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Heat flux and Heat transfer coefficient

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Old   May 7, 2013, 00:45
Default Heat flux and Heat transfer coefficient
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mahmood
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In a flat plate (exposed in air) an inward heat flux E = 1000 W/m2 is applied. The same plate also receives a convection heat flux due to the difference between the plate temperature and the external air temperature which is imposed as Te = 20 ◦C. The value of the outdoor convection heat transfer coefficient is he = 10 W/m2 K.

Help me how can I do this in the boundary condition of wall as when constant heat flux is applied i cant take account the convection heat transfer(there is no input for heat transfer coefficient).

Again if convection boundary condition is chosen, there is no input for heat flux?

so how can i give this two condition together?

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Old   May 8, 2013, 00:08
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Can anyone help me??
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Old   May 8, 2013, 12:12
Default Create a UDF and calculate the overall net flux BC yourself
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Brandon Hathaway
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In general, you'll only be able to apply one type of boundary condition on a given boundary surface using the default boundary condition options.

This seems like a rather unphysical condition, what are you trying to simulate? Would having the heat generation within the plate itself better represent what you want?

If you are sure you would like to model it in the way you described, you could create a User Defined Function (UDF) with the "Define Profile" UDF macro. You would want to apply this UDF as a defined flux boundary condition. Within the code of the UDF, you can calculate the flux that would result from convection by evaluating the temperature of each surface element and manually calculating the convective flux based on:

q_conv = h * (T - T_ambient)

Then combine the set inward flux you desire to the convective flux value:

q_net = q_inward - q_conv

You then return q_net as the set profile value for the given surface element, which will include the convective loss and the inward heat flux you desire.

Reference the UDF manual and example UDFs for boundary conditions to figure out the exact coding syntax you'll need, but this general approach will do what you described (if that is what you truly desire to model!)
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Old   May 9, 2013, 21:42
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Thank you very much. I will try you suggestion.
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