Strength analysis and optimization method for sectional type liquid cooling condenser

Abstract

The invention discloses an intensity analysis and optimization method for a sectional type liquid cooling condenser, which comprises the following steps of: performing a pressure alternating experiment on an original structure of the sectional type liquid cooling condenser, recording the number of cycles, and checking the position of a leakage point through a water test; finite element model analysis is carried out on the original structure model, and the stress of the leakage point is determined; performing structure optimization, repeating the finite element analysis process, and recording the stress of the original leakage point after optimization; and determining the stress reduction ratio, and judging whether the optimized structure can meet the strength requirement or not according to the ratio of the target cycle index of the pressure alternating experiment to the cycle index of the original structure. According to the optimization method, the corrugation pitch and the corrugation plane width of the herringbone corrugated plate of the sectional type liquid cooling condenser are changed, and the number of welding spots and the welding area are increased, so that the strength of the sectional type liquid cooling condenser is enhanced. According to the method, the verification cost in a design period is reduced while the accuracy is met in a mode of combining experiments and simulation.

Description

Technical Field

[0001] The present invention relates to the field of optimization design of key components of an electric vehicle thermal management system, and particularly to an analysis and optimization method for the performance of a liquid-cooled condenser. Background Art

[0002] The liquid-cooled condenser of an electric vehicle is a heat exchange device between liquids, and is an important part of the electric vehicle thermal management system. Its main function is to cool and convert the high-temperature and high-pressure gaseous refrigerant into a liquid state, thereby releasing heat and maintaining the normal operation of the system. The liquid-cooled condenser cools by means of liquid cooling, which has higher heat dissipation efficiency and better heat dissipation effect compared with traditional air cooling. The working principle of the liquid-cooled condenser is that the liquid coolant (usually water or antifreeze) circulates inside the condenser to take away the heat in the refrigerant and transfer it to the external environment. The refrigerant is compressed into a high-temperature and high-pressure gas in the compressor and then enters the condenser. The high-temperature and high-pressure refrigerant flows through the pipeline in the condenser and exchanges heat with the coolant, and the refrigerant cools and is converted into a liquid state.

[0003] The refrigerant in the liquid-cooled condenser has a very high pressure, and the pressure of the refrigerant is usually dozens of atmospheric pressures. Limited by the overall size and brazing process, if the structural strength of the condenser is insufficient, refrigerant leakage is likely to occur during operation, posing a certain safety hazard. Therefore, the structural strength is the main design parameter to be considered when designing the liquid-cooled condenser.

[0004] In actual engineering applications, the strength of the liquid-cooled condenser is often tested through a pressure alternating experiment. Or the strength is calculated by means of simulation. However, the test cycle of the former is very long, and once the model of the liquid-cooled condenser is modified in design, it is necessary to remold, and the test cost is high. And the second analysis method has high hardware requirements. Since the number of plates of the liquid-cooled condenser is large and the structure is complex. If a complete model is used for simulation calculation, there will be problems such as a large number of meshes and a long calculation time. In the process of structural optimization, if the above methods are used to verify the strength of each version of the liquid-cooled condenser, there is a problem of too high design cycle cost. In addition, there is less structural optimization for the brazed liquid-cooled condenser at present, and the attention to fatigue or strength is mainly on the test process and test technology. For example, in a fatigue test process of a heat exchanger (CN202410615077.3), but based on the test results, a relatively clear structural optimization direction is not given. Therefore, a method combining experiment and simulation is proposed to analyze the strength of the liquid-cooled condenser, which reduces the test cost and calculation complexity while having high accuracy. Summary of the Invention

[0005] The object of the present invention is to address the problems of excessive cycle time and high cost in obtaining the strength of a liquid-cooled condenser in the above-mentioned prior art, and to propose a segmented liquid-cooled condenser strength analysis method combining experiments and simulations.

[0006] The present invention is achieved by at least one of the following technical solutions.

