# Convection heat transfer & rugosity

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 May 19, 2011, 03:26 Convection heat transfer & rugosity #1 New Member   Join Date: Jul 2009 Posts: 14 Rep Power: 10 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.

 May 24, 2011, 23:15 #2 New Member   Oky Andytya Join Date: Nov 2010 Posts: 26 Rep Power: 9 Hi everyone, I need help, how to get the value of convection coefficient [h] from Fluent directly? Thank you. Regrads, Oky

 May 25, 2011, 02:52 #3 New Member   Join Date: Jul 2009 Posts: 14 Rep Power: 10 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!

 May 25, 2011, 08:54 #4 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 195 Rep Power: 10 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, 10:06 #5 New Member   Join Date: Jul 2009 Posts: 14 Rep Power: 10 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, 10:12 #6 Senior Member   Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 195 Rep Power: 10 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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