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Inflow heat flux issue
Posted May 4, 2015, 3:57 a.m. EDT Fluid & Heat, Heat Transfer & Phase Change, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3b 2 Replies
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It looks like I'm having a little issue while using the inflow heat flux condition in the heat transfer module.
I'm studying a boiler where a burner in the middle is producing 24kW. Then the heat is transferred by air to a series of spirals all around with cooling water flowing through.
My problem is the following: because of the computational cost, I'm simulating only a 15 degrees slice of the boiler. Also, I'm not simulating the combustion inside the burner. My domain is limited by the outer surface of the burner, and there I apply an inlet condition to the air flow and an inflow heat flux condition (with a total heat of 24kW/360° * 15° = 1kW).
Now the problem is that this simulation is not giving the expected results.
First of all, I decided to simulate only the heat transfer physics. In this case I would expect a very high temperature on the surface of the burner and a lower temperature on the surfaces of the spiral. Instead, I get a solution where the temperature is constant and equal to the initial values everywhere (so it looks like the solver doesn't see the inflow heat flux).
Then when I try to simulate also the air flow physics, it doesn't work as it finds some roots of negative numbers.
I really don't know how to solve this issue, as my problem seems to be well-posed, with all the right boundary conditions and so on.
Every suggestion you may provide would be very important.
Thanks,
- Davide
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That is the variable that always stops the simulation as it is defined in my case as the root of a negative number.
Thanks.
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But I still have the issue on the heat flux. I figured out there are three possible boundary condition to simulate the surface of the boiler:
1) Heat flux. In this case the final temperature of the air is insanely high (up to 10^13 K), which does not make any sense.
2) Inflow heat flux. In this case it looks like the model does not see the heat flux and the final temperature is the everywhere equal to the initial values.
3) Temperature. In this case the final results are acceptable (when I say acceptable, it means they are close to the values I got from experimental results). However, from the physical point of view I don't think it's correct to use a temperature boundary condition (it would represent a different physics from the real one).
Do you have any suggestion?
- Davide