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UDF for Q_loss

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Old   March 26, 2020, 05:39
Default UDF for Q_loss
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In a transient analysis
I want to define Q_loss from tank walls to ambient as a function of
1- The average temp of the tank ( varied with each time step )
2- Temp of the surrounding (varied with each time step )

This will be used as a boundary condition for the tank wall

correlation:
Q_loss=1.2*(T_av_tank - T_surr)^1.26

If any one please can make udf function for that as i don't know how to make it or if there any other easier way to incorporate this as boundary condition of the tank wall?????
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Old   March 26, 2020, 06:17
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Someone might be willing to write a UDF, however, there are other aspects of this equation. Heat flux is not a function of the average temperature rather of the wall temperature. Secondly, whoever writes the UDF needs to know how would you vary the surrounding temperature. It is provided via a text file or via any equation? It is only because of the exponent 1.26 that you might require a UDF, otherwise, this can be done without the UDF.
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Old   March 26, 2020, 06:38
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Dear Mr vinerm,

Thanks for your reply and your effort.
The temp of water inside the tank will be initially AT 60 DEGREE C and then it will decrease with time by cooling in the ambient air

The temp of the surrounding will be initially 24 and will increase with time

That means that this equation of the heat flux is the only boundary condition which will affect the process

This is equation from a scientific paper that I am trying to validate and it was published in a very good journal

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Old   March 26, 2020, 06:51
Default Heat Transfer
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Cooling from a wall by convection is always governed by Newton's law, i.e., 1 in place of 1.26. 1.26 is possible only with augmented heat transfer, such as, simplified modeling of radiation or some other similar methodology. Secondly, until and unless the surroundings of the tank are confined, the temperature will remain at 24 and not increase. If the surroundings are confined, then it will increase but this has to be solved as a part of the system, i.e., CFD model will also have to include the surroundings of the tank.
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Old   March 26, 2020, 07:13
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so how to make the surrounding confined ?

To make it much bigger ?

And also what BC to give to the outer boundary of the surrounding after making it bigger ? Symmetry or wall ?

Thanks in advance
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Old   March 26, 2020, 07:19
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You don't make it confined. This has to be based on what you are trying to validate or simulate. If the surroundings are confined in that case, then you do it as well, otherwise not.
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