Simple Explaination of Temperature Difference

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Discussion Overview

The discussion revolves around understanding the temperature of a thin wall separating two gases at different temperatures, specifically how to determine the wall temperature given the gas temperatures and the role of material properties.

Discussion Character

  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions how to determine the temperature of a thin wall when one side has a gas at 20°C and the other at 0°C, asking if more information about the wall material is needed.
  • Another participant suggests that defining the wall's conduction coefficient and thickness is essential for understanding heat transfer.
  • A different participant proposes that for a thin wall, the temperature gradient is likely linear, and suggests assuming the wall temperature is the average of the two gas temperatures, while noting that convection on either side may affect this assumption.
  • This participant also mentions that if the convection coefficients differ on either side, the wall temperature could be skewed towards the temperature of either gas, and that radiation could also influence the wall temperature if one side faces a different temperature surface.
  • One participant seeks clarification on the theoretical basis for assuming the wall temperature is halfway between the two gas temperatures and expresses difficulty in finding resources to study this further.
  • Another participant references Fourier's Law of Heat Conduction, explaining that heat flow is proportional to the temperature difference and surface area, and inversely proportional to thickness, suggesting this may relate to the earlier question.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact determination of the wall temperature, with multiple viewpoints on the assumptions and factors influencing the temperature gradient. The discussion remains unresolved regarding the theoretical basis for the assumptions made.

Contextual Notes

Limitations include the lack of specific details about the wall material and its properties, as well as the assumptions made regarding convection and radiation effects, which are not fully explored.

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This is not a homework question but a simple equation I want to make clear.

If temperature of gas on one side of a thin wall with negligible thickness is 20 decs c and on the other is 0 degs c how do you determine the temp. of the wall? Is it possible or do you need more information about the material of the wall?

Thank you,
 
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You need to define the properties of the wall, most basically the conduction coefficient and thickness.
 
The wall is not the problem. The temperature gradient within a wall should follow be a linear relationship from one wall edge to the edge for a homogenous material and of suitable thickness.

But since your wall is thin, you could make a simple assumption that the wall temperature to be even across its width. You would also assume the temperature of the wall to be halfway between the two gas temperatures, and that the convection ( which it would be in most cases ) on either side is the predominate factor in determination of the heat flow.

If the amount of heat transfer by convection ( coeficient ) on either side of of wall is not the same, then the wall temperature will lean to towards the temperature of the hotter gas or the cooler gas.

Radiation could also be a factor if one side of the wall is facing a surface of different temperature than your gas. Your wall temperature could actually then be higher or lower than either temperature(s) of your gas(es).
 
Thanks for both your help.

256bits, I know it is a simple assumption to make that the wall temp. is half way between t1 and t2, but what theory is it based on do you know? As I want to read more into it and find it hard to find where to start.
 
Fourier Law of Heat Conduction is linear.

See
http://www.chemeurope.com/en/encyclopedia/Heat_conduction.html
for the formula
For conduction, the heat flow is directly proportional to the surface area, directly proportional to the temperature difference, and indirectly proportional to the thickness.

Is that what you ask?
 
Yes, that has cleared it up for me thank you very much.
 

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