TITLE.PM5

162 ENGINEERING THERMODYNAMICS

dharm

/M-therm/Th4-4.pm5

4.13. Throttling Process and Joule-Thompson Porous Plug Experiment

Throttling process involves the passage of a higher pressure fluid through a narrow
constriction. The effect is the reduction in pressure and increase in volume. This process is
adiabatic as no heat flows from and to the system, but it is not reversible. It is not an isentropic
process. The entropy of the fluid actually increases.
Such a process occurs in a flow through a porous plug, a partially closed valve and a very
narrow orifice. The porous plug is shown in Fig. 4.41.

Fig. 4.41. The Joule-Thomson porous plug experiment.

In this system,

Q = 0 (Q System is isolated)

W = 0 (Q There is no work interaction)

T,p 55

T,p 44 T,p 33

T,p 22

T , p (Initial state) 11

p (Pressure)

T (Temperature)

Fig. 4.42. Constant enthalpy curve.

∆ PE = 0 (Q Inlet and outlet are at the same level)

∆ KE = 0 (Q Kinetic energy does not change significantly)