Ejector with motive flow swirl

Abstract

An ejector (200; 300; 400) has a primary inlet (40), a secondary inlet (42), and an outlet (44). A primary flowpath extends from the primary inlet to the outlet. A secondary flowpath extends from the secondary inlet to the outlet. A mixer convergent section (114) is downstream of the secondary inlet. A motive nozzle (100) surrounds the primary flowpath upstream of a junction with the secondary flowpath to pass a motive flow. The motive nozzle has an exit (110). The ejector has surfaces (258, 260) positioned to introduce swirl to the motive flow.

Claims

1. An ejector (300) comprising: a primary inlet (40) for admitting a liquid or supercritical or two-phase motive flow; a secondary inlet (42); an outlet (44); a primary flowpath from the primary inlet; a secondary flowpath from the secondary inlet; a mixer convergent section (114) downstream of the secondary inlet; and a motive nozzle (100) surrounding the primary flowpath upstream of a junction with the secondary flowpath and having an exit (110), wherein the ejector further comprises: means (340) for introducing swirl to the motive flow prior to mixing with a saturated or superheated vapor or two-phase secondary flow from the secondary flowpath; and a control needle, wherein the means is selected from the group consisting of: the means mounted on the needle to move therewith; and the means through which the control needle slides.

2. The ejector of claim 1 wherein: there is only a single motive nozzle.

3. The ejector of claim 1 wherein: the means for introducing swirl introduces swirl upstream of the junction.

4. The ejector of claim 1 wherein: the means for introducing swirl is inside the motive nozzle.

5. The ejector of claim 4 wherein: the means for introducing swirl comprises a plurality of vanes (242).

6. The ejector of claim 5 wherein: the vanes are carried on the control needle (132).

7. The ejector of claim 5 wherein: the vanes are fixed upstream of a convergent portion (104) of the motive nozzle.

8. The ejector of claim 5 wherein: the vanes extend radially outward from a centerbody (244).

9. The ejector of claim 4 wherein: a swirl angle at a beginning of a convergent section of the motive nozzle is 30-50.

10. The ejector of claim 1 wherein: a swirl angle at a beginning of a convergent section of the motive nozzle is at least 20.

11. A vapor compression system comprising: a compressor (22); a heat rejection heat exchanger (30) coupled to the compressor to receive refrigerant compressed by the compressor; the ejector of claim 1; a heat absorption heat exchanger (64); and a separator (48) having: an inlet (50) coupled to the outlet of the ejector to receive refrigerant from the ejector; a gas outlet (54); and a liquid outlet (52).

12. A method for operating the system of claim 11, the method comprising: compressing the refrigerant in the compressor; rejecting heat from the compressed refrigerant in the heat rejection heat exchanger; passing said liquid or supercritical or two-phase motive flow of the refrigerant through the primary inlet; and passing said saturated or superheated vapor or two-phase secondary flow of the refrigerant through the secondary inlet to merge with the motive flow.

13. The method of claim 12 wherein: the refrigerant comprises at least 50% CO.sub.2 by weight.

14. The method of claim 12 wherein: a swirl angle at a beginning of a convergent section of the motive nozzle is at least 20.

15. The ejector of claim 1 wherein: the control needle slides through the means for introducing swirl.

16. A method for operating an ejector (300), the method comprising: passing a liquid or supercritical or two-phase motive flow (103) through a motive nozzle; axially translating a control needle (132) to control the motive flow; passing a saturated or superheated vapor or two-phase suction flow (112) through a suction port; mixing the motive flow and the suction flow; and imparting swirl to the motive flow prior to the mixing, wherein: the imparting swirl to the motive flow comprises passing the motive flow over redirecting surfaces (258, 260) in the motive nozzle; and the redirecting surfaces are formed along vanes (242) selected from the group consisting of: vanes (242) mounted to the control needle; and vanes extending from a centerbody within which centerbody the control needle slides.

17. The method of claim 16 wherein: the vanes (242) are mounted to the control needle.

18. The method of claim 16 wherein: the vanes extend from the centerbody.

19. The method of claim 16 wherein: a swirl angle at a beginning of a convergent section of the motive nozzle is at least 20.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a prior art ejector refrigeration system.

