Methods for Measuring and Evaluating the Condition of Tube and Fin Heat Exchangers

Abstract

This application discloses a method for measuring and evaluating the condition of tube-fin heat exchangers, belonging to the field of tube-fin heat exchanger testing. The method for measuring the condition of tube-fin heat exchangers includes the following steps: S1, obtaining the structural information of the tube-fin heat exchanger and using image reconstruction technology to form a reconstructed three-dimensional image of the sample; S2, axially segmenting the reconstructed three-dimensional image to obtain the tube-fin condition of n different axial sections; S3, extracting the air area of ​​the axial section from the processed image; S4, calculating the average air area Aa of the n axial sections. The beneficial effect of this application is that it provides an accurate method for measuring and evaluating the condition of tube-fin heat exchangers.

Description

Technical Field

[0001] This application relates to the field of tube-fin heat exchanger testing, and more specifically, to a method for measuring and evaluating the condition of tube-fin heat exchanger tubes. Background Technology

[0002] Tube-fin heat exchangers are widely used in products requiring heat exchange, such as refrigerators, air conditioners, and medical devices. They mainly consist of heat exchange tubes and fins, which are typically made of metals such as copper, aluminum, and stainless steel. Based on manufacturing processes, tube-fin heat exchangers can be broadly classified into integral finned heat exchangers, welded finned heat exchangers, high-frequency welded finned heat exchangers, and mechanically connected finned heat exchangers.

[0003] For mechanically connected tube-fin heat exchangers, the fastening of the heat exchange tubes and fins is achieved through mechanical tube expansion. The process generally involves an expansion head advancing along the heat exchange tube axis under thrust, compressing the heat exchange tube through the outer contour of the expansion head, thus expanding its inner diameter and compressing the fins, causing them to deform. After the expansion head is unloaded, the fins elastically retract and fasten to the heat exchange tube. In actual tube expansion, various factors can affect tube-fin contact, thereby affecting heat exchange. Poor tube-fin contact can result in minute gaps on the same order of magnitude as the surface roughness of the tube and fins, as well as other process-related problems, such as uneven contact between the tube circumferentially and the fins, or inconsistent contact between the fins and the tube. Currently, there is much research on tube-fin heat exchangers. However, most research focuses on fin-side and tube-side heat exchange, without considering the impact of tube-fin contact on heat exchange. Furthermore, due to limitations in testing methods, a comprehensive evaluation method for tube-fin contact conditions has not yet been developed.

[0004] The method for examining the condition of tubes and fins is usually to use destructive wire cutting to cut a surface along the tube axis for observation. However, cutting can lead to uneven stress distribution, resulting in a discrepancy between the cross-sectional condition and the actual condition of the tubes and fins, which cannot accurately reflect the condition of the tubes and fins. Furthermore, the cut section cannot accurately measure the air zone and the contact length between the tubes and fins.

[0005] This application proposes to use non-contact industrial CT (industrial computed tomography) to measure the condition of tube wings, use image processing technology to analyze the test data, and propose an evaluation method. Summary of the Invention

[0006] The summary section of this application is intended to provide a brief overview of the concepts, which will be described in detail in the detailed description section below. This summary section is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0007] To address the technical problems mentioned in the background section, some embodiments of this application provide a method for measuring the condition of tube fins in a tube-fin heat exchanger, comprising the following steps:

[0008] S1. Obtain the structural information of the tube-fin heat exchanger and use image reconstruction technology to form a reconstructed three-dimensional image of the sample;

[0009] S2. Perform axial subdivision on the reconstructed 3D image to obtain n tube fin states with different axial sections;

[0010] S3. Extract the air area of ​​a single axial section from a single axial section diagram;

[0011] S4. Calculate the average air area Aa of n axial cross sections;

[0012] S5. In a single axial cross-sectional view, identify the start and end points of the contact between a single fin and the heat exchange tube, and calculate the distance between the start and end points, which is the fin contact length.

[0013] S6. Calculate the average tube-fin contact length Lc for all axial sections;

[0014] S7. Calculate the equivalent air domain thickness based on the average tube-fin contact length Lc and the average air domain area Aa.

