemperatures of max 250°C

Now I tried to simulate this but I got much larger temperatures (above the melting point).

So has anyone an idea how I can set up the simulation so that it fits the real measured data?

I tried the following heat sources without luck:
Volumesource at the complete cylinder
Surfacesource on the complete inner cylinderwall
Surfacesource on the upper inner cylinderwall (were the combustion takes place)
I treid: 7kW (leads to temp. ~1000°C); 5kW (leads to temp. ~800°C)

So any ideas or hints for me?

kind regards
CP

 YYY October 28, 2009 08:22

How did you apply the air volume flow for it in the box? by the surface? and the temperature of air?

why do not you use the external analysis?

 CP85 October 28, 2009 08:57

I'll make a Screenshot of how I applied the boundary conditions and how the modell looks like.
Otherwise it will be hard to describe.
I'll post it within the next 24h.

I did not set up an external analysis, because it would not fit to reality.

 CP85 October 29, 2009 09:56

1 Attachment(s)
Here the picture:

Red Arrows: Volume Flow: 218 m³/h
Blue Arrows: Enviromental pressure

 YYY October 29, 2009 14:32

It seems OK

1) if you define the heat source for surface,you can have W/m^2 or W. You should check it is W or W/m^2.
2) The material is Aluminum, could you check the thermal conductivity of it in the default material setting? I always input the material by myself.
3) refining mesh
4) I believe the results could be a little higher than the experiment results since you have defined the box as the insulator. but 1000C vs. 250C is too much difference.

Your case is not complicated actually. The air flow cool the 7KW heat source with Al material.

 YYY October 29, 2009 14:34

By the way

what is gerneral setting you defined over the wall condition?

 CP85 October 30, 2009 04:30

1) it is W
2) seems to be ok:
150K = 248 W/(m*K)
200K = 237 W/(m*K)
300K = 237 W/(m*K)
400K = 240 W/(m*K)
600K = 230 W/(m*K)
3) I tried this a few days ago. Indeed the temperatur drecreesed a bit, but not enough to reach the 250°C. Seems that a fine wall boundary resolution is needed.
4) I think I will give it up to use the same heat source as in reality.
I will try modify and decreese the Heat Source as long as I reach the measured temperatures.
5) general settings:
Default outer wall thermal condition: adiabatic
Roughness: 0 mircometer

Thank you for your thoughts and informations!

 YYY October 30, 2009 07:11

do you try to calculate heat transfer by emperical way

I think you will have the insights about it.
I suggest you contact your F LOEFD supplier and post your problem to them. they may give your some hints.
success!

 murat November 2, 2009 18:41

Quote:
 Originally Posted by CP85 (Post 234600) 1) it is W 2) seems to be ok: 150K = 248 W/(m*K) 200K = 237 W/(m*K) 300K = 237 W/(m*K) 400K = 240 W/(m*K) 600K = 230 W/(m*K) 3) I tried this a few days ago. Indeed the temperatur drecreesed a bit, but not enough to reach the 250°C. Seems that a fine wall boundary resolution is needed. 4) I think I will give it up to use the same heat source as in reality. I will try modify and decreese the Heat Source as long as I reach the measured temperatures. 5) general settings: Default outer wall thermal condition: adiabatic Roughness: 0 mircometer Thank you for your thoughts and informations!
My suggestions

1- You use only volume heat source
2- You use refinement mesh which is in Calculation Control Options if the model need more mesh FloEFD add automatically while solving according to velocity gradient vector
3- You set up converge criteria again and decrase it
4- I do not know but fluid intial temperature is different from solid may be you should create intial conditions for heater solid

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