This applet models the Joule-Thomson experiment, where a gas moves through the left part of an insulated tube at a constant pressure p1 toward a throttle, after which the pressure drops to the final pressure p2. The process was proven by Joule and Lord Kelvin to be isoenthalpic (the chang ein enthalpy in the process is zero, ΔH=0). The temperature change T2 - T1 is important. If the pressure drops (dp <0) and the temperature drops (dT<0, i.e., the gas cools), then μ, the Joule-Thomson coefficient (∂T/∂p) > 0.
The regions where cooling is possible by expansion are temperature-dependent. Typical curves of these regions are shown in the small graph to the right of the model Joule-Thomson apparatus.
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