(2) FIG. 2 is an axial sectional view of a prior art ejector.

(3) FIG. 3 is an axial sectional view of a first ejector.

(4) FIG. 4 is a first enlarged view of a vane unit of the motive nozzle of the ejector of FIG. 3.

(5) FIG. 5 is a second view of the vane unit of FIG. 4.

(6) FIG. 6 is an axial sectional view of a second ejector.

(7) FIG. 7 is an axial sectional view of a third ejector.

(8) FIG. 8 is a transverse sectional view of the ejector of FIG. 7, taken along line 8-8.

(9) FIG. 9 is a comparative flow simulation plot of liquid fraction for a baseline swirl-less ejector and an ejector with swirled motive flow.

(10) FIG. 10 is a calculated graph of ejector efficiency vs. motive nozzle inlet swirl for an exemplary ejector configuration

(11) Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

(12) FIG. 3 shows an ejector 200. The ejector 200 (and 300 described later) may be formed as a modification of the ejector 38 and may be used in vapor compression systems (e.g., FIG. 1) where conventional ejectors are presently used or may be used in the future. An exemplary ejector is a two-phase ejector used with CO.sub.2 refrigerant (e.g., at least 50% CO.sub.2 by weight). For ease of illustration, the exemplary ejector 200 is shown as a modification of the baseline ejector 38 of FIG. 2. Accordingly, the exemplary ejector may have similar features and, for ease of illustration, many reference numerals are not repeated. However, the ejector may be formed as modification of other configurations of ejector.

(13) The ejector 200 comprises means for imparting swirl to the motive flow. Exemplary means is, therefore, located along the primary flowpath upstream of the motive nozzle exit. More particularly, in the FIG. 3 embodiment, the exemplary means comprises a fixed swirler 240 positioned not merely upstream of the motive nozzle exit but also upstream of the motive nozzle throat and of the motive nozzle convergent section. The exemplary swirler 240 is located in a straight section 220 of the motive nozzle immediately between the motive nozzle inlet 40 and the upstream end of the convergent section 104. The exemplary swirler 240 comprises a plurality of pitched vanes 242 extending radially outward from a centerbody 244. The centerbody 244 is centered along the axis 500 from an upstream end 246 to a downstream end 248. Each vane extends radially outward from an inboard end 250 at the centerbody to an outboard end 252 at the inner surface of the straight section 220. Each exemplary vane has a leading edge 254 and a trailing edge 256 with a respective upstream surface 258 and downstream surface 260 extending therebetween. The exemplary upstream and downstream surfaces are generally flat so that, in circumferential cross-section, they appear straight and joined by exemplary semicircular transitions at the leading edge 254 and trailing edge 256. Other configurations are possible with relatively airfoil-like sections. The exemplary embodiment has four such vanes although greater or fewer numbers are possible (e.g., 2-8 such vanes).

(14) The motive (liquid) flow swirl enhances penetration and mixing of the suction (gas) phase flow. If a liquid core is rotating sufficiently fast within a gas core (which may be rotating or non-rotating), the liquid has a tendency to be moved outward by centrifugal force because the initial situation is hydrodynamically unstable. By such mixing, ejector efficiency, which measures the pressure rise relative to the entrainment ratio, can be increased.

(15) FIG. 6 shows a similar ejector 300 but wherein the swirler 340 is mounted on the needle. The swirler may move with the needle (with the outboard ends 252 thus slide against the inner surface of the straight portion 220). Alternatively, the swirler may be fixed and the needle may simply slide through a bore in the centerbody.

(16) FIG. 7 shows yet an alternative configuration of an ejector 400 wherein the primary flow enters not purely axially but rather with a tangential component. In this exemplary embodiment, a plate 420 closes the axially upstream end of the motive nozzle (the exemplary plate 420 has an aperture through which the needle may extend). The flow enters an inlet 440 along the sidewall of the straight section 220 at the terminus of the inlet conduit 442. The exemplary inlet flow 424 has a tangential component about the centerline 500 (e.g., it is not aimed directly at the centerline).

