Heat Transfer - Heat Flux (thermal Resistance)

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SUMMARY

The discussion centers on the concept of heat flux in thermal resistance, specifically addressing the relationship between conduction and convection. The user successfully applied an energy balance to determine the outer surface temperature of a wire by equating q_{conduction} and q_{convection}. However, it was clarified that heat flux cannot simply equal q_{conduction} or q_{convection} due to its variation with radial position within the wire and the changing circumferential perimeter available for heat flow.

PREREQUISITES
  • Understanding of heat transfer principles, specifically conduction and convection.
  • Familiarity with thermal resistance concepts.
  • Knowledge of radial heat flow calculations in cylindrical coordinates.
  • Basic proficiency in energy balance equations.
NEXT STEPS
  • Study the derivation of Fourier's Law for heat conduction.
  • Learn about the principles of thermal resistance in cylindrical systems.
  • Explore the concept of heat flux in varying geometries.
  • Investigate the impact of radial position on heat transfer rates in wires.
USEFUL FOR

Students and professionals in mechanical engineering, thermal engineering, and anyone involved in heat transfer analysis and design.

Icetray
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Homework Statement



qoC85IB.jpg




Hi guys,

I don't really need help with answering the dollowing question but just have a quick question about it.

I solved the first part of the question with an energy balance by letting q_{conduction} = q_{convection} to get the temperature of he outer surface temperature of the wire.

For the heat flux part, why can't the heat flux = q_{conduction} = q_{convection}? Shouldn't the heat flux be constant throughout?

Thanks in advance guys!
 
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Icetray said:

Homework Statement



qoC85IB.jpg




Hi guys,

I don't really need help with answering the dollowing question but just have a quick question about it.

I solved the first part of the question with an energy balance by letting q_{conduction} = q_{convection} to get the temperature of he outer surface temperature of the wire.

For the heat flux part, why can't the heat flux = q_{conduction} = q_{convection}? Shouldn't the heat flux be constant throughout?

Thanks in advance guys!
Because the heat flux is varying with radial position within the wire, and, even if it weren't, the circumferential perimeter available for heat flow is varying with radius. At any radial location, the product of the heat flux and 2πr represents the local radial heat flow per unit length of wire.
 

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