Interactive Self-Study Module: Throttling and Joule-Thomson Expansion
Department of Chemical and Biological Engineering, University of Colorado Boulder 

This module uses screencasts and interactive simulations to explain throttling (Joule-Thomson expansion) of single-component liquids and gases. When a mixture is throttled, the liquid and vapor compositions are different, and this is a basis for separations; see the Flash Separations module. This module then provides example problems to allow the user to test themselves. We suggest using the learning resources in the following order:

  1. Attempt to answer the multiple-choice ConcepTests before watching the screencasts or working with the simulations.
  2. Watch the screencasts that explain Joule-Thomson expansion and answer the questions within the screencasts.
  3. Use the two interactive simulations to further understand throttling and Joule-Thomson expansion.
  4. Try to solve the example problems before watching the solutions in the screencasts.
  5. Answer the ConcepTests.

Throttling or Joule-Thomson expansion results in a temperature change when a high-pressure liquid or ideal gas undergoes an adiabatic pressure drop. For most gases the temperature decreases. For most liquids, the temperature drops as some of the liquid evaporates.

This module is intended for a thermodynamics course.

Before studying this module, you should:

  • Be able to apply the first law of thermodynamics for steady-state flow systems.
  • Be able to use steam tables.
  • Be able to apply Antoine equation.
  • Be able to use an equation of state for real gases.

After studying this module, you should be able to:
           Determine the outlet conditions for a throttle, given the inlet pressure and temperature, the outlet pressure, and an equation of state or a table of properties