An apparatus includes an electric generator having a stator and a rotor. A turbine is coupled to an end of the rotor to rotate at the same speed as the rotor. The turbine may rotate in response to expansion of a working fluid flowing from an inlet side to an outlet side of the turbine. The apparatus also includes a housing assembly with an inwardly oriented shroud, which is located at close proximity to the turbine. The proximity of the shroud to the turbine establishes the pressure ratio of the turbine, allowing the system to operate without seals. Magnetic bearings and position sensors are used to maintain the distance between the shroud and the wheel. In certain implementations, the positioning of the turbine can be controlled to optimize machine performance.