The expansion of gas through an orifice or partly opened valve is called as throttling.
q1-2 = 0 and w1-2 = 0
The throttling process is constant enthalpy process.
If readings of pressure and temperature of Joule
Thompson porous plug experiments are plotted,
h1 = h2 = h3 = h4 = h5
The slope of constant enthalpy curve is called as Joule
Thompson coefficient. p = dT/dP
For perfect gas, p = 0.