[0007] A segmented liquid-cooled condenser strength analysis and optimization method includes the following steps:

[0008] (1) Conduct a pressure alternating experiment using the structure of the segmented liquid-cooled condenser before optimization, and record the number of cycles when the structure of the segmented liquid-cooled condenser fails.

[0009] (2) Locate the failure points of the failed segmented condenser.

[0010] (3) Establish a finite element model based on the segmented liquid-cooled condenser before optimization, conduct FEM analysis, and record the stress and stress point positions of the local peak points of the stress near the leakage point.

[0011] (4) Optimize the structure of the segmented liquid-cooled condenser before optimization, and repeat the FEM analysis in step (3).

[0012] (5) After the structure is optimized, repeat the stress analysis in step (3), conduct FEM analysis on the segmented liquid-cooled condenser after the structure is optimized, and compare the stress magnitudes at the leakage points. If the stress decreases, the structure optimization scheme can increase the strength of the segmented liquid-cooled condenser.

[0013] Further, in step (1), the failure judgment method: during the experimental test, use a leakage / flow detector to record the flow rates at the inlet and outlet of the segmented liquid-cooled condenser; if the outlet flow rate suddenly changes or the difference between the inlet and outlet flow rates is greater than 5%, it is determined that the segmented liquid-cooled condenser has failed.

[0014] Further, in step (2), adopt the water inspection method to immerse the failed segmented liquid-cooled condenser in water, observe whether there are bubbles, and the position where bubbles emerge is the failure point; remove one layer of brazed corrugated plate each time after observation, and then repeat the above immersion step to record the failure point position.

[0015] Further, in step (3), the CAD model used to construct the finite element model during stress analysis is the minimum unit model, that is, each section area of the segmented liquid-cooled condenser is composed of the fewest number of plates.

[0016] Further, in step (3), the finite element model is meshed using tetrahedral elements. When meshing, it is necessary to constrain the number of mesh layers in the thickness direction of the plates of the segmented liquid-cooled condenser. Fixed constraints are applied to the mounting holes, and all six degrees of freedom of the mounting holes are restricted. Pressure conditions are applied to the inner surface of the refrigerant flow channels.

[0017] Further, during the stress analysis process in step (3), record the positions of stress points where the stress is greater than 120 Mpa, and by looking up the corresponding material fatigue curve, find the stress corresponding to the failure cycle times.

[0018] Further, in step (4), optimize by changing the corrugation pitch and corrugation plane width of the herringbone corrugated plate of the segmented liquid-cooled condenser, and increase the number of solder joints and the welding area to enhance the strength of the segmented liquid-cooled condenser.

[0019] Further, the leakage point of the segmented liquid-cooled condenser is close to the inlet and outlet. By increasing the number of inlet and outlet bosses or changing the size of the inlet and outlet bosses, the welding area is increased, thereby increasing the strength of the segmented liquid-cooled condenser.

[0020] Further, the stress analysis is optimized according to the target cycle times n. In the material fatigue curve, find the stress σ corresponding to the target cycle times n. The stress at the target leakage point should be reduced by at least σ0 - σ, and the peak stress at the leakage point should be reduced to σ 01 -(σ0 - σ), where σ0 represents the stress corresponding to failure, and σ 01 represents the stress at the peak point.

[0021] Further, the structure of the segmented liquid-cooled condenser is a plate structure, composed of herringbone brazed corrugated plates. The segmented liquid-cooled condenser has an additional function of a liquid storage tank, and is divided into a gas-liquid two-phase section, a liquid storage section, and a subcooling section;

[0022] The segmented liquid-cooled condenser is shown as three regions. The three regions are a gas cooling region, a liquid storage region, and a liquid cooling region respectively. The gas cooling region is the gas-liquid two-phase section, and the liquid cooling region is the subcooling section. The gaseous refrigerant first enters the gas cooling region from the inlet. In the gas cooling region, the gaseous refrigerant exchanges heat with the coolant and becomes a liquid refrigerant, and a small part of the refrigerant remains gaseous. The gas-liquid two-phase refrigerant enters the liquid storage section, and the liquid storage region stores high-pressure liquid. The gas-liquid two-phase refrigerant enters the liquid cooling region. In the liquid cooling region, the gas-liquid two-phase refrigerant further exchanges heat with the coolant and becomes a subcooled refrigerant, ensuring that all the refrigerant at the condenser outlet is in a liquid state.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The strength analysis method of the segmented liquid-cooled condenser in the embodiment of the present invention can greatly reduce the cost of verifying structure optimization during the design cycle.

