DrAmine
Ansys Employee

If you require a built-in van't hoff correlation it will require just to set the temperature on 21 C. Enable Energy Equation, set the temperature to 21 C (Initialization and all boundaries) and do not solve the energy equation. But bear in mind that doing this you will aslo ignore the secondary source terms due to phase change (might be okay as they are very very small and might be ignored here).