# How to introduce a scalar as C(t) = f(C(t-1))

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 February 23, 2006, 00:13 How to introduce a scalar as C(t) = f(C(t-1)) #1 Mahad Guest   Posts: n/a I'm trying to model a scalar distribution in a reactor. The problem is that I need to intrudce an expression for the scalar flux through one of the walls of the reactor. I need the flux to accounts for the value of the scalar in the reactor one time step before it determine the new value; say C(t) = A*C(t-1)* exp(-kt); where A and k are constants. Hope you guys can help with that. Thanks

 February 23, 2006, 13:21 Re: How to introduce a scalar as C(t) = f(C(t-1)) #2 Robin Guest   Posts: n/a Hi Mahad, In a steady state calculation, if you make the scalar a function of itself, the value it will use will come from the previous timestep. Similarly, if you use any of the integral functions on boundaries in your expressions, the results are returned for the values at the previous timestep. Regards, Robin

 February 23, 2006, 13:58 Re: How to introduce a scalar as C(t) = f(C(t-1)) #3 Mahad Guest   Posts: n/a Thanks a lot Robin. But what about transient simulations.

 February 23, 2006, 16:12 Re: How to introduce a scalar as C(t) = f(C(t-1)) #4 Mahad Guest   Posts: n/a The CFX-Pre didn't accept self referencing of the function (using the expression option) even for steady state simulations. Do you know how to get though that?!

 February 23, 2006, 16:30 Re: How to introduce a scalar as C(t) = f(C(t-1)) #5 Robin Guest   Posts: n/a Create an algebraic additional variable equal to your variable. If you're using this in a transient simulation, I don't think what I suggested applies as it will end up using the value from the previous coefficient loop. -Robin

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