A method for process control and online quality assessment of hydraulic expansion joints for tube-fin heat exchangers

Abstract

The present invention discloses a method for controlling the hydraulic expansion process and online quality evaluation of a tube-and-fin heat exchanger. A method for controlling the hydraulic expansion process and comprehensively evaluating the expansion quality of a tube-and-fin heat exchanger by monitoring and analyzing the relationship between the two parameters of the outer diameter of the heat exchange tube and the expansion pressure and their set target values ​​during the hydraulic expansion process of a tube-and-fin heat exchanger. The method is implemented according to the following steps: Step 1, setting the expansion parameters: setting the target diameter and target pressure of the hydraulic expansion parameters in the system; Step 2, installation and fixing: installing the heat exchange tube and fin assembly to be expanded on the hydraulic expansion device; Step 3, filling with high-pressure fluid medium and starting expansion; Step 4, monitoring and analyzing data and evaluating the expansion quality; Step 5, unloading the hydraulic pressure and removing the expanded heat exchanger assembly. The present invention is used for controlling the hydraulic expansion process and online quality evaluation of a tube-and-fin heat exchanger.

Description

Technical Field

[0001] The present invention relates to an online evaluation method for the hydraulic expansion quality of a tube-fin heat exchanger, and more particularly to a method for controlling the hydraulic expansion process and comprehensively evaluating the expansion quality of a tube-fin heat exchanger by monitoring and analyzing the relationship between the outer diameter of the heat exchange tube and the expansion pressure and their set target values ​​during the hydraulic expansion process of the tube-fin heat exchanger. Background Art

[0002] Air conditioners primarily consist of three parts: the refrigeration system, the air circulation system, and the electronic control system. The refrigeration system, the core of the air conditioner, consists of components such as the compressor, condenser, expansion valve, and evaporator. Tube-and-fin heat exchangers, offering high heat exchange efficiency, low refrigerant charge, and excellent corrosion resistance, are widely used in the condensers and evaporators of air conditioning refrigeration systems. They are key components in determining the energy efficiency and operational stability of air conditioners. Considering the hardness, strength, ductility, and thermal conductivity of metals, tube-and-fin heat exchangers primarily use copper or aluminum alloy internally threaded heat exchange tubes as refrigerant flow channels. Aluminum foil fins are installed on the outside of the tubes to increase the heat exchange area with the external environment. To reduce thermal resistance and ensure good heat transfer efficiency between the tubes and fins, expansion joints are required to create a tight, interference fit between the tubes and fins.

[0003] Currently, tube-fin heat exchangers are mostly manufactured using the traditional mechanical expansion method. This method involves pressing a mechanical expansion bead, whose diameter is larger than the inner diameter of the heat exchange tube, into the tube, causing the tube to plastically deform. This increases the tube diameter and contacts the fins, causing some deformation. Once the force exerted by the mechanical expansion bead on the tube is unloaded, both the tube and the fin undergo elastic recovery deformation simultaneously, with the elastic recovery deformation of the tube being less than that of the fins, thus forming an interference fit between the tube and the fin. However, the uneven force exerted by the mechanical expansion bead on the inner wall of the tube during expansion can easily lead to problems such as buckling, bursting, and internal thread damage.

[0004] Hydraulic expansion utilizes a liquid medium to apply a uniform load to the inner tube wall, causing the tube to bulge. This method overcomes the uneven force encountered during mechanical expansion and is an advanced technology suitable for the expansion of multi-layer hollow tube components. This flexible, uniform load applied by the liquid medium during hydraulic expansion avoids the hard contact of the expansion bead with the inner tube wall during mechanical expansion. This results in more uniform tube deformation without damaging the internal threads, resulting in better tube-fin contact and higher heat transfer efficiency. As an efficient and reliable expansion technology, hydraulic expansion has garnered significant attention in the air conditioning industry.

