Compressible and Imcompressible ?

Pathway

I simulate two cases. One is using air as fluid through a small volume, and the other is using water-liquid as fluid through a small volume.

I only konw the mass flow rate, so I set inlet as mass flow inlet and outlet as pressure outlet.

Do the two cases set correct?

In fluent, it says using mass flow inlet for compressible flow.

And what's the meaning of mass imbalance?

Thanks a lot.