How to determine the airflow due to a change in temperature?

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Discussion Overview

The discussion revolves around determining airflow resulting from temperature changes within a cylinder. It includes concepts related to air circulation, temperature differentials, and thermal stratification, with a focus on both theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants inquire about the basic principles of airflow related to temperature changes after a long absence from physics.
  • One participant suggests providing a diagram to clarify the discussion.
  • Another participant proposes that internal air circulation can occur within the cylinder, influenced by temperature differentials, and references external resources for further context.
  • A follow-up question is raised regarding the possibility of unidirectional airflow from the hot end to the cold end, driven by density differences.
  • It is noted that stratification may occur, leading to layers of air at different temperatures, with heat transfer happening between these layers until thermal balance is achieved.
  • Some participants mention that despite stratification, there will still be some up-down movement of air due to density homogenization and heat exchange with the surroundings.

Areas of Agreement / Disagreement

Participants express varying views on the nature of airflow and stratification, indicating that multiple competing perspectives remain without a clear consensus on the mechanisms involved.

Contextual Notes

The discussion does not resolve the complexities of airflow dynamics, such as the specific conditions under which unidirectional flow occurs or the precise impact of temperature differentials on circulation patterns.

foal_11
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TL;DR
If I have a large hollow pipe and heat one end of it (by, say, 10 degrees Celsius), how do I calculate the air flow from the cold to the hot end?
(Sorry for the really basic question. Been 20 years since high school physics and I've been working in a different industry)
 
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Can you please provide a diagram?
 
Would this help? Can ignore the material for the cylinder for now.
 

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An internal simultaneous up and down air circulation may be established within the cylinder, as long as the temperature differential is kept (that circulation itself tends to make the internal temperature homogeneous).

This is only a reference, as it is applicable for open ends shafts or chimneys, but it can give you an idea:
https://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html

:cool:
 
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Thank you. I had a follow-up question on this.

When you say simultaneous internal up and down circulation, could it end up being unidirectional ?From the hot end (base) to the cold end, as the higher density of air at the base pushes air up as I maintain the temperature differential.
 
In that situation, stratification happens, where static layers of air at different temperatures form.
Heat will then will be transferred from layers of higher temperature to ones of lower temperature until a thermal balance within the whole mass of air is reached, while inducing some internal flow of mass.

In most practical cases, some up-down movement of air will always happen as density becomes homogeneous and some heat is absorbed by or released from the cylinder to the surroundings (think of a lava lamp).
 
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Lnewqban said:
In that situation, stratification happens, where static layers of air at different temperatures form.
Heat will then will be transferred from layers of higher temperature to ones of lower temperature until a thermal balance within the whole mass of air is reached, while inducing some internal flow of mass.

In most practical cases, some up-down movement of air will always happen as density becomes homogeneous and some heat is absorbed by or released from the cylinder to the surroundings (think of a lava lamp).
Great, thank you. This definitely helps.
 
You are welcome. :smile:
 

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