[0015] S8. The obtained data can reflect the overall tube-fin contact state.

[0016] Furthermore, the average air area Aai of a single cross-section is calculated as follows:

[0017]

[0018] Furthermore, the average fin contact length Lci of a single cross-section is calculated as follows:

[0019]

[0020] Furthermore, the average fin contact length Lc for all n cross sections is calculated as follows:

[0021]

[0022] Furthermore, the equivalent air domain thickness is calculated using the following formula:

[0023]

[0024] Among them, L fin It is the fin spacing;

[0025] T fin It refers to the fin thickness.

[0026] Furthermore, the tube-fin contact ratio is calculated using the following formula:

[0027]

[0028] Furthermore, n is greater than or equal to 4.

[0029] Furthermore, m is greater than or equal to 20.

[0030] A method for evaluating the condition of tube-fin heat exchangers is provided. The tube-fin condition of the heat exchanger is evaluated based on the value of the air zone thickness Da and the tube-fin contact ratio α. When Da ≤ 0.15 and α ≥ 0.5, the tube-fin contact of the heat exchanger is qualified.

[0031] The beneficial effect of this application is that it provides a method for accurately measuring and evaluating the condition of tubes and fins in a tube-fin heat exchanger. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.

[0033] Furthermore, throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the elements are not necessarily drawn to scale.

[0034] In the attached diagram:

[0035] Figure 1 This is a schematic diagram of using the outer contour of an expanding head to compress the heat exchange tube;

[0036] Figure 2 This is a schematic diagram of the fin structure after fin arrangement;

[0037] Figure 3 This is a schematic diagram showing how the energy of the heat exchange tube is transferred to the fins through two pathways.

[0038] Figure 4 This is a schematic diagram of different axial cross-sectional designs of the tube fins.

[0039] Figure label:

[0040] 101. Fins;

[0041] 102. Heat exchanger tubes;

[0042] 103. Swelling head. Detailed Implementation

[0043] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0044] It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other.

[0045] It should be noted that the concepts of "first" and "second" mentioned in this disclosure are used only to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies.

[0046] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0047] This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] Reference Figure 1-4 Methods for measuring the condition of tubes and fins in tube-fin heat exchangers.

[0049] Fins are typically formed on a multi-station continuous machining center by repeatedly stamping, stretching, and flanging copper / aluminum foil, followed by processes such as fin arrangement, fin threading, tube expansion, and welding to complete the tube-fin heat exchanger. The arranged fins look like... Figure 2 As shown. Theoretically, the energy of the heat exchange tube is transferred to the fins through two pathways: part through the tube-fin contact, and the other through the fin flanges and the air formed by the fins and heat exchange tube. The thermal resistances of these two parts are different, as shown below. Figure 3 As shown. The tube-fin contact length, the minute gap between the tubes and fins, and the air domain formed by the fin flanges are important factors affecting the performance of tube-fin heat exchangers. Since the order of magnitude of the minute gap is close to the mean free path of gas molecules, it will not be discussed in this patent. The tube-fin contact length and the air domain are mainly used to characterize the tube-fin state of the tube-fin heat exchanger.

[0050] Industrial CT utilizes X-rays or gamma rays with specific energy and intensity emitted by radioactive nuclides or other radiation sources. These rays irradiate a sample placed on a rotating platform, which rotates continuously. An energy receiver at a fixed position collects the rays passing through the sample from different angles. Because different materials absorb radiation differently, the attenuation patterns and distribution of rays within the tested object vary. By irradiating the sample from multiple angles and continuously acquiring and receiving information, computer information processing and image reconstruction techniques are used to create a three-dimensional image of the sample on the image receiver. This allows for the acquisition of more detailed information about the sample's internal structure.

