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Problem during Residence time distribution in fluent

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Old   April 18, 2013, 10:31
Default Problem during Residence time distribution in fluent
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venkat
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hi,

I am doing "Residence Time Distribution" by pulse input method in fluent.But
i am getting tracer (area weighted average) concentration greater than 1. I did experiments also. I compared with simulation results with experimental. The simulation results are less than 5 time the experimental results. In simulations, sum of tracer concentration is greater than 1. The simulation results are (mean residence time) is less than theoretical residence time.


Can anybody help me please.

Thanks in advance
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Old   April 19, 2013, 15:46
Default Residence Time in FLUENT
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Bill Wangard
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Easy way to do residence time in fluent (without particles):

1. Define a User-scalar
2. Set its diffusivity to very small: 1E-11 or so should work
3. Use default flux vector and unsteady term

Compille the following UDF and hook it to the SOURCES for the UDS:

#include "udf.h"
DEFINE_SOURCE(uds_source,c,t,dS,eqn)
{
dS[eqn] = 0;
return C_R(c,t);
}

Set the UDS to 0 at the inlet.

Then, when you solve, the UDS will have the value of residence time.

Regards,
Bill Wangard
Engrana LLC
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Old   April 20, 2013, 03:31
Default Problem during Residence time distribution in fluent
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venkat
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Thank for your reply Mr.Billwangard,
I am newer to UDF that why i choose the pulse method. I don't much about UDF.I attached my geometry.The above one is my geometry. Its converging-converging channel.one end is inlet and one end is outlet. Total length of my channel is 68 mm.The Inlet dia 1 mm
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