[mumtazcore]

Hi,
I am trying define temperature profile on the circumference of a tube cross-section (circle). I learned that it has to use DEFIFE_PROFILE macro, but all examples show a straight line inlet. Can anybody show me how to include cartisean coordinates in C language. or is it that I am assuming it and nothing needs to be done here?
I am modeling heat flux on a parabolic trough receiver without using the parabolic reflector to work on the temperature contours of the liquid inside .

thanks in advance

[asmita_iitb]

Hello,

have you got the solution ?
actually I am also facing the same kind of problem, can you give suggestion
regarding this kind of problem?

thank you.

[`e`]

Originally Posted by asmita_iitb

have you got the solution ?
actually I am also facing the same kind of problem, can you give suggestion
regarding this kind of problem?

What profile are you trying to apply to your inlet? The DEFINE_PROFILE macro can be used in cases where the variable is space and/or time dependent. For example, a non-uniform (space dependent) profile could be a parabolic velocity inlet of a fully developed pipe flow. Furthermore, a space and time dependent inlet velocity profile could be a pulsatile flow within an artery. First, form an equation of your variable as a function of the coordinates.

[asmita_iitb]

hi,

I have to apply heat flux on surface.and in my case heat flux and wall temperature is varying wrt x direction and time.

[`e`]

The DEFINE_PROFILE macro can be used for the temperature profile and DEFINE_HEAT_FLUX can be used for the heat flux profile.

Originally Posted by `e`

First, form an equation of your variable as a function of the coordinates.

[asmita_iitb]

Hi,
please check and tel me is this correct or not?


#include "udf.h"
#include "mem.h"
#include "stdio.h"

#define Ta 27.
#define h 7.528
#define PRINT printf
#define C_S 1710.0


DEFINE_ADJUST(udf9,d)
{
real FC[2];
cell_t c;
int ID = 5;
Thread *t;
d=Get_Domain(1);
real temp_wall;
real q_wall;

t = Lookup_Thread(d,ID);

begin_c_loop(c,t)

{
F_CENTROID(FC,c,t);
temp_wall=C_UDSI(c,t,1)/C_S-273.;

q_wall=h*(Ta-temp_wall);

/*printf("x-coord = %f y-coord = %f", FC[0], FC[1]); */
/* printf("temp_wall=%f",temp_wall)
printf("q_wall=%f",q_wall);*/

C_UDMI(c,t,11) = q_wall;

return q_wall;



}
end_c_loop(c,t)
}

DEFINE_PROFILE(udf10,t,i)
{
real FC [2];
real y;
face_t f;
cell_t c;
real heat_flux;

begin_c_loop(c,t)

{
F_CENTROID(FC,c,t);

F_PROFILE(f,t,i) = C_UDMI(c,t,11);

C_UDMI(c,t,12)= heat_flux;

return heat_flux;
}
end_c_loop(c,t)
}

[`e`]

The DEFINE_ADJUST macro should return void, whereas you're returning 'q_wall'. Have a read of the section on DEFINE_HEAT_FLUX in the UDF manual to determine if this macro is suitable, otherwise use another DEFINE_PROFILE for your heat flux boundary.

For your DEFINE_PROFILE code block, you've assigned 'heat_flux' to UDM-12 which hasn't been initialised (only declared), and then returning this 'heat_flux' variable. I suspect you'd get errors when running this UDF (garbage numbers being used). I recommend you step back and check your boundary condition definitions and explain them in detail so we can better help you.

[asmita_iitb]

Hi,

actualy, I didnt get any error. but what u mentioned is correct. I will consider your suggestion and redo udf.

thank you.

[asmita_iitb]

Hi,

i am solving PCM problem, in this all pcm properties are dependent on temperature, i am using fluent software and energy equation is solving through UDF. so how i incorporate specific heat in udf

[`e`]

Originally Posted by asmita_iitb

i am solving PCM problem, in this all pcm properties are dependent on temperature, i am using fluent software and energy equation is solving through UDF.

Are you using Fluent's energy equation to solve for the temperature field or are you using a UDF (and probably user-defined scalars, UDS)? If the former, then you can use the C_T(c,t) macro for retrieving a cell temperature. For the latter, use the relevant UDS macros.

Originally Posted by asmita_iitb

so how i incorporate specific heat in udf

The specific heat can be modified with the DEFINE_SPECIFIC_HEAT macro.

[asmita_iitb]

I am using UDF for solving energy equation (UDS) not fluent energy eqn.
all thermophysical properties are temperature dependent .

(Cp is used for calculating temperature in present case)

[`e`]

What do you currently have for your UDF? Have a read of the theory guide if you want the equations of the energy equation. If you want to have temperature-dependent specific heat then you could either use a function (if one exists; probably an approximation) or a look up table (reads and interpolates specific heat from a range of values according to temperature).

[asmita_iitb]

hello,

actualy, I tried a lot to incorporate specific heat through udf for solving energy equation but result is not coming correct. now, i have insert all temperature dependent thermophysical properties through udf except specific heat. (I consider avg specific heat).and result is coming according to trend.
once again thank you for your suggestion.