EP3099988B1

EP3099988B1 - Vapor compression system and methods for its operation

Info

Publication number: EP3099988B1
Application number: EP15703184.0A
Authority: EP
Inventors: Parmesh Verma; Larry D. Burns; Alexander Lifson
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2014-01-30
Filing date: 2015-01-23
Publication date: 2022-04-27
Anticipated expiration: 2035-01-23
Also published as: DK3099988T3; WO2015116480A1; US20170108256A1; EP3099988A1

Description

The present disclosure relates to refrigeration. More particularly, it relates to a vapor compression system comprising an ejector and alternative methods of operation of said system.
Earlier proposals for ejector refrigeration systems are found in US1836318 and US3277660 . FIG. 1 shows one basic prior art example of an ejector refrigeration system 20. The system includes a compressor 22 having an inlet (suction port) 24 and an outlet (discharge port) 26. The compressor and other system components are positioned along a refrigerant circuit or flowpath 27 and connected via various conduits (lines). A discharge line 28 extends from the outlet 26 to the inlet 32 of a heat exchanger (a heat rejection heat exchanger in a normal mode of system operation (e.g., a condenser or gas cooler)) 30. A line 36 extends from the outlet 34 of the heat rejection heat exchanger 30 to a primary inlet (liquid or supercritical or two-phase inlet) 40 of an ejector 38. The ejector 38 also has a secondary inlet (saturated or superheated vapor or two-phase inlet) 42 and an outlet 44. A line 46 extends from the ejector outlet 44 to an inlet 50 of a separator 48. The separator has a liquid outlet 52 and a gas outlet 54. A suction line 56 extends from the gas outlet 54 to the compressor suction port 24. The lines 28, 36, 46, 56, and components therebetween define a primary loop 60 of the refrigerant circuit 27. A secondary loop 62 of the refrigerant circuit 27 includes a heat exchanger 64 (in a normal operational mode being a heat absorption heat exchanger (e.g., evaporator)). The evaporator 64 includes an inlet 66 and an outlet 68 along the secondary loop 62. An expansion device 70 is positioned in a line 72 which extends between the separator liquid outlet 52 and the evaporator inlet 66. An ejector secondary inlet line 74 extends from the evaporator outlet 68 to the ejector secondary inlet 42.
In the normal mode of operation, gaseous refrigerant is drawn by the compressor 22 through the suction line 56 and inlet 24 and compressed and discharged from the discharge port 26 into the discharge line 28. In the heat rejection heat exchanger, the refrigerant loses/rejects heat to a heat transfer fluid (e.g., fan-forced air or water or other fluid). Cooled refrigerant exits the heat rejection heat exchanger via the outlet 34 and enters the ejector primary inlet 40 via the line 36.
The exemplary prior art ejector 38 (generically shown in FIG. 2) is formed as the combination of a motive (primary) nozzle 100 nested within an outer member 102. The primary inlet 40 is the inlet to the motive nozzle 100. The outlet 44 is the outlet of the outer member 102. The primary refrigerant flow 103 enters the inlet 40 and then passes into a convergent section 104 of the motive nozzle 100. It then passes through a throat section 106 and an expansion (divergent) section 108 through an outlet (exit) 110 of the motive nozzle 100. The motive nozzle 100 accelerates the flow 103 and decreases the pressure of the flow. The secondary inlet 42 forms an inlet of the outer member 102. The pressure reduction caused to the primary flow by the motive nozzle helps draw the secondary flow 112 into the outer member. The outer member includes a mixer having a convergent section 114 and an elongate throat or mixing section 116. The outer member also has a divergent section or diffuser 118 downstream of the elongate throat or mixing section 116. The motive nozzle outlet 110 is positioned within the convergent section 114. As the flow 103 exits the outlet 110, it begins to mix with the flow 112 with further mixing occurring through the mixing section 116 which provides a mixing zone. Thus, respective primary and secondary flowpaths extend from the primary inlet and secondary inlet to the outlet, merging at the exit. In operation, the primary flow 103 may typically be supercritical upon entering the ejector and subcritical upon exiting the motive nozzle. The secondary flow 112 is gaseous (or a mixture of gas with a smaller amount of liquid) upon entering the secondary inlet port 42. The resulting combined flow 120 is a liquid/vapor mixture and decelerates and recovers pressure in the diffuser 118 while remaining a mixture. Upon entering the separator, the flow 120 is separated back into the flows 103 and 112. The flow 103 passes as a gas through the compressor suction line as discussed above. The flow 112 passes as a liquid to the expansion valve 70. The flow 112 may be expanded by the valve 70 (e.g., to a low quality (two-phase with small amount of vapor)) and passed to the evaporator 64. Within the evaporator 64, the refrigerant absorbs heat from a heat transfer fluid (e.g., from a fan-forced air flow or water or other liquid) and is discharged from the outlet 68 to the line 74 as the aforementioned gas.
