The physics interfaces found under the Thin-Film Flow branch () when adding a physics interface describe momentum transport. These physics interfaces can be added either singularly or in combination with other physics interfaces describing mass and energy transfer. The thin-film flow interfaces are shown in Table 9-1.

Each of the physics interfaces can be configured to solve either the standard Reynolds equation for liquids (with a material or user-defined density specified at the absolute pressure), or the modified Reynolds equation for gas flow. The modified Reynolds equation assumes the ideal gas law, and it applies when pressure changes in the flow itself result in significant density changes.