Structural Design Method of a High-Pressure Brazed Plate-Type Gas Cooler for a Transcritical CO2 Heat Pump

Abstract

The present invention belongs to the technical field of transcritical CO2 heat pumps, and particularly relates to a structural design method for a high-pressure brazed plate gas cooler used in a transcritical CO2 heat pump. The present application provides a structural design method based on classical strength theory, which collaboratively considers the corrugation depth, corrugation pitch, corrugation curve, and plate thickness, simplifies the calculation model, and also proposes a pressure fatigue check criterion for stainless steel thin plates based on the finite element analysis design method, realizing a highly reliable structural design of the high-pressure brazed plate gas cooler. Through the implementation of this design method, the precise design of the product can be achieved to a certain extent, and the manufacturing cost of the product can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of transcritical CO2 heat pumps, and particularly relates to a structural design method for a high-pressure brazed plate gas cooler for a transcritical CO2 heat pump. Background Technique

[0002] As a natural refrigerant, carbon dioxide (CO2) has very excellent thermodynamic properties and is a potential alternative environmentally friendly refrigerant. The transcritical CO2 heat pump system uses CO2 as the refrigerant and can obtain high-quality heat sources (produce high-temperature hot water or steam) while refrigerating through the CO2 transcritical reverse Carnot cycle of "compression - heat release - pressure reduction - heat absorption - recompression", achieving rapid large-temperature-difference refrigeration and heating. If this technology is used in the industrial field, waste heat can be turned into energy, replacing high-energy-consuming equipment such as boilers, saving energy and reducing carbon emissions, and achieving the goals of zero energy consumption, zero cost, and zero emissions at the heating end for the upgrading of low-grade industrial waste heat, that is, heating electrification. Therefore, the transcritical CO2 heat pump technology has great potential in promoting the utilization and conversion of energy.

[0003] In China, the commercialization of some small and medium-sized CO2 heat pump systems has been achieved, but they are mainly applied to household or commercial fields such as CO2 heat pump water heaters, CO2 heat pump drying, automotive air conditioners, and refrigeration units. There is still little research on the development of large-scale megawatt-level transcritical CO2 heat pump systems in the industrial field. Generally speaking, due to the relatively low critical temperature (31.1°C) and high critical pressure (7.39 MPa) of CO2, its technical threshold is high, and the manufacturing cost of the device is high, which limits its large-scale application. Especially for the key core equipment in the system - the high-pressure CO2 gas cooler, due to its high working pressure (up to 14 MPa at most), complex heat transfer mechanism (the physical properties of CO2 change violently in the pseudo-critical region), and high compactness requirements, the development of this equipment is difficult.

[0004] Diffusion-welded plate heat exchangers have the advantage of being able to withstand high temperatures and pressures simultaneously, but their high manufacturing costs limit their widespread application. Although brazed plate heat exchangers have relatively weak pressure-bearing capabilities, they are structurally compact, have high heat transfer efficiency, small pressure drops, high production efficiency, and low costs, and are more suitable for the application scenarios of high-pressure gas coolers in transcritical CO2 heat pumps.

[0005] However, at present, the products produced by brazed plate heat exchanger manufacturers in China mainly target Freon units (with a maximum design pressure of about 5 MPa), and they are still unable to break through the bearing limit of 14 MPa for the design pressure of brazed plate heat exchangers for refrigeration. There are also no mature domestic high-pressure brazed plate CO2 gas coolers on the market. In addition, at present, some products (such as Alfa Laval AXP27, Alfa Laval AXP52, Alfa Laval AXP112, Kelvion GBH-HP series, SWEP B16DW, etc.) use an external frame plate structure to achieve a relatively high product bearing pressure, but this design violates the design concept of high manufacturing efficiency, compact and lightweight structure of the fully brazed plate heat exchanger; and simply increasing the plate thickness and brazing material thickness by overly focusing on improving the product structure strength is also not advisable.

[0006] Therefore, according to the special requirements of the structure of high-pressure brazed plate gas coolers, providing a brand-new and complete structural design method for high-pressure brazed plate gas coolers is an important link in the commercialization process of transcritical CO2 heat pump technology and equipment. Summary of the Invention

[0007] The present invention is to solve the above problems and provides a structural design method for a high-pressure brazed plate gas cooler for a transcritical CO2 heat pump.