Use of an ejector serves to recover pressure/work. Work recovered from the expansion process is used to compress the gaseous refrigerant prior to entering the compressor. Accordingly, the pressure ratio of the compressor (and thus the power consumption) may be reduced for a given desired evaporator pressure. The quality of refrigerant entering the evaporator may also be reduced. Thus, the refrigeration effect per unit mass flow may be increased (relative to the non-ejector system). The distribution of fluid entering the evaporator is improved (thereby improving evaporator performance). Because the evaporator does not directly feed the compressor, the evaporator is not required to produce superheated refrigerant outflow. The use of an ejector cycle may thus allow reduction or elimination of the superheated zone of the evaporator. This may allow the evaporator to operate in a two-phase state which provides a higher heat transfer performance (e.g., facilitating reduction in the evaporator size for a given capability).
FIG. 2 shows controllability provided by a needle valve 130, according to the prior art, having a needle 132 and an actuator 134. The actuator 134 shifts a tip portion 136 of the needle into and out of the throat section 106 of the motive nozzle 100 to modulate flow through the motive nozzle and, in turn, the ejector overall. Exemplary actuators 134 are electric (e.g., solenoid or the like). The actuator 134 may be coupled to and controlled by a controller 140 which may receive user inputs from an input device 142 (e.g., switches, keyboard, or the like) and sensors (not shown). The controller 140 may be coupled to the actuator and other controllable system components (e.g., valves, the compressor motor, and the like) via control lines 144 (e.g., hardwired or wireless communication paths). The controller may include one or more: processors; memory (e.g., for storing program information for execution by the processor to perform the operational methods and for storing data used or generated by the program(s)); and hardware interface devices (e.g., ports) for interfacing with input/output devices and controllable system components.
The FIG. 1 configuration according to the prior art also shows bypass lines 80 and 82 for operating in a second mode wherein flow through the ejector is shut off. The bypass line 80 bypasses the ejector and allows refrigerant to pass from the heat rejection heat exchanger 30 to the separator without passing through the ejector. The bypass line 82 allows refrigerant to pass from the heat absorption heat exchanger 64 back to the compressor. Thus, the second mode represents a basic non-ejector vapor compression system. To enter the second mode, the system may include valves (e.g., on-off solenoid valves) 84, 86, 88, and 90. The valves 84 and 86 are respectively in the lines 80 and 82 and, in the first mode, are off/shut/closed. The valve 88 is in the line 36 downstream of the junction between the bypass line 80 and the ejector inlet so as to be able to close off ejector motive flow only. The valve 90 is in the line 72 downstream of where the bypass 82 intersects. The valves 88 and 90 are open in the first mode. The states of the valves are reversed between the first mode and the second mode.
In yet further variations, additional expansion devices and heat exchangers may be added to such prior art systems.
In one example, an economizer heat exchanger 94 has a first leg 96 along the line 72 upstream of the expansion device 70 and a second leg 98 along the line 56 from the vapor outlet 54 upstream of the junction with the bypass 82. An expansion device 92 may be upstream of the second leg. An expansion valve 99 is also shown downstream of the heat rejection heat exchanger. Valve 92 is used to provide further cooling (sub-cooling) effect to the primary flow in the line 72. Valve 70 is the primary expansion valve at the inlet to the heat absorption heat exchanger 66 to control the heat exchanger 66 superheat. Expansion valve 99 could be used to do partial expansion before the flow enters the ejector in one mode and acts as the primary expansion valve on the high side for the basic cycle mode. Valve 84, 88, 90 are on/off valves.
There have been a number of prior art proposals wherein the ejector needle has a fully closed/seated condition blocking flow through the motive nozzle. FIG. 3 shows one such example based upon the configuration of US7178360 . In this situation, the needle 132 has a main cylindrical portion 150 and a compound tip portion having a proximal portion 152 at relatively shallow angle and a distal portion 154 converging to the actual tip 156. The motive nozzle converging portion also has a compound angle with a relatively steep proximal portion 160 leading to a relatively shallow distal portion 162 which, in turn, leads to a divergent surface 170 along the divergent portion 108. The exemplary portions 152 and 162 may have similar angles so as to sealingly mate in the closed condition.
A first aspect of the invention provides a vapor compression system, as defined by appended independent claim 1, inter alia comprising: a compressor; a heat rejection heat exchanger coupled to the compressor to receive refrigerant compressed by the compressor; an ejector; ; a heat absorption heat exchanger; and a separator having: an inlet coupled to the outlet of the ejector to receive refrigerant from the ejector; a gas outlet; and a liquid outlet. The ejector comprises: a motive flow inlet; a secondary flow inlet; an ejector outlet; a motive flow nozzle having an outlet; a primary flowpath from the motive flow inlet through the motive flow nozzle to the ejector outlet; a secondary flowpath from the secondary flow inlet to the ejector outlet, merging with the primary flowpath at the motive nozzle outlet; a control needle shiftable along a range of motion between a first condition and a second condition and seated against the motive flow nozzle in the second condition. The needle comprises: a main shaft; a tip; a first portion converging toward the tip; and a shoulder portion between the first portion and the main shaft and seated against the motive flow nozzle in the second condition and converging toward the tip at a greater angle (θ₁; θ_1-2) than an angle (θ₂; θ_2-2) of the first portion.
