In CFX > Options > Units, you can change the System setting to Custom to select from a pre-defined list of Volumetric Flow units. The list in CFX-Pre cannot be modified. This means that you cannot add a custom unit such as barrels/hr, for instance. A possible workaround is as follows: 1) Create a flow rate expression called Qbph that is dimensionless and reflects the desired value of flowrate in barrels/hr. 2) Create an expression Q where Q = Qbph*(3.31188e-4 [m^3 s^-1]) Q can then be used in an expression for velocity or massflow to be applied in an inlet/outlet boundary condition. Note that in CFD-Post it is possible to add to the list using different combinations of volume and time units that are not currently present in the list.