Hydraulic expanded connection process control and quality online evaluation method for finned tube heat exchanger

Abstract

The invention discloses a hydraulic expanded connection process control and quality online evaluation method for a finned tube heat exchanger. The invention relates to a method for controlling the hydraulic expanded connection process and comprehensively evaluating the expanded connection quality of a heat exchanger by monitoring and analyzing the relationship between two parameters of the outer diameter and the bulging pressure of a heat exchange tube and set target values in the hydraulic expanded connection process of a finned tube heat exchanger. The method is implemented according to the following steps that firstly, expanded connection parameters are set, wherein the target diameter and the target pressure of hydraulic expanded connection parameters are set in a system; 2, mounting and fixing, wherein the heat exchange tube and fin assembly to be subjected to expanded connection is mounted on a hydraulic expanded connection device; thirdly, a high-pressure fluid medium is filled, and expanded connection is started; fourthly, data are monitored and analyzed, and the expanded connection quality is evaluated; and fifthly, the hydraulic pressure is unloaded, and the heat exchanger assembly subjected to expanded connection is taken down. The method is used for hydraulic expanded connection process control and quality online evaluation of the finned tube 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 heat exchanger by monitoring and analyzing the relationship between two parameters, the outer diameter of a heat exchange tube and the expansion pressure, and their set target values ​​during the hydraulic expansion process of a tube-fin heat exchanger. Background Art

[0003] Air conditioners are mainly composed of three parts: refrigeration system, air circulation system and electronic control system. The refrigeration system is the core of the air conditioner, which consists of components such as compressor, condenser, expansion valve and evaporator. As a heat exchanger with high heat exchange efficiency, small refrigerant charge and good corrosion resistance, the tube-fin heat exchanger is widely used in condensers and evaporators in air conditioning refrigeration systems. It is a key component that determines the energy efficiency and operation stability of air conditioners. Considering the hardness, strength, ductility and thermal conductivity of metals, the tube-fin heat exchanger mainly uses copper or aluminum alloy internal threaded heat exchange tubes as the flow channel of the refrigerant, and aluminum foil fins are installed on the outside of the heat exchange tubes to increase the heat exchange area with the external environment. In order to reduce thermal resistance and ensure good heat exchange efficiency between the heat exchange tubes and fins, the heat exchange tubes and fins must be closely fitted to form an interference fit through the expansion process.

[0004] At present, the tube-fin heat exchanger is mostly manufactured by the traditional mechanical expansion method. The principle is to press a mechanical expansion bead with a diameter larger than the inner diameter of the heat exchange tube into the tube, so that the heat exchange tube undergoes plastic deformation, the diameter of the heat exchange tube increases and contacts the fins, causing the fins to undergo a certain deformation; when the force of the mechanical expansion bead on the heat exchange tube is unloaded, the heat exchange tube and the fin undergo elastic recovery deformation at the same time, and the elastic recovery deformation of the heat exchange tube is smaller than the elastic recovery deformation of the fin, thereby forming an interference fit between the heat exchange tube and the fin. However, the force of the mechanical expansion bead on the inner wall of the tube is uneven during expansion, which is prone to problems such as expansion bending, expansion bursting defects and internal thread damage.

[0005] The hydraulic expansion method uses liquid medium to apply a uniform load to the inner wall of the tube to expand the tube, which can overcome the problem of uneven force during mechanical expansion. It is an advanced technology suitable for the expansion of hollow tube multi-layer components. During hydraulic expansion, the liquid medium applies a flexible uniform load to the heat exchange tube, avoiding the hard contact of the expansion bead with the inner wall of the tube during mechanical expansion. The heat exchange tube deforms more evenly and does not damage the internal thread, which can obtain better tube-fin contact quality and higher heat exchange efficiency. As an efficient and reliable expansion technology, the hydraulic expansion method has received much attention from the air-conditioning industry.

[0006] 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.g Bulging 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.

[0007] Assuming that the heat exchange tube satisfies the bilinear strain hardening characteristics expressed by formula (1), the target bulging pressure value p required for expansion can be estimated by formula (2), which corresponds to the bulging 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 bulging pressure value and its allowable deviation for actual production need to be verified through experiments.

[0008]

[0009]

[0010] 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, A 1 , A 2 is a constant, 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.

[0011] It can be seen from formula (2) that for a heat exchange tube of a certain diameter, 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, g and σ s The smaller the value, the smaller the expansion pressure p required for the heat exchange tube to expand 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 fin will also be a constant value. The expansion process can be controlled by controlling the expansion pressure.

