User defined scalars!!
Hi all,
If some one has worked on user defined scalars can you please share me your experience on that please. I need to find out the age of air. how long it takes to reach the outlet. If there is another way around please let me know. Thanks Kind regards Mischelle 
Re: User defined scalars!!
hi yes you can use a UDS for mean age of air which seeds the domain with time and needs a few more iterations to solve only. It is implemented the same in Airpak that uses Fluent but in a more automatic fashion. I can provide this but need time to gather info.

Re: User defined scalars!!
Instructions for mean age of air UDS:
Convert this text to a *.c file then compile as usual and follow notes to hook in. Then solve for scalar only and post process UDS displayed as mean age in seconds. /* Diffusivity for mean age of air is solved using a userdefined scalar. This calculation can be performed after the normal problem has already been solved ... just turn off all of the previous equations being solved for and activate solution of the userdefined scalar0 equation. Make sure to select  mean_age_diff as the uds diffusivity in the materials panel  mass flow rate as the uds flux function  mean_age_source as the uds volumetric source term in all fluid regions Use a journal like this to do that in F63 : def bc fluid fluid1 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n def bc fluid fluid2 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n def bc fluid fluid3 n y 0 0 0 0 0 0 0 1 n y "mean_age_source" n y 0 0 0 0 0 0 n n n etc  set uds0 scalar values = 0.0 at all inlets and outlets mean age of air calculations do not require any energy, radiation, or species transport calculations to have been performed */ /************************************************** *****/ #include "udf.h" #include "prop.h" DEFINE_DIFFUSIVITY(mean_age_diff, c, t, i) { return C_R(c,t)*2.88e05+C_MU_EFF(c,t)/0.7; } DEFINE_SOURCE(mean_age_source, c, t, dS, eqn) { dS[eqn]=0; return C_R(c,t); } 
Hi red lemon,
thanks for the post. I just did not get the part regarding the "mean_age_source" and the journal. whats the function of the mean_age_source in conjunction with the mean_age_diff and what is the meaning and application of the journal text you mentioned? thanks 
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