Heating Time of Compressed Air

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Discussion Overview

The discussion revolves around the heating time of compressed air when compressed into a small volume at a high initial temperature. Participants explore concepts related to heat capacities, energy requirements, and the nature of adiabatic processes.

Discussion Character

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

Main Points Raised

  • One participant questions whether air would reach a temperature of 3,000 degrees C instantly when compressed, seeking to understand heat capacities and energy requirements.
  • Another participant clarifies that for air to reach a given temperature "in an instant," the process must be adiabatic, meaning no heat transfer occurs.
  • A calculator is referenced that suggests a final temperature of 5800 K under certain conditions, prompting a caution about potential input errors.
  • One participant expresses that while the air would heat quickly, it would still take some time, and raises concerns about the cylinder potentially exploding.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact nature of the heating process or the implications of the calculations, indicating multiple competing views and unresolved questions regarding the heating time and safety of the cylinder.

Contextual Notes

Limitations include assumptions about the adiabatic process, the accuracy of the calculator results, and the specific conditions under which the heating occurs.

Who May Find This Useful

Individuals interested in thermodynamics, heat transfer, and the behavior of gases under compression may find this discussion relevant.

s.p.q.r
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HI,

If you compressed 300 litres (about 12 moles) into a 3 litre cylinder which was already at 3,000 degrees C. Would the air reach this temperature in an instant?

Im trying to get my head around this stuff about heat capacities and amounts of energy needed to heat materials.

Please help me to understand.

Thanks in advance.

PS- This isn't homework (im not even a physics student).
 
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I should mention that the tank that it will heat in is more of a long pipe.
 
Here is a nice explanation about adiabatic processes as well as a calculator to do the calculation you want.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/adiab.html#c1

The only way for air to reach a given temperature "in an instant" is for the process to be adiabatic. This means that there is no heat transfer. If there must be any heat transfer then the process cannot be "in an instant" since heat transfer always takes time.

On that calculator, plugging in 12 moles, .3 m^3 initial volume, .003 m^3 final volume, and an initial temperature of 273 K, you get a final temperature of 5800 K (which is about the temperature of the sun, so I may have punched in the numbers wrong, you had best do the calculations yourself).
 
Last edited:
Hi,

Great thanks for this link. It is helpful to understand why they must cool down compressors.

Cheers.
 
it would hate quickly, no doubt about it, but it would take some time. that, and the cylindar would expload.
 

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