(17) FIG. 8 characterizes this tangential component with a radial offset R.sub.OFFSET of the inlet flow vector relative to the axis 500.

(18) FIGS. 9 and 10 disclose flow parameters and performance for an ejector where swirl is introduced upstream of the motive nozzle convergent section 104 (e.g., immediately upstream). This example facilitates a simple characterization of the swirl as an inlet swirl (as being measured at the beginning of the convergent section). Swirl, however may be introduced further downstream but may be more complicated to quantify for purposes of illustration.

(19) For a given inlet swirl angle (the tangent of which is the ratio of circumferential to axial velocity components), the swirl angle increases from the inlet to the throat and then decreases to the nozzle exit. If the inlet-to-throat diameter ratio is larger than the exit-to-throat diameter ratio, there is more swirl at the nozzle exit. It may be impractical to place a swirler in the supersonic-flow portion of the nozzle (e.g., the portion of the motive nozzle downstream of the throat, or minimum area location) because the swirler will generate shocks and possibly choke the flow, in either case increasing the exit pressure. It is generally desirable to have the nozzle flow over-expanded; the nozzle exit pressure is then less than the local static pressure of the suction flow.

(20) FIG. 9 shows comparative flow simulation plots of liquid fraction for a baseline swirl-less ejector and an ejector with swirled motive flow at an exemplary 45. From this, it is seen that the flow with motive-nozzle inlet swirl is better mixed in the divergent mixer, as indicated by the contour colors indicating lower liquid volume fraction. Swirl introduced into the motive flow leads to hydrodynamically unstable flow at mixing with high-density swirling flow contained within low-density, non-swirling flow. Centrifugal forces displace the motive flow outward, drawing the suction flow inward, improving mixing and phase change leading to increased efficiency.

(21) FIG. 10 shows ejector efficiency vs. motive nozzle inlet swirl for an exemplary ejector configuration. Above an inlet swirl angle of 20 (to about 45 or somewhat higher), there is a notable increase in performance (efficiency or pressure rise). The particular angles associated with performance increase in a given ejector configuration and given operating condition will depend on ejector operating conditions (e.g., inlet pressures, temperatures and entrainment ratio) and geometry. Thus, broadly, exemplary swirl angles at the beginning of the convergent section of the motive nozzle are greater than 20, more narrowly greater than 30, with exemplary ranges of 20-50 or 30-50. For swirl introduced further downstream, the swirl-inducing surfaces might be chosen to produce swirl at the mixer outlet/exit of the same magnitude as the mixer outlet/exit swirl associated with those ranges of inlet swirl.

(22) The ejectors and associated vapor compression systems may be fabricated from conventional materials and components using conventional techniques appropriate for the particular intended uses. Control may also be via conventional methods. Although the exemplary ejectors are shown omitting a control needle, such a needle and actuator may, however, be added.

(23) In the exemplary ejector, the motive and suction flows are arranged in the typical fashion, with the motive flow nozzle surrounded by the suction flow. The motive flow density is generally higher than that of the suction flow. When swirl is imparted to the motive fluid in a manner, such as described above, and the motive and suction flows are then allowed to interact (mix), centrifugal force tends to displace outward the rotating, higher-density motive flow into the lower-density suction flow, thereby enhancing mixing and increasing ejector performance (pressure rise). The situation is termed fluid dynamically, or hydrodynamically, unstable because the rotating, higher-density fluid is moved by the swirl-induced centrifugal force from the center of the mixing section toward the outer region, displacing inward the lower density suction flow, thereby creating a hydrodynamically stable configuration. In U.S. Pat. No. 4,378,681 (the '681 patent), swirl is imparted to the suction flow. In the '681 patent, the performance enhancing mechanism is evidently the longer contact time between the two flows increasing shear-driven mixing. The fluid particles at the interface of the two flows will follow a spiral path that is longer than the axial distance from the point where the two flows first interact to the point when they are sufficiently mixed.

(24) Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the remanufacturing an existing system or the reengineering of an existing system configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.