[Jack0210Jack]

Hi,

I am new to udf and c programming. Currently I am working on a project to simulate ammonia absorption into water droplets using two-film theory and DPM. I have read the udf manuals and researching online for examples but I am not sure whether my functions are correct. Below is the code:

#include "udf.h"

DEFINE_DPM_HEAT_MASS(nh3absorption, tp, Cp, hgas, hvap, cvap_surf, Z, dydt, dzdt)
{
int is;
int nc = TP_N_COMPONENTS(tp); /*number of particle components*/
real gas_index;
printf("\n######");
for (is = 0; is < nc; is++)
{
int gas_index = TP_COMPONENT_INDEX_I(tp, is); /* index of vaporizing component in the gas phase */
printf(" gas_index=%d is=%d TP_COMPONENT_I=%e ", gas_index, is, TP_COMPONENT_I(tp, is));
}
printf("#######$\n");
Thread* t0 = P_CELL_THREAD(tp); /*thread where the particle is in*/
cell_t c0 = P_CELL(tp); /*cell where the particle is in*/
Material* gas_mix = THREAD_MATERIAL(DPM_THREAD(t0, tp)); /*gas mixture material*/
Material* cond_mix = P_MATERIAL(tp); /*particle mixture material*/
cphase_state_t* c = &(tp->cphase); /*cell information of particle location*/\
real mp = P_MASS(tp); /* particle mass */
real Dp = DPM_DIAM_FROM_VOL(mp / P_RHO(tp)); /* particle diameter */
real Ap = DPM_AREA(Dp); /*particle surface area*/
real v = P_VEL(tp);/*water droplet velocity*/
real vg = 15.69e-6; /*kinematic viscosity of air*//*[m2/s]*/
real Re = Dp * v / vg;

real D = 1.64e-7; /*molecular diffusivity coefficient*//*[m/s]*/
real Sc = vg / D;

real ky = 2.0 + 0.6 * sqrt(Re) * pow(Sc, 1. / 3.); /*mass transfer coefficient in liquid phase*/

real T = 300; /*Temperature*//*[K]*/

real H = 0.59 * exp(4200 * ((1 / T) - 1 / (298.15))); /*Henry Constant*//*[mol/(m3*Pa)]*/

real MW_NH3 = 17.031e-3; /*Molecular mass of ammonia*//*[kg/mol]*/

real den_g = C_R(c, gas_index); /*density of gas in air*/
real yi_NH3_g = C_YI(c, gas_index, 4); /*mass fraction of ammonia in air*/
real C_g = yi_NH3_g * den_g / MW_NH3; /*molar concentration of NH3 in air*//*[mol/m3]*/
real P_g = C_g * 8.314 * T; /*partial pressure of ammonia in air*/

real den_l = P_RHO(tp); /*density of particle*/
real yi_NH3_l; /*mass fraction of ammonia in particle*/

for (yi_NH3_l = 0; yi_NH3_l < 1; ++TP_COMPONENT_I(tp, is))
{
real C_l = yi_NH3_l * den_l / MW_NH3; /*molar concentration of ammonia in water droplet*//*[mol/m3]*/
real NA = ky * (P_g - H * C_l); /*Mass transfer flux of ammonia*/
dydt[2] = NA;
}
return 0;
}

Below are the errors shown after compiled.

..\..\src\two-film.c(38): error C2223: left of '->storage' must point to struct/union
..\..\src\two-film.c(39): error C2223: left of '->storage' must point to struct/union
..\..\src\two-film.c(52): warning C4098: 'nh3absorption': 'void' function returning a value
..\..\src\two-film.c(19): warning C4047: 'initializing': 'cphase_state_t *' differs in levels of indirection from 'cphase_state_t **'
..\..\src\two-film.c(23): error C2440: 'initializing': cannot convert from 'real *' to 'real'

The idea of this project is to simulate the ammonia absorption into water droplet. Water droplet will be injected via DPM and ammonia absorption will be added via udf. When the ammonia mass fraction in water droplet is less than 1, the ammonia will be absorbed into the water droplet and the mass transfer rate is based on the mass fraction of ammonia in water droplet.

Does anyone know how to solve the errors? Thanks a lot

[pakk]

Compile them, load them, try them.

Do you get errors? Does it do what you want? That is the best test.

[Jack0210Jack]

Originally Posted by pakk

Compile them, load them, try them.

Do you get errors? Does it do what you want? That is the best test.

I see. Sure. Will reply here if I get errors that I can't solve. Thanks.

[Jack0210Jack]

Originally Posted by pakk

Compile them, load them, try them.