[0012] However, the geometric dimensions and mechanical properties of different batches of tube billets actually fluctuate, and some tube billets may even have defects such as insufficient wall thickness and insufficient yield stress, which poses a challenge to the hydraulic expansion process control and online quality assessment. In terms of hydraulic expansion process control, the expansion pressure required to achieve an effective expansion deformation degree of the tube billet fluctuates with the fluctuation of 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 tube billet size and performance fluctuations, 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 reduces the ability of the tube billet to bear internal pressure and is prone to rupture during expansion; even if it does not rupture, the defective heat exchanger obtained is prone to leakage and has a short life.

[0013] Therefore, a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger is needed, which can fully consider the influence of tube size fluctuation, yield stress fluctuation and defects. Summary of the invention

[0014] 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 two parameters of 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.

[0015] The technical solution of the present invention:

[0016] A method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger, the steps are as follows:

[0017] 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 ;

[0018] Step 2: Install and fix:

[0019] 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 respectively fixed on the movable crossbeam 6 and the workbench 9 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;

[0020] 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 ;

[0021] Step 4: Analyze the experimental parameters and evaluate the expansion quality:

[0022] 1) If the bulging pressure p* drops sharply, the heat exchange tube 2 bulges and ruptures;

[0023] 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;

[0024] 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;

[0025] Step 5: Release the pressure and remove the parts: Unload the hydraulic pressure and remove the expanded heat exchanger assembly.

[0026] Further, in step two, the oil cylinder 5, the movable crossbeam 6 and the workbench 9 are replaced by the tie rod 13, the upper fixed plate 14 and the lower fixed plate 15, and the upper fixed plate 14 and the lower fixed plate 15 are fixed by the tie rod 13 and bolts, and the upper fixed plate 14 and the lower fixed plate 15 are used to fix the support block 4.

[0027] Furthermore, the high-pressure fluid medium is pure water, an emulsion of HFAE20-5 emulsified oil mixed with water, and volatile stamping oil.

[0028] Furthermore, the diameter monitoring unit 8 adopts a non-contact laser displacement sensor 17 .

[0029] Beneficial effects of the present invention:

[0030] (1) The present invention controls the hydraulic expansion process of the 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, taking into account the influence of the geometric dimensions of the tube blank, the fluctuation of the yield stress and the defects, and can provide support for the mass production application of the hydraulic expansion technology of the tube-fin heat exchanger;

[0031] (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;

[0032] (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

[0033] Figure 1 The flowchart is for the process control and quality online assessment method of the hydraulic expansion of tube-fin heat exchangers.

[0034] Figure 2 Diagram of the online assessment method for the hydraulic expansion quality of tube-fin heat exchangers.

[0035] Figure 3 Schematic diagram of the automatic hydraulic expansion device for tube-fin heat exchanger.

[0036] Figure 4 It is a schematic diagram of a simple hydraulic expansion device for a tube-fin heat exchanger.

[0037] Figure 5 Schematic diagram of the contact diameter measurement method.

[0038] Figure 6 Schematic diagram of laser diameter measurement method.

[0039] In the figure: 1-tube end sealing head, 2-heat exchange tube, 3-fin, 4-support block, 5-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

[0040] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0041] Example 1

[0042] Combination Figure 1 , Figure 2 , Figure 3 and Figure 5 The invention provides a method for controlling the process of hydraulic expansion of a tube-fin heat exchanger and evaluating the quality online, comprising: 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-expansion pressure loading unit, 12-expansion pressure monitoring unit. It is implemented according to the following steps.

[0043] 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 .

[0044] 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, a cylinder 5 and a movable crossbeam 6. The cylinder 5 can drive the movable crossbeam 6 to move up and down to achieve 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 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 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 uses a contact displacement sensor 16. The method for measuring the outer diameter of the tube with a contact displacement sensor is shown in Figure 5 Two displacement sensors are installed on both sides of the heat exchange tube. The increase in the diameter of the tube will push the sensor measuring head to move. The displacement measured by the two displacement sensors is used to calculate the diameter change of the tube. The control system is used to analyze the received process data and send control instructions to the bulging pressure loading unit 11.

[0045] Step 3: Start expansion: gradually fill the heat exchange tube 2 with high-pressure fluid medium, 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 .

[0046] Step 4: Analyze data and evaluate expansion quality:

[0047] 1) If the bulging pressure p* drops sharply, the heat exchange tube will bulge and rupture;

[0048] 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the tube expansion pressure is low, and the product quality needs to be further tested;

[0049] 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.