[0025] 2) The strength analysis method of the segmented liquid-cooled condenser in the embodiment of the present invention can accurately find the positions where the strength is weak, so as to facilitate structure optimization.

[0026] 3) The strength optimization method for the segmented liquid-cooled condenser in the embodiments of the present invention can significantly increase the strength of the segmented liquid-cooled condenser and increase the number of cycles of the pressure alternating experiment. Description of the Drawings

[0027] Figure 1 is a flowchart of a performance optimization method for a segmented liquid-cooled condenser according to an embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of the principle of a segmented liquid-cooled condenser according to an embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of the corrugated plate structure of the segmented liquid-cooled condenser in the embodiment;

[0030] Figure 4 is a schematic diagram of the distribution of refrigerant and coolant in the embodiment;

[0031] Figure 5 is a schematic diagram of the finite element model in the embodiment;

[0032] Figure 6 is a schematic diagram of the fatigue curve. Detailed Embodiments

[0033] To make the objectives, technical solutions and advantages of the present invention clearer and more definite, the following describes the present invention in further detail with reference to the accompanying drawings and by way of examples.

[0034] A segmented liquid-cooled condenser provided in this embodiment. This new type of segmented liquid-cooled condenser is based on the structure of a brazed corrugated plate condenser, and includes herringbone corrugated plates arranged in an alternating pattern. The herringbone corrugated plates arranged in an alternating pattern form a refrigerant side flow channel and a coolant side flow channel. The segmented liquid-cooled condenser is shown as three regions, namely a gas cooling region, a liquid storage region, and a liquid cooling region. Further, the gas cooling region is a gas-liquid two-phase section, and the liquid cooling region is a subcooling section. Specifically, the gaseous refrigerant first enters the gas cooling region from the inlet. In this region, most of the gaseous refrigerant exchanges heat with the coolant and becomes liquid refrigerant, and a small part of the refrigerant remains gaseous. Further, the gas-liquid two-phase refrigerant enters the liquid storage section. The liquid storage tank can effectively store the high-pressure liquid from the condenser, reduce the burden on the condenser, and ensure its continuous and efficient operation. Further, the gas-liquid two-phase refrigerant enters the subcooling section. In this region, the gas-liquid two-phase refrigerant further exchanges heat with the coolant and becomes subcooled refrigerant, ensuring that all the refrigerant at the outlet of the condenser is in a liquid state.

[0035] As Figure 1 shown, a strength analysis and optimization method for a segmented liquid-cooled condenser in this embodiment includes the following steps:

[0036] Step 1: Conduct a pressure cycling test using a segmented liquid-cooled condenser in its initial version (a segmented liquid-cooled condenser before optimization with insufficient strength that requires structural optimization). The pressure cycling test is carried out on a MAXIMATOR pulse test bench. The test equipment includes a pressure pump, a control system, a data acquisition system, etc. When the segmented liquid-cooled condenser leaks before reaching the required number of pressure cycles, it is judged as failed, indicating that the structural strength of this initial version of the segmented liquid-cooled condenser is unqualified.

