Departure function

The departure function computes the difference between the fluid in the real state of interest and the hypothetical ideal gas state. Mathematically, this function is equivalent to the following equation:

In practice, there are several direct ways to evaluate this integral depending on the specific form of the equation of state that your Fluid Type uses for the enthalpy calculations. You can use the Vapor Equilibrium list in the Property Options section on the Fluid Editor to change the equation of state for your Fluid Type.

If you select Ideal Gas Law in the Vapor Equilibrium list, the departure function becomes zero.

If you select one of the following equations of state in the Vapor Equilibrium list, AVEVA Process Simulation evaluates the integral according to the selected equation of state:

• Hayden-O'Connell (HOCV): See HOCV — Hayden-O'Connell equation of state for more information.

• Redlich-Kwong (RK): See RK — Redlich-Kwong equation of state for more information.

• Soave-Redlich-Kwong (SRK): See SRK — Soave-Redlich-Kwong equation of state for more information.

• Peng-Robinson (PR): See PR — Peng-Robinson equation of state for more information.

• SRK-Modified Panag.-Reid (SRKM): See SRKM — Soave-Redlich-Kwong Modified Panagiotopoulos-Reid method for more information.

• PR-Modified Panag.-Reid (PRM): See PRM — Peng-Robinson Modified Panagiotopolous-Reid method for more information.

• SRK-Huron-Vidal (SRKH): See SRKH — Soave-Redlich-Kwong Huron-Vidal method for more information.

In all cases, when we calculate the departure term, we clip temperatures greater than the critical temperature (Tc) at Tc, because we assume ideal gas behavior at temperatures greater than Tc.