[0005] In order to ensure the expansion quality between the heat exchange tube and the fin during hydraulic expansion and avoid the phenomenon of the heat exchange tube bursting due to excessive pressure, it is necessary to accurately control the hydraulic expansion process parameters and reasonably evaluate the expansion quality. gBulging to target diameter D±δ D In the range, δ D To allow diameter deviation, the target diameter D is equal to the initial diameter D of the heat exchange tube. g and the initial diameter of the fin hole D c Satisfying the relationship D>D g >D c Reasonable target diameter D and its allowable deviation δ D This needs to be confirmed through sufficient experimental verification.

[0006] Assuming that the heat exchange tube satisfies the bilinear strain hardening characteristics expressed by formula (1), the target expansion pressure value p required for expansion can be estimated by formula (2), which corresponds to the expansion pressure value required when the heat exchange tube and the fin are just in contact (Hong Ying, Wang Xuesheng, Chen Qinzhu, Wang Jianfu. Bilinear simplification of material model in theoretical calculation of hydraulic expansion tube [J]. Mechanical Design and Research, 2018, 34(01): 199-202.). The target expansion pressure value and its allowable deviation for actual production need to be verified through experiments.

[0007]

[0008]

[0009] Where, σ is the flow stress when the heat exchange tube is deformed, σ s is the yield strength of the heat exchange tube, ε is the strain generated by the heat exchange tube, E is the elastic modulus of the heat exchange tube, A1 and A2 are constants, and D g , t g are the initial diameter and wall thickness of the heat exchange tube, D c is the initial diameter of the fin hole.

[0010] From formula (2), it can be seen that for a certain diameter of heat exchange tube, the expansion pressure p required for expansion is mainly determined by the wall thickness t of the heat exchange tube. g and yield strength σ s Decision, t g and σ s The smaller the value of , the smaller the expansion pressure p required to expand the heat exchange tube to the target diameter D. Assuming that the geometric dimensions and yield stress of the heat exchange tube blank are constant under ideal conditions, the expansion pressure required to achieve a good expansion of the tube fins will also be a constant value. Simply controlling the expansion pressure can achieve control over the expansion process.

[0011] However, the geometric dimensions and mechanical properties of different batches of tube billets actually fluctuate. Some tube billets may even have defects such as insufficient wall thickness and insufficient yield stress, which poses a challenge to the control of the hydraulic expansion process and the online quality assessment. In terms of hydraulic expansion process control, the expansion pressure required to achieve an effective expansion deformation of the tube billet fluctuates with the fluctuations in the tube billet's geometric dimensions and yield stress. Using only the expansion pressure to control the expansion process cannot fully consider the impact of fluctuations in tube billet size and performance, and may also cause problems such as excessive expansion or poor expansion of the heat exchange tube. In terms of online expansion quality assessment, the heat exchange tube billet itself may also have defects such as insufficient wall thickness and insufficient yield stress, which reduce the tube billet's ability to bear internal pressure and are prone to rupture during expansion. Even if it does not rupture, the defective heat exchanger obtained is prone to leakage and has a short service life.

[0012] Therefore, a method for controlling the hydraulic expansion process and online quality assessment of tube-fin heat exchangers is needed that can fully consider the influence of tube billet size fluctuation, yield stress fluctuation and defects. Summary of the Invention

[0013] The purpose of the present invention is to provide a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger. By monitoring and analyzing the relationship between the outer diameter of the heat exchange tube and the expansion pressure and their set target values, the expansion process is controlled and the expansion quality of the heat exchanger is comprehensively evaluated to achieve high-quality and high-efficiency expansion of the tube-fin heat exchanger.

