A radial turbine includes a housing, a rotor mounted on a shaft, an inlet channel for supplying a defined working medium, and an outlet channel. The rotor includes working cavities, with a generally spiral shape, which conduct the defined working medium from the inlet channel to the outlet channel, located near the center of the rotor. The working cavities have a generally rectangular cross-section, with a width (W), parallel to an axis of rotation of the rotor, and a height (H), parallel to a radius of the rotor. The width (W) is greater than the height (H), and the height (H) is not greater than six times a thickness of a boundary layer of the defined working medium.