[FFerrario]

Greetings everyone.


I have made this UDF code that is part of a larger whole, but right now I'm concentrated in this temperature change section. I want to see how the temperature of the inlet, which simulates the evaporation rate of a small pool in a fully diffusive manner (no wind current), changes. Account for the flow rate and convective heat transfer from the surroundings, I have the following code:





DEFINE_PROFILE(temperature,t,i)
{
real T_Face, M_Face,MF_rate, V_mag, A_dish, HTC;
face_t f;
HTC = K/0.0002;
A_dish = 0.003619;
begin_f_loop(f,t)
{
/*Mass flow rate estimation*/
V_mag = pow((pow(F_U(f,t),2)+pow(F_V(f,t),2)+pow(F_W(f,t), 2)),0.5);
MF_rate = V_mag*A_dish*F_R(f,t);
/*Mass estimation*/
F_UDMI(f,t,1) = F_UDMI(f,t,2)-0.05*MF_rate;
/*Current mass value*/
M_Face = F_UDMI(f,t,1);
/*Temperature estimation*/
F_UDMI(f,t,3) = F_UDMI(f,t,4);
/*Current temperature value*/
T_Face = F_UDMI(f,t,3);
F_PROFILE(f,t,i) = T_Face-((DHev*MF_rate*0.05)/(M_Face*Cp))+((HTC*A_dish*0.05*(293.15-T_Face))/(M_Face*Cp));
F_UDMI(f,t,4) = F_T(f,t);
/*Save current temperature for the next timestep*/
F_UDMI(f,t,2) = M_Face;
/*Save current mass for next timestep*/
Message("M_face= %f", M_Face);
}
end_f_loop(f,t)


As you see, I account for the previous time step temperature and mass reduction from the pool through F_UDMIs, but they don't seem to be updating. Do you think you could help me?


Thanks a lot,
Fabio.

[vemula]

Sometimes it can be due to an option in fluent in the run calculation tab called as update profile interval if you set to 1 and try again it might help

[AlexanderZ]

F_UDMI(f,t,1) = F_UDMI(f,t,2)-0.05*MF_rate;

F_UDMI(f,t,2) is not define for the irst times step

[FFerrario]

Right, this value is defined during the initialization step. To tell the truth, the code does work, but results are not what I expected. Due to the nature of diffusive evaporation, not including the temperature change in the simulation while estimating the evaporation is not a big deal, thus I did do some simulations where I can get a mass flow rate with a constant temperature. With this mass flow rate, I can use the data listed in the equation to estimate how the temperature profile SHOULD behave (it would lose 1 K in 12 minutes, which makes sense). Instead, my model loses 10 K (in fluent) in 12 minutes, by evaporating 1 g of liquid in that time. This is very excessive. From the code above, what could lead to this gross overprediction? I have checked all values possible. The only one being actively calculated by the model is the mass flow rate, that is in the order of 10e-6 Kg.