[0014] The technical solution of the present invention:

[0015] A method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger comprises the following steps:

[0016] Step 1: Set the hydraulic expansion parameters: Set the target expansion diameter D, target expansion pressure value p, and allowable diameter deviation δ of the heat exchange tube in the control system 7. D and allowable pressure deviation δ p ;

[0017] Step 2: Install and fix:

[0018] The heat exchange tube 2 and fin 3 to be expanded are installed on the automatic hydraulic expansion device; the automatic hydraulic expansion device includes a workbench 9, an expansion pressure loading unit 11, an expansion pressure monitoring unit 12, a diameter monitoring unit 8 and a control system 7; the workbench 9 is equipped with a tube end sealing head 1, a support block 4, a cylinder 5 and a movable crossbeam 6, and the cylinder 5 can drive the movable crossbeam 6 to move up and down to realize the loosening and clamping of the heat exchange tube 2; the support block 4 is fixed on the movable crossbeam 6 and the workbench 9 respectively, and is used to support the heat exchange tube 2; the expansion pressure loading unit 11 fills the high-pressure fluid medium required for expansion into the heat exchange tube 2 through the hydraulic pipeline 10 and the tube end sealing head 1; the expansion pressure monitoring unit 12 is used to monitor the expansion pressure in the heat exchange tube and feed it back to the control system 7; the diameter monitoring unit 8 uses a contact displacement sensor 16 to monitor the diameter of the heat exchange tube and feed it back to the control system 7; the control system 7 analyzes the received process data and sends a control instruction to the expansion pressure loading unit 11;

[0019] Step 3: Start expansion: gradually fill the heat exchange tube 2 blank with high-pressure fluid, monitor the diameter D* of the heat exchange tube 2 and the expansion pressure p*, and stop the expansion when one of the following three conditions is met: 1) the expansion pressure p* drops sharply, 2) the diameter D* of the heat exchange tube 2 reaches D+δ D , 3) D* ≥ D-δ D And p*≥p-δ p ;

[0020] Step 4: Analyze experimental parameters and evaluate expansion quality:

[0021] 1) If the bulging pressure p* drops sharply, the heat exchange tube 2 will bulge and rupture;

[0022] 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the expansion pressure of heat exchange tube 2 is low, and further product quality testing is required;

[0023] 3) If D-δ D ≤D*≤D+δ D And p*≥p-δ p At this time, the expansion quality of the heat exchange tubes and fins is good, forming a heat exchanger component that meets the design requirements;

[0024] Step 5: Release the pressure and remove the components: Unload the hydraulic pressure and remove the expanded heat exchanger components.

[0025] Furthermore, in step 2, the oil cylinder 5, the movable beam 6 and the workbench 9 are replaced by the pull rod 13, the upper fixed plate 14 and the lower fixed plate 15. The upper fixed plate 14 and the lower fixed plate 15 are fixed by the pull rod 13 and bolts. The upper fixed plate 14 and the lower fixed plate 15 are used to fix the support block 4.

[0026] Furthermore, the high-pressure fluid medium is pure water, an emulsion of HFAE20-5 emulsified oil mixed with water, and volatile stamping oil.

[0027] Furthermore, the diameter monitoring unit 8 adopts a non-contact laser displacement sensor 17 .

[0028] Beneficial effects of the present invention:

[0029] (1) The present invention controls the hydraulic expansion process of a tube-fin heat exchanger and comprehensively evaluates the expansion quality by monitoring and analyzing the relationship between the expansion pressure and the outer diameter of the heat exchange tube and their set target values. This takes into account the geometric dimensions of the tube blank, the fluctuation of the yield stress, and the influence of defects. This can provide support for the mass production application of the hydraulic expansion technology of tube-fin heat exchangers.

[0030] (2) The present invention can realize online evaluation of the expansion quality of tube-fin heat exchangers, reduce manual inspection costs, and help improve production efficiency and product qualification rate;

[0031] (3) The present invention is applicable to pipes with different cross sections, such as plain pipes, internally threaded pipes and externally threaded pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the process control and online quality assessment method for the hydraulic expansion of tube-fin heat exchangers.

[0033] Figure 2 Diagram of the online assessment method for the hydraulic expansion quality of tube-fin heat exchangers.

[0034] Figure 3 Schematic diagram of the automatic hydraulic expansion device for tube-fin heat exchanger.

