# UDF for cell zone condition

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 May 20, 2013, 12:13 UDF for cell zone condition #1 New Member   Rachana Vidhi Join Date: Dec 2012 Posts: 8 Rep Power: 13 Hi, I am modeling a system in which the temperature of a large block needs to change with time and with depth (inside the block). A thin pipe (carrying hot liquid) is passing through the block and the temperature of the block around the pipe is affected by that. So, how do I provide a time-dependent cell zone temperature condition? I cannot use "Fixed value" because the temperature profile inside the block needs to be affected by the pipe. Can I use "Source term" somehow for this? I think I will be able to make the UDF but how (and where) do I use it? Please help me out.

 May 22, 2013, 08:04 #2 Senior Member   Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17 Can you put some light on problem? Yes, You can model temperature as a source term which varies with space and time. If you have mathematical model then you can easily put down this into UDF. Best wishes

 May 22, 2013, 12:28 #3 New Member   Rachana Vidhi Join Date: Dec 2012 Posts: 8 Rep Power: 13 I am modeling underground heat pump and i need to study the seasonal variations. So, I have a solid block, which represents the earth, and a horizontal pipe passing through it. Now the temperature of the underground soil will vary with depth and with season. I have an expression for that, where it varies exponentially with depth and sinusoidally with time (in the same equation). Now the temperature of the soil in the pipe vicinity will be affected by the heat pump and the heat pump performance will in turn be affected by the soil temperature. And this is where I get stuck. If I patch the earth block for a temperature profile that varies with depth, it doesn't include the time dependence. Please help me. Is there any more information I need to provide?

 May 23, 2013, 02:05 #4 Senior Member   Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17 Is it possible to upload schematic diagram along with BC and the expression for temperature?

May 23, 2013, 18:55
#5
New Member

Rachana Vidhi
Join Date: Dec 2012
Posts: 8
Rep Power: 13
I am attaching the schematic of the problem. This is the temperature profile of undisturbed soil:
T_soil = T_avg - A exp[-z (π/365a)^(1⁄2) ]∙ cos{2π/365 [t-t0 - z/2 (365/πa)^(1/2) ]}

Tavg, A, t0 are constants. As you see the "exp" term signifies the change with depth (z). The "cosine" term depends on time (t) and has a phase term that depends on depth.

As the air passes through the pipe at a temperature of T_air, the soil temperature around the pipe will get affected. But the total size of the earth block is very large (decided from literature and personal experience). So at the top, side and bottom surfaces of the earth block, heat flux is zero.
Attached Images
 air_2D_3.jpg (49.2 KB, 105 views)

 May 24, 2013, 00:33 #6 Senior Member   Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17 where are you going to define the temperature i.e on which face? When you represent temp. as a function of 'z', it will have 1D variation. Now if you are saying that this temperature will be for same throughout the 'x', then this condition can be defined by profile condition. This profile can be incorporated as a function of time also. or else you have add the second coordinate into expression. and then you can have UDF.

May 24, 2013, 11:35
#7
New Member

Rachana Vidhi
Join Date: Dec 2012
Posts: 8
Rep Power: 13
This profile applies to the complete earth block, where z=0 at the top of the surface. The variation occurs vertically. The resulting profile (undisturbed soil) at a fixed time should be something like that shown in the figure. It doesn't change horizontally. I obtained this by defining a custom field function and patching the earth block with that. This profile doesn't include time variation. How do I include that? Please let me know.
Attached Images
 field_function.jpg (56.7 KB, 80 views)

 August 23, 2013, 15:10 Temp.varying with space and Time #8 New Member   AMSharma Join Date: Apr 2012 Posts: 12 Rep Power: 14 Did you write udf for mentioning temperature on block surfaces? I am also trying to model this problem..would you please share the model udf for temp.varying with depth and time. Shall be thankful

 October 15, 2013, 05:08 #9 New Member   Flavio G. Join Date: Sep 2013 Posts: 4 Rep Power: 12 How did you solve this problem?? Is it possible to define time dependent cell condition? Thanks.

 December 3, 2014, 15:12 #10 Member   Join Date: May 2014 Posts: 31 Rep Power: 12 could anyone write this udf ? i have the same problem

June 1, 2018, 16:30
#11
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Join Date: Nov 2016
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Quote:
 Originally Posted by rachana This profile applies to the complete earth block, where z=0 at the top of the surface. The variation occurs vertically. The resulting profile (undisturbed soil) at a fixed time should be something like that shown in the figure. It doesn't change horizontally. I obtained this by defining a custom field function and patching the earth block with that. This profile doesn't include time variation. How do I include that? Please let me know.
Hello, rachana,

Now I have the same problem, and I see some users and researchers are facing the same problem, could you please share this UDF for us in your convenience?

Thank you!

 March 15, 2020, 04:45 #12 New Member   sajjan Join Date: Jan 2016 Location: Nepal Posts: 13 Rep Power: 10 I am facing the similar problem. Can someone please share the UDF file or any idea if anyone was able to solve the issue? Thanks

 March 15, 2020, 08:06 Scenario #13 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36 It is not the UDF that is difficult but the approach. If the objective is clear then UDF can be written in a few minutes. sajjan likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 Tags cell zone, time dependent, udf