The shoulder portion angle (θ₁) may be15° to 75°; and the first portion angle (θ₂) is 5° to 60°.
The shoulder portion angle (θ_1-2) may be 75° to 115°; and the first portion angle (θ_2-2) may be 5° to 60°.
The shoulder portion angle (θ₁) may be10° to 30° greater than the first portion angle (θ₂).
The shoulder portion angle (θ_1-2) may be 5° to 80° greater than the first portion angle (θ_2-2).
A throat of the motive nozzle may have clearance relative to the needle in the second condition.
The motive nozzle may be made of stainless steel; and the needle may be made of stainless steel.
The needle may comprise a transition section between the first portion and the second portion and being closer to cylindrical than the first portion and the second portion.
The motive nozzle may be a convergent-divergent nozzle.
The ejector may further comprise: a mixer comprising a convergent portion at least partially downstream of the motive nozzle; and a divergent diffuser portion downstream of the convergent portion.
A method for operating the system, as defined by appended independent claim 11, comprises either: compressing the refrigerant in the compressor; rejecting heat from the compressed refrigerant in the heat rejection heat exchanger; passing a flow of the refrigerant through the primary ejector inlet; and passing a secondary flow of the refrigerant through the secondary inlet to merge with the primary flow; or driving a motive flow along the primary flowpath; and shifting the needle to the second condition so as to stop the motive flow.
The details of one or more embodiments are set forth by way of example only in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. The invention is solely defined by the scope of appended independent claims.
FIG. 1 is a schematic view of a prior art ejector refrigeration system.
FIG. 2 is an axial sectional view of a prior art ejector.
FIG. 3 is an axial sectional view of an end of a prior art needle.
FIG. 4 is an axial sectional view of a needle.
FIG. 4A is an enlarged view of a tip region of the needle of FIG. 4.
FIG. 5 is an axial sectional view of an ejector including the needle of FIG. 4 in an open condition.
FIG. 5 A is an enlarged view of a motive nozzle region of the ejector of FIG. 5.
FIG. 6 is a view of the motive nozzle region in a closed condition.
FIG. 7 is an enlarged axial sectional view of a tip region of an alternate needle.
FIG. 8 is an enlarged axial sectional view of the needle of FIG. 7 in a closed condition in an ejector motive nozzle.
FIG. 9 is an enlarged axial sectional view of a tip region of yet another alternate needle.
Like reference numbers and designations in the various drawings indicate like elements.
FIG. 4 shows an a needle 200 extending from a proximal end 202 to a tip 204. Near the proximal end, the needle may have a mounting feature 206 (e.g., an external thread) for mounting to an actuator. The exemplary needle has a main section 210 along which the outer surface portion 212 is cylindrical (e.g., a circular cylinder of diameter D₁). At a downstream end of the section 210 there is a convergent shoulder portion 214 (FIG. 4A) along which the outer surface 216 converges toward the tip 204 at an angle θ₁ (a half angle of the cone being half of this). There is thus an annular transition 218 between the sections 210 and 214 and their associated surfaces 212 and 214. Similarly, at a downstream end of the section 214 is a section 220 along which the exterior surface portion 222 converges towards the tip at a shallower angle than the surface portion 216. FIG. 4A shows this angle as θ₂. Again, this leaves an annular junction 224 between the section 220 and section 214 and their associated surfaces 222 and 216.
FIG. 5A shows the needle in a relatively retracted condition/position. A yet further retracted condition may be possible. In the FIG. 5A condition, the tip 204 is approximately at the throat 240 of the motive nozzle 242. The exemplary throat is formed as a short cylindrical area between a convergent surface 244 upstream and a divergent surface 246 downstream. The exemplary divergent surface 246 extends at a shallow angle to the outlet 110. The exemplary convergent surface 244 is at a slightly greater angle (θ₃ of FIG. 6) chosen to mate with the surface 216 in a closed condition discussed below. The exemplary motive nozzle 242 is formed as an insert into a body assembly and carries a needle guide 250 (e.g., at a step or discontinuity in the surface 244).
