The Joule Thomson Effect
The phenomenon of change of temperature produced when a gas is made to expand adiabatically from a region of high pressure to a region of externally low pressure is known as the Joule-Thomson Effect.
The ratio of change in temperature w.r.t. change in pressure at constant enthalpy is known as JouleThomson coefficient. This experiment is known as Joule Thomson experiment.
Suppose a certain amount of gas is passed through the porous plug. We than have
Change in volume on the left hand side = – V1
Work involved on the left hand side = P1V1
Change in volume on right hand side = V2
Work involved on the right hand side = – P2V2
Net work involved in the system = – P2V2 + P1V1
Because the process is adiabat ic, dq = 0 then from first law
We have, dq = dU – ω = 0
dU = ω
or U2 – U1 = – P2V2 + P1V1
U2 + P2V2 = U1 + P1V1
H2 = H1
i.e., adiabatic process is isoenthalpic in Joule-Thomson experiment.
Joule Thomson coefficient is represented by mJ.T and is equal to
We now that,
H = H(P,T)
We know that
then we have,
Inversion temperature: The temperature at which the Joules-Thomson coefficient changes sign is known as the inversion temperature. Another words, inversion temperature is the temperature at which real gas behave ideally.
We know that μJ .T. = 0 for ideal gas
Where Ti is known as inversion temperature.
Zeroth law of thermodynamics: “If body A is in equilibrium with body B is also in equilibrium with body C, then bodies A and B are in equilibrium with each other.”