Units of Henry's Law in General Mode

[Amy Rice]

Hello PFLOTRAN Gurus,

I am modeling PCE vapor migration in the vadose zone and need to use Henry's Law. The PFLOTRAN User's Guide states that the units for Henry's constant are [Pa]. Henry's constant is defined as aqueous concentration divided by gas partial pressure. How is that modeled in Pa?

Thank you!

https://documentation.pflotran.org/user_guide/cards/subsurface/eos_card.html

Amy

Amy K. Rice, Ph.D.

Neptune & Company, Inc.

505-309-1091

[Hammond, Glenn E]

Amy,

In GENERAL mode, Henry’s constant is calculated from Eq. 15 of Fernandez-Prini et al., 2003 (https://doi.org/10.1063/1.1564818).

Based on that equation, the units are [Pa]. We employ Henry’s constant to calculate the partial pressure of air in equilibrium with an air mole fraction in the liquid phase or vice versa.

Nevertheless, I do not recommend using GENERAL mode for simulating PCE flow, as it is designed for scenarios with a single gas component. In your case, the gas phase would include a mixture of PCE, air, and water vapor, which requires a flow model capable of accounting for gas mixtures. While it may be possible to model PCE transport in the gas phase utilizing the reactive transport features of the code, you would need to add an equilibrium constant for PCE to gas section of the reaction database.

Regards,

Glenn

From: 'Amy Rice' via pflotran-users <pflotra...@googlegroups.com>
Date: Wednesday, May 6, 2026 at 2:35 PM
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