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-   -   DPM mass flow rate (https://www.cfd-online.com/Forums/fluent/33641-dpm-mass-flow-rate.html)

 Szabolcs Varga May 4, 2004 10:50

DPM mass flow rate

Dear all, The particle mass flow rate is defined at the injection panel. I wrote a UDF where the I use the function(see the whole udf below): C_UDMI(c,t,p_frate)=P_FLOW_RATE(p) to store particle flow rate in a user memory for each cell. After solution, the values summed in the surface integral panel e.g over the outlet (any closed surface around the injection point) should give the total injection mass flow rate, shouldn't it? In my model it doesn´t. Could you help me please what I might be doing wrong?

/* UDF for computing the magnetic force on a charged particle */

#include "udf.h" #include "surf.h" #define charge_per_meter 1.6e-11 /* particle electric charge */

DEFINE_DPM_BODY_FORCE(particle_l_forcemod, p, i) { cell_t c = RP_CELL(&(p->cCell)); Thread *t = RP_THREAD(&(p->cCell)); real l_force, mp, ex_t, er_t, Elp; real charge_on_p;

int V_x=0, V_r=1, E_x=0, E_r=1, numb_part=3, p_frate=4, p_m=5;

mp=P_MASS(p);

C_UDMI(c,t,p_frate)=P_FLOW_RATE(p); C_UDMI(c,t,p_m)=P_MASS(p); C_UDMI(c,t,numb_part)=P_FLOW_RATE(p)/P_MASS(p);

charge_on_p= P_DIAM(p)*charge_per_meter; ex_t=C_UDMI(c,t,E_x); er_t=C_UDMI(c,t,E_r);

 Allan Walsh May 4, 2004 14:02

Re: DPM mass flow rate

I'm not sure it should add up. Be careful that the units are the same for both variables - and how would you factor in residence time for the particles in Lagrangian form.

 Szabolcs Varga May 5, 2004 06:08

Re: DPM mass flow rate

Dear Alan, Thank you for your answer. I checked again the UDF manual, and it says that the P_FLOW_RATE(p) returns the particle mass P_MASS(p) times the number of particles in this stream (p) that passes a particular point in a second. It should give kg/s. My doubt is that, if there are two streams in the same cell, does it sum up? How can I caculate the total mass flow rate of particles in each cell? The problem is relatively simple, it is a conduct with and injection surface and an outlet surface. The particles are tracked in between these two. In principle every cross section should have the same mass flow rate both particles and fluid. When Fluent gives me the summary at the end of the particle tracking, the flow rates at the injection and escape boundary (no trap in between) match, but not using the sum of the P_FLOW_RATE(p) over the outlet surface. I am certain that I am doing something incorrectly, but cannot figure out what. Finest regards, Szabolcs

 Allan Walsh May 6, 2004 15:21

Re: DPM mass flow rate

There is a difference between the particle mass and the fraction of the total particle mass represented by each drop. For example, a particle may have a mass of 0.001 kg but represent say 10% of the particle mass flow rate of say 1 kg/s for 0.1 kg/s.

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