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May 3, 2020, 21:11 |
Natural convection in oven
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#1 |
New Member
Pablo Diaz
Join Date: Apr 2020
Posts: 4
Rep Power: 6 |
Hello, I'm new in CFD and I need some advisement or some light about if I'm in the right way.
I'm making a simulation of an oven. I want to manipulate the power of the heaters to achieve around 550-600 ºC in the central zone of the oven. I don't need extreme accuracy, with +-10 or 20 ºC is enough. The geometry is simple, a box of 650x650x350 mm with a hole (340x340mm) at the bottom. The heaters are at two of the sides. The other sides are insulation. I have created a space around the hole to get away the ambient air and I placed BCs of outlet and inlet pressure in there. Based on what I found in other threads about natural convection I made a pressure-based, transient study with the following parameters: Energy: On Viscous: Laminar (If my calculations are not wrong I have a maximum Re of around 720, corresponding to a max vel of 0.1 m/s) Radiation: Surface to surface Heat transfer coefficient: 5 W/m^2K (I'm not sure about this value. It's normal for natural convection but maybe at these temperatures is invalid) Air density: Incompressible ideal gas Scheme: Coupled Pressure discretization: Body Force Weighted Transient Formulation: Second order HOTR Activated Relaxation Factors reduced to 0.65 (momentum) and 0.8 (energy) Step size: 0.5 s, with 10 iterations per step. I'm not sure if I can trust the results. I have residuals of 10^-3 in continuity and 10^-4 in the other variables. The results are these: https://imgur.com/ChYBz9O Thanks for the help! Last edited by PDH; May 4, 2020 at 11:47. |
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May 5, 2020, 08:56 |
Natural Convection
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#2 |
Senior Member
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For natural convection, it is not Re that is looked at but Grashof number. If Gr is greater than , then turbulence model must be enabled; most likely you need that. Secondly, use a URF higher than 0.9 for energy. Since you have some openings, i.e., inlet and outlet, you do not need to run a transient case. A steady-state case will work. Turbulence will have major effect on thermal diffusion and the thermal field would change drastically.
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Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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May 5, 2020, 11:30 |
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#3 |
New Member
Pablo Diaz
Join Date: Apr 2020
Posts: 4
Rep Power: 6 |
Quote:
For heat tranfer what is better, low y+ with k-omega or big y+ with k-epsilon? |
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May 5, 2020, 12:16 |
Heat Transfer
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#4 |
Senior Member
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Every phenomenon happening close to a wall is called low phenomenon, such as, conjugate heat transfer, drag and lift, natural convection, etc. But you can use either or . Just use low
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Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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May 6, 2020, 09:13 |
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#5 |
New Member
Pablo Diaz
Join Date: Apr 2020
Posts: 4
Rep Power: 6 |
Finally, I used SST k-omega. Much better (and logical) results now. Thank you!
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May 6, 2020, 10:20 |
Good
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#6 |
Senior Member
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Nice to know that you got good results.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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