[0008] The present invention adopts the following technical solutions:

[0009] A structural design method for a high-pressure brazed plate gas cooler for a transcritical CO2 heat pump, in which a number of herringbone corrugated plates are stacked alternately in opposite directions, and the wave crests of adjacent corrugated plates are brazed together to form the design area of the high-pressure brazed plate gas cooler; define the corrugation angle in the herringbone corrugated plate as β , the center distance between two adjacent wave crests of the corrugation, that is, the corrugation pitch, is p , the vertical distance between the wave crest and the wave trough in a single herringbone corrugated plate, that is, the corrugation depth, is b , and the vertical distance from the top surface to the bottom surface in a single herringbone corrugated plate, that is, the plate thickness, is t ;

[0010] Define the space formed by the wave troughs after the wave crests of adjacent corrugated plates are brazed together as the bearing unit, and the orthographic projection area of the bearing unit is A s , and the brazing material attachment area in the orthographic projection area is A t ;

[0011] The design method includes the following steps:

[0012] S1. Set the corrugation pitch as the value of p according to experience, and calculate the area of the brazing material attachment area according to the following formulaA t The minimum value, and obtain the side length of the solder attachment area l ;

[0013] ;

[0014] ;

[0015] ;

[0016] In the formula, P is the design pressure, P ≥ 14 MPa; is the allowable stress of the brazing joint material for brazing two adjacent corrugated plates, with the unit of MPa;

[0017] S2. Set the corrugation depth b value according to experience, and calculate the current value of the plate thickness t based on the strength design theory of the elliptical head of the pressure vessel t m :

[0018] ;

[0019] ;

[0020] In the formula is the allowable stress of the plate material at the design temperature, K is the shape factor of the elliptical head, and the value is taken according to Table 7-1 of GB / T 150.3-2024;

[0021] S3. Set the range of the plate thickness t [t min , t max according to experience. If t m ∈ [t min , t max , then fix the current corrugation pitch p , corrugation depth b and plate thickness t m values; otherwise, adjust the corrugation pitch p and / or corrugation depth b values until t m ∈ [t min , t max ;

[0022] S4. Based on finite element analysis, calculate the maximum stress amplitude N of the designed structure under the cyclic pressure fatigue condition of S alt1; According to the design of austenitic stainless steel S - N curve, obtain the S - N allowable stress amplitude S N at the alt2 th cycle; if S alt1 ≤ S alt2 , then confirm the corrugation pitch p、 corrugation depth b , sheet thickness t m values, and complete the design; if S alt1 > S alt2 , then adjust the corrugation pitch p or adjust the corrugation depth b and sheet thickness t m values until S alt1 ≤ S alt2 , and obtain the confirmed corrugation pitch p、 corrugation depth b , sheet thickness t m values, and complete the design.

[0023] Preferably, the herringbone corrugated plate is a double-sided corrugated plate, the herringbone corrugation is axially symmetrically arranged, and the axis of symmetry is centrally arranged along the length direction of the sheet.

[0024] Preferably, the empirical range of the corrugation pitch p is 2.5 - 5.0 mm, and the empirical range of the corrugation depth b is 1.2 - 1.8 mm.

[0025] Preferably, the value of the allowable stress is determined according to the material property manual or the technical data provided by the manufacturer; in step S1, the allowable stress is taken with the brazed joint material being pure copper T2 or T1 and the working temperature 150°C ≤ T ≤ 200°C; in step S2, the allowable stress is taken with the head material being 316L and the working temperature T ≤ 200°C.

[0026] Preferably, in step S3, the range of the sheet thickness t is set as [t min , t max specifically as 0.3 mm ≤ t ≤ 0.8 mm, and t is a decimal with one decimal place; the calculated t mRound up the value to one decimal place and then compare.

[0027] Preferably, in the step S3, adjust the corrugation pitch p and / or the corrugation depth b The value is adjusted once either alternatively or simultaneously. The single adjustment amplitude of the corrugation pitch p is 0.1 mm, and the single adjustment amplitude of the corrugation depth b is 0.05 mm.

