Heat flow through aluminium rod

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Homework Help Overview

The problem involves calculating the heat flow through an aluminium rod with specified dimensions and a temperature difference. The subject area is thermodynamics, focusing on heat transfer and thermal conductivity.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to apply the formula for heat transfer but expresses confusion regarding their calculations. Some participants question the cross-sectional area used in the calculations, while others clarify the distinction between total surface area and cross-sectional area.

Discussion Status

The discussion is ongoing, with participants providing guidance on how to correctly interpret the problem and calculate the necessary area. There is an acknowledgment of a misunderstanding regarding the area calculation, and some participants are exploring the implications of assuming the rod is a solid cylinder.

Contextual Notes

The original poster notes a lack of information about inner or outer diameters, which leads to questions about the assumptions that can be made regarding the rod's geometry.

em3
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Homework Statement


An Aluminium rod has a diameter of 40mm. and is 750mm long. If the temperature difference between the ends of the rod is 100C .

Take the thermal conductivity of Aluminium to be 235 Wm-1K-1

Homework Equations


k * A * ΔT / L

The Attempt at a Solution


235 * 0.097 m * 100 / 0.75

The answer is supposed to be 39.4 Js-1 but I can't get it right? So I don't know if I'm doing something wrong, and I've tried so many times. I don't know what I'm doing wrong.
Thanks
 
Last edited:
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Hi em3,

Welcome to Physics Forums!

em3 said:
235 * 0.095 m * 100 / 0.75
How did you arrive at 0.095 m for the cross sectional area?
 
40mm. and is 750mm into m, 0.04m and 0.75m. Then did A=2πrL+2πr2

2 * ∏ * 0.02 * 0.75 + 2∏0.022≈ 0.097
Sorry, made a typo in first post
 
em3 said:
40mm. and is 750mm into m, 0.04m and 0.75m. Then did A=2πrL+2πr2
You want the cross sectional area, not the total surface area.
 
How do I find that? The question only gives me the diameter and length, no inner or outer diameter.
 
em3 said:
How do I find that? The question only gives me the diameter and length, no inner or outer diameter.
Assume that a rod is a solid cylinder.
 
Oh ok thanks, I got it. Thanks a lot!
 

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