A high-efficiency heat exchange system and method for a natural working medium falling film evaporator based on a high-pressure ejector cycle

Abstract

This invention discloses a high-efficiency heat exchange system and method for a falling film evaporator based on a high-pressure ejector cycle, belonging to the field of refrigeration and air conditioning technology. It includes a falling film evaporator, a gas-liquid ejector, a liquid level sensor, and a control unit. The falling film evaporator internally features a two-stage gas-liquid separator and a liquid reservoir. The former separates the gas-liquid mixture of refrigerant flowing in through the second inlet, resulting in a liquid film forming on the heat exchange tubes. The gas-liquid ejector uses compressor exhaust or economizer flash gas as power to draw liquid from the liquid reservoir, forming a circulating liquid flow. The control unit adjusts the ejector gas volume based on the liquid level signal to maintain the circulation ratio of each zone within a predetermined range. The operation method includes ejector cycle liquid replenishment, two-stage gas-liquid separation, zoned differentiated spraying, and dynamic closed-loop regulation steps. This invention effectively suppresses liquid carryover during suction through two-stage gas-liquid separation, achieving safe operation.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration and air conditioning technology, and relates to a high-efficiency heat exchange system and method for a natural working fluid falling film evaporator based on a high-pressure ejector cycle. Background Technology

[0002] With increasingly stringent environmental regulations, hydrofluorocarbon (HFC) refrigerants are being phased out due to their high global warming potential (GWP). Natural refrigerants such as ammonia (R717), carbon dioxide (R744), propane (R290), and propylene (R1270) have become the core alternatives to HFCs in the refrigeration industry due to their zero ODP (ozone depletion potential) and low GWP.

[0003] However, the aforementioned natural working fluids have strict material compatibility limitations: ammonia is highly corrosive to copper and copper alloys; carbon dioxide operates at a transcritical cycle pressure as high as 100 barG; and hydrocarbon working fluids such as propane and propylene are flammable and must meet explosion-proof design requirements. These limitations prevent the use of high-efficiency copper heat exchange tubes with excellent heat exchange performance in natural working fluid falling film evaporators, limiting them to carbon steel, stainless steel, or titanium heat exchange tubes.

[0004] The heat transfer coefficient of the aforementioned non-copper heat exchange tubes is only 1 / 3 to 1 / 5 that of high-efficiency copper tubes. To meet the same cooling capacity requirements, the heat exchange area needs to be increased by 3 to 5 times. Traditional falling film evaporators, based on the design premise of fewer tubes and high heat transfer characteristics of copper tubes, cause the sprayed refrigerant liquid to completely evaporate and dry out when it flows down to 1 / 3 to 1 / 2 of the tube height on the outer surface of the heat exchange tubes. This leaves a large number of lower heat exchange tubes in a dry-burning state, resulting in a significant decrease in heat transfer efficiency. This is the core industry pain point faced by the engineering application of natural working fluid falling film evaporators.

[0005] 1. Refrigerant pump circulation scheme The liquid accumulated at the bottom of the evaporator is pumped back to the distributor via a shielded pump, forming a forced circulation. This solution is the mainstream production solution in the industry. Inherent defects: 1) The power consumption of the circulating pump accounts for 2% to 5% of the total energy consumption of the unit, which offsets the energy-saving benefits of the natural working fluid itself; 2) The natural working fluid has a low evaporation temperature (ammonia can reach below -30℃). When the liquid subcooling before the pump is insufficient, cavitation is likely to occur. Weld slag, oxide scale and other particles in the system can easily damage the pump body. 3) Pumps are rotating machinery, and their failure rate is high and maintenance costs are high under low temperature conditions; 4) To ensure the pump's net positive suction head, the evaporator installation height needs to be significantly increased, resulting in a non-compact equipment size. The matching filters, control valves, and other components further increase the equipment cost, making it less economically competitive.

[0006] 2. Conventional ejector scheme High-pressure gas is used to pump out accumulated liquid, replacing the circulating pump. However, existing ejectors are designed for single-phase fluids and use a single-nozzle structure.

[0007] Inherent defects: 1) The static pressure boosting capability of the ejector is limited, making it unsuitable for low-temperature conditions of large-scale falling film evaporators with evaporation temperatures below -20℃ (corresponding to an evaporation pressure of approximately 0.9 barG) and diameters greater than 1m, severely limiting its application scenarios; 2) Incomplete gas-liquid separation leads to gas entering the spray zone, causing liquid film turbulence and rupture, uneven spraying, deterioration of heat exchange efficiency, and is prone to causing liquid carryover in the falling film evaporator and liquid slugging damage to the compressor. 3) The single-nozzle structure has low ejection efficiency and high gas consumption (accounting for 15% to 20% of the exhaust volume), resulting in limited improvement in system energy efficiency; 4) In the frigid winters of northern regions, the extremely low ambient temperature leads to a significant drop in condensation temperature, resulting in a substantial reduction in the pressure difference between the compressor discharge pressure and the evaporator side pressure. The static pressure boosting capacity of conventional ejectors cannot meet the needs of circulating liquid replenishment.

[0008] The refrigerant pump circulation solution (the mainstream mass production solution in the industry) and the conventional single-phase ejector solution have the following inherent drawbacks: 1. The pump circulation scheme has inherent defects of rotating machinery: cavitation of the canned pump under low temperature conditions, damage to the pump body by dirty particles in the system, the need to increase the installation height of the falling film evaporator to ensure net positive suction head, the equipment size is not compact, and the supporting cost is high; 2. Conventional ejectors are single-nozzle, single-phase structures with limited static pressure boosting capabilities. They are not suitable for low-temperature conditions in large-scale falling film evaporators with evaporation temperatures below -20℃ (corresponding to an evaporation pressure of approximately 0.9 barG) and diameters greater than 1m, severely limiting their application scenarios. 3. Existing ejector schemes do not achieve complete gas-liquid separation. Gas entering the spray zone causes liquid film turbulence and rupture, resulting in uneven spraying and risks of liquid carryover during intake and liquid slugging in the compressor. 4. The lack of zoned differentiated spray design results in insufficient liquid film coverage after the non-copper tube heat exchange area is increased by 3 to 5 times, and the dry burning of the lower tube bundle leads to a significant decrease in heat exchange efficiency.

[0009] Technicians attempted to improve the ejector structure by increasing the number of nozzles, adding simple baffles for gas-liquid separation, or implementing simple stratified spraying. However, none of these solutions addressed the system-wide technical challenges of "efficient ejector liquid enhancement, thorough gas-liquid separation, precise zoned spraying, and real-time closed-loop control." The multi-nozzle ejector solution lacked a secondary gas-liquid separation stage, allowing gas to directly enter the falling film evaporator and cause turbulent film formation. The simple stratified spraying solution failed to determine differentiated circulation rates based on the heat exchange characteristics of non-copper tubes. Furthermore, none of these solutions formed a complete closed-loop control strategy. None of them could simultaneously achieve the four objectives of "full-length liquid film coverage, reliable pump-free operation, high energy efficiency and low loss, and significantly reduced liquid carryover risk."

[0010] In summary, existing technologies cannot comprehensively address the core challenges faced by natural fluid non-copper tube falling film evaporators, such as insufficient liquid film coverage, inherent defects in pump circulation, limited application scenarios for ejectors, and incomplete gas-liquid separation. These issues severely restrict the engineering application of natural fluid falling film evaporators. Summary of the Invention

[0011] To address the inherent defects of rotating machinery in traditional pump circulation schemes (cavitation, malfunctions, increased height), overcome the application bottlenecks of low ejection efficiency and insufficient static pressure enhancement capacity of conventional single-nozzle ejectors, and simultaneously solve the problems of liquid carryover and turbulent falling film caused by incomplete gas-liquid separation in existing schemes, as well as the industry problem of insufficient liquid film coverage after increasing the heat exchange area of ​​non-copper tubes, the technical solution adopted in this invention is as follows: a high-efficiency heat exchange system for a natural working fluid falling film evaporator based on high-pressure ejector circulation, comprising a falling film evaporator, multiple gas-liquid ejectors, a liquid level sensor, and a control unit; The falling film evaporator includes: The first tube bundle region is located in the upper part of the falling film evaporator shell; The second tube bundle region is located below the first tube bundle region; The first inlet is used to introduce the refrigerant into the second tube bundle region, and the refrigerant in the second tube bundle region then flows into the first tube bundle region. The first outlet is used for the outflow of refrigerant within the first tube bundle region; The second inlet is located at the bottom of the falling film evaporator for the inflow of gas-liquid mixed refrigerant; The two-stage gas-liquid separator is used to separate the liquid and gas of the gas-liquid mixed refrigerant flowing in from the second inlet. The separated liquid flows from top to bottom and forms a liquid film on the heat exchange tubes in the first tube bundle region and the second tube bundle region. A liquid reservoir is used to store the refrigerant liquid flowing down from the falling film evaporator; The plurality of gas-liquid ejectors are located below the falling film evaporator and are used to draw refrigerant liquid from the liquid tank to form a circulating liquid flow, using refrigerant gas from compressor exhaust or economizer flash as power. The liquid level sensor is used to collect the liquid level of the refrigerant in the liquid tank; The control unit is used to control the gas flow rate ejected by the plurality of gas-liquid ejectors based on the liquid level height signal transmitted by the liquid level sensor, so as to keep the circulation ratio of the first tube bundle region and the second tube bundle region within a predetermined range.