[0037] In an embodiment of the present invention, a segmented liquid-cooled condenser is provided, and its principle and structure are as Figures 2 - 4 shown. Specifically, this segmented liquid-cooled condenser is of a plate structure, mainly composed of herringbone brazed corrugated plates. The corrugation structure is as Figure 3 shown. The herringbone directions between adjacent two plates are opposite, forming a refrigerant-side flow channel and a coolant-side flow channel. The refrigerant-side flow channel and the coolant-side flow channel are arranged in an alternating pattern. Further, on the basis of the condensation function of a general condenser, this segmented liquid-cooled condenser is provided with a liquid storage tank. Specifically, the segmented liquid-cooled condenser is manifested as three regions, namely a gas cooling region, a liquid storage region, and a liquid cooling region, as Figure 2 shown. Further, the gas cooling region is a gas-liquid two-phase section, and the liquid cooling region is a subcooling section. Specifically, gaseous refrigerant first enters the gas cooling region from the inlet. In this region, most of the gaseous refrigerant exchanges heat with the coolant and turns into liquid refrigerant, and a small part of the refrigerant remains gaseous. Further, the gas-liquid two-phase refrigerant enters the liquid storage section. The liquid storage tank can effectively store the high-pressure liquid from the condenser (refrigerant in an air-conditioning system and hydraulic oil in the experiment), reducing the burden on the condenser and ensuring its continuous and efficient operation. Further, the gas-liquid two-phase refrigerant enters the subcooling section. In this region, the gas-liquid two-phase refrigerant further exchanges heat with the coolant and turns into subcooled refrigerant, ensuring that all the refrigerant at the condenser outlet is in a liquid state. In this condenser, the refrigerant flow channel and the coolant flow channel are arranged in an alternating pattern, as Figure 4 shown.

[0038] In the above-mentioned embodiment of the invention, the condenser structure to be analyzed and optimized is denoted as the initial version. As long as there is any change in the structure of the subsequent condenser, it is no longer the initial version. Each time a stress analysis is performed after the structure optimization, the recorded structure version number is incremented by one.

[0039] As an embodiment, in the pressure alternating experiment method in the above-mentioned invention embodiment, only a medium is introduced into the refrigerant-side flow channel, the experimental pressure is controlled by a pressure pump, the experimental medium is hydraulic oil, and the medium temperature is 135 °C. The minimum pressure of the pressure alternation is set to 4 bar, and the maximum pressure is 30 bar. The pressure linearly increases from 4 bar to 30 bar at a pressure increase rate of 30 bar / s, and then linearly decreases from 30 bar to 4 bar. When the pressure reaches 4 bar and 30 bar, the pressure remains unchanged for 0.5 s respectively. This process is recorded as one cycle.

[0040] The failure condition of the above pressure alternating experiment: When the corrugated plate structure in the gas cooling area or the liquid cooling area of the segmented liquid-cooled condenser is damaged, at this time, the refrigerant in the refrigerant-side flow channel of the condenser will leak into the coolant-side flow channel in the condenser, and this situation is the failure condition.

[0041] The following are two judgment methods. It is possible to only observe the outlet flow rate, or to observe the inlet and outlet flow rates simultaneously, both of which can judge the failure: During the experimental test, a leakage / flow rate detector is used to record the inlet and outlet flow rates of the segmented liquid-cooled condenser. If the refrigerant outlet flow rate suddenly changes or the difference between the inlet and outlet flow rates is greater than 5%, it is judged that the segmented liquid-cooled condenser has failed. Record the number of cycles when the structure of the segmented liquid-cooled condenser fails as n0.

[0042] Step 2: Find the failure point of the failed segmented liquid-cooled condenser. The failed segmented liquid-cooled condenser is immersed in water using the water inspection method, and observe whether there are bubbles. The position where the bubbles emerge is the failure point. Specifically, since there are many plates in the liquid-cooled condenser, it is difficult to observe the internal failure points. Therefore, one layer of welding plate needs to be removed each time it is observed, and then the above-mentioned immersion step is repeated to record the position of the failure point.

[0043] Step 3: Conduct stress analysis. As Figure 4 shown, a finite element model is established based on the CAD model of the initial version of the segmented liquid-cooled condenser for FEM analysis. The CAD model used to construct the finite element model during stress analysis is the minimum unit model. Record the position of the stress points where the stress is greater than 120 Mpa and their stress magnitudes.