[0051] During testing, the test section of the tube-fin heat exchanger is placed on the test bench of the industrial CT equipment. Once the measuring equipment is started, the structural information of the tube-fin heat exchanger can be obtained. Observing the tube-fin condition requires axial sectioning; therefore, the 3D image reconstructed from the measurement is axially segmented to obtain the tube-fin contact state at different axial sections. The tube-fin can be in contact with or not in contact with the heat exchange tube. The air area of ​​this section can be extracted from the processed image, and the average air area Aai of a single section can be calculated using the following formula:

[0052]

[0053] The average air area Aa of all n cross sections is calculated as follows:

[0054]

[0055] The contact length between the fins and the heat exchange tube can be determined by identifying the start and end points of the contact between a single fin and the heat exchange tube through abrupt changes in image grayscale. This allows for the calculation of the average fin contact length Lci for a single cross-section, as shown in the following formula:

[0056]

[0057] The average fin contact length Lc for all n cross sections is calculated as follows:

[0058]

[0059] Based on this, the equivalent air domain thickness can be calculated using the following formula:

[0060]

[0061] Among them, L fin It is the fin spacing; T fin It refers to the fin thickness.

[0062] Based on this, the tube-fin contact ratio is calculated using the following formula:

[0063]

[0064] To ensure that the heat exchange tube section tested is long enough to reflect the overall tube-fin contact state, m should be greater than or equal to 20.

[0065] To obtain an overall picture of the circumferential tube-fin contact, the tube-fin contact length and equivalent air domain thickness should be measured and calculated at least four different axial cross-sections, such as... Figure 4 As shown, cross-sections AA, BB, CC, and DD are obtained. Finally, the processed data of multiple cross-sections with different axial directions are averaged, and the resulting data can reflect the overall tube-fin contact state. The larger the tube-fin contact length and the smaller the equivalent air domain thickness Da, the better the tube-fin contact of the heat exchanger, the smaller the thermal resistance, and the better the heat transfer performance.

[0066] Specifically, when Da ≤ 0.15 mm and α ≥ 0.5, the heat exchanger tube-fin contact is qualified. The smaller Da is and the larger α is, the tighter the tube-fin contact is, and vice versa.

[0067] Measuring the condition of tubes and fins in a tube-fin heat exchanger using the above methods can effectively avoid the impact of destructive wire cutting on measurement accuracy, thus greatly improving the accuracy of the measurement.

[0068] The above description is merely a selection of preferred embodiments of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. A method for measuring the condition of tubes and fins in a tube-fin heat exchanger. Its features are: Includes the following steps: S1. Obtain the structural information of the tube-fin heat exchanger and use image reconstruction technology to form a reconstructed three-dimensional image of the sample; S2. Perform axial subdivision on the reconstructed 3D image to obtain n tube fin states with different axial sections; S3. Extract the air area of ​​a single axial section from a single axial section diagram; S4. Calculate the average air area Aa of n axial cross sections; S5. In a single axial cross-sectional view, identify the start and end points of the contact between a single fin and the heat exchange tube, and calculate the distance between the start and end points, which is the fin contact length. S6. Calculate the average tube-fin contact length Lc for all axial sections; S7. Calculate the equivalent air domain thickness Da based on the average tube-fin contact length Lc and the average air domain area Aa.

2. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 1, characterized in that: The average air area Aai of a single cross-section is calculated as follows:

3. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 2, characterized in that: The average air area Aa of all n cross sections is calculated as follows:

4. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 3, characterized in that: The average fin contact length Lci of a single cross section is calculated as follows:

5. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 4, characterized in that: The average fin contact length Lc for all n cross sections is calculated as follows:

6. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 5, characterized in that: The equivalent air domain thickness is calculated using the following formula: Among them, L fin It is the fin spacing; T fin It refers to the fin thickness.

7. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 6, characterized in that: The fin-tube contact ratio is calculated using the following formula:

8. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 5, characterized in that: n is greater than or equal to 4.

9. The method for measuring the condition of tube fins in a tube-fin heat exchanger according to claim 4, characterized in that: m is greater than or equal to 20.

10. A method for assessing the condition of tubes and fins in a tube-fin heat exchanger. Its features are: The condition of the tube fins of a tube-finned heat exchanger is evaluated based on the values ​​of the air zone thickness Da and the tube-fin contact ratio α. When Da ≤ 0.15 and α ≥ 0.5, the tube-fin contact of the heat exchanger is qualified.

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