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-   -   Changing the unknown(target) variable in convection;From WallTemperature to HTC! (https://www.cfd-online.com/Forums/star-ccm/99855-changing-unknown-target-variable-convection-walltemperature-htc.html)

 fshak92 April 13, 2012 11:17

Changing the unknown(target) variable in convection;From WallTemperature to HTC!

In a convection simulation of a surface we set the ambient temperature and the heat transfer coefficient to find the wall temperature.
Is there anyway to change the unknown variable?
i mean set ambient temperature and wall temperature to find HTC!

I used two kinds of simulation but there are some problems in both of these ways:

1) having 2 regions: my body and a block surrounded it as air.
(the problem is that we cannot set any constant ambient temperature for the block(air)***)

2) having 1 region: in this case we cannot set both 'constant temperature boundary' and 'convection boundary' for our body .

***I can set some constant temperature for the block's outer surface but its not a good way because the simulation are influenced by some unwanted parameters like the dimensions of the block and ... .

I would appreciate if anyone has any idea or suggestion.

 abdul099 April 28, 2012 08:14

Again, like mentioned in another post:

You will not have a constant temperature in your air when the block is hot. NEVER! Not in this universe!

What you can try to do is to put a temperature boundary condition to the block. The HTC will be calculated from the heat flux and the temperature difference of block surface temperature and the reference temperature. The reference temperature can be specified in the heat transfer coefficient field function.

But be aware, the HTC will be calculated by taking the heat flux into account. And the heat flux is influenced by the air temperature near the wall, therefore the heat flux will be lower than it would be when the air temperature would really be constant!
But also the block temperature will not be constant in the real world since the heat flux going out of the block will slightly cool it down

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