[0012] Furthermore, the heat exchange tubes in the first tube bundle region and the second tube bundle region are made of carbon steel, stainless steel or titanium.

[0013] Furthermore, the gas-liquid ejector includes: ejector body; A liquid inlet pipe is located on the side of the middle part of the ejector body and is used to connect the refrigerant liquid conveyed by the liquid package. The high-pressure inlet pipe is used to introduce refrigerant gas from the compressor exhaust or the economizer flash, and is located at one end of the ejector body. The nozzle array comprises N nozzles, which are evenly arranged circumferentially at the outlet end of the high-pressure intake pipe; N ranges from 2 to 6. A mixing chamber, located above the nozzle array, is used to mix the refrigerant liquid delivered by the inlet pipe and the refrigerant gas delivered by the nozzle array. The cross-sectional diameter of the mixing chamber is 3 to 5 times the cross-sectional diameter of the nozzle array; The angle between the axis of the nozzle outlet and the axis of the mixing chamber is 15° to 30°. The diffusion chamber, located on the outlet side of the mixing chamber, is used to reduce the flow velocity of the gas-liquid two-phase mixed fluid as it flows through, thereby converting kinetic energy into static pressure energy and completing fluid diffusion.

[0014] Furthermore, the outer surface of the heat exchange tube is provided with a micron-level rough structure, which is used to ensure that the contact angle of the refrigerant liquid on the outer surface of the heat exchange tube is ≤30°; the roughness Ra of the outer surface of the heat exchange tube is 3.2~6.3μm.

[0015] Furthermore, the secondary gas-liquid separator includes: The first gas-liquid separator is located above the first tube bundle region; The second gas-liquid separator is located between the first tube bundle region and the second tube bundle region.

[0016] Furthermore, the circulation rate of the first tube bundle region is controlled between 3.0 and 5.0, and the circulation rate of the second tube bundle region is controlled between 2.0 and 2.5.

[0017] Furthermore, the first gas-liquid separator includes: The cyclone pre-separation chamber is located above the first tube bundle region and is used to perform primary gas-liquid separation on the confluence of the circulating liquid flow output from the gas-liquid ejector and the refrigerant gas-liquid mixture after throttling in the condenser. The wire mesh fine separation component achieves secondary gas-liquid separation based on the refrigerant gas containing droplets separated by the cyclone pre-separation chamber, through the interception and coalescence of multiple layers of stainless steel wire mesh. A high-pressure liquid supply and distribution branch pipe is installed in the lower layer of the wire mesh fine separation component, and multiple distribution holes are evenly arranged on the high-pressure liquid supply and distribution branch pipe; A secondary liquid separator is located below the high-pressure liquid supply and liquid separator branch pipe, and is used to guide and uniformly distribute the liquid flowing down from the high-pressure liquid supply and liquid separator branch pipe and the gas-liquid ejector; the secondary liquid separator is provided with a liquid outflow hole. A primary liquid distributor plate is located below the secondary liquid distributor plate and is used to further subdivide and homogenize the liquid after it has been guided by the secondary liquid distributor plate; a liquid outflow hole is provided in the primary liquid distributor plate. A primary liquid distribution plate partition is vertically installed inside the primary liquid distributor's liquid distribution plate to independently divide the plate surface of the primary liquid distributor's liquid distribution plate into partitions, so that each partition independently supplies liquid to the first tube bundle area and the second tube bundle area. Edge wire mesh is set in the vertical channel between the outer edge of the first gas-liquid separator and the inner wall of the falling film evaporator on both sides above the first tube bundle area. Curtain baffles are provided on both sides of the first tube bundle region and the second tube bundle region; The second gas-liquid separator includes: A secondary liquid distributor branch pipe is located below the first gas-liquid separator, and multiple liquid distribution holes are evenly arranged on the secondary liquid distributor branch pipe. The secondary liquid distributor distribution plate is located below the secondary liquid distributor distribution branch pipe and is used to guide and even out the liquid flowing down from the secondary liquid distributor distribution branch pipe. The secondary liquid distributor has a liquid distribution baffle that is vertically installed inside the secondary liquid distributor's liquid distribution plate to divide the plate surface into independent zones.

[0018] Furthermore, the height-to-diameter ratio of the cyclone pre-separation chamber is 1.5 to 2.5, and the wire mesh fine separation component includes M layers of wire mesh. The wire mesh is made of 80 to 120 mesh stainless steel wire mesh, and a wire mesh baffle is provided below each layer of wire mesh. The opening positions of adjacent wire mesh baffles are staggered, with 3 ≤ M ≤ 5.

[0019] Furthermore, it also includes a secondary ejector assembly, which, after being throttled by high-pressure refrigerant liquid, serves as a high-pressure power source to eject the fluid from the gas-liquid ejector mixing outlet.

[0020] A method for a high-efficiency heat exchange system of a natural working fluid falling film evaporator based on a high-pressure ejector cycle includes the following steps: The S1 ejector circulation replenishment step uses the refrigerant gas from the compressor exhaust or the economizer flash as power to draw the liquid accumulated at the bottom of the falling film evaporator through the gas-liquid ejector to form a circulating liquid flow. In the S2 secondary gas-liquid separation step, the circulating liquid flow and the refrigerant gas-liquid mixture after throttling in the condenser are converged into the secondary gas-liquid separator liquid distributor. The secondary gas-liquid separation is completed through the cyclone pre-separation chamber and the wire mesh fine separation component. The separated gas is sent to the compressor suction port through the independent channel at the top of the falling film evaporator. In the S3 zoned differentiated spraying step, the liquid separated by the secondary gas-liquid separator is sprayed in a zoned differentiated manner along the height of the heat exchange tubes in the first tube bundle region and the second tube bundle region. The circulation ratio of the first tube bundle region is maintained at 3.0 to 5.0, and the circulation ratio of the second tube bundle region is maintained at 2.0 to 2.5, so as to ensure the minimum wetting flow rate of the second tube bundle region by the circulation ratio of the first tube bundle region. The S4 dynamic closed-loop control step dynamically adjusts the flow rate of high-pressure ejector gas ejected by the gas-liquid ejector based on the liquid level signal transmitted by the liquid level sensor, maintaining the circulation ratio of each zone within the set range.

[0021] The high-efficiency heat exchange system and method for a natural working fluid falling film evaporator based on a high-pressure ejector cycle provided by the present invention have the following technical advantages: 1. Overcome the inherent defects of rotating machinery in traditional pump circulation schemes (cavitation, failure, increased height), and replace pumping circulation with gas-liquid two-phase ejector circulation to achieve reliable operation without pumps; 2. Overcoming the application bottlenecks of low ejection efficiency and insufficient static pressure enhancement capacity of conventional single-nozzle ejectors, a gas-liquid two-phase ejection with a multi-nozzle array structure is used to achieve high-efficiency ejection and liquid enhancement in large-diameter falling film evaporators under low evaporation pressure conditions. 3. To address the issues of liquid carryover and turbulent falling film formation caused by incomplete gas-liquid separation in existing solutions, a two-stage gas-liquid separation system and an independent gas return channel are implemented to achieve safe operation with low liquid carryover risk. 4. Solve the industry problem of insufficient liquid film coverage after increasing the heat exchange area of ​​non-copper tubes. Based on closed-loop control of liquid level signal, supplemented by protective adjustment of heat exchange status detection signal, achieve full-length liquid film coverage and optimal energy efficiency.

[0022] Compared with the closest existing technology, the present invention has the following outstanding substantive features and significant technical advancements: 1. Full-length liquid film coverage: Through the synergistic effect of zoned differentiated spraying and jet liquid enhancement, the high circulation ratio of 3.0 to 5.0 in the upper part ensures a minimum wetting flow rate of 2.0 to 2.5 in the lower tube bundle, achieving a liquid film coverage rate of over 96%, which is 9% higher than the traditional pump circulation scheme (coverage rate of 88%), effectively solving the industry problem of premature evaporation of liquid film in non-copper tube heat exchange tubes.