[0044] Due to the large number of plates in the segmented liquid-cooled condenser, the finite element model in Step 3 has a large number of meshes and a large amount of calculation. Therefore, the segmented liquid-cooled condenser needs to be simplified to the simplest structure. Specifically, the simplest structure is manifested as each section area of the segmented liquid-cooled condenser being composed of the fewest plates. As an embodiment, as Figure 5As shown, in this embodiment, a simplest model of a segmented liquid-cooled condenser is provided. The segmented liquid-cooled condenser in this embodiment is composed of three plates in the gas cooling zone, three plates in the liquid storage zone, three plates in the liquid cooling zone, and partitions between the three sections, a total of eleven plates.

[0045] The finite element model of this example uses tetrahedral elements, and the average size of the element mesh is 0.5 mm. Since the plates of the segmented liquid-cooled condenser are relatively thin, when performing mesh division, it is necessary to constrain the number of mesh layers in the thickness direction of the plates to avoid causing characteristic errors. Further, fixed constraints are applied to the mounting holes, and all six degrees of freedom of the mounting holes are restricted. A pressure condition is applied to the inner surface of the refrigerant flow channel, and the pressure magnitude is 30 bar.

[0046] The stress analysis does not consider the overall stress maximum point, but records the local peak points of the stress near the leakage point, and the stress at the peak point is denoted as σ 01 . The schematic diagram of the material fatigue curve is as Figure 6 , in the figure, as the stress decreases, the theoretical number of cycles increases. When the stress is less than σ x , theoretically, it can cycle infinitely. By looking up the corresponding material fatigue curve, the stress σ0 corresponding to the failure cycle number n0 is found. The form of the fatigue curve is as Figure 6 , and the specific actual coordinate values are different for different materials.

[0047] Step 4: Perform structural optimization. Specifically, by changing the corrugation pitch and corrugation plane width of the herringbone corrugated plates of the segmented liquid-cooled condenser, increasing the number of solder joints and the welding area, to enhance the strength of the segmented liquid-cooled condenser. If the leakage point of the segmented liquid-cooled condenser is close to the inlet and outlet, by increasing the number of inlet and outlet bosses or changing the size of the inlet and outlet bosses, to increase the welding area, and thus increase the strength of the segmented liquid-cooled condenser.

[0048] Step 5: Analyze the results of strength optimization.

[0049] In the structural optimization, optimization is carried out according to the target cycle number n. The magnitude of the stress σ corresponding to the target cycle number n is found in the material fatigue curve. Specifically, the stress at the target leakage point should be reduced by at least σ0 - σ, that is, the peak stress at the leakage point should be reduced to σ 01 -(σ0 - σ).

[0050] After each structural optimization, repeat the stress analysis step in Step 3, perform FEM analysis on the optimized segmented liquid-cooled condenser, and compare the stress magnitudes at the leakage point. If the stress decreases, the structural optimization scheme can increase the strength of the segmented liquid-cooled condenser. The stress at the leakage point needs to be reduced to σ 01 -(σ0 - σ), otherwise continue with the structural optimization.

[0051] A pressure alternating test is carried out every time a round of optimization is completed. If new leakage points appear, repeat the strength analysis process until the strength of the segmented liquid-cooled condenser meets the requirements.

[0052] The above-described embodiments merely represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A strength analysis and optimization method for a segmented liquid cooling condenser, characterized in that: The following steps are involved: (1) Use the segmented liquid-cooled condenser structure before optimization to conduct a pressure alternation experiment and record the number of cycles when the segmented liquid-cooled condenser structure fails; (2) Find the failure point of the failed sectional condenser; (3) Establish a finite element model based on the segmented liquid-cooled condenser before optimization, perform FEM analysis, and record the stress and stress point position of the local peak point of stress near the leakage point; (4) Optimize the structure of the segmented liquid-cooled condenser before optimization and repeat the FEM analysis in step (3); (5) After structural optimization, repeat the stress analysis in step (3), perform FEM analysis on the segmented liquid-cooled condenser after structural optimization, and compare the stress magnitude at the leakage point. If the stress is reduced, the structural optimization scheme can increase the strength of the segmented liquid-cooled condenser.

