Value of Heat transfer coefficient

In summary, the conversation discusses the calculation of heat flux for a circular steel cross-section with air flow at constant temperature. The person is looking for the heat transfer coefficient, h, at 350C and is advised to look up the Nusselt number for their specific setup. The conversation also mentions sources for finding the Nusselt number and addresses the issue of temperature profile and heat transfer time.
  • #1
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
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.
 
  • #3
boneh3ad said:
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
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/ .
 
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  • #5
Sorry about that. Please check now.
 

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  • #6
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.
 
  • #7
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
I keep telling you it isn't. You have all the information you need. Use the Nusselt number. I even gave you a link.
 

1. What is the definition of heat transfer coefficient?

The heat transfer coefficient is a measure of the amount of heat that is transferred between two surfaces per unit of temperature difference. It is a key parameter in heat transfer analysis and is often used to compare the efficiency of different heat transfer processes.

2. How is heat transfer coefficient calculated?

The heat transfer coefficient can be calculated using the formula h = q/(AΔT), where h is the heat transfer coefficient, q is the heat flux, A is the surface area, and ΔT is the temperature difference between the two surfaces.

3. What factors affect the value of heat transfer coefficient?

The value of heat transfer coefficient can be influenced by a variety of factors such as the type of fluid, the properties of the surfaces, the temperature difference, the flow rate, and the presence of fouling or deposits on the surfaces.

4. How important is the heat transfer coefficient in practical applications?

The heat transfer coefficient is a crucial parameter in many industrial and engineering processes, from designing efficient heat exchangers to optimizing cooling systems. It is also an important consideration in building and HVAC design, as it affects the rate of heat loss or gain in a space.

5. Can the heat transfer coefficient be increased?

Yes, the heat transfer coefficient can be increased by increasing the surface area between the two surfaces, increasing the temperature difference, or by improving the fluid flow rate. Additionally, using materials with higher thermal conductivity can also lead to a higher heat transfer coefficient.

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