[0023] 2. Reliable operation without pumps: The gas-liquid ejector replaces the circulating pump, eliminating rotating parts and the risk of cavitation. It is unaffected by system contaminants and particles, reducing the failure rate by more than 90% under low-temperature conditions. It eliminates the need to increase the installation height of the falling film evaporator, resulting in a more compact equipment size and significantly reduced maintenance costs and related investments.

[0024] 3. High energy efficiency and low loss: Under rated operating conditions, the ejector coefficient of the multi-nozzle array structure can reach over 300, and the high-pressure gas consumption for ejection accounts for less than 1% of the compressor's exhaust volume, which is more than 90% lower than the gas consumption of conventional single-nozzle ejectors; the heat exchange deterioration caused by gas turbulence and film falling is avoided through two-stage gas-liquid separation, and the waste heat recovery of flash gas in the economizer further reduces the compressor's power consumption. The overall energy efficiency of the system is 8% to 12% higher than that of traditional solutions.

[0025] 4. Low risk of liquid carryover: The secondary gas-liquid separation efficiency reaches over 99%, and there are no liquid carryover events during 100 hours of continuous operation, effectively eliminating the risk of liquid slugging in the compressor.

[0026] 5. Full-Scenario Adaptability: The single-stage ejector solution is suitable for small and medium-sized refrigeration units. The two-stage ejector assembly relay solution uses the high-pressure refrigerant liquid from the condenser, after throttling, as the secondary ejector medium to eject the low-pressure liquid delivered by the first-stage gas-liquid ejector. This solves the problem of insufficient static pressure increase in single-stage ejection and is suitable for low-temperature conditions of large industrial falling film evaporators with evaporation temperatures below -20℃, corresponding to evaporation pressures of approximately 0.9 barG and diameters >1m. The pumping auxiliary unit serves as a backup for low-temperature condensation in winter and other conditions with insufficient pressure difference, and is compatible with ultra-large (diameter >1m) applications, ensuring compatibility with all operating conditions. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a front view of the falling film evaporator structure; Figure 2 This is a side view of the structure of a falling film evaporator; Figure 3 This is a cross-sectional view of a gas-liquid ejector; Figure 4 It is a nozzle array; Figure 5 This is a front view of the structure of the secondary separation liquid distributor; Figure 6 This is a side view of the structure of the secondary separation liquid distributor; Reference numerals: 1. Falling film evaporator; 2. First tube bundle region; 3. Second tube bundle region; 5. First gas-liquid separator distributor; 6. Second gas-liquid separator distributor; 7. Gas-liquid ejector; 8. Liquid tank; 17. Liquid level sensor; 18. Second outlet; 19. Second inlet; 26. First outlet; 27. First inlet; 30. First layer of wire mesh; 31. Second layer of wire mesh; 32. Third layer of wire mesh; 34. High-pressure liquid supply and distribution main pipe; 35. High-pressure liquid supply and distribution branch pipe; 36. First-stage distributor distribution plate; 37. Secondary distribution plate; 38. First-stage distribution plate partition; 39. Edge wire mesh; 40. Curtain baffle; 42. First layer wire mesh baffle plate; 43. Second layer wire mesh baffle plate; 44. Third layer... 49. Wire mesh baffle plate, 50. Secondary liquid distributor branch pipe, 51. Secondary liquid distributor partition plate, 52. Ejector body, 53. Inlet pipe, 54. Nozzle array, 57. High-pressure air inlet pipe, 59. Mixing chamber, 61. Diffusion chamber, 62. Secondary liquid distributor distribution plate, 65. Swirl pre-separation chamber, 66. Wire mesh fine separation assembly, 67. Pumping auxiliary unit, 68. Secondary ejector assembly, 69. Secondary gas-liquid separator. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] A high-efficiency heat exchange system based on a high-pressure ejector cycle and a natural working fluid falling film evaporator includes a falling film evaporator 1, multiple gas-liquid ejectors 7, a liquid level sensor 17, and a control unit.

[0032] Figure 1This is a front view of the falling film evaporator structure; Figure 2 This is a side view of the structure of a falling film evaporator; The falling film evaporator 1 includes: The first tube bundle region 2 is located in the upper part of the shell of the falling film evaporator 1; The second tube bundle region 3 is located below the first tube bundle region 2; The first inlet 27 is used to introduce the refrigerant into the second tube bundle region 3, and the refrigerant in the second tube bundle region 3 flows back into the first tube bundle region 2. The first outlet 26 is used for the outflow of refrigerant within the first tube bundle region 2; The second inlet 19 is located at the lower part of the falling film evaporator 1. After the gas-liquid mixed refrigerant enters from the lower part, it is first guided to the top liquid distribution area by the guide structure in the evaporator, and then flows down the film from the top. A control valve is installed on the liquid supply pipeline at the second inlet 19 to control the on / off of high-pressure liquid supply according to working conditions. The second outlet 18 is used for the outflow of the separated gas; The secondary gas-liquid separator 69 is used to separate the liquid and gas of the gas-liquid mixed refrigerant flowing in from the second inlet 19. The separated liquid flowing from top to bottom forms a liquid film on the heat exchange tubes of the first tube bundle region 2 and the second tube bundle region 3. Liquid reservoir 8 is used to store the refrigerant liquid flowing down from the bottom of the heat exchange tubes in the second tube bundle region 3; The plurality of gas-liquid ejectors 7 are located below the falling film evaporator 1 and are used to draw refrigerant liquid from the liquid package 8 to form a circulating liquid flow, which is then transported to the secondary gas-liquid separator distributor 69 via the circulating liquid supply pipe. The liquid level sensor 17 is used to collect the refrigerant liquid level in the liquid tank 8; The control unit is used to control the gas flow rate of the plurality of gas-liquid ejectors 7 through a proportional regulating valve assembly based on the liquid level height signal transmitted by the liquid level sensor 17, so as to keep the circulation ratio of the first tube bundle region 2 and the second tube bundle region 3 within a predetermined range.

[0033] Furthermore, the heat exchange tubes in the first tube bundle region 2 and the second tube bundle region 3 are made of carbon steel, stainless steel or titanium.

[0034] When the number of tube bundle region partitions is ≥3, the circulation ratio decreases sequentially from top to bottom along the height direction; Figure 3 This is a cross-sectional view of a gas-liquid ejector; Figure 4 It is a nozzle array; Furthermore, the gas-liquid ejector 7 includes: The ejector body 52 is the core base component that carries the various functional components of the ejector and constitutes the main frame of the ejector. The liquid inlet pipe 53 is located on the side of the middle part of the ejector body 52 and is used to connect the refrigerant liquid conveyed by the liquid package 8. High-pressure inlet pipe 57, used to introduce refrigerant gas from compressor exhaust or economizer flash, is located at one end of ejector body 52; The nozzle array 54 includes N nozzles, which are evenly arranged circumferentially at the outlet end of the high-pressure inlet pipe 57. The axis of the nozzle outlet forms an angle of 15° to 30° with the axis of the side of the middle part of the mixing chamber 59. The refrigerant working fluid matching parameters are: ammonia 2-4mm / 15°-20°, CO2 1.0-2.5mm / 25°-30° (double nozzles facing each other at 180° can be used), propane / propylene 2.5-5mm / 20°-25°, and N is a positive integer, with a value range of 2-6. The mixing chamber 59, located at the outlet of the nozzle array 54, is used to mix the refrigerant liquid delivered by the inlet pipe 53 and the refrigerant gas delivered by the nozzle array 54. Multiple airflows converge at the center of the mixing chamber to form a stable negative pressure core area. The classical ejector coefficient ≥300 is achieved by utilizing the 200-600 times liquid-gas density difference of the natural working fluid. The cross-sectional diameter of the mixing chamber 59 is 3 to 5 times the cross-sectional diameter of the nozzle array 54; The angle between the axis of the nozzle outlet and the axis of the mixing chamber 59 is 15° to 30°. A diffusion chamber 61 is disposed at the outlet of the mixing chamber 59 for the diffusion of the mixed liquid and gas. The diffusion chamber 61 is conical, and the cone angle of the diffusion chamber 61 is 8° to 12°.

[0035] A gas-liquid ejector 7 employs a multi-nozzle array 54 structure with uniform circumferential arrangement, ensuring that high-pressure gas is evenly distributed around the mixing chamber 59. Multiple gas streams converge at the center of the mixing chamber to form a stable negative pressure core region, achieving efficient ejection through a gas-liquid two-phase momentum exchange mechanism. Under refrigeration conditions, the density difference between saturated liquid and saturated vapor in the natural working fluid can reach 200 to 600 times. A small mass of high-speed gas can drag a huge mass of liquid. With the coordinated optimization of the number of nozzles, the axial angle, and the flow field, the theoretical ejection coefficient can exceed 300.

