Joule throttled expansion

Figure 5.9 The Joule-Thompson cycle (Linde cycle). The gas is first compressed and then cooled in a heat exchanger, before it passes through a throttle valve where it undergoes an isenthalpic Joule-Thomson expansion, producing some liquid. The cooled gas is separated from the liquid and returned to the compressor via the heat exchanger.

Joule-Thomson expansion Expression representing an isenthalpic throttling process. 

Because of the variation of the Joule-Thomson coefficient with both temperature and pressure it is not easy to calculate the change of temperature resulting from a given throttled expansion, even when such data as in Table IV are available. This can be done, however, by a series of approximations. By estimating a rough average for the Joule-Thomson coefficient, some indication of the fall of temperature can be obtained. 

The Linde cycle is a simple cryogenic process based on Joule-Thompson effect. It is composed of different steps the gas is first compressed, then preliminarily cooled in a heat exchanger using liquid nitrogen, finally it passes through a lamination throttle valve to exploit the benefits of Joule-Thomson expansion. Some liquid is produced, and the vapour is separated from the liquid phase and returns back to the compressor through the heat exchanger. A simplified scheme of the overall process is reported in Fig. 2.9. 

But T(t ) is temperature in the tank. What about temperature of gas leaving the throttling valve Gas going thru valve undergoes a Joule-Thomson expansion => Hin = H Qal. Since gas is ideal, this implies... 

The Joule-Thomson expansion occurs at constant enthalpy through a valve or throttling device... 

Ethylene is liquefied by a Joule-Thomson expansion. It enters the throttling process at 50 bar and 0°C and leaves at 10 bar. What is the fraction of the inlet stream that is liquefied ... 

The temperature of the gas thus falls. The cooled air enters the chamber E from below and then goes up as shown. Thus, the gas cools the portion of the compressed air passing down the coil CE. This chilled gas then passes through a jet or throttle J and is further cooled by Joule-Thomson effect on account of expansion. This process goes on till the gas is converted into the liquid state. 

Thus we conclude that in a Joule-Thomson throttling process the enthalpy is conserved. Therefore, the temperature of an ideal gas does not change as the heat capacity Cp and thus the enthalpy H do not depend on pressure. The change of temperature of a real gas during such an isenthalpic expansion is characterized by the Joule-Thomson coefficient... 

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