A UDF of Chemical Recation
 

hello everyone:

I'm learning about the UDF of chemical recation recently and faced several problems, can anyone help me to solve them?

1.I'm trying to make a UDF of methanation using Xu & Froment equation ("Methane Steam Reforming, Methanation and Water-Gas Shift:I.Intrinsic
Kinetics"). And the reaction is conducted in a gas-solid fluidized bed. My question is about unit convertion. The unit of Xu & Froment
equation(kgmol/kgcatalyst/hr) is different from that of the DEFINE_VR_RATE macro in Fluent UDF(kgmol/m^3/s). How can I convert the unit?

2.I found an example of making a UDF of chemical recation which is also conducted in a fluidized bed. The reaction is O3==>1.5O2 and the UDF of
this example is as fallow:
#include "udf.h"
DEFINE_VR_RATE(rrate,c,t,r,mw,yi,rr,rr_t)
{
*rr = (1.-C_VOF(c,t))*1.57*C_R(c,t)*yi[1]/mw[1];
return;
}
I think (1.-C_VOF(c,t)) is the solid volume fration in the fluidized bed. My question is why multiply by (1.-C_VOF(c,t)) in *rr equation.

I will be appreciated if anyone can help me......

Thanks a LOT!