# Modelling multiphase heat transfer coefficient in UDF with DEFINE_PROFILE

Hi,

I am doing a multiphase simulation ( Euler-Euler )with gas and solid.

I have two heat transfer coefficients. h(wall-gas) and h(wall-solid).

The simplified equations are

h(gas-wall) = 1.54*Re_g*k_g/D

and

h(solid-wall) = D/k_s + [2 * sqrt(k_s * rho_s * cp_s / pi)]^(-1)

First, I tried to code only the h(gas-wall) as follows.

```#include "udf.h"
DEFINE_PROFILE(heat_test,t,i)
{
face_t f;
real D = 1;
real beta = 90;
real v_x=0., v_y=0., v_z=0.;
real vel;
real De = 0.5*D*(2*M_PI-beta+sin(beta*M_PI/180))/(M_PI-beta/2-sin((beta*M_PI/180)/2));

begin_f_loop(f,t)
{
v_x = F_U(f,ti);
v_y = F_V(f,ti);
v_z = F_W(f,ti);
vel = sqrt(v_x*v_x + v_y*v_y + v_z*v_z);
real Re = vel;
F_PROFILE(f,t,i) = 1.54*Re/De;
}
end_f_loop(f,t)
}
```

The above code works when I use v_x = F_U(f,t) and produces a SIGSEGV error when I use F_U(f,ti).

Is this the correct way to code this type of UDF?

Thanks,

Senthil

Tagged:

• Because the wall has only one temperature and that is the mixture level.

• I am not using temperature field. I am using only velocity field.

• What is the thread "ti" in your UDF? Where are you hooking the UDF?

• Thread ti is the phase thread of primary phase in the multiphase simulation. I am hooking the UDF in the boundary conditions for wall as convection heat transfer coefficient.

• Okay that will explain the issue: There is no phase velocity associated with wall boundary. You can however access the near wall cell velocity values of each phase.

• I also tried with the adjacent cell thread and it produced the same error.

DEFINE_PROFILE(heat_gas_wall,t,i)

{

face_t f;

Message0("TEst 00000000000");

cell_t c = F_C0(f,ti);

Message0("TEst 0");

real v_x=0., v_y=0., v_z=0.;

real vel;

v_x = C_U(c,tcj) - C_U(c,tci);

v_y = C_V(c,tcj) - C_V(c,tci);

v_z = C_W(c,tcj) - C_W(c,tci);

vel = sqrt(v_x*v_x + v_y*v_y + v_z*v_z);

..

....

....

}

• Yes because it is wrong: you are no doing any loops. Check the documentation to know how things are working.

• The loops are below. I didn't post the full code. The full code is lengthy. I kept three dots in the bottom..!!

• edited November 2020

I cannot forecast what you are telling with your 3 dots.