# QI have doubts about specifying sources of 'additional variable'. For example, I have to implement following equationD(phi)/Dt = S_phi where phi is dimensionless. Therefore units of source term S_phi are s^-1. However when I implemented additional variable as ADDITIONAL VARIABLE: ICVariance Option = Definition Units = [ ] Variable Type = Specific ENDthe units of sources need to be implemented are [kg m-3 s-1]. Do I need to multiply the source terms Rpi and RDi with density? And what is the difference between specification of 'additional Variable' Volumetric or Specific.ALooking at the transient term and source only, for specific AVs the transport equation isd(rho.phi)/dt = S_phi (1)and for volumetric AVs it isd(phi)/dt = S_phi (2)It might be expected that a dimensionless specific AV should have units of kg^-1, and a dimensionless volumetric AV, m^-3. However, dimensionless AVs are exactly that (dimensionless) and have dimensions [ ]. From (1) and (2) we therefore see that for dimensionless, specific AVs sources are in units of kg m^-3 s^-1, whilst for volumetric AVs, they are s^-1.So, to return to your original question, you should multiply your source terms by density.

 QI have doubts about specifying sources of `additional variable`. For example, I have to implement following equationD(phi)/Dt = S_phiwhere phi is dimensionless. Therefore units of source term S_phi are s^-1. However when I implemented additional variable as ADDITIONAL VARIABLE: ICVariance Option = Definition Units = [ ] Variable Type = Specific ENDthe units of sources need to be implemented are [kg m-3 s-1]. Do I need to multiply the source terms Rpi and RDi with density? And what is the difference between specification of `additional Variable` Volumetric or Specific.ALooking at the transient term and source only, for specific AVs the transport equation isd(rho.phi)/dt = S_phi (1)and for volumetric AVs it isd(phi)/dt = S_phi (2)It might be expected that a dimensionless specific AV should have units of kg^-1, and a dimensionless volumetric AV, m^-3. However, dimensionless AVs are exactly that (dimensionless) and have dimensions [ ]. From (1) and (2) we therefore see that for dimensionless, specific AVs sources are in units of kg m^-3 s^-1, whilst for volumetric AVs, they are s^-1.So, to return to your original question, you should multiply your source terms by density.