FIG. 6 shows the needle further inserted into a closed condition wherein the needle tip 204 is concentrically within the divergent section of the nozzle formed by the surface 246. In this closed condition, the surface 216 abuts a terminal portion of the surface 244 to close/seal the motive nozzle. The outer diameter D₂ (FIG. 4A) at the downstream end of the surface 216 may be slightly smaller than the corresponding diameter of the nozzle at the throat 240 to allow clearance and avoid sticking. For example, the outer diameter D2 could be 1 to 5% smaller than the corresponding diameter of the throat so as to provide a clearance fit and yet avoid sticking of the needle into the throat upon actuation under pressurized conditions.
In use, the closing of the ejector may serve the role of the solenoid valve 88 of the FIG. 1 system, thereby allowing elimination of such valve.
Exemplary θ₁ is 40°, more broadly, 30° to 50° or 15° to 75°. Exemplary θ₂ is 24°, more broadly, 20° to 30° or 5° to 60°. An exemplary difference between θ₁ and θ₂ is at least 2°, more particularly at least 5°, more particularly, 10° to 30° or 10° to 20°. Exemplary θ₃ is the same as θ₁ (e.g., within 1° thereof). Relative to the FIG. 3 prior art, the change in taper may be relatively rearward on the top and allow a relatively low angle θ₂. It is better to have double taper at the back of the needle tip as it allows for better flow control by having a finer needle tip (smaller angle) used to control a typical 2-phase sonic flow conditions that could exist at the throat. Sharp angle changes (as shown by larger sealing angles) near the throat could lead to eddy formation near the throat that could lead to shocks in the divergent section of the motive nozzle leading to energy being lost in the form of heat.
FIG. 7 shows a needle 300 which may be otherwise similar to the needle 200 of FIG. 4. The main section surface is still shown as 212 and the tip is still shown as 204. The overall tip region may differ from that of the needle 200 in one or more of several aspects , as long as it still comprises all features of appended independent claim 1. A first exemplary aspect is the angle θ_1-2 of the surface 316 of a shoulder 314 relative to the angle θ₁ of the surface 216 of FIG. 4A. In this exemplary embodiment, angle θ_1-2 is larger than that illustrated for angle θ₁.
A second illustrated difference is the presence of a step discontinuity 315 (e.g., shallower than either adjacent section) between the surface 322 of the section 320 and the surface 316 when compared with the intersection of the surface 222 and the surface 216. The exemplary discontinuity in the form of a straight section 330 having a circular cylindrical outer surface 332 and respective junctions 334 and 336 with the surfaces 316 and 322. An exemplary length L_S of the surface 332 is at least 0.01 inches (0.25mm), more particularly, an exemplary 0.04 inches to 0.2 inches (1mm to 5mm) or 0.5mm to 10mm.
Exemplary values for θ_2-2 are similar to those given above for θ₂. An exemplary value for θ_1-2 is 90°, more broadly, 75° to 115° or 15° to 145° or 45° to 120°. An exemplary difference between θ_2-2 and θ_1-2 is at least 2°, more particularly at least 5°, or 40°-70°, more broadly, 5°-80°.
FIG. 7 shows the needle 300 in a seated/closed condition with at least a portion of the section 336 accommodated in the throat of the nozzle. FIG. 8 shows that there may be angular mismatch between the angle θ_1-2 and the corresponding angle θ_3-2 of the convergent portion of the motive nozzle. The exemplary θ_3-2 is similar to exemplary θ₃. This mismatch helps with a better (tighter) sealing of the flow.
In yet alternative embodiments, θ₂ or θ_2-2 may go to an exemplary 180° with the associated surface portions being radial. The angels may even go beyond radial. In alternative implementations with such a radial surface or of the shallower surfaces, one or both exemplary surfaces may be formed by separate members carried by the needle or by a main portion of the motive nozzle. FIG. 9 shows a needle 400 which may be otherwise similar to the needle 300 of FIG. 7. Along the straight section 330, the needle carries a ring 420. The exemplary ring 420 is nested up against the junction 334 with the surface 316. The outer diameter (OD) of the ring 420 is less than the main section diameter D₁. A downstream surface 422 of the ring 420 forms a sealing surface for engaging to seal against a fixed surface in the closed condition. An exemplary fixed surface is an upstream-facing surface 432 of a ring 430 inserted within the throat of the nozzle main body to, in turn, form a functional throat of the combination of the main body and ring. Thus, the exemplary surfaces 422 and 432 are essentially radial. Such a radial surface may be easier to machine. It may also be easier to machine by placing it on separate members (the rings). Also the use of separate members allows for selection of ring materials to provide desired sealing properties while not changing material properties of remainders of the needle and the nozzle body.
Exemplary ejector materials and manufacture techniques may be those conventionally known in the art (e.g., casting and/or machining from various metals and alloys, typically stainless steels). Use may similarly mirror use in the art with, in particular, use including actuating the ejector to fully close off flow therethrough in the absence of a separate valve.
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 scope of the invention as defined by the claims. For example, details of the particular refrigeration system in which the ejector is to be used may influence details of any particular implementation. Accordingly, other embodiments, than the ones described above, are also within the scope of the following claims.

