Value of Heat transfer coefficient

  • Thread starter ruzfactor
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I have a circular cross-section of steel, around which I have air of constant temperature flowing. I want to calculate the heat flux, but I don't have the value of heat transfer coefficient,h (W/m^2.K) between steel and this air at 350C. Please suggest how to get the value for h. I am neglecting any heat loss.
 

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  • #2
boneh3ad
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Look up a parameter called the Nusselt number. I am pretty sure there are empirical relations that will give you the Nusselt number for your exact setup.
 
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Look up a parameter called the Nusselt number. I am pretty sure there are empirical relations that will give you the Nusselt number for your exact setup.

where can I get nusselt number for my geometry [please see the pic]??
 
  • #4
boneh3ad
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You didn't post a pic. Check out "Introduction to Heat Transfer" by Incropera and DeWitt or "Heat Transfer" by Mills, for example.

Also, a quick Google search nets a lot, for example http://www.egr.msu.edu/~somerton/Nusselt/ [Broken].
 
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Sorry about that. Please check now.
 

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  • #6
boneh3ad
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And? If your goal is to get the heat transfer around the cylinder, it doesn't depend on the inside if you are just assuming the cylinder is a certain temperature. Either way, the inside doesn't affect the heat transfer coefficient, only the heat conduction through the cylinder itself.

In other words, look up the relation in a book or through Google (hint: the link I gave you) and just compute the heat transfer coefficient. You just have to look up the values for a few parameters in your flow so you know the Reynolds number, Prandtl number and thermal conductivity of the fluid. Those can be readily found from many sources.
 
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basically, I am trying to see the temperature profile inside the cylinder after a certain period using COMSOL. I am using internal heat flux boundary condition where my external temperature is at 350C and value of heat transfer coefficient has to be given also. So how much time it takes for the cyllinder inside to reach 350C, is my objective. But value of h seems to be very complicated.
 
  • #8
boneh3ad
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I keep telling you it isn't. You have all the information you need. Use the Nusselt number. I even gave you a link.
 

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