[0028] Preferably, in the step S4, for calculating S alt The design structure of takes 9 adjacent bearing units for finite element analysis.

[0029] Preferably, in the step S4, when S alt1 >S alt2 First, find the position of the point with the maximum local stress in the design structure. If the maximum point is located at the welded joint, keep the corrugation depth b and the sheet thickness t m unchanged, and only adjust the corrugation pitch p to increase the brazing spread area. The single adjustment amplitude of the corrugation pitch p is 0.1 mm; otherwise, keep the corrugation pitch p unchanged, and adjust the corrugation depth b and the sheet thickness t m The single adjustment amplitude of the corrugation depth b is 0.05 mm, and the single adjustment amplitude of the sheet thickness t m is 0.1 mm.

[0030] The beneficial effects of this application are as follows:

[0031] This application forms a design method based on failure modes for the pressure-bearing core area of the high-pressure brazed plate air cooler - the corrugated plate heat exchange area. Considering the fact that when copper is brazed to stainless steel, there is no obvious diffusion of the joint tissue elements and the joint strength is low, the inventor believes that the main failure modes are the strength failure of the copper joint and the plastic deformation failure of the stainless steel thin plate. On this basis, an analytical calculation method based on classical strength theory is proposed, and the calculation model is simplified, thus obtaining a structural design method that jointly considers the corrugation depth, corrugation pitch, corrugation curve, and sheet thickness. In addition, aiming at the current situation that the high-pressure brazed plate air cooler may suffer from mechanical fatigue failure but has not been widely taken seriously, a pressure fatigue checking criterion for stainless steel thin plates based on the finite element analysis design method is proposed. Through the above two aspects, the high-reliability structural design of the high-pressure brazed plate air cooler is realized.

[0032] In addition, through the implementation of this design method, the precise design of the product is also realized to a certain extent, and the manufacturing cost of the product is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of a high-pressure brazed plate gas cooler for a transcritical CO2 heat pump involved in this application;

[0034] Figure 2 It is a schematic diagram of the formation of a load-bearing unit by brazing corrugated plates in this application;

[0035] Figure 3 It is a schematic diagram of the corrugated plate structure in this application;

[0036] Figure 4 It is an enlarged side view of the corrugated plate in this application;

[0037] Figure 5 It is a schematic structural diagram of the improved high-pressure brazed plate gas cooler for a transcritical CO2 heat pump in this application.

[0038] The meanings of the reference numerals in the drawings are as follows:

[0039] 10 - end plate, 11 - connecting pipe, 12 - honeycomb cell;

[0040] 21 - herringbone corrugated plate on the high-pressure CO2 side, 22 - herringbone corrugated plate on the low-pressure water side, 23 - load-bearing unit;

[0041] 30 - corner hole, 31 - support and reinforcement gasket ring;

[0042] p- Corrugation pitch, β- Corrugation angle, t - plate thickness, b - corrugation depth. SPECIFIC EMBODIMENTS

[0043] The technical solutions of the present invention will be described in more detail below in conjunction with the embodiments.

[0044] For easy understanding, the structure of the high-pressure brazed plate gas cooler for a transcritical CO2 heat pump involved in this application is described. It should be emphasized that the structure of this high-pressure brazed plate gas cooler can refer to the structure of plate heat exchangers on the market. The following is only a general description and not a limitation to the high-pressure brazed plate gas cooler.

[0045] See Figure 1, A high-pressure brazed plate gas cooler for a transcritical CO2 heat pump, comprising a corrugated plate heat exchange area and end plates 10 covering the upper and lower sides of the corrugated plate heat exchanger. The corrugated plate heat exchange area is formed by alternately and reversely stacking herringbone corrugated plates 21 on the high-pressure CO2 side and herringbone corrugated plates 22 on the low-pressure water side, and the crests of adjacent corrugated plates are brazed and connected. The herringbone corrugated plates 21 on the high-pressure CO2 side and the herringbone corrugated plates 22 on the low-pressure water side have the same structure, both are double-sided corrugated plates, and the herringbone corrugations on the plates are symmetrically arranged about the axis of symmetry, and the axis of symmetry is arranged in the middle along the length direction of the plate. In this application, the shape of the herringbone corrugations on the plate can refer to Fig. 2 in the paper "Longo G A, Gasparella A. Heat transfer and pressure drop during HFC refrigerant vaporisation inside a brazed plate heat exchanger[J]. International Journal of Heat & Mass Transfer, 2007, 50(25-26):5194-5203".