[0036] Under rated operating conditions of -30℃ / 35℃ using ammonia as the working fluid, the classic ejector coefficient can reach over 300, and the ejector gas consumption accounts for ≤1% of the exhaust volume, which is more than 90% lower than that of conventional single-nozzle ejectors (ejector coefficients are generally 80-150). When the compressor exhaust is used as the power source, the ejector gas consumption is ≤1%, and when the economizer flash gas is used as the power source, the ejector gas consumption accounts for 2-3% of the exhaust volume and does not occupy the effective exhaust volume of the main cycle.

[0037] Multi-nozzle gas-liquid two-phase ejector replaces pump circulation: no rotating parts, no cavitation risk, unaffected by contamination, failure rate reduced by over 90%, more compact equipment size, and reliable pump-free operation. This flow field organization—multiple high-pressure airflows converging at the center of the mixing chamber to form a stable negative pressure core region—is impossible to achieve with existing single-nozzle structures and conventional multi-nozzle designs, representing the core advantage of this invention's order-of-magnitude breakthrough in ejection efficiency.

[0038] To address the differences in the physical properties of various working fluids, optimal entrainment efficiency is achieved under different operating conditions by adjusting nozzle parameters: ammonia working fluid is suited to nozzle diameters of 2–4 mm and axial angles of 15°–20°; carbon dioxide working fluid is suited to nozzle diameters of 1.0–2.5 mm and axial angles of 25°–30°; propane / propylene working fluid is suited to nozzle diameters of 2.5–5 mm and axial angles of 20°–25°. The greater the density difference between the liquid and gas, the smaller the axial angle of the nozzle outlet. For scenarios requiring compact design, such as CO2, a dual-nozzle 180° opposing arrangement can be used. The two high-speed airflows form a stable opposing negative pressure core region at the center of the mixing chamber, complementing the circumferential converging flow field of three or more nozzles, thus achieving a classic entrainment coefficient of over 300.

[0039] To address the limitations of single-stage ejector in static pressure enhancement under extreme conditions of large evaporators and low evaporation pressures, this invention further provides a two-stage ejector relay solution: Secondary ejector assembly 68: After being throttled by high-pressure refrigerant liquid, it serves as the high-pressure power source for the gas-liquid ejector, ejecting the fluid from the gas-liquid ejector mixing outlet. The secondary ejector assembly 68 is activated under low-temperature conditions where the evaporator diameter is >1m or the pressure difference between the condensing and evaporating pressures is less than 2 bar. The ejector medium inlet of the secondary ejector assembly 68 is connected to the high-pressure liquid supply throttling pipe, the ejected medium inlet is connected to the gas-liquid mixing outlet of the gas-liquid ejector 7, and the outlet of the secondary ejector assembly 68 is connected to the inlet of the secondary gas-liquid separator distributor 69 via a circulating liquid supply pipe.

[0040] For large falling film evaporators with diameters greater than 1m and low-temperature operating conditions where the pressure difference between condensing and evaporating pressures is less than 2 bar, the static pressure boosting capacity of a single-stage ejector may not meet the height and flow rate requirements of the circulating liquid replenishment. This invention utilizes a two-phase gas-liquid fluid, primarily liquid, formed after throttling the high-pressure liquid in the condenser, as the secondary ejector medium to perform a second ejection of the low-pressure gas-liquid mixture following the primary ejection, achieving a relay ejection effect. The overall ejection coefficient can reach over 384, and the ejector static pressure head is increased by 80% compared to a single-stage process (this data comes from Example 4, propylene -30℃, falling film evaporator diameter 1.5m). This significantly expands the applicability of this invention in large industrial refrigeration unit scenarios. Unlike existing conventional two-stage ejector designs that only target gaseous media, this solution utilizes the high-density momentum of the liquid phase as the secondary ejector medium, creating a synergistic effect with the primary gas-liquid two-phase ejection.

[0041] Furthermore, to enhance the liquid film spreading ability and heat exchange efficiency, the outer surface of the heat exchange tube is provided with a micron-level rough structure. The micron-level rough structure is used to ensure that the contact angle of the refrigerant liquid on the outer surface of the heat exchange tube is ≤30°. The micron-level rough structure is a groove-type or pit-type laser microtexture, and the surface roughness Ra of the outer surface of the heat exchange tube is 3.2 to 6.3 μm.

[0042] Figure 5 This is a front view of the structure of the secondary separation liquid distributor; Figure 6 This is a side view of the structure of the secondary separation liquid distributor; Furthermore, the secondary gas-liquid separator 69 includes: First gas-liquid separator distributor 5: disposed above the first tube bundle region 2; The second gas-liquid separator distributor 6 is located between the first tube bundle region 2 and the second tube bundle region 3. This invention achieves safe operation with low liquid load through two-stage gas-liquid separation.

[0043] The above-mentioned two-stage gas-liquid separation distributor structure, with the cyclone pre-separation chamber 65 and the wire mesh fine separation component 66 connected in series, achieves a separation efficiency of ≥99% and a total pressure drop of <0.025 bar. After separation, the gas returns directly to the compressor suction port through the independent channel at the top of the falling film evaporator 1, avoiding gas turbulence that could damage the liquid film. Combined with zoned differentiated spraying and closed-loop control, the liquid film coverage rate can be ≥96%, and the system energy efficiency can be improved by 8% to 12%.

[0044] Furthermore, the circulation ratio of the first tube bundle region 2 is controlled between 3.0 and 5.0, and the circulation ratio of the second tube bundle region 3 is controlled between 2.0 and 2.5. These circulation ratios are determined based on the operating condition where the heat transfer coefficient of the non-copper heat exchange tube is 1 / 3 to 1 / 5 that of the copper tube, and the heat exchange area is increased by 3 to 5 times.

[0045] Based on the heat transfer characteristics of non-copper tube heat exchangers (heat transfer coefficient is 1 / 3 to 1 / 5 that of copper tubes, and the heat transfer area is increased by 3 to 5 times), spray nozzles are set in the upper first tube bundle region 2 and the lower second tube bundle region 3 along the height of the heat exchange tubes, supplying liquids with different zone circulation ratios of 3.0–5.0 and 2.0–2.5, respectively. The high circulation ratio in the upper part ensures sufficient liquid film thickness in the region with the highest heat load density, allowing continuous evaporation of the liquid during its downward flow, and still meeting the minimum wetting flow requirement when it reaches the lower part. Dynamic closed-loop regulation finely adjusts the ejector gas volume in real time based on liquid level signals and heat transfer status detection signals, so that the actual zone circulation ratio is always maintained within the optimal range.

[0046] Furthermore, the first gas-liquid separator distributor 5 includes: Swirl pre-separation chamber 65: Located above the first tube bundle region 2, it is used to perform primary gas-liquid separation on the confluence of the circulating liquid flow output from the gas-liquid ejector 7 and the refrigerant gas-liquid mixture after throttling in the condenser, and to achieve primary separation of large-diameter droplets by using centrifugal acceleration. Wire mesh fine separation component 66: Based on the refrigerant gas containing a small amount of small droplets after separation by the cyclone pre-separation chamber 65, the fine droplets are separated in a secondary manner by the interception and coalescence of multiple layers of stainless steel wire mesh, resulting in gas with a very small amount of droplets. The gas-liquid separator 69 employs a two-stage gas-liquid separator consisting of cyclone pre-separation and wire mesh fine separation, achieving a separation efficiency of ≥99%. After separation, the gas returns to the compressor suction port via an independent channel, avoiding turbulence and film falling. The problems of liquid carryover and turbulence caused by incomplete gas-liquid separation are solved by using cyclone pre-separation and wire mesh fine separation. The cyclone pre-separation chamber 65 utilizes centrifugal acceleration to achieve primary separation of large-diameter droplets, while the wire mesh fine separation component 66 achieves secondary fine separation of fine droplets through the interception and coalescence of multiple layers of stainless steel wire mesh. The two stages connected in series achieve a separation efficiency of ≥99%. The separated gas does not pass through the spray zone but returns directly to the compressor suction port through an independent channel at the top of the falling film evaporator 1, fundamentally avoiding the problem of gas turbulence and falling film formation.

