Mechanical Solutions, Incorporated (MSI) was commissioned to design a single stage radial turboexpander for a novel geothermal application. The active fluid in the turboexpander is R134-A. The turboexpander was optimized using STAR-CCM+. MSI utilized the real gas capability in STAR-CCM+ through the application of the Peng Robinson Equation of State. Results will be presented for the design. The test of the turboexpander is scheduled for the first quarter of 2015, so there may be an opportunity to compare the results with experimental data.