[f_rojas]

Hello everyone. I´ve a question regarding implementation of BC on a transient heat flow model. In my problem I´ve got a cubic shaped object in which their top and bottom faces are exposed to a heat flow by convection with heat transfer coefficients of 5[W/m2K] and 10[W/m2K], respectively. Now if the temperature of the bottom face drops below 275[K], then its new heat coefficient needs to do change to 10[W/m2K] and the coefficient of the bottom face to 5[W/m2K]. My problem is that when I implement this BC on the top face using a UDF, then I need to program it so that it can access the temperature field on the bottom face and monitor when it drops below 275[K], but I dont know how to program the UDF so it can have access to the temperature field in multiple boundaries.

If any of you have know how to help me i´d very much appreciate it.

[vinerm]

There are at least two ways to do this. You can use (pick...) command in Fluent to access average temperature of a boundary and store it in a scheme variable. This scheme variable can be access in a C based UDF and then used to define boundary condition on the other boundary. For (pick...), type (pick-docu) in Fluent's user interface. It will give you an example of determining the value. To access the value in C based UDF, use RP_Get_Real(name of rp variable that stores the output of pick... command).

Other option is to provide the ID of other boundary within DEFINE_PROFILE. So, you will need to two face loops within DEFINE_PROFILE. First one to calculate average temperature of the other boundary. Second one to apply boundary condition on current boundary. For first loop, you have to use following commands

Thread *ts = Lookup_Thread(Get_Domain(1), 4);

You need to replace 4 with the ID of the other boundary from boundary conditions panel. Then, within first loop, use ts instead of the second argument of DEFINE_PROFILE.