[0035] Figure 4 Schematic diagram of a simple hydraulic expansion device for a tube-fin heat exchanger.

[0036] Figure 5 Schematic diagram of the contact diameter measurement method.

[0037] Figure 6 Schematic diagram of the laser diameter measurement method.

[0038] In the figure: 1-tube end sealing head, 2-heat exchange tube, 3-fin, 4-support block, 5-oil cylinder, 6-movable crossbeam, 7-control system, 8-diameter monitoring unit, 9-workbench, 10-hydraulic pipeline, 11-bulging pressure loading unit, 12-bulging pressure monitoring unit, 13-pull rod, 14-upper fixed plate, 15-lower fixed plate, 16-contact displacement sensor, 17-laser displacement sensor. DETAILED DESCRIPTION

[0039] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0040] Example 1

[0041] Combine Figure 1 、 Figure 2 、 Figure 3 and Figure 5 The present invention proposes a method for controlling the hydraulic expansion process and conducting online quality assessment for a tube-fin heat exchanger, comprising: 1. tube end sealing heads; 2. heat exchange tubes; 3. fins; 4. support blocks; 5. oil cylinders; 6. movable crossbeams; 7. control systems; 8. diameter monitoring units; 9. work platforms; 10. hydraulic pipelines; 11. expansion pressure loading units; and 12. expansion pressure monitoring units. This method is implemented according to the following steps.

[0042] Step 1: Set the hydraulic expansion parameters: Set the target expansion diameter D and target expansion pressure p of the heat exchange tube in the control system, and the allowable diameter deviation δ D and allowable pressure deviation δ p .

[0043] Step 2, installation and fixation: install the heat exchange tube and fin assembly to be expanded on the automated hydraulic expansion device. The automated hydraulic expansion device mainly includes a workbench, an expansion pressure loading unit, an expansion pressure monitoring unit, a diameter monitoring unit and a control system. The workbench 9 is equipped with a pipe end sealing head 1, a support block 4, an oil cylinder 5 and a movable crossbeam 6. The oil cylinder 5 can drive the movable crossbeam 6 to move up and down to realize the loosening and clamping of the heat exchanger. The expansion pressure loading unit 11 is used to provide the high-pressure liquid required for expansion. The high-pressure liquid is hydraulic oil and enters the heat exchange tube 2 through the hydraulic pipeline 10 and the pipe end sealing head 1. The expansion pressure monitoring unit 12 is used to monitor the expansion pressure in the heat exchange tube and feed it back to the control system 7. The core component is the pressure sensor. The diameter monitoring unit 7 is used to monitor the diameter of the heat exchange tube and feed it back to the control system 7. The core component is the displacement sensor. This embodiment adopts a contact displacement sensor 16. The method of measuring the outer diameter of the tube with a contact displacement sensor is shown in FIG. Figure 5 Two displacement sensors are installed on either side of the heat exchange tube. An increase in the tube diameter causes the sensor head to move. The displacement measured by the two displacement sensors is used to calculate the change in tube diameter. The control system analyzes the received process data and sends control instructions to the bulging pressure loading unit 11.

[0044] Step 3: Start expansion: gradually fill the heat exchange tube 2 blank with high-pressure fluid, monitor the diameter D* and expansion pressure p* of the heat exchange tube 2, and stop the expansion when one of the following three conditions is met: 1) the expansion pressure p* drops sharply, 2) the diameter D* reaches D+δ D , 3) D* ≥ D-δ D And p*≥p-δp .

[0045] Step 4: Analyze data and evaluate expansion quality:

[0046] 1) If the bulging pressure p* drops sharply, the heat exchange tube will bulge and rupture;

[0047] 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the tube expansion pressure is low and further product quality testing is required;

[0048] 3) If D-δ D ≤D*≤D+δ D And p*≥p-δ p At this time, the expansion quality of the heat exchange tubes and fins is good, forming a heat exchanger component that meets the design requirements.