[0046] On each corrugated plate, two groups of corner holes 30 are arranged symmetrically about the axis of symmetry of the herringbone corrugation, and the two groups of corner holes 30 are respectively arranged at both ends of the corrugated plate in the length direction. The corner holes 30 are stacked in the corrugated plate heat exchange area to form a CO2-side fluid channel communicating with the herringbone corrugated plate 21 on the high-pressure CO2 side and a water-side fluid channel communicating with the herringbone corrugated plate 22 on the low-pressure water side respectively. The corrugated plate heat exchange area is connected to the end plate 10 by brazing, and corresponding nozzles 11 are arranged on the end plate 10 to connect with the CO2-side fluid channel and the water-side fluid channel.

[0047] The corrugated plate heat exchange area is the design area of the high-pressure brazed plate gas cooler described in this application. The design factors include the center distance between two adjacent crests of the corrugation, that is, the corrugation pitch p , the vertical distance between the crest and the trough in a single herringbone corrugated plate, that is, the corrugation depth b , the vertical distance from the top to the bottom surface in a single herringbone corrugated plate, that is, the plate thickness t .

[0048] In the structure of the high-pressure brazed plate gas cooler for a transcritical CO2 heat pump, an overly thick brazing filler metal will result in too large a gap in the welded joint. During vacuum brazing in the furnace, due to the good fluidity of pure copper, its gap filling ability may be affected, resulting in a virtual weld in the brazed joint, thus affecting the structural strength. In addition, the accumulation of excess brazing filler metal reduces the flow area, affects the heat transfer and resistance characteristics, and also greatly increases the risk of scaling and blockage when generating high-temperature hot water above 65°C. Therefore, on the premise of meeting the brazing requirements, the thickness of the brazing filler metal should be as thin as possible.

[0049] For convenient design, the structure of the high-pressure brazed plate gas cooler for transcritical CO2 heat pumps was adjusted in the early stage of this application. Among them, the thickness selection of the brazing filler metal was considered in coordination with the structural strength, prevention of high-temperature hot water scaling and blockage, and welding process. The thermal and resistance characteristics of the high-pressure brazed plate gas cooler were considered in coordination, and the thickness of the brazing filler metal and the corrugation angle in the herringbone corrugated plate β were set as fixed values and used by default in the design.

[0050] The method involved in this application will be described in detail below. For convenient calculation, this application defines the space formed by the troughs after the wave crests of adjacent corrugated plates are brazed and connected as the bearing unit 23, and the orthographic projection area of the bearing unit 23 is A s , and the brazing filler metal attachment area in the orthographic projection area is A t ;

[0051] Then, the design method of the structure of the high-pressure brazed plate gas cooler for transcritical CO2 heat pumps includes the following steps:

[0052] S1. Set the corrugation pitch as the value of p according to experience, calculate the minimum value of the brazing filler metal attachment area A t according to the following formula, and obtain the side length l of the brazing filler metal attachment area;

[0053] ;

[0054] ;

[0055] ;

[0056] In the formula, P is the design pressure, P ≥ 14 MPa; is the allowable stress of the brazing joint material (pure copper T2 or T1) for brazing adjacent two corrugated plates at the working temperature T (150°C ≤ T ≤ 200°C), and its value is determined according to GB / T 5231-2012 or the material property manual or the technical data provided by the manufacturer, with the unit of MPa;

[0057] S2. Set the corrugation depth as the value of b according to experience. Since the side length l is the laying length of the wave crest of the corrugation along the curve extension direction, when the corrugation depth is determined, the corrugation curve can be determined, so the plate thickness tIt can be equivalently calculated as the thickness of the elliptical head of a pressure vessel: Calculate the thickness of the plate according to the strength design theory of the elliptical head of a pressure vessel (the head material is selected as 316L, and the allowable stress is taken as its value at 200 °C). t The current value of t m :

[0058] ;