[0047] High-pressure liquid supply and distribution branch pipe 35: It is set in the lower layer of the wire mesh fine separation component 66, and multiple distribution holes are evenly arranged on the high-pressure liquid supply and distribution branch pipe 35; Secondary liquid distribution plate 37: disposed below the high-pressure liquid supply distribution branch pipe 35, used to guide and uniformly flow the liquid flowing down from the high-pressure liquid supply distribution branch pipe 35; the secondary liquid distribution plate 37 is provided with a liquid outflow hole; Primary liquid distributor distribution plate 36: Located below the secondary liquid distributor plate 37, it is used to further subdivide and evenly distribute the liquid after it has been guided by the secondary liquid distributor plate 37; the primary liquid distributor distribution plate 36 is provided with a liquid outflow hole. First-stage liquid distribution plate 38: Vertically installed inside the first-stage liquid distributor distribution plate 36, used to divide the plate surface of the first-stage liquid distributor distribution plate 36 into 2 to 4 independent zones; to prevent liquid from flowing laterally, so that each zone independently supplies liquid to the first tube bundle area 2 and the second tube bundle area 3. Edge mesh 39: Set in the vertical channel between the outer edge of the first gas-liquid separator 5 and the inner wall of the falling film evaporator 1 on both sides above the first tube bundle area 2, to intercept liquid droplets carried in the upward backflow gas after the liquid on the outer surface of the heat exchange tube evaporates, and to prevent the liquid from entering the evaporator outlet with the airflow. Curtain baffle 40: disposed on both sides of the first tube bundle region 2 and the second tube bundle region 3 to prevent liquid from splashing into non-heat exchange areas; Among them: multiple high-pressure liquid supply and distribution trunk lines 34 are used to introduce gas-liquid mixed refrigerant flowing out of the second inlet 19, and are installed inside the first gas-liquid separator distributor 5; The second gas-liquid separator distributor 6 includes: Secondary liquid distributor branch pipe 49: Located below the first gas-liquid separator 5, with multiple liquid distribution holes evenly arranged on the secondary liquid distributor branch pipe 49; Secondary liquid distributor distribution plate 62: disposed below the secondary liquid distributor distribution branch pipe 49, used to guide and uniformly flow the liquid flowing down from the secondary liquid distributor distribution branch pipe 49 and the first tube bundle region 2; Secondary liquid distributor dividing plate 50: Vertically installed inside the secondary liquid distributor dividing plate 62, used to divide the plate surface into independent zones.

[0048] Furthermore, the height-to-diameter ratio of the swirl pre-separation chamber 65 is 1.5 to 2.5. The wire mesh separation component 66 comprises multiple layers of wire mesh. Replacing a single, thicker wire mesh with multiple layers of thinner wire mesh helps reduce resistance loss and improves gas-liquid separation. A baffle plate is installed at the bottom of each layer of wire mesh, with the openings of different baffle plates staggered to allow the gas to flow around multiple times, preventing the gas-liquid mixture from directly penetrating the wire mesh and enhancing the gas-liquid separation effect.

[0049] The wire mesh used is 80-120 mesh stainless steel wire mesh.

[0050] This embodiment has three layers of wire mesh, including a first layer of wire mesh 30, a second layer of wire mesh 31 and a third layer of wire mesh 32. A first layer of wire mesh liquid baffle 42 is provided below the first layer of wire mesh 30, a second layer of wire mesh liquid baffle 43 is provided below the second layer of wire mesh 31 and a third layer of wire mesh liquid baffle 44 is provided below the third layer of wire mesh 32.

[0051] Circulation ratio: The ratio of the total mass flow rate of the sprayed liquid to the rated evaporation mass flow rate of the falling film evaporator 1 is the core parameter for controlling the liquid film coverage of this invention. The rated control range of the system is 2.0 to 5.0. Among them, the zonal circulation ratio is the ratio of the mass flow rate of the sprayed liquid in that zone to the evaporation mass flow rate corresponding to the heat load of the corresponding zone. Ejection coefficient: In the gas-liquid ejector 7, the ratio of the mass flow rate of the liquid accumulated in the falling film evaporator 1 to the mass flow rate of the refrigerant gas used for ejection is the core parameter characterizing the efficiency of the gas-liquid ejector 7; the above mass flow rates are all calculated based on the steady-state parameters at the inlet of the gas-liquid ejector 7. Return gas superheat: The difference between the compressor return gas port temperature and the refrigerant saturation temperature at the corresponding evaporation pressure.

[0052] Overall ejection coefficient: In the two-stage ejection relay scheme, the ratio of the total mass flow rate of the liquid accumulated in the ejected falling film evaporator 1 to the mass flow rate of the refrigerant gas used for the first-stage ejection is the core parameter characterizing the overall efficiency of the two-stage ejection system.

[0053] The operation method of the above system includes the following steps: The S1 ejector circulation replenishment step uses the refrigerant gas from the compressor exhaust or the economizer flash as power to draw the liquid accumulated at the bottom of the falling film evaporator 1 through the gas-liquid ejector 7 to form a circulating liquid flow. The gas-liquid ejector 7 ensures that the high-pressure ejector gas and the ejected refrigerant liquid are fully mixed to achieve momentum exchange between the gas and liquid phases. The classically defined ejector coefficient can reach more than 300. Under rated operating conditions, the ejector gas consumption accounts for ≤1% of the compressor exhaust volume. The above parameters are conventionally determined by the gas-liquid ejector 7 design software based on the working fluid properties and rated operating conditions.

[0054] In the S2 secondary gas-liquid separation step, the circulating liquid flow and the refrigerant gas-liquid mixture after throttling in the condenser are merged into the secondary gas-liquid separator distributor 69. The secondary gas-liquid separation is completed through the cyclone pre-separation chamber 65 and the wire mesh fine separation component 66. The separated gas is sent to the compressor suction port through the independent channel at the top of the falling film evaporator 1 to prevent the gas from entering the spray area and causing turbulence in the falling film. In the S3 zoned differentiated spraying step, the liquid separated by the secondary gas-liquid separator 69 is sprayed in a zoned differentiated manner along the height of the heat exchange tubes in the first tube bundle region 2 and the second tube bundle region 3. The circulation ratio of the first tube bundle region 2 is maintained at 3.0 to 5.0, and the circulation ratio of the second tube bundle region 3 is maintained at 2.0 to 2.5. The circulation ratio of the first tube bundle region ensures the minimum wetting flow rate of the second tube bundle region 3. The heat load density of the upper first tube bundle region 2 is 1.5 to 2.5 times that of the lower second tube bundle region 3. A high circulation ratio of 3.0 to 5.0 is used to enhance the liquid film coverage and prevent the outer surface of the heat exchange tubes from drying out. The heat load density of the lower second tube bundle region 3 is relatively low. A low circulation ratio of 2.0 to 2.5 is used to maintain the minimum wetting flow rate, balancing energy efficiency and coverage effect. The circulation ratio is determined based on the operating condition that the heat transfer coefficient of the non-copper heat exchange tube is 1 / 3 to 1 / 5 of that of the copper tube and the heat transfer area is increased by 3 to 5 times. The high circulation ratio of the upper part ensures the minimum wetting flow rate of the lower tube bundle.

[0055] The S4 dynamic closed-loop adjustment step dynamically adjusts the flow rate of high-pressure ejector gas ejected by the gas-liquid ejector 7 based on the liquid level signal transmitted by the liquid level sensor 17, so as to maintain the circulation ratio of each zone within the above-mentioned set range.

[0056] Furthermore, step S1 also includes: after the high-pressure refrigerant liquid from the condenser is throttled, it is used as a secondary ejector medium to perform secondary ejection of the low-pressure refrigerant liquid delivered by the first-stage gas-liquid ejector, thereby achieving jet relay. The gas-liquid mixture after the secondary ejection flows into the liquid distributor to complete the secondary gas-liquid separation and spraying.

[0057] Furthermore, when the pressure difference between the compressor discharge pressure and the evaporation pressure is less than 2 bar, the pumping auxiliary unit 67 is started to operate in parallel with the gas-liquid ejector 7.

[0058] Example 1: Ammonia-working stainless steel tube falling film evaporator 1 1. System Configuration The working fluid is R717 (ammonia), the evaporation temperature is -30℃, and the condensation temperature is 35℃; the heat exchange tubes are made of S30408 ​​stainless steel, with an outer diameter of 19mm, a wall thickness of 1.5mm, and 360 tubes. The heat exchange area is approximately 4 times that of the copper tube scheme with the same cooling capacity. The gas-liquid ejector 7 has a three-nozzle array 54 structure, with each nozzle having a diameter of 3mm. The axis of the nozzle outlet forms a 20° angle with the axis of the mixing chamber 59. The equipment has a design pressure of 50 barG and a rated working pressure of 12 barG. The cyclone pre-separation chamber 65 of the secondary gas-liquid separator 69 has a height-to-diameter ratio of 2.0, and the wire mesh fine separation component 66 is a 4-layer 100-mesh S30408 ​​stainless steel wire mesh.

