What is the temperature of an iron bar after 1 hour of convection heating?

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Discussion Overview

The discussion revolves around determining the temperature of an iron bar after one hour of convection heating, considering both scenarios where the heating power is on and off. Participants explore the theoretical and practical aspects of heat transfer in this context.

Discussion Character

  • Technical explanation
  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a formula for calculating the final temperature of the iron bar, T_final = F + Q/(u*A*L), where F is an updating formula, Q is the power, u is the convective exchange coefficient, A is the area of the bar, and L is the length of the cable.
  • Another participant questions whether the original post is a homework problem, referencing forum guidelines.
  • A participant provides detailed specifications of the iron bar, including dimensions, mass, heat capacity, thermal conductivity, and initial temperatures, while seeking to find the new internal temperature after one hour of heating.

Areas of Agreement / Disagreement

There is no consensus on the correctness of the proposed temperature calculation or the applicability of the formula presented. Multiple viewpoints regarding the nature of the problem (homework vs. theoretical inquiry) are evident.

Contextual Notes

The discussion includes various assumptions about the parameters involved, such as the initial temperatures and the characteristics of the iron bar and the surrounding environment. The dependence on specific definitions and conditions for heat transfer is acknowledged but not resolved.

Who May Find This Useful

This discussion may be useful for individuals interested in heat transfer, thermodynamics, or those working on similar problems involving convection heating in materials.

dvd84
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Hello, my problem is the following:

I have an iron bar, which can be heated by convection through an electric cable with power Q.
I want to know the temperature of the iron bar after 1 hour has passed, both in the case when the power is
turned on and when it is off (Q=0).

the input parameters are the temperature of the iron bar at instant zero and the environmente temperature,
the output is the new temperature of the iron bar after 1 hour.

Thank you.
 
Last edited:
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Dr. Courtney said:
Is this a homework problem?

https://www.physicsforums.com/threads/guidelines-for-students-and-helpers.686781/

no it is not an homework problem, I have a solution which is

T_final = F + Q/(u*A*L)

where F is the formula that updates the temperature and it works quite well.
The term

Q/(u*A*L)

represents the increment of temperature due to the electric cable, where Q is the power, u the coefficient of convective exchange, A the area of the iron bar and L the length of the cable. I want to check the correctness of the term Q/(u*A*L), if you may help me.
 
I have an iron bar not insulated, of length 6 meters, heigth 28 cm and width 4 cm, hence the area is 1.68 m^2 and the mass is 529.13 Kg.
The heat capacity of iron is 450 J/Kg*K.
The thermal conductivity of iron is 0.023 W/m*K.
The thermal expansion coefficient is 0.0037 C^-1.
The density of air is 1.30 Kg/m^3.
The dynamic viscosity of air is 17.157 * 10^-6 Pa*sec.
I assume that at time zero the internal temperature of the iron bar is 5 degrees Celsius, the external temperature is -4 degrees Celsius (the bar is not insulated).
The power Q that pass through the cable is 22,5 KWatt, and the length of the cable is 14 meters, the heat transfer between the cable and the iron bar is by convection.

I need to know after 1 hour has passed the new internal temperature of the iron bar.

Thanks
 

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