[0059] ;

[0060] In the formula is the allowable stress of the plate material at the design temperature, K is the shape factor of the elliptical head, and the value is taken according to Table 7-1 of GB / T 150.3-2024;

[0061] S3. Set the thickness of the plate according to experience t The range of[t min ,t max , if t m ∈[t min ,t max , then fix the current corrugation pitch p and the thickness of the plate t m ; otherwise, adjust the corrugation pitch p and / or the corrugation depth b until t m ∈[t min ,t max ;

[0062] In this step S3, since the thickness of the finished plate rolled by the processing factory is generally 0.3 mm, 0.4 mm,..., 0.8 mm, etc., the range of the thickness of the plate t The range of[t min ,t max is specifically 0.3mm ≤ t ≤ 0.8mm, and t is a decimal with one decimal place; round up the calculated value of the t m to one decimal place and then compare.

[0063] S4. Based on finite element analysis, refer to the fatigue test method in 6.3.5 of "JB / T 8701-2019 Plate Heat Exchangers for Refrigeration" to calculate the maximum stress amplitude N under the cyclic pressure fatigue condition of S alt1 cycles; According to the design of austenitic stainless steelS - N The curve (in page 293 of GB / T 4732.4-2024 Figure 4 ), obtain the S - N allowable stress amplitude under the N cycle in the curve S alt2 .

[0064] If S alt1 ≤ S alt2 , then confirm the corrugation pitch p、 corrugation depth b , sheet thickness t m values, and complete the design;

[0065] If S alt1 > S alt2 , first find the position of the point with the maximum local stress in the design structure. If the maximum point is located at the welded joint, keep the corrugation depth b and sheet thickness t m unchanged, and only adjust the corrugation pitch p to increase the brazing filler metal spreading area; otherwise, keep the corrugation pitch p unchanged, and adjust the corrugation depth b and sheet thickness t m ; adjust until S alt1 ≤ S alt2 , and obtain the confirmed corrugation pitch p、 corrugation depth b , sheet thickness t m values, and complete the design.

[0066] In this method, the empirical range of the corrugation pitch p is 2.5~5.0 mm, and the empirical range of the corrugation depth b is 1.2~1.8 mm; adjust the corrugation pitch p and / or the value of the corrugation depth b by single adjustment either alternatively or simultaneously. The single adjustment amplitude of the corrugation pitch p is 0.1 mm, the single adjustment amplitude of the corrugation depth b is 0.05 mm, and the single adjustment amplitude of the sheet thickness t m is 0.1 mm.

[0067] In this method, for calculating S alt1 the design structure, the adjacent 9 load-bearing units 23 are taken for finite element analysis.

[0068] In a complete design scheme, the steps are as follows:

[0069] For a high-pressure brazed plate-type gas cooler for a transcritical CO2 heat pump, the corrugation angle β is set to 120° to increase the number of heat transfer units on the weak heat transfer side (CO2 side).

[0070] S1. According to experience, the corrugation pitch is set to p the value of 4.8 mm, and the minimum value of the brazing filler metal attachment area A t is calculated according to the following formula, and the side length l of the brazing filler metal attachment area is obtained;

[0071] ;

[0072] ;

[0073] ;

[0074] In the formula, P is the design pressure, P = 14 MPa; is the allowable stress of the brazed joint (the material is pure copper T2) where two adjacent corrugated plates are brazed at the working temperature T ( T = 200 °C), determined according to GB / T 5231-2012, and the unit is MPa;

[0075] In this step, the calculated minimum value of the brazing filler metal attachment area A t is 5.7 mm 2 , and the side length l of the brazing filler metal attachment area is 2.57 mm;

[0076] S2. According to experience, the corrugation depth b is set to 1.65 mm, and the current value t of the plate thickness t m is calculated based on the strength design theory of the elliptical head of a pressure vessel (the head material is selected as 316L, and the allowable stress is taken as its value at 200 °C):

[0077] ;

[0078] ;

[0079] In the formula is the allowable stress of the plate material at the design temperature, K is the shape factor of the ellipsoidal head, which is taken according to Table 7-1 of GB / T 150.3-2024; in this step, the calculated plate thickness t m is 0.51 mm.

