# UDF for Q_loss

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 March 26, 2020, 05:39 UDF for Q_loss #1 New Member   Ahmed Join Date: Sep 2019 Posts: 19 Rep Power: 2 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?????

 March 26, 2020, 06:17 Udf #2 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 1,305 Blog Entries: 1 Rep Power: 21 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. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum

 March 26, 2020, 06:38 #3 New Member   Ahmed Join Date: Sep 2019 Posts: 19 Rep Power: 2 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 Regards

 March 26, 2020, 06:51 Heat Transfer #4 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 1,305 Blog Entries: 1 Rep Power: 21 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. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum

 March 26, 2020, 07:13 #5 New Member   Ahmed Join Date: Sep 2019 Posts: 19 Rep Power: 2 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

 March 26, 2020, 07:19 Confined Surrounding #6 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 1,305 Blog Entries: 1 Rep Power: 21 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. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared on the Forum