1. Field of the Invention
The present invention is related to a compact closed-loop Brayton cycle rotating machine. In addition, the invention is directed to a propulsion system comprising this type of machine, and a vehicle provided with propulsion means of this kind.
2. Description of the Prior Art
The closed-loop Brayton cycle is a thermodynamic cycle in which a gas, a mixture of gases, or working fluid, referred to together hereinafter as "working fluid", flows in a closed circuit through the following stages:
the cold working fluid is compressed, PA1 the compressed cold working fluid is heated, PA1 the compressed heated working fluid is expanded, PA1 the expanded heated working fluid is cooled, and PA1 the cooled working fluid is recycled to the compressor stage, thus completing the cycle.
Various types of heat sources may heat the working fluid, such as a nuclear reactor or a boiler with burners fed with fuel oil or natural gas.
The working fluid is expanded in a turbine, or the like, so as to recover mechanical energy.
Closed-loop Brayton cycle turbines are used in nuclear power plants in which size is not critical. Furthermore, these turbines are constructed individually for a specific power plant and with higher power ratings appropriate to the substantial heat source that the specific nuclear reactor represents.
Closed-loop Brayton cycle turbines have also been developed for use in underwater craft and spacecraft. Once again, they are constructed individually at a cost that is unthinkable in the context of large series production. Furthermore, the proposed turbines always have a high power rating and/or large overall dimensions.
Turbines have been proposed having two structurally separate parts disposed one after the other or one in parallel with the other. The first part constitutes the main working fluid heating stage (boiler) and the second part constitutes the working fluid compression, preheating and expansion stages. However, this separate arrangement has disadvantages, including high head losses in the pipes conveying the working fluid between the two parts of the turbine, and loss of heat dissipated by the structures of the boiler part and along the pipes connecting the various parts. Furthermore, prior art turbines operate with temperatures in the order of 1000.degree. C. As a result the thermal efficiency is not very high.