Reply To: Volume fraction gradient in VOF models for imposing interfacial heat sources

[Rob]

You need to decide how you're applying heat to the system. Gradient or isovalue are sensible, but check you don't have any other regions meeting those criterion too. 

Not sure about the units, it could be an omission in the documentation or code notes. If adding those units allows you to use the value then good, and double check it's giving you what you expect. Expressions are fairly new, and features/functions/values are being added with nearly every update.