[0059] The control unit uses a PLC controller, which connects the dual photoelectric liquid level switches (installed in the middle and lower liquid accumulation areas of the falling film evaporator 1) to the return gas port temperature sensor, and the control cycle is 1 second.

[0060] 2. Core Implementation Steps Step S1: Ejection and circulation fluid replenishment Powered by compressor exhaust (pressure 12 bar, temperature 85°C), the liquid accumulated at the bottom of the falling film evaporator 1 (temperature -30°C, pressure 0.2 barG) is drawn in through the gas-liquid ejector 7. A multi-nozzle array 54 ensures that the high-pressure exhaust is evenly distributed around the mixing chamber 59, and the three airflows converge at the center to form a negative pressure core area. Under standard operating conditions in this embodiment (R717, evaporation temperature -30°C, condensation temperature 35°C), the classically defined ejector coefficient is measured to be 320, and the ejector liquid volume is approximately four times the evaporation volume. The high-pressure gas consumption for ejection accounts for 0.92% of the compressor exhaust volume.

[0061] Step S2: Secondary gas-liquid separation The gas-liquid mixture after ejection, along with the refrigerant gas-liquid mixture after throttling in the condenser, flows into the first gas-liquid separator distributor. It first enters the cyclone pre-separation chamber 65 (height-to-diameter ratio 2.0), where centrifugal acceleration achieves primary separation of large-diameter droplets, with a separation efficiency of approximately 92%. Subsequently, it enters the wire mesh fine separation assembly 66 (4 layers of 100-mesh stainless steel wire mesh), where the wire mesh intercepts and coalesces to achieve secondary fine separation of small droplets. The total separation efficiency of the two stages in series is ≥99.5%. The separated gas is directly fed into the compressor suction port through an independent straight-through channel at the top of the falling film evaporator 1, bypassing the spray zone.

[0062] Step S3: Differentiated Spraying by Zone The separated liquid enters the zoned spray chamber. The spray nozzles in the first tube bundle region 2 supply liquid with a circulation ratio of 4.0, while the spray nozzles in the second tube bundle region 3 supply liquid with a circulation ratio of 2.1. The high circulation ratio in the first tube bundle region 2 ensures sufficient liquid film thickness in the superheated zone with the highest heat load density. As the liquid flows down the outer surface of the heat exchange tubes, it continues to evaporate, and the minimum wetting flow rate requirement is still met when it reaches the lower two-phase zone.

[0063] Step S4: Dynamic closed-loop adjustment The PLC controller prioritizes the liquid level signal. When the liquid level is below the set lower limit, it increases the ejector gas flow; when it is above the set upper limit, it decreases the ejector gas flow, maintaining the circulation ratio of each zone within the aforementioned set range. Simultaneously, it monitors the return gas superheat: when the return gas superheat exceeds 5°C, it determines that the liquid film has dried out and automatically increases the circulation ratio by 0.5 until the superheat recovers to below 3°C. Under partial load conditions (load rate 30%–80%), the PLC dynamically adjusts the upper and lower circulation ratio distribution based on the real-time heat load distribution; when the load rate is below 50%, the circulation ratio of the lower two-phase zone is increased to 2.0–2.5, and the circulation ratio of the upper superheated zone is decreased to 2.5–3.5, ensuring stable liquid film coverage across the entire pipe length throughout the full load range.

[0064] 3. Boundary conditions and anomaly handling 1) Low liquid level protection: When both photoelectric liquid level switches detect that the liquid level is lower than the safety lower limit (for 3 consecutive control cycles), the system automatically reduces the injection gas volume to the minimum value and triggers a low liquid level alarm at the same time; if the liquid level continues to drop, it switches to the fixed liquid supply mode to maintain the minimum wetting flow rate by directly supplying liquid to the condenser. 2) Return gas superheat protection: When the return gas superheat is continuously higher than 8°C for more than 5 control cycles, it is judged as a serious liquid shortage. The system will automatically increase the circulation ratio to the maximum value of 5.0 and trigger a high temperature alarm at the same time. 3) Sensor fault switching: When the liquid level sensor 17 or temperature sensor signal is abnormal (outside the physical reasonable range or communication interruption), the system automatically switches to the preset fixed cycle ratio of 3.0 as a minimum operating mode to maintain basic liquid film coverage, and at the same time triggers the sensor fault alarm.

[0065] 4) Dynamic variable operating condition control: The start-up and stop conditions adopt progressive ramp-up / ramp-down control, with the ejector gas volume changing linearly at a rate of 10% / min. This adapts to the thermal inertia characteristics of the cold start / stop process of the falling film evaporator 1, ensuring the smooth establishment and receding of the liquid film. There is no risk of liquid carryover or liquid film drying during the transition process. The ramp-up rate and the dynamic response rate of 0.5 to 2 seconds under the scenario of sudden load change are set independently to adapt to the control requirements of different operating conditions.

[0066] 4. Control effect of this embodiment All test data in this embodiment are based on the following standard operating conditions: working fluid R717, evaporation temperature -30℃, condensation temperature 35℃, and full load operation.

[0067] Liquid film coverage is 97.3%; no liquid carryover during 100 hours of continuous operation; compressor current fluctuation is less than ±2%; high-pressure gas flow rate for ejector accounts for 0.92% of compressor discharge volume; compared with traditional pumping circulation scheme, energy efficiency is improved by 10% and failure rate is reduced by 95%; compared with conventional single-phase ejector scheme (ejection coefficient 1.3), based on the different physical mechanisms of gas-liquid two-phase and single-phase ejection, a breakthrough of two orders of magnitude is achieved in mass flow ejection efficiency, and cold loss is reduced by 73%.

[0068] Example 2: Carbon Dioxide Transcritical Working Fluid Stainless Steel Tube Falling Film Evaporator 1 1. System Configuration The working fluid is R744 (carbon dioxide), the evaporation temperature is -35℃, and the gas cooler outlet temperature is 25℃; the heat exchange tubes are made of S30408 ​​stainless steel, with an outer diameter of 10mm, a wall thickness of 1.0mm, and 480 tubes in total; the gas-liquid ejector 7 is a dual-nozzle array 54 structure, with each nozzle having a diameter of 2.5mm and a design pressure of 100barG; the power source is the flash gas from the economizer (pressure 60barG). The cyclone pre-separation chamber 65 of the secondary gas-liquid separator 69 has a height-to-diameter ratio of 2.0, and the wire mesh fine separation component 66 is made of 4 layers of 100-mesh stainless steel wire mesh. The dual nozzles are a special case of compact design for small-diameter CO2 evaporators, and adopt a 180° opposing arrangement structure. The two high-speed airflows form a stable opposing negative pressure core area in the center of the mixing chamber 59, which complements the circumferential converging flow field of three or more nozzles. This adapts to the spatial constraints of the compact falling film evaporator 1 for small-diameter CO2 evaporators and can achieve a classic entrainment coefficient of over 100. In conventional industrial scenarios, a structure of 3 to 6 nozzle arrays 54 is preferred.

[0069] 2. Key differences from Example 1 1) The CO2 transcritical cycle operates at a high pressure (100 barG). The falling film evaporator 1 is a small-diameter, compact design, matched with a dual-nozzle ejector. 2) Add high-pressure side safety valve trigger protection in boundary treatment (automatic pressure relief when pressure > 105 barG).

[0070] 3. Control effect The system circulation ratio is 2.8, and the classically defined ejector coefficient is 135 as measured. The circulation ratio in the upper superheated zone is 5.0, and the circulation ratio in the lower two-phase zone is 2.0. The measured high-pressure gas flow rate for ejection accounts for 0.85% of the compressor's discharge volume. The system COP (coefficient of performance) is 2.15, which is 9% higher than that of the pumped circulation scheme.

[0071] Example 3: Propane working fluid titanium tube falling film evaporator 1 1. System Configuration The working fluid is R290 (propane), and the evaporation temperature is -25℃. The heat exchange tubes are made of industrial pure titanium (to meet the flammability and explosion-proof requirements of propane), with an outer diameter of 16mm and 420 tubes. The gas-liquid ejector 7 is a three-nozzle array 54 structure, with each nozzle having a diameter of 3.5mm.

[0072] 2. Control effect The system has a circulation ratio of 3.0 and a measured ejector coefficient of 350 (as defined in classical methods). The circulation ratio in the upper superheated zone is 4.5, and the circulation ratio in the lower two-phase zone is 3.0. The measured high-pressure gas flow rate for ejection accounts for 0.88% of the compressor's discharge volume. The liquid film coverage is 96.8%. There is no liquid carryover or cavitation during continuous operation.