[0049] Step 5: Release the pressure and remove the components: Unload the hydraulic pressure and remove the expanded heat exchanger components.

[0050] The beneficial effects of this embodiment are: the oil cylinder can drive the movable crossbeam to move up and down, which can adapt to the hydraulic expansion of heat exchange tubes of different lengths and has strong adaptability. By setting the sequence of execution of each action, automatic expansion can be achieved.

[0051] Example 2

[0052] Combine Figure 3 Description: The present invention proposes a method for controlling the hydraulic expansion process and online quality assessment of a tube-fin heat exchanger, in which a high-pressure fluid medium is gradually filled into the heat exchange tube 2. The hydraulic medium uses pure water, emulsion or volatile stamping oil and other media. The rest is the same as Example 1.

[0053] The beneficial effect of this embodiment is that the pure water, emulsion, and volatile stamping oil media remaining in the heat exchange tube 2 after the expansion is completed are easy to clean.

[0054] Example 3

[0055] Combine Figure 6 It is explained that the present invention proposes a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger. The diameter monitoring unit 8 adopts a laser displacement sensor 17 , and the rest is the same as that of embodiment 1 or 2.

[0056] The beneficial effects of this embodiment are: the laser displacement sensor has high precision and fast response, does not contact the heat exchange tube, and facilitates the installation and removal of the heat exchanger.

[0057] Example 4

[0058] Combine Figure 1 、 Figure 2 、 Figure 4 and Figure 6 The present invention proposes a method for controlling the process of hydraulic expansion of a tube-fin heat exchanger and evaluating its quality online, comprising: 1-tube end sealing head, 2-heat exchange tube, 3-fin, 4-support block, 7-control system, 8-diameter monitoring unit, 11-expansion load monitoring unit, 12-expansion force monitoring unit, 13-pull rod, 14-upper fixing plate, 15-lower fixing plate, and 17-laser displacement sensor. The method is implemented according to the following steps:

[0059] Step 1: Set the hydraulic expansion parameters: Set the target expansion diameter D and target expansion pressure p of the heat exchange tube in the control system, and the allowable diameter deviation δ D and allowable pressure deviation δ p .

[0060] Step 2: Mounting and Fixing: Install the heat exchange tube and fin assembly to be expanded on a simplified hydraulic expansion device. This simplified hydraulic expansion device primarily comprises a simple workbench, an expansion pressure loading unit, an expansion pressure monitoring unit, a diameter monitoring unit, and a control system. The simple workbench, consisting of tie rods 13, an upper fixing plate 14, and a lower fixing plate 15, is used to secure the heat exchanger. The expansion pressure loading unit 11, expansion pressure monitoring unit 12, diameter monitoring unit 8, and control system 7 are identical to those in Embodiment 1.

[0061] Step 3: Start expansion: gradually fill the heat exchange tube blank with high-pressure fluid, monitor the heat exchange tube diameter D* and expansion pressure p*, and stop filling and expanding when one of the following three conditions is met: 1) the expansion pressure p* drops sharply, 2) the diameter D* reaches D+δ D , 3) D* ≥ D-δ D And p*≥p-δ p .

[0062] Step 4: Analyze data and evaluate expansion quality:

[0063] 1) If the bulging pressure p* drops sharply, the heat exchange tube will bulge and rupture;

[0064] 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the tube expansion pressure is low and further product quality testing is required;

[0065] 3) If D-δ D ≤D*≤D+δ D And p*≥p-δ p At this time, the expansion quality of the heat exchange tubes and fins is good, forming a heat exchanger component that meets the design requirements.

[0066] Step 5: Release the pressure and remove the components: Unload the hydraulic pressure and remove the expanded heat exchanger components.

[0067] The beneficial effects of this embodiment are: the heat exchanger is fixed by upper and lower fixing plates and tie rods, the device is simple and easy to operate, and it is suitable for exploring the hydraulic expansion process parameters of new tube-fin heat exchanger products.

