CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

reversed flow in the pressure outlet

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 27, 2013, 02:50
Default reversed flow in the pressure outlet
  #1
New Member
 
Andhra Pradesh
Join Date: Jan 2013
Posts: 13
Rep Power: 4
vismayie is on a distinguished road
hello,

I am simulating a tubular reactor in Fluent with reaction as the wall boundary condition. The simulations didnt show any problem till temperature 775 K but suddenly at that temperature there is something like the reversed flow at the pressure outlet. and the outlet concentration of the reactant which is expected to decrease is increasing.

When i ask Fluent to compute the weighted average of the rate of reaction at the wall it shows the following : -1.#IND

So to my best knowledge something is wrong with the reaction rate at this temperature. Is it because of a very fine mesh or something ? I am using a 2D mesh.

the following is my UDF:


#include "udf.h"
#define R 8.314
#define p 101325
#define pi 3.14159


DEFINE_SR_RATE(my_rate,f,t,r,mw,yi,rr)
{
Thread *t0 = t -> t0;
cell_t c0=F_C0(f,t);


real n2 = yi[0];
real n2o = yi[1];
real co = yi[2];
real co2 = yi[3];
real he = yi[4];

real rho_w = 1.0, T_w, sd=2.68*1e-5;
real xno = 1.0, xco = 1.0, xn2o = 1.0, xn2 = 1.0, xco2 = 1.0;

real pco2, pco, pn2o, pn2;
real k1, k2, k3, k4, k5, k6, k7, k8, k9, k10, k11, k12, k13, k14, k15, k16;
real K1, K2, K3, K4, K5, K6, K7, K8;
real zor3, kor3, denom4new, denom5new, denom8new, R4, R5, R8, rate;


T_w = F_T(f,t);
rho_w = C_R(c0,t0)*C_T(c0,t0)/T_w;


co *= rho_w/mw[2];
n2o *= rho_w/mw[1];
co2 *= rho_w/mw[3];
n2 *= rho_w/mw[0];
he *= rho_w/mw[4];



xco = co/(co+n2o+co2+n2+he);
xn2o = n2o/(co+n2o+co2+n2+he);
xn2 = n2/(co+n2o+co2+n2+he);
xco2 = co2/(co+n2o+co2+n2+he);

pn2 = xn2*p;
pco = xco*p;
pco2 = xco2*p;
pn2o= xn2o*p;



k1 = 0.67*(sqrt(1000/(R*T_w*2*pi*mw[3])));
k2 = (1e13*sd)*exp(-26*4185.8/(R*T_w));
k3 = (1e11*sd)*exp(-6.7*4185.8/(R*T_w));
k4 = (1e11*sd)*exp(-47.6*4185.8/(R*T_w));
k5 = (1e11*sd)*exp(-27*4185.8/(R*T_w));
k6 = (0.001)*(sqrt(1000/(R*T_w*2*pi*mw[1])));
k7 = (1e14*sd)*exp(-24.3*4185.8/(R*T_w));
k8 = (1e14*sd)*exp(-2.1*4185.8/(R*T_w));
k9 = (1e13*sd)*exp(-10*4185.8/(R*T_w));
k10 = 0.001*(sqrt(1000/(R*T_w*2*pi*mw[2])));
k11 = 0.67*(sqrt(1000/(R*T_w*2*pi*mw[3])));
k12 = (1e13*sd)*exp(-32*4185.8/(R*T_w));
k13 = (1e11*sd)*exp(-24.35*4185.8/(R*T_w));
k14 = (1e11*sd)*exp(-11.3*4185.8/(R*T_w));
k15 = (1e13*sd)*exp(-5.17*4185.8/(R*T_w));
k16 = 0.005*(sqrt(1000/(R*T_w*2*pi*mw[4])));

K1 = k1/k2;
K2 = k3/k4;
K3 = k5/k6;
K4 = k7/k8;
K5 = k9/k10;
K6 = k11/k12;
K7 = k13/k14;
K8 = k15/k16;

denom4new=1+((pow((pn2/K3), 0.5))+(K6*pco))+((((pow((pn2/K3), 0.5))*(pco2/(K7*K8*K6*pco)))/K2));
R4=(pow(denom4new,2))/(k8*(pn2o/K5));

denom5new=1+((pow((pn2/K3), 0.5))+(K6*pco))+(((pow((pn2/K3), 0.5))*(pco2/(K7*K8*K6*pco)))/K2);
R5=(denom5new)/(k10*(pn2o));


denom8new=1+((pow((pn2/K3), 0.5))+(K6*pco))+((pn2o/K5)/(K4*(pow((pn2/K3), 0.5))));
R8=(denom8new)/((k15)*(((K6*pco)/(K7))/(((K2*pn2o)/K5)/(K4*((pn2/K3))))));

kor3=((K2*K3*K6*K7*K8)/(K4*K5));

zor3=(((pco2*pn2))/(kor3*(pn2o*pco)));

rate = (((1-zor3)))/(R4+R5+R8);

if (STREQ(r->name, "reaction-1"))
{
*rr = 0.0013*rate;
C_UDMI(c0,t0,0) = *rr;
}


}


Please suggest me a way out. I have my project submission very soon and i am not able to figure out anything.

Thanking you,

Vismayie
IIT Madras
vismayie is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problems in pressure when using mass flow rate outlet rafiktharwat CFX 11 January 2, 2014 18:21
total pressure boundary problem ==> flow from outlet to inlet!! mrshb4 OpenFOAM 0 November 20, 2010 13:41
Reversed flow on pressure outlet MDinc FLUENT 1 January 1, 2010 05:47
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 21:31
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00


All times are GMT -4. The time now is 16:56.