Most of the gases exhibit drop in temperature upon expansion. However, this may not be true in case of

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This question was previously asked in

BPSC AE Paper 5 (Mechanical) 2019 Official Paper

Answer 1

Explanation:

Joule – Thomson coefficient

When the gas in steady flow passes through a constriction, e.g. in an orifice or valve, it normally experiences a change in temperature.
From the first law of thermodynamics, such a process is isenthalpic and one can usefully define a Joule – Thomson coefficient as
\(\mu = {\left( {\frac{{\partial T}}{{\partial P}}} \right)_H}\)
As a measure of the change in temperature which results from a drop in pressure across the construction.
- For an ideal gas, μ = 0, because ideal gases neither warm not cool upon being expanded at constant enthalpy. ex. air
- If μ is +ve, then the temperature will fall during throttling. ex. oxygen, nitrogen, etc
- If μ is -ve, then the temperature will rise during throttling. ex. hydroge, helium, neon, etc