Units for UDS Diffusivity, Source Terms and Boundary Values

Why does Ansys Fluent show units for UDS diffusivity, but not for source terms or boundary values?

Fluid density is multiplied throughout the UDS transport equation. The diffusion coefficient has units kg/(m*s), consistent with the Ansys Fluent GUI. If the UDS defined by the user is dimensionless, then the source term Sϕk has units kg/(m3*s). Note that this Sϕk is directly the "source" that gets returned in the DEFINE_SOURCE macro. As for C_UDSI(c,t,0), which is the scalar ϕk itself (with k=0), it has no units.

If the user defines a scalar that does have units, then all terms in the transport equation simply get multiplied by those units, and the equation remains dimensionally consistent.

For more details, refer to this document.