Claims

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;

an ejector comprising;
a motive flow inlet (40),

a secondary flow inlet (42),

an ejector outlet (44),

a motive flow nozzle (242) having an outlet (110),

a primary flowpath from the motive flow inlet (40) through the motive flow nozzle (242) to the ejector outlet (44),

a secondary flowpath from the secondary flow inlet (42) to the ejector outlet (44), merging with the primary flowpath at the motive nozzle outlet (110),

a control needle (200; 300; 400) shiftable along a range of motion between a first condition and a second condition and seated against the motive flow nozzle (242) in the second condition,

wherein the needle comprises:
a main shaft (210),

a tip (204),

a first portion (220; 320) converging toward the tip, and

a shoulder portion (214; 314; 422) between the first portion and the main shaft and seated against the motive flow nozzle in the second condition and converging toward the tip at a greater angle (θ_l; θ 1-2 ) than an angle (θ 2 ; θ 2-2 ) of the first portion;

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).
The vapor compression system of claim 1 wherein:
the shoulder portion angle (θ_l) is 15° to 75°; and

the first portion angle (θ 2 ) is 5° to 60°.
The vapor compression system of claim 1 wherein:
the shoulder portion angle (θ 1-2 ) is 75° to 115°; and

the first portion angle (θ 2-2 ) is 5° to 60°.
The vapor compression system of claim 1 wherein:
the shoulder portion angle (θ_l) is 10° to 30° greater than the first portion angle (θ 2 ).
The vapor compression system of claim 1 wherein:
the shoulder portion angle (θ 1-2 ) is 5° to 80° greater than the first portion angle (θ 2-2 ).
The vapor compression system of claim 1 wherein:
a throat of the motive flow nozzle has clearance relative to the needle in the second condition.
The vapor compression system of claim 1 wherein:
the motive flow nozzle is made of stainless steel; and

the needle is made of stainless steel.
The vapor compression system of claim 1 wherein:
the needle comprises a transition section (330) between the first portion and the second portion and being closer to cylindrical than the first portion and the second portion.
The vapor compression system of claim 1 wherein:
the motive flow nozzle is a convergent-divergent nozzle.
The vapor compression system of claim 1 further comprising:
a mixer comprising a convergent portion at least partially downstream of the motive nozzle; and

a divergent diffuser portion downstream of the convergent portion.
A method for operating the vapor compression system of any preceding claim, the method comprising either:
compressing the refrigerant in the compressor;

rejecting heat from the compressed refrigerant in the heat rejection heat exchanger;

passing a flow of the refrigerant through the primary ejector inlet; and

passing a secondary flow of the refrigerant through the secondary inlet to merge with the primary flow; or

driving a motive flow along the primary flowpath; and

shifting the needle to the second condition so as to stop the motive flow.