# UDF :Unsteady concentration profile

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 July 11, 2003, 18:18 UDF :Unsteady concentration profile #1 umesh Guest   Posts: n/a hi I want to simulate a batch process. It consists of a Packed bed reactor and Recycle Tank with a mixer. Output of Reactor (C1) goes to Tank and then recycled back to the Reactor (c2) Its a cyclic batch process. I had got steady state solution for the Reactor case. To get Unsteady solution, I had to use a UDF to describe the Tank Model which is C2 = C1 * exp (- t / T ) I need to use the Exit conc. from reactor (c1), Calcuate C2 using UDF, which is function of time.T is constant 1. Is it possible to write such UDF. 2. Which Macros to use ? 3. How can I use the Exit Conc. (C1 ) Please give me some hint.. or a Sample UDF Any comments will be appreciated. Thanks in advance -Umesh

 July 12, 2003, 03:45 Re: UDF :Unsteady concentration profile #3 Umesh Guest   Posts: n/a Dear ap, You got my prooblem correctly. Your suggestions are useful. Here, C1 is constant at the OUTFLOW BOUNDRY, but it will change with time. But it has a profile along the Bed height. I will Need C1 only at the OUTFLOW . so it is somewhat easier. Thanks for your time. --

 July 12, 2003, 09:21 Re: UDF :Unsteady concentration profile #4 umesh Guest   Posts: n/a Hi, For the system I mentioned previous message, It contains Two different speces .. So, I had to write the model C2 = C1 * exp(-t/T) for two different species. Can I use IF..Else statement Like if ( i = 1) conc = C_YI(c,t,0)*exp(-t/T); else conc = C_YI(c,t,1)*exp(-t/T); Will such UDF give correct results ? Any comments are welcome.. Thanks in advance.. -Umesh

 July 13, 2003, 17:07 Re: UDF :Unsteady concentration profile #5 ap Guest   Posts: n/a If both species are present at the same time, you don't need the if statement. You just have to define the model twice: in other words, you have to implement two equations like: C2 = C1*exp(-t/T) and C2' = C1'*exp(-t/T) where C1 and C2 refer to the first species and C1' and C2' refer to the second species. Hi ap

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