Reynold's Number related to heat transfer coefficientby badgermanb Tags: coefficient, heat, number, reynold, transfer 

#1
Oct2810, 12:20 PM

P: 9

Hi,
I am in a Heat Transfer class at school and my professor has set an interesting challenge before me. It is not a homework problem or anything, just a side project he challenged us to look into relating to external flow. The question is as follows: In fluid (e.g air, water) flow over a flat plate, if all that is given is the local Reynolds number Re_{x} at some distance from the edge of the plate, is it possible to calculate the local heat transfer coefficient h at that point? Is there some form an equation for Reynold's number that can relate to the heat transfer coefficient h? If I knew the thermal coefficient k I could use the Nusselt number equation and Reynolds number to solve for h, but all I know is the local Reynold's number. Any suggestions/help? Where I can find the answer or how to derive some equation that will work? I'm actually kind of interested in this so it would be cool to actually figure out. Thanks! 



#2
Oct2810, 12:58 PM

P: 136

yes there is a lot of correlations for the reynold number , you should have a table or a data sheet for all the correlations of Re for each case
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#3
Oct2810, 01:06 PM

P: 1,440

So you aren't supposed to assume that you know the conductivity? I would have thought that you would just need to note that the Nusselt number can be correlated to Reynolds number. After all, you can find k for pretty much any fluid listed in a table somewhere.




#4
Oct2810, 01:34 PM

P: 9

Reynold's Number related to heat transfer coefficient
I can use the Nusselt number if I know the thermal conductivity, viscosity, and specific heat, since
N_{u}=f(Re,Pr) and Pr=c_{p}*mu/k And the relation for local cases (laminar flow) usually takes the form: N_{ux} = h_{x}*x/k = C_{1}*Re^{y}*Pr^{z} where C_{1}, y, and z are constants determined by the magnitude of Prandtl number. I suppose k, c_{p}, and viscosity mu can be found from a table for most any fluid, but the way my professor asked the question makes it seem like there is a way to correlate a Reynold's number and the heat transfer coefficient without having to look up values. 



#5
Oct2810, 08:21 PM

P: 1,440

That wouldn't make any sense though since Reynolds number doesn't actually tell you anything about the heat transfer properties of a gas. If such correlations exist, they are purely empirical and will only work for the single gas for which they were meant. The way around that limitation is to use Nusselt, and that is still empirical.



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