TURBINE EXPANDER PROVIDED WITH VARIABLE NOZZLE MECHANISM

PROBLEM TO BE SOLVED: To provide a turbine expander provided with a variable nozzle mechanism in which an actuator and most parts of a nozzle drive mechanism can be installed in a room temperature range at an atmospheric pressure, and in which input heat can be restricted to the minimum in driving a variable nozzle of an expansion turbine, to lead very low temperature gaseous helium to adiabatic expansion. SOLUTION: This expander is provided with an adiabatic expansion device 22 incorporatol with a turbine impeller 12 to lead very low temperature gas, to adiabatic expansion by its rotation, a brake device 24 coaxially connected to the turbine impeller 12 for braking this; and a variable nozzle mechanism 30 for changing a throat area of the very low temperature gas introduced to the turbne impeller 12. The adiabatic expansion device 22 is installed in a vacuum vessel 14, and the brake device 24 is installed outside the vacuum vessel 14. The variable nozzle mechanism 30 comprises a nozzle member 32 built in the adiabatic expansion device 22, and a drive member 34 installed outside the vacuum vessel 14. The nozzle member 32 and the drive member 34 are connected to each other by a thin cylindrical member 36 which is coaxial with the turbine impeller 12, and the nozzle member 32 is driven by oscillation of the cylindrical member 36 around an axial center Z of the turbine impeller 12.