Heat flux
Hi all,
I have a gearbox filled with oil. The motion of the internal gears heat the oil. I want to calculate the temperature distribution in the oil bath. Which BC should I set on the external boundaries (the case of the gearbox)? I do not know the temperature of the walls but only the temperature of the ambient (air). I know that the heat transfer coeff. h is depending on the delta T between the walls and the external air. If I want define that coefficient according to a known law, what should I do? Can someone help me writing an UDF? Regards F air | wall | oil | gears |
Hi,
I haven't done conjugated heat transfer with fluent, but I did it with CFX .... so I might be able help you. First question is, what are you interested about? Are you interested in a temperature distribution after a specific time? -> Transient run or "just" in a steady state case? As boundary condition: for the wall | air interaction use a heat flux. This heat flux is, as you mentioned, not constant it is rather dependent on the surface temperature. So you have to create a "heat-flux-function"(Temperature) .... I haven't done this in fluent, but in CFX this is quite simple. Hope some other guys here can help you out with a UDF. And how do you define your "heat-source"? Are you simulating the gears as well, I guess the gears would lead to some motion of the nearby oil .... |
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In my case I have a single gear that is rotating in the oil bath, so the heat is directly generated by the motion of the gear. I have already performed transient simulations without the energy equations, so I already know the power losses (--> heat source). In order to calculate them a transient simulation was mandatory, but now I think it is possible to distribuite this power on the whole gear surfaces so to be able to solve only a steady thermal analysis... I hope it is clear what I mean. What do you think about? Franco |
Okay, so steady state should be fine.
But as I mentioned, you need to define a UDF for the heat flux .... sorry that I canīt hekp you with that. |
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Tscüß! |
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What is your known law for heat transfer coefficient? |
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Regards F |
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Ignoring units you have: q" = h(DeltaT) and h = 0.1 DeltaT + 10 so that leads to: q" = (0.1 DeltaT^2 + 10DeltaT) This type of heat transfer coefficient will lead to nonlinear results. I imagine the solution would also be highly unstable since the heat flux is a quadratic in temperature difference, with the potential to lead to runaway solutions and diverge. Am I overthinking this? |
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Thanks F |
Nobody can help me in writing the UDF?
F |
Really nobody can help me in writing the UDF?
At least some tips.... F |
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