Refrigeration ejector cycle having control for supercritical to subcritical transition prior to the ejector

Abstract

A system (170) has a compressor (22). A heat rejection heat exchanger (30) is coupled to the compressor to receive refrigerant compressed by the compressor. A non-controlled ejector (38) has a primary inlet coupled to the heat rejection exchanger to receive refrigerant, a secondary inlet, and an outlet. The system includes means (172, e.g., a nozzle) for causing a supercritical-to-subcritical transition upstream of the ejector.

Claims

1. A method for operating a system, the system comprising: a compressor; a heat rejection heat exchanger coupled to the compressor to receive refrigerant compressed by the compressor; an ejector having: a primary inlet coupled to the heat rejection heat exchanger to receive refrigerant; a secondary inlet; an outlet; and a motive nozzle between the primary inlet and the outlet; a heat absorption heat exchanger coupled to the outlet of the ejector to receive refrigerant; and at least one nozzle inline between the heat rejection heat exchanger and the primary inlet, the method comprising running the compressor in a first mode wherein: the refrigerant is compressed in the compressor; refrigerant received from the compressor by the heat rejection heat exchanger rejects heat in the heat rejection heat exchanger to produce initially cooled refrigerant; and the initially cooled refrigerant passes through the at least one nozzle and transitions in the at least one nozzle from supercritical to subcritical and enters the primary inlet subcritical.

2. The method of claim 1 wherein: a control system controls flow through the at least one nozzle by receiving input from one or more sensors; and responsive to the input, controlling the at least one nozzle so as to maintain motive nozzle inlet pressure below supercritical.

3. A system (170) comprising: a compressor (22); a heat rejection heat exchanger (30) coupled to the compressor to receive refrigerant compressed by the compressor; an ejector (38) having: a primary inlet (40) coupled to the heat rejection heat exchanger to receive refrigerant; a secondary inlet (42); an outlet (44); and a motive nozzle (100) between the primary inlet and the outlet; a heat absorption heat exchanger (64) coupled to the outlet of the ejector to receive refrigerant; and at least one nozzle inline between the heat rejection heat exchanger and the primary inlet, so that a flowpath passes sequentially through the at least one nozzle and then to the motive nozzle primary inlet.

4. The system of claim 3 wherein: the at least one nozzle comprises a convergent nozzle or convergent-divergent nozzle.

5. The system of claim 3 wherein: the at least one nozzle consists of a single nozzle being a convergent nozzle or convergent-divergent nozzle.

6. The system of claim 5 further comprising: a control valve either upstream of an inlet of the single nozzle or downstream of an outlet of the single nozzle.

7. The system of claim 6 wherein: the refrigerant comprises at least 50% carbon dioxide, by weight.

8. The system of claim 3 wherein: the refrigerant comprises at least 50% carbon dioxide, by weight.

9. The system of claim 3 further comprising: a separator (48) having: an inlet (50) coupled to the outlet of the ejector to receive refrigerant from the ejector; a gas outlet (54) coupled to the compressor to return refrigerant to the compressor; and a liquid outlet (52) coupled to the secondary inlet of the ejector to deliver refrigerant to the ejector, wherein: the heat absorption heat exchanger (64) is between the separator and the secondary inlet.

10. The system of claim 9 wherein: the system has no other separator.

11. The system of claim 9 wherein: the refrigerant comprises at least 50% carbon dioxide, by weight.

12. The system of claim 3 further comprising: an expansion device (70) immediately upstream of an inlet (66) of the heat absorption heat exchanger (64).

13. The system (170) of claim 3 wherein: the ejector is a non-controlled ejector.

14. The system of claim 13 wherein: the at least one nozzle comprises a convergent-divergent nozzle.

15. The system of claim 13 wherein: a control valve is in series with the at least one nozzle.

16. The system of claim 15 wherein: the at least one nozzle comprises a convergent nozzle.

17. The system of claim 15 wherein: the at least one nozzle comprises a convergent-divergent nozzle.

18. The system of claim 3 wherein: a flowpath is non-branching between the heat rejection heat exchanger and the ejector.

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 an ejector.

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

(4) FIG. 4 is a schematic view of a first refrigeration system.

(5) FIG. 5 is a view of a first refrigerant transitioning means.

(6) FIG. 6 is a pressure-enthalpy (Mollier) diagram of the system of FIG. 4.