2. A segmented liquid cooling condenser strength analysis and optimization method according to claim 1, characterized in that: In step (1), the failure judgment method is as follows: during the experimental test, a leakage / flow detector is used to record the inlet and outlet flow of the segmented liquid-cooled condenser; if the outlet flow changes suddenly or the difference between the inlet and outlet flow is greater than 5%, the segmented liquid-cooled condenser is judged to have failed.

3. A segmented liquid cooling condenser strength analysis and optimization method according to claim 1, characterized in that: In step (2), the failed segmented liquid-cooled condenser is immersed in water using a water inspection method to observe whether there are bubbles. The location where bubbles emerge is the failure point. After each observation, a layer of brazed corrugated plate is removed, and then the above immersion steps are repeated to record the location of the failure point.

4. The strength analysis and optimization method of a segmented liquid cooling condenser according to claim 1, characterized in that: In step (3), the CAD model used to construct the finite element model during stress analysis is a minimum unit model, that is, each section of the segmented liquid-cooled condenser is composed of the least number of plates.

5. A segmented liquid cooling condenser strength analysis and optimization method according to claim 1, characterized in that: In step (3), the finite element model is meshed using tetrahedral units. When meshing, it is necessary to constrain the number of mesh layers in the thickness direction of the segmented liquid-cooled condenser plate. The mounting holes are fixedly constrained, the six degrees of freedom of the mounting holes are restricted, and pressure conditions are applied to the inner surface of the refrigerant flow channel.

6. A segmented liquid cooling condenser strength analysis and optimization method according to claim 1, characterized in that: During the stress analysis process of step (3), the positions of stress points where the stress is greater than 120 MPa are recorded, and the stress corresponding to the number of failure cycles is found by searching the corresponding material fatigue curve.

7. A segmented liquid cooling condenser strength analysis and optimization method according to claim 1, characterized in that: In step (4), the strength of the segmented liquid-cooled condenser is enhanced by changing the corrugation pitch and corrugation plane width of the herringbone corrugated plate of the segmented liquid-cooled condenser and increasing the number of welding points and welding area for optimization.

8. A segmented liquid cooling condenser strength analysis and optimization method according to claim 7, characterized in that: The leakage point of the segmented liquid-cooled condenser is close to the inlet and outlet. By increasing the number of inlet and outlet bosses or changing the size of the inlet and outlet bosses, the welding area is increased, thereby increasing the strength of the segmented liquid-cooled condenser.

9. The strength analysis and optimization method of a segmented liquid cooling condenser according to claim 1, characterized in that: Stress analysis is optimized according to the target number of cycles n. The stress σ corresponding to the target number of cycles n is found in the material fatigue curve. The stress at the target leakage point should be reduced by at least σ0-σ, and the peak stress at the leakage point should be reduced to σ 01 -(σ0-σ), where σ0 represents the stress corresponding to failure, σ 01 Represents the stress at the peak point.

10. The strength analysis and optimization method of a segmented liquid cooling condenser according to claim 1, characterized in that: The structure of the segmented liquid-cooled condenser is a plate structure, which is composed of a herringbone brazed corrugated plate. The segmented liquid-cooled condenser adds the function of a liquid storage tank and is divided into a gas-liquid two-phase section, a liquid storage section and a supercooling section. The segmented liquid-cooled condenser is composed of three areas, namely the gas cooling area, the liquid storage area and the liquid cooling area; the gas cooling area is a gas-liquid two-phase area, and the liquid cooling area is a supercooling area. The gaseous refrigerant first enters the gas cooling area from the inlet. In the gas cooling area, the gaseous refrigerant exchanges heat with the coolant to become liquid refrigerant, and a small part of the refrigerant remains in gaseous state; the gas-liquid two-phase refrigerant enters the liquid storage area, and the liquid storage area stores high-pressure liquid; the gas-liquid two-phase refrigerant enters the liquid cooling area. In the liquid cooling area, the gas-liquid two-phase refrigerant further exchanges heat with the coolant to become supercooled refrigerant, ensuring that the condenser outlet is all liquid refrigerant.

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