CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   Did you ever use it? (

greg July 6, 2006 11:48

Did you ever use it?
did you use mass transfer UDF provided by UDF manual?? bellow is the UDF (I use it for boiling):

/*3 is gas ID (secondary phase in phases panel)(water vapour - one species ID=0); , 2 is solution ID(primary phase in phases panel)(salt+water) 2 species: salt ID 0, water ID 1)*/

/* UDF to define a simple mass transfer based on Saturation Temperature. The "from" phase is the gas and the "to" phase is the liquid phase */

#include "udf.h" DEFINE_MASS_TRANSFER(from_gas_to_liquid_source,cel l,thread,from_3,from_species_0, to_2, to_species_1) { real m_lg; real T_SAT = 373; Thread *gas = THREAD_SUB_THREAD(thread, from_3); Thread *liq = THREAD_SUB_THREAD(thread, to_2); m_lg = 0.; if (C_T(cell, liq) >= T_SAT) { m_lg = -0.1*C_VOF(cell,liq)*C_R(cell,liq)* fabs(C_T(cell,liq)-T_SAT)/T_SAT; } if ((m_lg == 0. ) && (C_T(cell, gas) <= T_SAT)) { m_lg = 0.1*C_VOF(cell,gas)*C_R(cell,gas)* fabs(T_SAT-C_T(cell,gas))/T_SAT; } return (m_lg); }

So I wanted my UDF to change salt mass fraction (it should rise). C_YI(of salt in solution)=0,55 (C_YI(c,t,0)) at the begining of calculations. After boiling start C_YI(c,t,0) decrease. WHY??? Only water boils (I hope) from solution so speciess mass fraction of salt should rise (C_YI(c,t,0)= mass of salt / mass of solution). Whats more solution density decrease too (I use mass veighted average).

Solver: unstady multiphase: VOF with body implict, 2 phases boundary conditions (it is open container), bottom wall thickness = 1mm, temperature =450K, rest 0; up : outflow

rest of the walls are walls without any mass and heat transfers or sources.

any ideas what to do??

All times are GMT -4. The time now is 08:35.