UDF macro to get relative humidity of air?
 

Hi

Does any one know what is the UDF macro to get the relative humidity of air (%) in a certain cell?

Thnak you.

Relative humidity
 

hi, have you find the answer ? if yes please share the answer.i am modeling a spray in the air using Fluent . I want to get the relative humidity at a various points at different temperature within the domain. if u know the UDF or any other way please share your experience.

thanks

Hi,
there is a macro to get RH in cell:
relative_humidity(cell, thread)

I found it by checking the fluent files one by one.

thanks
 

thanks Jaskull, i will try it and reply you as soon as possible.
thanks

Can you give some details of this macro?
 

How to use it, and where did you find some description?

I didn't find any description. I fount it in one of the fluent files. To use it you need to find the particle cell and thread:
cell_t cc = P_CELL(p);
Thread *t0 = P_CELL_THREAD(p);

then you can find RH in cell where the particle is e.q.:
humidity = relative_humidity(cc, t0);

I'm using it in calculation of equilibrium moisture content of drying particles and it works well.

Hi, Jaskull
 

That is not all indispensable to run this macro.
Ii is yet necessary to declare a suitable file in the header:

#include "udf.h"
#include " ???"

What a file one should include?

Im using this function in macro:
DEFINE_DPM_HEAT_MASS(multivap,p,Cp,hgas,hvap,cvap_ surf,Z,dydt,dzdt)
and read those files:
#include "udf.h"
#include "math.h"

In my opinion "math" is not necessary.

so, there is a problem
 

I tried using it as a trial in EXECUTE_ON_DEMAND macro whith:

#include "udf.h"
#include "math.h" // not neccessary in this case
#include "species.h" // I foundin this file a string ".. real relative_humidity..."

But I receive a compilation error "...unresolved external symbol RELATIVE_HUMIDITY... "

I think you are more lucky whith this issue...

Solution:
 

#include "udf.h"
#include "species.h"

// your code, for instance:

DEFINE_ON_DEMAND(NaZadanie)
{
Domain *dom = Get_Domain(Dzie);
Thread *th_flu = Lookup_Thread(dom, ID_flu); //
cell_t ce_flu;

relative_humidity(ce_flu, th_flu) // lower case only !!! uppercase - you get error!

}

Final remark
 

relative_humidity() works on node values, so if your calculation is cell-based be carefull...