[Lorena]

Hello Mr/Mrs.

I am making a simulation in a square (2D) of 1cm X 1cm of an Heterogeneous Reaction using the VOF option for the multiphase model. I'm working with two phases, the primary phase is gas (compound by two species) and the secondary phase is liquid (compound by two species too). I consider it a transient process. In order to make the correct initialization I used a patch where I define the zones that each species fill.

The heterogeneous reaction develops in the next manner:
a*A(L) ---> b*B(g) + c*C(L) , this means that the liquid reactive produce two products one in gas phase and the other in liquid phase.

I'm using this UDF for the reaction rate function:

/*Heterogeneous net reaction*/
# include "udf.h"
/************************************************** ********/
/*Definiendo valores constantes*/
/************************************************** ********/
# define R 8.31434 /*Constante universal de los gases J/mol-K*/
# define Pre 3.97E+12/*factor Pre-exponential, 1/s*/
# define EA 228000.0 /*Energía de activación, J/mol*/

/************************************************** ********/
/*11...*Definiendo posición de fases [fase primaria 0,fase secundaria 1,……………….] y especies [especie 0,especie 1,……………….] */
/************************************************** ********/
#define gas_index 0 /* index(índice) de la fase gaseosa */
#define gas_vola_index 0 /* index de volátiles en la fase gaseosa */
#define gas_n2_index 1 /* index de n2 en la fase gaseosa */
#define liquid_index 1 /* index de la fase liquida*/
#define liquid_coke_index 0 /* index del coke en la fase líquida */
#define liquid_pp_index 1 /* index del PP en la fase líquida */
/************************************************** ********/
/* 20...Ecuación de laminar de Arrhenius para PP */
/************************************************** ********/
DEFINE_HET_RXN_RATE(reation_rate,c,t,r,mw,yi,rr,rr _t)
{
/************************************************** ************************************************** ****/
/*25 asignación de fases: fase primaria volátiles-nitrógeno [0] y fase secundaria pp fundido y coke [1]*/
/************************************************** ************************************************** ***/
Thread **pt = THREAD_SUB_THREADS(t);
Thread *Prim_t = pt[0]; /*Thread para la fase primaria volátiles-nitrógeno*/
Thread *sec_t = pt[1]; /*Thread para la fase secundaria pp-coke*/
/************************************************** ********/
/*31..llamando valores que se necesitan*/
/************************************************** ********/
real T_sec = C_T(c,sec_t); /*Temperatura de la fase secundaria, K*/
/*34*********************************************** ***********/
/*cálculo de la concentración del pp*/
/************************************************** ********/
real PP_conc;
real AA;
real RHO,Fmpp,Pm,V_sec;
RHO=C_R(c,sec_t);
Fmpp=C_YI(c,sec_t,1);
Pm=mw[liquid_index][liquid_pp_index];
PP_conc=(RHO*Fmpp)/(mw[liquid_index][liquid_pp_index]);
V_sec=C_VOF(c,sec_t);


/************************************************** ********/
/*cálculo de la velocidad de reacción pp*/
/*49*********************************************** ***********/

*rr = Pre*exp(-EA/(R*T_sec))*PP_conc;
AA = Pre*exp(-EA/(R*T_sec))*PP_conc;

C_UDMI(c,t,0)=Pre;

C_UDMI(c,t,1)=EA;

C_UDMI(c,t,2)=R;

C_UDMI(c,t,3)=T_sec;

C_UDMI(c,t,4)=PP_conc;

C_UDMI(c,t,5)=RHO;

C_UDMI(c,t,6)=Fmpp;

C_UDMI(c,t,7)=V_sec;

C_UDMI(c,t,8)=AA;

}

I successfully load and compile the UDF but as you can see in the code I save the values in order to compare them with the the data obtained in the post-processing. The problem is that the data saved in memory doesn't match with those displayed in contours. For example, I save the mass fraction data of an species (memory 6, in red) but it doesn't match with the data shown in mass fraction species contours displayed for that species.

I don't understand why the values defined in my UDF don't respect the initial patch established. Do you think there is something wrong in my UDF?

I will appreciate your comments.

Regards,

Lorena.

[MayTheFlowBeWithYou]

I think this has to do with the way CFD post draws the contours based on your data. I think they do it by calculating gradients between all the cell center values and then drawing contours around that. For many variable something like that will give a more natural looking solution then when you would purely draw the cell values on there.

What you need to do is as follows: in your contour details click on the little "+" where in sais "advanced properties". Then click on the circle next to where it sais "Face". This will make it just draw the "raw" data.

[H.Almrayatee]

You need to multiply the reaction rate equation *rr with VOF of the phase.