(7) FIG. 7 is a view of a second transitioning means.

(8) FIG. 8 is a view of a third transitioning means.

(9) FIG. 9 is a view of a fourth transitioning means.

(10) FIG. 10 is a view of a fifth transitioning means.

(11) FIG. 11 is a view of a sixth transitioning means.

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

DETAILED DESCRIPTION

(13) FIG. 4 shows an ejector cycle vapor compression (refrigeration) system 170. The system 170 may be made as a modification of the system 20 or of another system or as an original manufacture/configuration. In the exemplary embodiment, like components which may be preserved from the system 20 are shown with like reference numerals. Operation may be similar to that of the system 20 except as discussed below with the controller controlling operation responsive to inputs from various temperature sensors and pressure sensors

(14) The ejector is a non-controllable ejector. Directly upstream of the ejector primary inlet is a means 172 for providing a supercritical-to-subcritical transition of refrigerant before entering the primary inlet. A first exemplary means comprises a convergent nozzle 180 (FIG. 5) and a control valve 182 in series therewith. The convergent nozzle 180 has an inlet 184 and an outlet 186 A flow cross-sectional (interior surface) area of the outlet is less than that of the inlet (e.g., 10-95%, more narrowly, 20-80% or 40-60%). The outlet cross-sectional area may be nominally the same as that of the ejector primary inlet and any intervening conduit/line. The inlet cross-sectional area may be the same as the conduit/line from the heat rejection heat exchanger. The exemplary valve (e.g., a needle valve or ball valve) may be directly upstream of the inlet 184 or downstream of the outlet (FIG. 7).

(15) FIG. 6 is a Mollier diagram of the system of FIG. 4 with the means of FIG. 5. The exemplary evaporator pressure is P3 and the discharge or high side gas cooler pressure is P1. The means 172 lowers the ejector inlet pressure to P4. The flow rate and inlet condition of the motive nozzle can be controlled by the means 172 to keep the ejector motive nozzle inlet pressure below critical.

(16) In operation, the expansion device 70 is controlled to maintain a desired superheat of refrigerant exiting the evaporator. A target superheat exiting the evaporator may be maintained. The superheat may be determined by input from a pressure transducer P and temperature sensor T downstream of the evaporator. Alternatively, the pressure can be estimated from a temperature sensor along the saturated region of the evaporator. To increase superheat, the expansion device is closed, to increase opened.

(17) A third exemplary means comprises a convergent-divergent nozzle 220 (FIG. 8) in place of the convergent nozzle 180. The convergent-divergent nozzle 220 has an inlet 224 and an outlet 226, and a throat 228, between the inlet and the outlet. A flow cross-sectional (interior surface) area of the throat is less than that of the smaller of the inlet and outlet (e.g., 10-95%, more narrowly, 20-80% or 40-60%). An exemplary flow cross-sectional (interior surface) area of the outlet is greater or less (depending on the outlet refrigerant velocity requirement; higher velocity demands the outlet area be greater, less for lower velocity) than that of the inlet (e.g., 20-175%, more narrowly, 50-150%). The outlet cross-sectional area may be nominally the same as that of the ejector primary inlet and any intervening conduit/line. The inlet cross-sectional area may be the same as the conduit/line from the heat rejection heat exchanger.

(18) Further variations on the means involve omitting the control valve 182 (FIG. 9 for the nozzle 220). In such situations, the dimensions of the nozzle 180 or 220 are pre-selected to maintain the ejector inlet pressure below the critical pressure over the anticipated range of operating conditions.

(19) Yet further variations of the means modify the nozzle 220 to have a controllable flow cross-section. For a convergent-divergent nozzle 240 (FIG. 10), this may involve a controllable throat cross-section (e.g., via a needle valve having a needle 242 and an actuator (not shown). The needle may be controlled to control the nozzle outlet pressure or system parameters such as flow rates and temperatures, etc.

(20) FIG. 11 shows yet a further variation on the means involving an orifice plate 250 having an orifice 252. An exemplary orifice 252 is an orifice plate or Venturi tube. Yet further variations of the means involve a series of convergent and/or convergent-divergent nozzles with or without control valves. For example, there may be just a convergent nozzle before the ejector.

(21) The system may be fabricated from conventional components using conventional techniques appropriate for the particular intended uses.

(22) 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 or the disclosure. For example, when implemented in the remanufacturing of an existing system of 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.