[0080] S3. Set the plate thickness according to experience, 0.3 ≤ t ≤ 0.8, and t is a decimal with one digit after the decimal point, t m is rounded to 0.6 mm, which satisfies t m ∈ [t min , t max , so the current corrugation pitch p and the plate thickness t m are fixed;

[0081] S4. Select 9 load-bearing units 23 in adjacent local areas as the design structure. Based on the finite element analysis design method, calculate the maximum stress amplitude S alt1 of the design structure under the cyclic pressure fatigue condition of 100,000 times. According to the design S - N curve of austenitic stainless steel, obtain the allowable stress amplitude at S - N cycles in the N - S alt2 and S alt1 relationship to confirm the values of the corrugation pitch p、 corrugation depth b, and plate thickness t m .

[0082] In this design scheme, through finite element analysis, the maximum stress amplitude S alt1 in the structure is 184 MPa. According to the design S - N curve of austenitic stainless steel, it can be seen that S alt2 = 200 MPa. That is S alt1 ≤ S alt2 , which meets the requirements. Therefore, the corrugation pitch p of the corrugated plate in this design is 4.8 mm 、 The corrugation depth b is 1.65 mm, and the plate thicknesst m is 0.6 mm.

[0083] Furthermore, after the design of the corrugated plate heat exchange area is completed, the pressure-bearing weak links of the high-pressure brazed plate type gas cooler, namely the nozzle 11, the outermost corrugated plate and the corrugated plate corner hole 30 area, are adaptively adjusted. Refer to Figure 5 , in which the end plate 10 is selected to be thickened, for example, a 2 mm thick plate is used to increase the brazing area of the nozzle. A support reinforcing gasket 31 is added at the edge of the corner hole 30 of the herringbone corrugated plate 21 on the high-pressure CO2 side and / or the herringbone corrugated plate 22 on the low-pressure water side to improve the pressure-bearing capacity of the corrugated plate corner hole 30 area. The material of the support reinforcing gasket 31 is 304 or 316, its thickness is equal to twice the corrugation depth, and it is provided with a notch for the drainage of CO2 in the corner hole area; a reliable connection is formed between the support reinforcing gasket 31 and the corrugated plate by brazing. A turbulent flow structure is also provided in the corrugated plate corner hole 30 area to enhance the pressure-bearing and heat exchange capacities of the corrugated plate corner hole 30 area. The turbulent flow structure is multiple groups of irregular-shaped cells 12, and the thickness of the cells 12 is equal to twice the corrugation depth.

[0084] Furthermore, the inner diameter of the CO2 side inlet nozzle 11 is adjusted to be larger than the inner diameter of the outlet nozzle 11 to match the drastic change in the density of CO2 and minimize the flow pressure drop at the corner hole 30 as much as possible.

[0085] Verification

[0086] Currently, there are no mature domestic high-pressure fully brazed plate type CO2 gas coolers on the market. Taking the brazed plate type condenser in a common Freon heat pump unit as an example, the corrugation pitch of its corrugated plate p is 7.5 mm 、 The corrugation depth b is 1.95 mm, and the plate thickness t m is 0.4 mm. Its design pressure is 5 MPa, and the bursting pressure is usually not higher than 20 MPa.

[0087] For the transcritical CO2 high-pressure brazed plate type gas cooler developed after being redesigned by the solution of this application, the corrugation angle of the corrugated plate β is 120°, the corrugation pitch p is 2.8 mm 、 The corrugation depth b is 1.4 mm, and the plate thickness t m is 0.3 mm. After the bursting test, the bursting pressure reaches 50 MPa, which is greater than 3 times the design pressure. In addition, no leakage is found after 100,000 pressure fatigue cycle tests. All have met the requirements of the product type test.