[0073] Example 4: Propylene working fluid stainless steel tube falling film evaporator 1 1. System Configuration The working fluid is R1270 (propylene), and the evaporation temperature is -30℃. The heat exchange tubes are made of S30408 ​​stainless steel with an outer diameter of 19mm and 480 tubes. The falling film evaporator 1 has a diameter of 1.5m (large industrial falling film evaporator). The gas-liquid ejector 7 is a three-nozzle array 54 structure with each nozzle having a diameter of 3mm. It is equipped with a secondary ejector assembly 68. The ejector medium is the high-pressure liquid after throttling in the condenser (pressure 12barG), and the ejected medium is the low-pressure gas-liquid mixture sent by the primary ejector.

[0074] 2. Details of the Secondary Ejection Implementation First-stage ejector: Powered by compressor exhaust, a three-nozzle ejector draws liquid from the bottom of the falling film evaporator 1, with a first-stage circulation ratio of 2.5. Second-stage ejector: High-pressure liquid in the condenser is throttled to an intermediate pressure (approximately 6 barG) and used as the ejector medium to perform a second ejection of the low-pressure gas-liquid mixture after the first-stage ejection, with a second-stage circulation ratio of 2.0. The combined circulation ratio of the two-stage series system is 4.5, and the measured combined ejection coefficient as defined in the classic system is 384. The ejector static pressure head is increased by 80% compared to the single-stage system, effectively solving the problem of insufficient ejection height under large-diameter falling film evaporators and low evaporation pressures.

[0075] The inlet of the ejected medium of the secondary ejector assembly 68 is located at its lower end and is connected to the gas-liquid mixing outlet of the gas-liquid ejector 7; the high-pressure ejector medium inlet is located on its middle side and is connected to the high-pressure liquid supply throttling pipe; the mixed and diffused medium flows out from its upper end and merges into the secondary gas-liquid separator distributor 69.

[0076] 3. Control effect The circulation ratio in the upper superheated zone is 3.5, and the circulation ratio in the lower two-phase zone is 2.2; the measured high-pressure gas flow rate for ejector accounts for 0.78% of the compressor's discharge volume; the liquid film coverage is 97.1%; and there is no liquid carryover or cavitation during continuous operation.

[0077] Comparative Example Comparative Example 1 is the refrigerant pump circulation scheme of the current mainstream production in the ammonia refrigeration industry, and Comparative Example 2 is the conventional single-nozzle single-phase ejector scheme in the prior art. Both are existing technologies known in the field.

[0078] Comparative Example 1: Traditional Pumping Circulation Solution Under the same operating conditions as Example 1 (R717, evaporation temperature -30℃, condensation temperature 35℃, full load), a canned motor pump (4.5kW) was used for circulation. Cavitation noise appeared after 48 hours of operation, and the pump impeller was damaged after 69 hours; the liquid film coverage was 88%, and the temperature in the local dry area exceeded the saturation temperature by 5-8℃; the system energy efficiency was 10% lower than that of Example 1.

[0079] Comparative Example 2: Conventional Single-Phase Ejector Scheme Under the same operating conditions as in Example 1, a traditional single-nozzle single-phase ejector was used, without a two-stage gas-liquid separation design. The ejector coefficient was 1.3, high-pressure gas consumption accounted for 18% of the exhaust volume, cooling loss was 11%, and the system COP decreased by 7%; the liquid film coverage was 85%, with localized drying; and two minor liquid carryover events occurred after 12 hours of continuous operation.

[0080] Example 5: Pumping Assistance in Extreme Low Temperature Conditions 1. Application Scenarios The pumping auxiliary feature corresponding to this embodiment is for the low-temperature cold storage refrigeration system in the frigid winter of northern regions. When the ambient temperature is extremely low in winter, the condensing temperature drops significantly. When the pressure difference between the compressor discharge pressure and the evaporation pressure is less than 2 bar, the available pressure difference margin for ejection is drastically reduced. The single-stage ejection efficiency cannot meet the circulation flow requirements of liquid film coverage. At this time, the pumping auxiliary unit 67 is started to operate in parallel with the gas-liquid ejector 7.

[0081] 2. System Configuration Based on the system in Example 1, a pumping auxiliary unit 67 (canned pump, power 2.2kW) is added and connected in parallel with the gas-liquid ejector 7. During normal operation, the gas-liquid ejector 7 is the main circulating power source. When the PLC detects that the pressure difference between the exhaust pressure and the evaporation pressure is <2 bar, the pumping auxiliary unit 67 is automatically started and operates in coordination with the gas-liquid ejector 7. The inlet of the pumping auxiliary unit 67 is equipped with a 100-mesh filter to prevent particulate matter from damaging the pump body. The outlet of the pumping auxiliary unit 67 is connected to the inlet of the ejected medium of the secondary ejector assembly 68, and after diffusion by the secondary ejector assembly 68, it flows into the secondary gas-liquid separator distributor 69. The 2-bar pressure difference trigger threshold is determined based on engineering calculations of the minimum operating pressure difference of the gas-liquid ejector 7, serving as the critical inflection point value to ensure the effective liquid replenishment capacity of the gas-liquid ejector 7.

[0082] 3. Control effect When the gas-liquid ejector 7 is operated in parallel with the pumping auxiliary, the circulation ratio remains stable at 3.0; the liquid film coverage is 95.5%; and the system energy efficiency is improved by 6% compared to the pure pump circulation scheme. This embodiment verifies the technical feasibility of using the pumping auxiliary as a backup in extreme operating conditions and expands the full-condition adaptability of the present invention.

[0083] Example 6: Laser Microtexturing Enhancement of Heat Exchanger Tubes 1. Application Scenarios This embodiment corresponds to the microtexture characteristics of the heat exchange tube. Based on the system in Embodiment 1, the outer surface of the heat exchange tube is subjected to laser microtexture treatment to further enhance the liquid film spreading ability and heat exchange efficiency.

[0084] 2. System Configuration The heat exchange tube is made of S30408 ​​stainless steel, and its outer surface is processed with a grooved microtexture using pulsed laser technology. The grooves are 30–50 μm deep, 200 μm apart, and spirally distributed at 45°. The surface roughness Ra is 4.5 μm, and the measured contact angle is 22°. The microtexture promotes the radial spread of the liquid film on the outer surface of the heat exchange tube through capillary action, increasing the effective wetting area. The pitted microtexture has a Ra of 5.2 μm and a contact angle of 25°. A contact angle ≤30° is the critical value for uniform liquid film spread; when the contact angle is >30°, the liquid film is prone to shrinking into droplets, leading to localized drying.

[0085] 3. Control effect The liquid film coverage was increased to 98.5% (1.2% higher than in Example 1); the heat transfer coefficient was increased by 8% to 10% at the same cycle rate; the critical cycle rate for liquid film evaporation and drying was reduced from 2.0 to 1.5, and the lower two-phase region could maintain safe wetting at a lower cycle rate, further expanding the energy-saving potential.

[0086] Example 7: Waste Cooling Recovery Scheme for Flash Gas from Economizer 1. Application Scenarios This embodiment corresponds to the preferred implementation of step S2, using the flash gas from the economizer instead of the compressor exhaust as the ejector power source, and is equipped with an independent heat exchange chamber to achieve waste cooling recovery, further reducing compressor power consumption. It is suitable for energy-saving retrofit scenarios of large and medium-sized ammonia refrigeration units (refrigeration capacity ≥ 500kW).

[0087] 2. System Configuration Based on the system in Example 1, the ejector power source is switched from compressor exhaust to economizer flash gas (pressure 3.0 barG, saturation temperature around -5°C). The separated flash gas does not return directly to the compressor suction port, but first exchanges heat with the cooled medium (such as chilled water) in the upper independent heat exchange chamber of the falling film evaporator 1 (located outside the heat exchange tube bundle in the upper superheated zone), recovering its sensible heat and cooling capacity. After the temperature rises to -5°C, it is then sent to the compressor suction port.