Do you get errors? Does it do what you want? That is the best test.

Below are the errors shown after compiled.

..\..\src\two-film.c(38): error C2223: left of '->storage' must point to struct/union
..\..\src\two-film.c(39): error C2223: left of '->storage' must point to struct/union
..\..\src\two-film.c(52): warning C4098: 'nh3absorption': 'void' function returning a value
..\..\src\two-film.c(19): warning C4047: 'initializing': 'cphase_state_t *' differs in levels of indirection from 'cphase_state_t **'
..\..\src\two-film.c(23): error C2440: 'initializing': cannot convert from 'real *' to 'real'

Do you have any ideas how to solve them? Thanks

[AlexanderZ]

line 19
was

cphase_state_t* c = &(p->cphase);

to be

cphase_state_t *c = &(p->cphase);

P_VEL(tp) is a vector, which contains P_VEL(tp) [0] - velocity in x direction, P_VEL(tp) [1] - in y direction and P_VEL(tp) [2] in z direction.
in case you need velocity magnitude, you can use this

real v = NV_MAG(P_VEL(tp));

[Jack0210Jack]

Originally Posted by AlexanderZ

line 19
was

cphase_state_t* c = &(p->cphase);

to be

cphase_state_t *c = &(p->cphase);

tbh every time I close the line, it will change from

cphase_state_t *c = &(p->cphase);

to

cphase_state_t* c = &(p->cphase);

so I assume second line is the correct one. Btw, it still has error for line 19 even if I use

cphase_state_t *c = &(p->cphase);

but line 23 is fixed.

Actually the variable I used is "tp" because in some posts I saw people using "tp" instead of "p" and I assumed because "tp" is the latest format. Should I change all "tp" variable to "p" variable?

Thank you.

[Jack0210Jack]

Wait a min, after I change

cphase_state_t* c = &(p->cphase);

to

cphase_state_t** c = &(p->cphase);

It somehow has been solved.

[Jack0210Jack]

The errors I face currently are:

..\..\src\nh3absorption.c(38): error C2223: left of '->storage' must point to struct/union
..\..\src\nh3absorption.c(39): error C2223: left of '->storage' must point to struct/union

which reflect on these 2 lines:

real den_g = C_R(c, gas_index); /*density of air*/

real yi_NH3_g = C_YI(c, gas_index, 4); /*mass fraction of ammonia in air*/

I suppose the errors are due to the DEFINE macros do not have "c" variable. If that's the case what changes should I make? I tried pointing "c->rho", "c->mu", and "c->mut" for density (line 38) but it doesn't work.

I also tried to add in another macro "DEFINE_PROPERTY" for those 4 lines (38~41) but P_g in line 41 cannot be linked to P_g in line 49.

Any helps will appreciated. Thanks.

[pakk]

I guess you want info of the cell that your particle is in, and you call that c0, not c.

[Jack0210Jack]

Thanks but not really. I want the info of the cell where particle is not in.

[pakk]

But which cell is c then referring to? I don't know, and neither does fluent.

[Jack0210Jack]

Originally Posted by pakk

But which cell is c then referring to? I don't know, and neither does fluent.

That's the issue. I don't know how should I point the cell to.

[Jack0210Jack]

#include "udf.h"

DEFINE_DPM_HEAT_MASS(nh3absorption, tp, Cp, hgas, hvap, cvap_surf, Z, dydt, dzdt)
{
	int is;
	int nc = TP_N_COMPONENTS(tp); /*number of particle components*/
	real gas_index;
	printf("\n######");
	for (is = 0; is < nc; is++)
	{
		int gas_index = TP_COMPONENT_INDEX_I(tp, is); /* index of vaporizing component in the gas phase */
		printf(" gas_index=%d is=%d TP_COMPONENT_I=%e ", gas_index, is, TP_COMPONENT_I(tp, is));
	}
	printf("#######$\n");
	Thread* t0 = P_CELL_THREAD(tp); /*thread where the particle is in*/
	Material* gas_mix = THREAD_MATERIAL(DPM_THREAD(t0, tp)); /*gas mixture material*/
	Material* cond_mix = P_MATERIAL(tp); /*particle mixture material*/
	cphase_state_t** c0 = &(tp->cphase); /*cell information of particle location*/
	real mp = P_MASS(tp); /* particle mass */
	real Dp = DPM_DIAM_FROM_VOL(mp / P_RHO(tp)); /* particle diameter */
	real Ap = DPM_AREA(Dp); /*particle surface area*/
	real v = NV_MAG(P_VEL(tp)); /*water droplet velocity*/
	real vg = 15.69e-6;	/*kinematic viscosity of air*//*[m2/s]*/
	real Re = Dp * v / vg;