[0088] The developed air cooler prototype has passed the bursting test, with a bursting pressure reaching 50 MPa, and no leakage was found after 100,000 pressure fatigue cycle experiments.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A structural design method for a high-pressure brazed plate air cooler for a transcritical CO2 heat pump, characterized in that: A plurality of herringbone corrugated plates are stacked alternately and reversely, and the crests of adjacent corrugated plates are brazed and connected to form the design area of ​​the high-pressure brazed plate-type air cooler; the corrugation angle in the herringbone corrugated plate is defined as β , the distance between the centers of two adjacent wave peaks of the corrugation, that is, the corrugation pitch is p , the vertical distance between the crest and trough of a single herringbone corrugated plate, i.e. the corrugation depth, is b , the vertical distance from the top to the bottom of a single herringbone corrugated plate, i.e. the thickness of the plate, is t ; The space formed by the troughs of adjacent corrugated plates after brazing is defined as a load-bearing unit. The orthographic projection area of ​​the load-bearing unit is A s The solder attachment area in the orthographic projection area is A t ; The design methodology includes the following steps: S1. According to experience, the corrugation pitch is set to p The solder attachment area is calculated according to the following formula A t The minimum value of the solder attachment area is obtained l ; ； Where, P is the design pressure, P≥14MPa; ] T It is the allowable stress of the brazing joint material between two adjacent corrugated plates, in MPa; S2. Set the corrugation depth based on experience b The plate thickness is calculated based on the strength design theory of the elliptical head of the pressure vessel. t Current value of t m : ； In the formula is the allowable stress of the plate material at the design temperature, K is the shape coefficient of the elliptical head, which is taken according to Table 7-1 of GB / T150.3-2024; S3. Set the plate thickness based on experience t The range of [t min ,t max ],like t m ∈[t min ,t max ], then fix the current corrugation pitch p , Corrugation Depth b and plate thickness t m Otherwise, adjust the corrugation pitch p and / or corrugation depth b until the value of t m ∈[t min ,t max ]; S4. Based on finite element analysis, the design structure is calculated and N Maximum stress amplitude under sub-cyclic pressure fatigue condition S alt1 ; Design based on austenitic stainless steel S - N curve, obtain the S - N In the curve N Allowable stress amplitude S under the cycle alt2 ,like S alt1 ≤S alt2 , then confirm the corrugation pitch p、 Corrugation Depth b , Plate thickness t m The design is completed; if S alt1 >S alt2 , then adjust the corrugation pitch p Or adjust the ripple depth b and plate thickness t m until the value of S alt1 ≤S alt2 , get the confirmed corrugation pitch p、 Corrugation Depth b , Plate thickness t m value to complete the design.

2. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: The herringbone corrugated plate is a double-sided corrugated plate, the herringbone corrugations are axisymmetrically arranged, and the axis of symmetry is arranged in the center along the length direction of the plate.

3. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: The corrugation pitch p The empirical range is 2.5~5.0 mm, and the corrugation depth b The empirical range is 1.2~1.8 mm.

4. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: The value of the allowable stress is determined according to the material performance manual or the technical data provided by the manufacturer; in step S1, the allowable stress is based on the brazing joint material being pure copper T2 or pure copper T1, and the working temperature being 150°C ≤ T ≤200℃; in step S2, the allowable stress is based on the head material being 316L and the working temperature T ≤200℃ value.

5. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: In step S3, the thickness of the plate is set t The range of [t min ,t max ]Specifically 0.3mm≤ t ≤0.8mm, and t is a decimal place; the calculated t m The value is rounded up to one decimal place for comparison.

6. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 3, characterized in that: In step S3, the corrugation pitch is adjusted p and / or corrugation depth b The value of either or both can be adjusted at once, the corrugation pitch p The single adjustment range is 0.1 mm, and the corrugation depth b The single adjustment range is 0.05 mm.

7. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: In step S4, for calculating S alt1 The designed structure takes nine adjacent load-bearing units for finite element analysis.

8. The structural design method of a high-pressure brazed plate air cooler for a transcritical CO2 heat pump according to claim 1, characterized in that: In step S4, when S alt1 >S alt2 When the corrugation depth is kept constant, first find the location of the maximum local stress point in the design structure. If the maximum point is located at the welded joint, b and plate thickness t m No change, only the corrugation pitch is adjusted p To increase the solder spreading area, the corrugation pitch p The single adjustment range is 0.1 mm; otherwise, the corrugation pitch is maintained p No change, adjust the ripple depth b and plate thickness t m , the corrugation depth b The single adjustment range is 0.05 mm, the plate thickness t m The single adjustment range is 0.1 mm.

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