[0088] 3. Control effect The return gas superheat decreased from 12°C to 5°C, the compressor delivery coefficient increased by 4%, and the shaft power decreased by 3%. The flash gas used for ejection accounted for 2.5% of the compressor's discharge volume (the flash gas itself is an ineffective refrigerant after condensation and throttling, and does not occupy the effective discharge volume of the main cycle; in this embodiment, the measured ejection coefficient is approximately 120, and stable circulation replenishment can be achieved using the natural flow rate of the flash gas in the economizer). The overall system energy efficiency was further improved by 2-3 percentage points compared to Embodiment 1. This embodiment verifies the technical feasibility and additional energy-saving benefits of recovering residual heat from the flash gas in the economizer.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-efficiency heat exchange system based on high-pressure entrainment cycle natural working medium falling film evaporator, characterized in that, Includes a falling film evaporator, multiple gas-liquid ejectors, a liquid level sensor, and a control unit; The falling film evaporator includes: The first tube bundle region is located in the upper part of the falling film evaporator shell; The second tube bundle region is located below the first tube bundle region; The first inlet is used to introduce the refrigerant into the second tube bundle region, and the refrigerant in the second tube bundle region then flows into the first tube bundle region. The first outlet is used for the outflow of refrigerant within the first tube bundle region; The second inlet is located at the bottom of the falling film evaporator for the inflow of gas-liquid mixed refrigerant; The two-stage gas-liquid separator is used to separate the liquid and gas of the gas-liquid mixed refrigerant flowing in from the second inlet. The separated liquid flows from top to bottom and forms a liquid film on the heat exchange tubes in the first tube bundle region and the second tube bundle region. A liquid reservoir is used to store the refrigerant liquid flowing down from the falling film evaporator; The plurality of gas-liquid ejectors are located below the falling film evaporator and are used to draw refrigerant liquid from the liquid tank to form a circulating liquid flow, using refrigerant gas from compressor exhaust or economizer flash as power. The liquid level sensor is used to collect the liquid level of the refrigerant in the liquid tank; The control unit is used to control the gas flow rate ejected by the plurality of gas-liquid ejectors based on the liquid level height signal transmitted by the liquid level sensor, so as to keep the circulation ratio of the first tube bundle region and the second tube bundle region within a predetermined range.

2. The high-efficiency heat exchange system based on the natural working medium falling-film evaporator with high-pressure ejector cycle according to claim 1, characterized in that, The heat exchange tubes in the first and second tube bundle regions are made of carbon steel, stainless steel, or titanium.

3. The high-efficiency heat exchange system based on the natural working medium falling-film evaporator with high-pressure ejector cycle according to claim 1, characterized in that, The gas-liquid ejector includes: ejector body; A liquid inlet pipe is located on the side of the middle part of the ejector body and is used to connect the refrigerant liquid conveyed by the liquid package. The high-pressure inlet pipe is used to introduce refrigerant gas from the compressor exhaust or the economizer flash, and is located at one end of the ejector body. The nozzle array comprises N nozzles, which are evenly arranged circumferentially at the outlet end of the high-pressure intake pipe; N ranges from 2 to 6. A mixing chamber, located above the nozzle array, is used to mix the refrigerant liquid delivered by the inlet pipe and the refrigerant gas delivered by the nozzle array. The cross-sectional diameter of the mixing chamber is 3 to 5 times the cross-sectional diameter of the nozzle array; The angle between the axis of the nozzle outlet and the axis of the mixing chamber is 15° to 30°. The diffusion chamber, located on the outlet side of the mixing chamber, is used to reduce the flow velocity of the gas-liquid two-phase mixed fluid as it flows through, thereby converting kinetic energy into static pressure energy and completing fluid diffusion.

4. The high-efficiency heat exchange system based on the natural working medium falling-film evaporator with high-pressure ejector cycle according to claim 1, characterized in that, The outer surface of the heat exchange tube is provided with a micron-level rough structure, which is used to ensure that the contact angle of the refrigerant liquid on the outer surface of the heat exchange tube is ≤30°; the roughness Ra of the outer surface of the heat exchange tube is 3.2~6.3μm.

5. The high-efficiency heat exchange system based on the natural working medium falling-film evaporator with high-pressure ejector cycle according to claim 1, characterized in that, The secondary gas-liquid separator includes: The first gas-liquid separator is located above the first tube bundle region; The second gas-liquid separator is located between the first tube bundle region and the second tube bundle region.

6. The high-efficiency heat exchange system based on a natural working fluid falling-film evaporator with a high-pressure ejector cycle according to claim 1, characterized in that, The circulation rate of the first tube bundle region is controlled between 3.0 and 5.0, and the circulation rate of the second tube bundle region is controlled between 2.0 and 2.

5.

7. The high-efficiency heat exchange system based on a natural working medium falling-film evaporator with a high-pressure ejector cycle according to claim 5, characterized in that, The first gas-liquid separator includes: The cyclone pre-separation chamber is located above the first tube bundle region and is used to perform primary gas-liquid separation on the confluence of the circulating liquid flow output from the gas-liquid ejector and the refrigerant gas-liquid mixture after throttling in the condenser. The wire mesh fine separation component achieves secondary gas-liquid separation based on the refrigerant gas containing droplets separated by the cyclone pre-separation chamber, through the interception and coalescence of multiple layers of stainless steel wire mesh. A high-pressure liquid supply and distribution branch pipe is installed in the lower layer of the wire mesh fine separation component, and multiple distribution holes are evenly arranged on the high-pressure liquid supply and distribution branch pipe; A secondary liquid separator is located below the high-pressure liquid supply and liquid separator branch pipe, and is used to guide and uniformly distribute the liquid flowing down from the high-pressure liquid supply and liquid separator branch pipe and the gas-liquid ejector; the secondary liquid separator is provided with a liquid outflow hole. A primary liquid distributor plate is located below the secondary liquid distributor plate and is used to further subdivide and homogenize the liquid after it has been guided by the secondary liquid distributor plate; a liquid outflow hole is provided in the primary liquid distributor plate. A primary liquid distribution plate partition is vertically installed inside the primary liquid distributor's liquid distribution plate to independently divide the plate surface of the primary liquid distributor's liquid distribution plate into partitions, so that each partition independently supplies liquid to the first tube bundle area and the second tube bundle area. Edge wire mesh is set in the vertical channel between the outer edge of the first gas-liquid separator and the inner wall of the falling film evaporator on both sides above the first tube bundle area. Curtain baffles are provided on both sides of the first tube bundle region and the second tube bundle region; The second gas-liquid separator includes: A secondary liquid distributor branch pipe is located below the first gas-liquid separator, and multiple liquid distribution holes are evenly arranged on the secondary liquid distributor branch pipe. The secondary liquid distributor distribution plate is located below the secondary liquid distributor distribution branch pipe and is used to guide and even out the liquid flowing down from the secondary liquid distributor distribution branch pipe. The secondary liquid distributor has a liquid distribution baffle that is vertically installed inside the secondary liquid distributor's liquid distribution plate to divide the plate surface into independent zones.

8. A high-efficiency heat exchange system for a natural working fluid falling film evaporator based on a high-pressure ejector cycle as described in claim 7, characterized in that, The height-to-diameter ratio of the cyclone pre-separation chamber is 1.5 to 2.

5. The wire mesh fine separation component includes M layers of wire mesh, which are made of 80 to 120 mesh stainless steel wire mesh. A wire mesh baffle is provided below each layer of wire mesh, and the opening positions of adjacent wire mesh baffles are staggered, with 3 ≤ M ≤ 5.

9. A high-efficiency heat exchange system for a natural working fluid falling film evaporator based on a high-pressure ejector cycle according to claim 1, characterized in that, It also includes a secondary ejector assembly, which, after being throttled by high-pressure refrigerant liquid, serves as a high-pressure power source to eject fluid from the gas-liquid ejector mixing outlet.

10. A method for a high-efficiency heat exchange system of a natural working fluid falling film evaporator based on a high-pressure ejector cycle according to any one of claims 1-9, characterized in that, Includes the following steps: The S1 ejector circulation replenishment step uses the refrigerant gas from the compressor exhaust or the economizer flash as power to draw the liquid accumulated at the bottom of the falling film evaporator through the gas-liquid ejector to form a circulating liquid flow. In the S2 secondary gas-liquid separation step, the circulating liquid flow and the refrigerant gas-liquid mixture after throttling in the condenser are converged into the secondary gas-liquid separator liquid distributor. The secondary gas-liquid separation is completed through the cyclone pre-separation chamber and the wire mesh fine separation component. The separated gas is sent to the compressor suction port through the independent channel at the top of the falling film evaporator. In the S3 zoned differentiated spraying step, the liquid separated by the secondary gas-liquid separator is sprayed in a zoned differentiated manner along the height of the heat exchange tubes in the first tube bundle region and the second tube bundle region. The circulation ratio of the first tube bundle region is maintained at 3.0 to 5.0, and the circulation ratio of the second tube bundle region is maintained at 2.0 to 2.5, so as to ensure the minimum wetting flow rate of the second tube bundle region by the circulation ratio of the first tube bundle region. The S4 dynamic closed-loop control step dynamically adjusts the flow rate of high-pressure ejector gas ejected by the gas-liquid ejector based on the liquid level signal transmitted by the liquid level sensor, maintaining the circulation ratio of each zone within the set range.

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