[0068] Example 5

[0069] Combine Figure 3 Description: The present invention proposes a method for controlling the hydraulic expansion process and online quality assessment of a tube-fin heat exchanger, in which a high-pressure fluid medium is gradually filled into the heat exchange tube 2. The hydraulic medium uses pure water, emulsion or volatile oil, and the rest is the same as Example 4.

[0070] The beneficial effect of this embodiment is that the pure water, emulsion, and volatile stamping oil media remaining in the heat exchange tube 2 after the expansion is completed are easy to clean.

[0071] Example 6

[0072] Combine Figure 6 It is explained that the present invention proposes a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger. The diameter monitoring unit 8 adopts a laser displacement sensor 17 , and the rest is the same as that of Example 4 or 5.

[0073] The beneficial effects of this embodiment are: the laser displacement sensor has high precision and fast response, does not contact the heat exchange tube, and facilitates the installation and removal of the heat exchanger.

Claims

1. A method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger, characterized in that: Here are the steps: Step 1: Set the hydraulic expansion parameters: Set the target expansion diameter D, target expansion pressure value p, and allowable diameter deviation δ of the heat exchange tube in the control system (7). D and allowable pressure deviation δ p ; Step 2: Install and fix: The heat exchange tube (2) and fin (3) to be expanded are mounted on an automated hydraulic expansion device; the automated hydraulic expansion device comprises a workbench (9), an expansion pressure loading unit (11), an expansion pressure monitoring unit (12), a diameter monitoring unit (8) and a control system (7); a pipe end sealing head (1), a support block (4), an oil cylinder (5) and a movable crossbeam (6) are mounted on the workbench (9); the oil cylinder (5) can drive the movable crossbeam (6) to move up and down to achieve the loosening and clamping of the heat exchange tube (2); the support blocks (4) are respectively fixed on the movable crossbeam (6) , on a workbench (9) for supporting the heat exchange tube (2); a bulging pressure loading unit (11) charges the high-pressure fluid medium required for bulging into the heat exchange tube (2) through a hydraulic pipeline (10) and a tube end sealing head (1); a bulging pressure monitoring unit (12) is used to monitor the bulging pressure in the heat exchange tube and feed it back to the control system (7); a diameter monitoring unit (8) uses a contact displacement sensor (16) to monitor the diameter of the heat exchange tube and feed it back to the control system (7); the control system (7) analyzes the received process data and sends a control instruction to the bulging pressure loading unit (11); Step 3: Start expansion: gradually fill the heat exchange tube (2) with high-pressure fluid medium, monitor the diameter D* of the heat exchange tube (2) and the expansion pressure p*, and stop the expansion when one of the following three conditions is met: 1) the expansion pressure p* drops sharply, 2) the diameter D* of the heat exchange tube (2) reaches D+δ D , 3) D* ≥ D-δ D And p*≥p-δ p ; Step 4: Analyze experimental parameters and evaluate expansion quality: 1) If the bulging pressure p* drops sharply, the heat exchange tube (2) bulges and ruptures; 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the bulging pressure of the heat exchange tube (2) is low, and further testing of product quality is required; 3) If D-δ D ≤D*≤D+δ D And p*≥p-δ p At this time, the expansion quality of the heat exchange tubes and fins is good, forming a heat exchanger component that meets the design requirements; Step 5: Release the pressure and remove the components: Unload the hydraulic pressure and remove the expanded heat exchanger components.

2. The method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger according to claim 1, characterized in that: In step 2, the oil cylinder (5), the movable crossbeam (6) and the workbench (9) are replaced by a pull rod (13), an upper fixed plate (14) and a lower fixed plate (15), and the upper fixed plate (14) and the lower fixed plate (15) are fixed by the pull rod (13) and the nut, and the upper fixed plate (14) and the lower fixed plate (15) are used to fix the support block (4).

3. The method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger according to claim 1, wherein: The diameter monitoring unit (8) adopts a non-contact laser displacement sensor (17).

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