[0050] Step 5: Release the pressure and remove the parts: Unload the hydraulic pressure and remove the expanded heat exchanger assembly.

[0051] The beneficial effect of this embodiment is that 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.

[0052] Example 2

[0053] Combination Figure 3 Description: The present invention proposes a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger, in which a high-pressure fluid medium is gradually filled into the heat exchange tube 2, and the hydraulic medium uses pure water, emulsion or volatile stamping oil and other media, and the rest is the same as Example 1.

[0054] The beneficial effect of this embodiment is that the pure water, emulsion and volatile stamping oil medium remaining in the heat exchange tube 2 after the bulging is completed are easy to clean.

[0055] Example 3

[0056] Combination Figure 6 It is explained that the present invention proposes a method for controlling the process of hydraulic expansion of a tube-fin heat exchanger and evaluating the quality online, wherein a laser displacement sensor 17 is used in the diameter monitoring unit 8, and the rest is the same as that of Embodiment 1 or 2.

[0057] 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 loading and unloading of the heat exchanger.

[0058] Example 4

[0059] Combination Figure 1 , Figure 2 , Figure 4 and Figure 6 Description: A method for controlling the process of hydraulic expansion of a tube-fin heat exchanger and evaluating the quality online is provided in the present invention, comprising: 1-tube end sealing head, 2-heat exchange tube, 3-fin, 4-support block, 7-control system, 8-diameter monitoring unit, 11-bulging load monitoring unit, 12-bulging force monitoring unit, 13-pull rod, 14-upper fixed plate, 15-lower fixed plate, 17-laser displacement sensor, which is implemented according to the following steps:

[0060] 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 .

[0061] Step 2: Install and fix: Install the heat exchange tube and fin assembly to be expanded on the simple hydraulic expansion device. The simple hydraulic expansion device mainly includes: a simple workbench, an expansion pressure loading unit, an expansion pressure monitoring unit, a diameter monitoring unit and a control system. The simple workbench consists of a pull rod 13, an upper fixing plate 14 and a lower fixing plate 15, which are used to fix the heat exchanger. The expansion pressure loading unit 11, the expansion pressure monitoring unit 12, the diameter monitoring unit 8 and the control system 7 are the same as those in the first embodiment.

[0062] Step 3: Start expansion: gradually fill the heat exchange tube blank with high-pressure fluid medium, monitor the heat exchange tube diameter D* and expansion pressure p*, and stop filling and 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-δ p .

[0063] Step 4: Analyze data and evaluate expansion quality:

[0064] 1) If the bulging pressure p* drops sharply, the heat exchange tube will bulge and rupture;

[0065] 2) If D-δ D ≤D*≤D+δ D And p*<p-δ p At this time, the tube expansion pressure is low, and the product quality needs to be further tested;

[0066] 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.

[0067] Step 5: Release the pressure and remove the parts: Unload the hydraulic pressure and remove the expanded heat exchanger assembly.

[0068] 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 products of tube-fin heat exchangers.

[0069] Example 5

[0070] Combination Figure 3 Description: The present invention proposes a method for controlling the hydraulic expansion process and evaluating the quality online of a tube-fin heat exchanger, in which a high-pressure fluid medium is gradually filled into the heat exchange tube 2, and the hydraulic medium uses pure water, emulsion or volatile oil and other media, and the rest is the same as Example 4.

[0071] The beneficial effect of this embodiment is that the pure water, emulsion and volatile stamping oil medium remaining in the heat exchange tube 2 after the bulging is completed are easy to clean.

[0072] Example 6

[0073] Combination 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, wherein a laser displacement sensor 17 is used in the diameter monitoring unit 8, and the rest is the same as that of Embodiment 4 or 5.

[0074] 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 loading and unloading 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: Setting hydraulic expansion parameters: Setting 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 tube 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) via 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 the experimental parameters and evaluate the 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 parts: Unload the hydraulic pressure and remove the expanded heat exchanger assembly.

2. The method for controlling the process of hydraulic expansion of a tube-fin heat exchanger and evaluating the quality online 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); the upper fixed plate (14) and the lower fixed plate (15) are fixed by the pull rod (13) and nuts; 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 process of hydraulic expansion of a tube-fin heat exchanger and evaluating the quality online according to claim 1, characterized in that: The high-pressure fluid medium is pure water, an emulsion of HFAE20-5 emulsified oil mixed with water, and volatile stamping oil.

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

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