Convection heat transfer & rugosity

Koranten · May 19, 2011, 04:26

Hello,

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,
Koranten.

oky · May 25, 2011, 00:15

Hi everyone,

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

Regrads,

Oky

Koranten · May 25, 2011, 03:52

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/m²)

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, 09:54

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, 11:06

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, 11:12

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.

May 19, 2011, 04:26	Convection heat transfer & rugosity	#1
Koranten New Member Join Date: Jul 2009 Posts: 14 Rep Power: 17	Hello, 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, Koranten.

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May 25, 2011, 00:15		#2
oky New Member Oky Andytya Join Date: Nov 2010 Posts: 26 Rep Power: 16	Hi everyone, I need help, how to get the value of convection coefficient [h] from Fluent directly? Thank you. Regrads, Oky

May 25, 2011, 03:52		#3
Koranten New Member Join Date: Jul 2009 Posts: 14 Rep Power: 17	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/m²) 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!

May 25, 2011, 09:54		#4
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	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

May 25, 2011, 11:06		#5
Koranten New Member Join Date: Jul 2009 Posts: 14 Rep Power: 17	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.

May 25, 2011, 11:12		#6
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	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.