natural convection over cylinders

[etorres]

Which is the most precise correlation for natural convection around horizontal cylinders?

Heat transfer books gives different expresions but they do not say anything about precission or preferred range of application

Could somebody recommend me any reference about it?

 

[25362]

J.P. Holman (Heat Transfer) gives for free convection of air around horizontal cylinders the following simplified equations:

for laminar flow, i.e., 10[sup]4[/sup]<Gr.Pr<10[sup]9[/sup], h = 1.32 ([&Delta;]T/d)[sup]0.25[/sup]

for turbulent flow, i.e., Gr.Pr>10[sup]9[/sup], h = 1.24([&Delta;]T)[sup]1/3[/sup]

h = heat-transfer coefficient, W/(m[sup]2[/sup].[sup]o[/sup]C);
d = diameter, m;
[&Delta;]T = T[sub]w[/sub] - T[sub][&infin;][/sub] , [sup]o[/sup]C

 

[quark]

There are many simplified correlations depending upon Rayleigh's number. However, one comprehensive equation given by Churchil covers wide range of Rayleigh's number.

For Ra<=10[sup]12[/sup]

Nu = [0.6 + ((0.387 Ra[sup]1/6[/sup])/(1+(0.559/Pr)[sup]9/16[/sup])[sup]8/27[/sup])][sup]2[/sup]

Properties of air should be at average air temperature and temperature of the cylinder is skin temperature.

 

[vpl]

etorres

This appears to be the fourth time you've posted a question regarding natural convection over horizontal cylinders. All of them have been very general about what you're wanting. How about a bit more information as to your application and what you're trying to achieve.

At this point, I'm thinking your a student who's not willing to look beyond his text book...

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[Saturninus]

I dealt with this stuff when I did my masters thesis. The correlations never dealt with the wall of the enclosure and the tubes, only the HT amongst the tubes themselves. If you figure that out, I would be curious to hear how people deal with this, other than ignore it.

For example, does the distance between the wall and the tubes matter? Of course it does. But noone has written about this that I know of.

Good luck.