[fonk]

Good morning,

I am trying to write a UDF to implement the Hibiki-Ishii formulation of the Nucleation site density in my Fluent simulation and there are 4 points for which I would appreciate some help:

1)This formulation depends on the contact angle. I was wondering if there was a way to access the contact angle value using a macro as Fluent has to calculate it to determine the bubble departure diameter when the Kocamustafaogullari - Ishii formulation is used to assess it or if I had to compute the contact angle within the UDF. I could not find any macro yet.

In the surface tension tab of the phase interaction window, I do use surface Tension Force Modelling using a continuum Surface Force and a constant value of the surface tension.

2)Is it possible to access, using a macro, the Standard State Enthalpy specified in the material properties? Indeed, I need the latent heat for the Hibiki - Ishii formulation of the nucleation site density. Right now I define the latent heat within the UDF but having access to it would be more convenient.

3)I would also like to know what will the macro C_R(c0,pt0[gas_phase]) give if there is no gas in the cell.

4) I have trouble to understand how the lines to get the specified surface tension work, specifically the line starting with the pointer property definition and the T_sfc definition. (I got that part in the customization manual where the surface tension is retrieved in the example 2 of DEFINE_EXCHANGE_PROPERTY.). I could not find any explanation about the macro used in the manual nor elsewhere.

here is the code for now:

#include "udf.h"

#define Nn_bar 4.72e5
#define mu 0.722
#define lambda_prim 2.5e-6
#define R 8.31
#define lat_heat 3.966077e4
DEFINE_BOILING_PROPERTY(nucleate_site_density,f,t,c0,t0,from_index,from_species_index,to_index,to_species_index)
 {	
 // f : 					wall face
 // t :						pointer to the wall face thread
 // c0 : 					cell index of the cell next to the wall
 // to :					pointer to mixture level thread
 // from_index :			        Liquid phase 
 // from_species_index :	        ID of liquid species
 // to_index :				Vapor phase
 // to_species_index :		        ID of vapor species
   real nuc_site_d, T_sfc, rho_plus, f_rho_plus, Rc, sigma, theta;
   
   int liq_phase = from_index;
   int gas_phase = to_index;
   Thread **pt0 = THREAD_SUB_THREADS(t0);
   real T_SAT = C_STORAGE_R(c0,t0,SV_SAT_TEMPERATURE);
   real T_l = C_T(c0, pt0[liq_phase]); 
   real rho_g = C_R(c0,pt0[gas_phase]); 
   real rho_l = C_R(c0,pt0[liq_phase]);
   real P_l = C_P(c0,pt0[liq_phase]);
   real T_g = C_T(c0,pt0[gas_phase]);  

   /* ------ Get surface tension  ------ */
   Property *prop = DOMAIN_COMPLEX_PROP_PROPERTY(DOMAIN_INTERACTION(root_domain),
COMPLEX_PROP_sfc_tension_coeff,liq_phase,gas_phase);
   T_sfc = (sg_temperature &&
NNULLP(THREAD_STORAGE(pt0[liq_phase],SV_T)))? C_T(c,pt0[liq_phase]) :  T_REF;
   if(prop == NULL || PROPERTY_METHOD(prop,0) == PROP_METHOD_NONE)
	{
		Error("Hibiki-Ishii nucleation site density: Please set value for surface tension !");
	}
	sigma = generic_property(c,t,prop,(Property_ID)0,T_sfc);
	if (sigma < 0.)
	{
		Error("Hibiki-Ishii nucleation site density: Please provide a nonzero value for surface tension");
	}  
   /*------------------------------------*/

   theta = 	

   rho_plus = log10((rho_l - rho_g)/rho_g);
   f_rho_plus = -0.01064 + 0.48246*rho_plus - 0.22712*rho_plus^2 +0.05468*rho_plus^3;
   Rc = (2*sigma*(1+(rho_g/rho_l))/P_l)/(exp(lat_heat*(T_g - T_SAT)/(R*T_g*T_SAT)-1);
   nuc_site_d = Nn_bar*(1-exp(-theta/(8*mu^2)))*(exp(f_rho_plus*lambda_prim/Rc)-1);
   return nuc_site_d;

 }

Thank you very much for your time.