This model is identical to
Buildings.Fluid.MixingVolumes.Validation.MixingVolumeTraceSubstanceReverseFlow,
except that the steady state volume volSte
is configured to have a prescribed heat flow rate,
which is in this case zero as the heat port is not connected.
This configures volSte to use the two port
steady state heat and mass balance model
Buildings.Fluid.Interfaces.StaticTwoPortConservationEquation.