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Koranten May 19, 2011 03:26

Convection heat transfer & rugosity

I would like to know if rugosity can have a significant impact on the value of the heat transfer convection coefficient ? My system is a long pipe in which I have free convection (Ra > 10^9 and Re > 12 000).

I am assuming a zero rugosity and I think this has no impact, what do you think?

Answers with references would be good!

Best regards,

oky May 24, 2011 23:15

Hi everyone,

I need help, how to get the value of convection coefficient [h] from Fluent directly?
Thank you.



Koranten May 25, 2011 02:52

You're not helping, but I can help you.

You just have to look a the definition of h, which is :

heat flux = h * DT (W/mē)

So :

h = heat flux / DT

With :

heat flux = area weighted average of surface heat flux
(be careful if you have radiation, you should not take it into account, by doing 'total surface heat flux - radiation heat flux')

DT = T_wall - T_infinite

T_wall = area weighted average of Wall Temperature

T_inf = it is up to you! You should choose what is your reference temperature!

mettler May 25, 2011 08:54

are you treating the rugosity as a change in the area or something like a friction factor for the pipe?..either way, I guess it could impact the convective coefficient if the value is large enough

Koranten May 25, 2011 10:06

I am using FLUENT. The rugosity is set to zero and I'm not sure this could have a real impact, and I cannot do any tests for the moment.

mettler May 25, 2011 10:12

my very limited experience with rugosity leans me to not thinking it would apply to pipe flow, but I could be wrong. I would leave it at zero. Or, you could step it up and see what happens to your results.

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