If you do not have access to Steam Table functions in Excel, you can use the empirical curves converted into formulas.
Here is the logic you embed into your Excel sheet: ejector design calculation xls
For incompressible liquids: [ A_t = \fracW_motive\rho_1 \cdot \sqrt2 \cdot \Delta P_nozzle / \rho_1 ] If you do not have access to Steam