General Convection Heat Transfer Coefficient
General Convection Heat Transfer Coefficient
(OP)
I am trying to get my arms around the methodology of calculating the subject term (typically, "h") when used in a finite difference scheme (or any other numerical approach to heat transfer) where the boundary includes a convection term. Is it as simple as calculating the convection heat transfer coefficient for a flat plate? Do you assume a constant temperature condition (as opposed to constant flux) due to the nature of the methodology (that is, the discretized cell is of a constant temperature by definition)? Any insight would be greatly appreciated from you numerical computation gurus out there.
See this webpage for an example of what I am talking about. NO, this is NOT homework.
http ://courses .ucsd.edu/ rherz/mae2 21a/notes/ transimpli cit5x5.pdf
See this webpage for an example of what I am talking about. NO, this is NOT homework.
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RE: General Convection Heat Transfer Coefficient
Beyond that, the question is how accurately do you care to make the model. In cases where you've determined the need to discretize there will be other geometry effects that are more relevant than the convection coefficient.
TTFN
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RE: General Convection Heat Transfer Coefficient
RE: General Convection Heat Transfer Coefficient
There is not a simple answer to your question. Calculating the heat transfer coefficient depends on your configuration and there are different formulas depending on the configuration. Depending on your set up, the temperatures may, or may not, be constant (it's easier if they are.) Assuming flow across a flat plate might be appropriate (but generally isn't.)
Patricia Lougheed
******
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RE: General Convection Heat Transfer Coefficient
RE: General Convection Heat Transfer Coefficient
TTFN
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RE: General Convection Heat Transfer Coefficient
Appearances can be deceiving. I've been asking the same question all along - just not very well apparently.
RE: General Convection Heat Transfer Coefficient
What I've written above might not be exactly correct, but I hope it helps in getting to the correct answer.
RE: General Convection Heat Transfer Coefficient
Thanks. I dug a little deeper and found something similar to what you said here on a CFD forum. I was getting confused by the fact that in discretization, we know the flux term out of the solid and into the fluid at the boundary is equivalent. So, yes, I can see that the convective heat transfer coefficient is a RESULT of the equations, not an input to them. I still need to think a little harder here though. Thank you for your help. You've gotten me closer to my goal.
RE: General Convection Heat Transfer Coefficient
Your FEA model does the math. You can input the heat flows, conditions, etc., and simultaneously solve for the resultant output flows and transfer coefficients. This is part of the iteration that's done at each time step.
TTFN
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RE: General Convection Heat Transfer Coefficient
h is a function of:
1.geometry
2.velocity distribution
3.fluid properties
4.temperature boundary condition, and
5.temperature initial condition
RE: General Convection Heat Transfer Coefficient
The conventional definitions of heat transfer coefficients for various geometries of the forms:
h=(Nu x Kf)/Lc {where Nu=f(Gr,Pr) or Nu=f(Re,Pr)}
are always averaged generalizations obtained by curve-fitting of experimental data. *Again, this data is obtained for equilibrium conditions.* To be really accurate your program should recalculate the heat transfer coefficient at each time step because these temperatures will be varying during a transient simulation.
RE: General Convection Heat Transfer Coefficient
corus