Abstract: An exemplary embodiment of the present techniques provides a system for decreasing a temperature of a fluid. The system includes an axial flow expander for expanding gas flowed in a direction along an axis thereof. The axial flow expander includes: an outer casing made as a unified structure having an inlet port and an outlet port. An inner casing is fixed inside the outer casing. A rotor shaft is accommodated inside the inner casing, and is aligned with the axis. A number of bearings allow the rotor shaft to rotate around the axis. Moving blades protrude from the rotor shaft and are arranged inside the gas passage in an alternating fashion with a number of stator vanes. The inner casing, the rotor shaft, the bearings, the stator vanes, and the moving blades are integrally assembled, and inserted into the outer casing in the direction along the axis.