# Help UDF to Boundary Conditions in Closed Loop Pipe

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 May 14, 2012, 06:58 Help UDF to Boundary Conditions in Closed Loop Pipe #1 New Member   blai Join Date: Mar 2012 Posts: 8 Rep Power: 5 Hello, I'm trying to simulate a closed loop pipe as the first figure. The fluid passes through an area where it is heated (wall-heated), and so on until reaching a stationary case where the fluid will have the same temperature as the hot wall (wall-heated). I have found the problem that Fluent can not give a closed fluid velocity. So I designed an open loop where the exit temperature is equal to the inlet temperature, as shown in the figure below. At first I tried to do with BC-Periodic function, but without results. For this reason and as a last solution, I want to do with a UDF. I want to take the temperature of the output and link it to the input, but just the temperature! Someone who understands the issue of UDF can help me write, because I am new to the UDF. Thanks in advance! Blader.

 May 14, 2012, 07:52 #2 Member   Daniel Tanner Join Date: Apr 2009 Posts: 54 Rep Power: 8 I think a periodic boundary condition would be best for this. Why did it fail for you? How about simulating one quarter of the loop (i.e., it is a series of 4 right angle bends). This would be more representative as the circuit is symmetric in this way and you don't have to leave the gap. Then use the periodic boundary condition to ensure that the conditions of fluid leaving the bend are imposed on the fluid entering it. For the periodic boundary condition you need to be careful to ensure that the mesh is the same on both inlet and outlet faces.

 May 14, 2012, 09:48 #3 New Member   blai Join Date: Mar 2012 Posts: 8 Rep Power: 5 Hi, To verify the functionality of the periodic boundary condition, I made the following fast simulation: In the curved wall, apply a heat of 400 K. The temperature in periodic BC is 300K. In the stationary case, the fluid temperature will be the same as wall heated, 400K,but as you see in the following figure, never reaches 400K ! That is why I ruled out the option of periodic boundary condition. Someone can help me with the UDF? Thanks

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