Ejectors

Abstract

An ejector has: a motive flow inlet; a secondary flow inlet; an outlet; and a motive nozzle. The motive nozzle has an exit. A motive flow flowpath proceeds through the motive nozzle and joins a secondary flow flowpath extending from the secondary flow inlet to form a combined flowpath to the outlet. From upstream to downstream along the motive flow flowpath, the motive nozzle has: a convergent section; a throat; a first divergent section commencing within 10% of a throat-to-exit length and diverging over a first length (L D1 ) of at least 10% of the throat-to-exit length (L TE ); a second divergent section, the second divergent section diverging over a second length (L D2 ) of at least 10% of the throat-to-exit length at a shallower angle than the first divergent section over said first length.

1 . An ejector comprising:
 a motive flow inlet;   a secondary flow inlet;   an outlet;   a motive nozzle having an exit; and   a motive flow flowpath proceeding through the motive nozzle and joining a secondary flow flowpath extending from the secondary flow inlet to form a combined flowpath to the outlet,   
       wherein from upstream to downstream along the motive flow flowpath, the motive nozzle has:
 a convergent section; 
 a throat; 
 a first divergent section commencing within 10% of a throat-to-exit length and diverging over a first length (L D1 ) of at least 10% of the throat-to-exit length (L TE ); and 
 a second divergent section, the second divergent section diverging over a second length (L D2 ) of at least 10% of the throat-to-exit length at a shallower angle than the first divergent section over said first length. 
 
     
     
         2 . The ejector of  claim 1  wherein, along the motive flow flowpath:
 the first divergent section extends at a single first half-angle (θ D1 ) directly from the throat; and 
 the second divergent section extends at a single second half-angle (θ D2 ) directly from the first divergent section. 
 
     
     
         3 . The ejector of  claim 2  wherein:
 the first half-angle is 1.0° to 4.0°; and 
 the second half-angle is 0.7° to 3.0°. 
 
     
     
         4 . The ejector of either of  claim 2  wherein:
 the first half-angle is 1.5° to 2.5°; and 
 the second half-angle is 0.8° to 1.5°. 
 
     
     
         5 . The ejector of either of  claim 2  wherein:
 the second half-angle is 30% to 80% of the first angle. 
 
     
     
         6 . The ejector of either of  claim 2  wherein:
 the second half-angle is 40% to 60% of the first angle. 
 
     
     
         7 . The ejector of  claim 1  wherein:
 the first length is at least 50% of the throat-to-exit length; and 
 the second length is at least 15% of the throat-to-exit length 
 
     
     
         8 . The ejector of  claim 1  wherein:
 the second divergent section ends within 5% of the throat-to-exit length from the exit. 
 
     
     
         9 . The ejector of  claim 1  wherein:
 the motive nozzle is metallic. 
 
     
     
         10 . The ejector of  claim 1  wherein:
 a convergent section length (L C ) is greater than the throat-to-exit length. 
 
     
     
         11 . The ejector of  claim 10  wherein:
 the convergent section length is at least 110% of the throat-to-exit length. 
 
     
     
         12 . The ejector of  claim 1  wherein:
 there is only a single said motive flow inlet; 
 there is only a single said secondary flow inlet; and 
 there is only a single said outlet. 
 
     
     
         13 . The ejector of  claim 12  wherein:
 the motive nozzle is metallic. 
 
     
     
         14 . A vapor compression system comprising the ejector of  claim 1 . 
     
     
         15 . The vapor compression system of  claim 14  further comprising:
 a compressor; 
 a first heat exchanger; 
 a second heat exchanger; and 
 a separator having:
 an inlet; 
 a liquid outlet; and 
 a vapor outlet; 
 
 an expansion device. 
 
     
     
         16 . The vapor compression system of  claim 15  further comprising:
 a plurality of conduits positioned to define a first flowpath sequentially through:
 the compressor; 
 the first heat exchanger; 
 the ejector from the motive flow inlet through the ejector outlet; and 
 the separator, and then branching into:
 a first branch returning to the compressor; and 
 a second branch passing through the expansion device and second heat exchanger to the secondary inlet. 
 
 
 
     
     
         17 . A method for using the ejector of  claim 1  comprising:
 passing a motive flow through the motive flow inlet; 
 passing a secondary flow through the secondary flow inlet; 
 merging the motive flow and the secondary flow to form a merged flow; and 
 passing the merged flow through the outlet, 
 
       wherein:
 the motive flow reaches a first Mach number of 0.9 to 1.2 at a downstream end of the first divergent section; and 
 the motive flow accelerates to a second Mach number of at least 0.05 greater than the first Mach number in the second divergent section. 
 
     
     
         18 . The method of  claim 17  wherein:
 the second Mach number is at least 0.2 greater than the first Mach number. 
 
     
     
         19 . An ejector comprising:
 a motive flow inlet;   a secondary flow inlet;   an outlet;   a motive nozzle having an exit; and   a motive flow flowpath proceeding through the motive nozzle and joining a secondary flow flowpath extending from the secondary flow inlet to form a combined flowpath to the outlet,   
       wherein from upstream to downstream along the motive flow flowpath, the motive nozzle has:
 a convergent section; 
 a throat; and 
 means for providing an a second acceleration upstream of the motive nozzle exit that is lower than a first acceleration downstream of the throat. 
 
     
     
         20 . The ejector of  claim 19  wherein the means comprises;
 a first divergent section; and 
 a second divergent section, the second divergent section diverging at a shallower angle than the first divergent section.