[Bill Hsu]

Hello everyone,

I tried to use an air conditioner and an air purifier to dilute the particles in a room, I set 2400 particles uniformly distributed in the room initially, and used a UDF to calculate the concentration. The simulation was carried out for 60 minutes (transient and unsteady particle tracking), and I calculated the particle concentration every 5 minutes. Here are my questions:

1. I expected that the particle concentration would decrease as time passed, but the particle concentrations at every timestep are the same as the initial concentration, did anything wrong with my UDF? I already set the escape condition for outlets, and trap condition for walls.

2. The number of particles tracked decreased as time passed, and the escaped and trapped information didn't show up. I am not sure how to fix it.

The following code is my UDF:

/*Particle mass concentration calculation*/
/*Using the particles-in-the-box method*/

#include "udf.h" /*The header file*/
#include "dpm.h"

DEFINE_EXECUTE_AT_END(get_dpm_conc) /*Calculate the flow quantities at the end of an iteration in a steady state run, or at the end of a time step in a transient run*/
{
Domain *d; /*Defined domain pointer*/
Thread *t; /*Defined thread pointer*/
cell_t c; /*cell identifier*/
d = Get_Domain(1);
Injection *I; /*Defined injection pointer*/
Particle *p; /*Defined particle pointer */

Injection *Ilist = Get_dpm_injections(); /*Get the list of all the injections*/

thread_loop_c(t, d) /*Reset the value of UDMI each time*/
{
begin_c_loop(c, t)
{
C_UDMI(c, t, 0) = 0;
}
end_c_loop(c,t)
}

loop(I, Ilist) /*loop over all the particles from a given injection*/
{
loop(p, I->p_init) /*loop over all the particles in transient simulation*/
{
c = P_CELL(p);
t = P_CELL_THREAD(p);
C_UDMI(c, t, 0) += P_N(p) * P_MASS(p) / C_VOLUME(c, t); /*The calculation of particle concentration*/
}
}
}