	real D = 1.64e-7; /*molecular diffusivity coefficient*//*[m/s]*/
	real Sc = vg / D;

	real ky = 2.0 + 0.6 * sqrt(Re) * pow(Sc, 1. / 3.); /*mass transfer coefficient in liquid phase*/

	real T = 300; /*Temperature*//*[K]*/

	real H = 0.59 * exp(4200 * ((1 / T) - 1 / (298.15)));	/*Henry Constant*//*[mol/(m3*Pa)]*/

	real MW_NH3 = 17.031e-3; /*Molecular mass of ammonia*//*[kg/mol]*/

	Domain* domain = Get_Domain(1); /* Get domain pointer */
	Thread* t;
	cell_t c;
	int i;
	/* Loop over all cell threads in domain */
	thread_loop_c(t, domain)
	{
		/* Loop over all cells */
		begin_c_loop(c, t)
		{
			{
				C_R(c, t) = 0.0;
				C_YI(c, t, i) = 0.0;
			}
		}
		end_c_loop(c, t);
	}

	real yi_NH3_g = C_YI(c, gas_index, 4); /*mass fraction of ammonia in air*/
	real den_g = C_R(c, gas_index); /*density of air*/
	real C_g = yi_NH3_g * den_g / MW_NH3; /*molar concentration of NH3 in air*//*[mol/m3]*/
	real P_g = C_g * 8.314 * T; /*partial pressure of ammonia in air*/

	real den_l = P_RHO(tp); /*density of particle*/
	real yi_NH3_l; /*mass fraction of ammonia in particle*/
		
	for (yi_NH3_l = 0; yi_NH3_l < 1; ++TP_COMPONENT_I(tp, is))
	{
		real C_l = yi_NH3_l * den_l / MW_NH3; /*molar concentration of ammonia in water droplet*//*[mol/m3]*/
		real NA = ky * (P_g - H * C_l); /*Mass transfer flux of ammonia*/
		dydt[2] = NA;
	}
	return;
}

I have added a get domain which I referred from Ansys udf manual but it still has the same error message. Btw, I removed "cell_t c0" because I didn't use "c0" in any lives below and "cphase_state_t** c" has changed to "cphase_state_t** c0" to avoid "c" variable being defined in 2 places.

[AlexanderZ]

if you look at definition of macros C_YI and C_R you will see, that they are using treads inside: C_R(c, t)
t has type thread not int

so based on expamle from manual Ansys Fluent Customization manual -> DEFINE_DPM_HEAT_MASS
I think you should change

real yi_NH3_g = C_YI(c, gas_index, 4); /*mass fraction of ammonia in air*/
real den_g = C_R(c, gas_index); /*density of air*/

to

real den_g = c->rho; /*density of gas*/
real yi_NH3_g = yi[gas_index]; /*mass fraction of ammonia*/

and in that case you need

cphase_state_t *c = &(p->cphase); /* cell information of particle location*/

with 1 star

[Jack0210Jack]

Hi AlexanderZ,

Thanks for your reply. It actually works for once (no error) but I don't know what happen afterward, it cannot work. Below are the errors shown:

..\..\src\nh3absorption_v1.c(56): error C2065: 'yi': undeclared identifier
..\..\src\nh3absorption_v1.c(56): error C2109: subscript requires array or pointer type
..\..\src\nh3absorption_v1.c(57): error C2223: left of '->rho' must point to struct/union

for the line with

cphase_state_t *c = &(p->cphase); /* cell information of particle location*/

it shows this error instead

..\..\src\nh3absorption_v1.c(18): warning C4047: 'initializing': 'cphase_state_t *' differs in levels of indirection from 'cphase_state_t **'

which is why I changed to using 2 stars.

Thanks.

[pakk]

Originally Posted by Jack0210Jack

That's the issue. I don't know how should I point the cell to.

Which cell?

After you tell me which cell it should point to, I can help. But all I know now is that it should not be the cell of the particle. That's not enough information.

[pakk]

Based on your description in your other question, I think you want the UDF from here, but then c0 in stead of c.

You said that you don't want the cell that the particle is in, but that statement makes no sense. Just use c0.

[Jack0210Jack]

I have made a huge modification since I messed up the steps. If anyone would like to continue helping me, please visit the link below:

UDF for DPM modelling to simulate ammonia absorption into water droplets

Thank you very much.