Learning Forum

[Manish Patel]

I am trying to simulate 2D conjugate heat transfer over a finned surface. The simulation works fine and shows some results as shown below which is temperature profile. 

But, the problem is that the wall temperature keeps rising even after simulating it for 60 seconds of time (transient) as shown below. 

I expect the wall temperature to reach some pseuso-steady state condition (like shown below). But it does not reach that stage. 

I have made mesh really small (having minimum cell size = 0.00005 m) and time step of 0.00005 s, which are the smaller values than what I see in literature. So, I think mesh or time step is not the problem. Also I use second order schemes. I tried all SIMPLE, PISO and coupled. and all does not show the desired result (Temp keeps rising)

I have also seen similar problem with other software as well. I am sure I have been doing something fundamental mistake here. What is it? 

[Rob]

Maybe it takes more than a minute to reach the equilibrium temperature? 

[Manish Patel]

With some googling I found that there can be two reasons:

1. Solid time step should be specified and should be much large. Can you please tell me how this solid time step is calculated. I did not find information about that in Fluent theory guide or tutorial guide. 
2. The Reference depth should be adjusted for 2D simulation so accordingly total heat supplied at the heated wall can be adjusted. Does this reference depth have any effect on the applied heat on heated wall? 

 

[Rob]

Leave the depth alone, it's a metre to make the maths easier. Just ensure you're adding the correct amount of temperature and energy. 

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