1. Field of the Invention
The present invention relates to a turbo compressor, and more specifically relates to a two-stage turbo compressor, in which two impellers are fixed in a direction with their backsides facing each other on the same rotation axis.
Priority is claimed on Japanese Patent Application No. 2008-27068, filed Feb. 6, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
As a refrigerator that cools or refrigerates an object to be cooled such as water, there is known a turbo refrigerator furnished with a turbo compressor that compresses a refrigerant by a compression stage provided with an impeller or the like, and discharges the refrigerant.
In the compressor, when the compression ratio increases, the discharge temperature of the compressor rises and volumetric efficiency drops. Therefore, in some cases, in the turbo compressor provided in the turbo refrigerator, compression of the refrigerant is performed in a plurality of stages.
For example, in Japanese Unexamined Patent Application, First Publication No. Hei 5-223090 there is disclosed a two-stage turbo compressor that has compression blades (impellers) at opposite ends of a drive motor shaft, and a fluid compressed by a first impeller is delivered to a second impeller.
In this turbo compressor, the fluid compressed by the first impeller is guided to a suction port of the second impeller via piping provided outside (external piping).
Moreover, in Japanese Unexamined Patent Application, First Publication No. 2007-177695 there is disclosed a turbo compressor in which two impellers are arranged adjacent to each other with their backsides facing each other.
In this turbo compressor, piping (internal piping) for introducing fluid compressed by a first impeller to a second impeller, is formed in a first housing enclosing the first impeller and a second housing enclosing the second impeller.
In the conventional turbo compressors described above, there are the following problems.
That is to say, the turbo compressor disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 5-223090, is one where a drive motor is arranged between the first impeller and the second impeller. Therefore a distance between these first and second impellers becomes necessarily long. Consequently if these impellers are connected via external piping, the piping structure becomes long and complicated. In addition, since there are many bent portions in the piping, flow of the fluid is disturbed and separation is likely to occur, so that pressure loss increases.
Moreover, the turbo compressor disclosed in Japanese Unexamined Patent Application, First Publication No. 2007-177695, is one where there is no drive motor between the two impellers, and the distance between the impellers can be shortened. However the structure has piping inside the housing. Therefore the curvature of the piping is small so that separation is likely to occur, and the pressure loss is increased. Moreover a space for arranging a diffuser to be provided around the impeller cannot be ensured sufficiently. As a result the pressure energy cannot be obtained efficiently, and improvement in performance of the compressor is difficult.