GB925946A - Improvements in centrifugal compressors - Google Patents

Abstract

925,946. Centrifugal compressors. SOC. NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION. Nov. 11, 1960 [Nov. 20, 1959], No. 38852/60. Class 110 (1). In a centrifugal compressor of transonic or supersonic type comprising a rotary bladed impeller surrounded by a stationary diffuser, there are provided two opposite annular disc extensions integral with the impeller and projecting radially outwardly therefrom, downstream of the impeller blades, to define a peripheral annular rotary passage extending radially between the impeller and the diffuser, means fast with the impeller being provided for extracting heat from the fluid flow on its way through the annular rotary passage. The extraction of heat increases the compression ratio. It is stated that in a perfect fluid (i.e. one having no viscosity) the stagnation pressure (i.e. the sum of the static pressure and the pressure equivalent of the velocity head) is always increased where heat is extracted from a flow of constant section, irrespective of whether the flow is subsonic or supersonic. With real fluids this increase of pressure is normally insufficient to compensate for the decrease of pressure due to friction. In the case of a centrifugal compressor this difficulty can be overcome by providing that the extraction of heat takes place in a bladeless peripheral portion of the impeller 1 beyond the impeller blades 5 whereby the friction between the gas and the side walls 3a, 4a of the bladeless portion adds energy to the gas. In addition, the absolute velocity of the gas, which determines the increase of stagnation pressure for a given rate of heat extraction, is considerably higher than the relative velocity, which determines the rate of heat extraction and the friction. The heat is extracted through the walls 3a, 4a by means of cooling fluid circulated through a heat-exchanger 8. Further extraction of heat occurs in a stationary bladeless passage 7 preceding a diffuser 6, the heat being extracted by means of a heat-exchanger 9. The absolute velocity is supersonic at the outlet of the impeller and is reduced to a subsonic value in the passage 7. The transfer of heat may be improved by the provision of fins conforming to the direction of flow. As an additional or alternative way of extracting heat, a liquid is introduced through a duct 10 within the impeller shaft 2. The liquid passes through the blades and is vaporized as it is discharged through nozzles 10a at the trailing edges of the blades, thereby cooling the gas. The gas being compressed and the vaporizable liquid may both be uranium hexafluoride.