Working of a Constant Volume Gas Thermometer

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SUMMARY

The discussion focuses on the operation of a constant volume gas thermometer, specifically its use in measuring temperatures near absolute zero. According to "Thermodynamics An Engineering Approach" by Cengal, these thermometers are typically filled with Hydrogen or Helium. A key point raised is the solidification of Hydrogen at 14.01 K, questioning the validity of the temperature-pressure relationship in this state. It is concluded that as long as the gas pressure remains above the equilibrium vapor pressure at the given temperature, the gas will not solidify, allowing for accurate temperature measurements.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically gas laws
  • Familiarity with the properties of gases, particularly Hydrogen and Helium
  • Knowledge of phase transitions and equilibrium vapor pressure concepts
  • Basic comprehension of temperature measurement techniques
NEXT STEPS
  • Research the properties of Hydrogen and Helium at low temperatures
  • Study the concept of equilibrium vapor pressure in thermodynamics
  • Explore alternative gas thermometers and their applications
  • Learn about the implications of solidification on gas behavior at low temperatures
USEFUL FOR

Students and professionals in thermodynamics, physicists, and engineers involved in low-temperature measurements and gas behavior analysis.

Ali Asadullah
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How a constant volume gas thermometer works?
In "Thermodynamics An Engineering Approach" by Cengal, author says that this type of thermometer is usually filled with Hydrogen or Helium and We use Constant volume gas thermometers for measuring temperatures near absolute zero.
Now if volume is constant and suppose we are using Hydrogen, then Hydrogen will solidify at 14.01 K. Then how can we measure the temperature when hydrogen becomes solid and in this state of matter, the postulate that Temperature is proportional to Pressure will not be valid.
Also let us suppose that we have container of constant volume filled with the gas, if we start decreasing its temperature, then its pressure and temperature will decrease but volume will remain same and it will never solidify. Where is the mistake in this statement?
 
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If the pressure is low enough, the gas won't become solid. The gas pressure has to be higher than the equilibrium vapor pressure of the substance at the temperature in question for the gas to begin to solidify.
 

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