Low-temperature phase-change material temperature field visual measurement device based on Mach-Zehnder interference

Abstract

The invention discloses a visual measurement device for a temperature field of a low-temperature phase-change material based on Mach-Zehnder interference. The visual measurement device comprises a Mach-Zehnder optical interference system, a low-temperature Dewar and an image acquisition and processing system, in the Mach-Zehnder optical interference system, laser generated by a laser generator enters a beam splitter after being expanded and collimated by a beam expander, and is divided into a reference light path and a test light path by the beam splitter; the reference light path is reflected by the optical path compensator and the first reflector in sequence and then enters the beam combiner, and the test light path passes through the second reflector, penetrates through a sample cavity in the low-temperature Dewar and then enters the beam combiner; the two paths of light are superposed at the beam combiner to form interference light and enter a high-speed camera to record interference fringes; and the image acquisition and processing system is connected with the high-speed camera and is used for performing interference fringe extraction, phase calculation, temperature field reconstruction and dynamic display. The invention provides a non-contact and high-resolution temperature field visualization test means for low-temperature phase change heat transfer mechanism research and related energy storage / refrigeration application.

Description

Technical Field

[0001] This invention relates to the fields of cryogenic engineering, phase change energy storage and optical precision measurement technology, and in particular to a visualization measurement device for the temperature field of cryogenic phase change materials based on Mach-Zehnder interferometry. Background Technology

[0002] Phase change materials (PCMs) have wide applications in cryogenic energy storage, spacecraft thermal control, superconducting magnet cooling, and cryogenic biopreservation due to their ability to absorb or release large amounts of latent heat during phase transitions. Studying the phase transition behavior of PCMs at low temperatures, especially the spatiotemporal distribution of the temperature field and the evolution of the phase interface during phase transitions, is crucial for optimizing material properties and improving system efficiency and reliability.

[0003] Currently, research methods for studying phase transition processes in low-temperature PCMs still have limitations. Traditional point-contact temperature measurement methods, such as thermocouples and platinum resistance thermometers, can only obtain temperature data at discrete points on the sample, failing to provide continuous, full-field temperature distribution information reflecting the dynamic phase transition process. This is especially true in regions near the phase interface where temperature gradients change drastically, where point measurements lack representativeness. While infrared thermal imaging technology can achieve non-contact measurements, accurate calibration of material surface emissivity is extremely difficult at low temperatures, and it cannot penetrate the sample to obtain internal information, rendering it ineffective for measuring the internal temperature field of PCMs encapsulated in transparent cavities.

[0004] Mach-Zehnder interferometry is a full-field optical measurement method based on the principle of optical wave interference. When a coherent beam of light passes through a transparent medium with a non-uniform refractive index distribution (such as a PCM with a temperature gradient), its optical path changes, causing the fringe pattern formed after interference with a reference beam to shift or deform. By analyzing the changes in the interference fringes, the refractive index field inside the medium can be deduced, and then the temperature field can be obtained by combining this with the material's thermo-optical coefficient (dn / dT). This technique has advantages such as being non-contact, highly sensitive, and capable of full-field measurement, making it very suitable for visualizing the temperature field inside transparent or semi-transparent PCMs.

[0005] For example, Chinese patent document CN106940300A discloses a method for studying the refractive index characteristics of liquids based on Mach-Zehnder filtering and long-period fiber gratings; Chinese patent document CN111982859A discloses a refractive index sensor based on Mach-Zehnder structure and its detection method.

[0006] However, successfully applying the Mach-Zehnder interferometer system to cryogenic PCM testing faces many challenges: (1) The introduction of low-temperature Dewars leads to an increase in the length and complexity of the test optical path, requiring a precise optical path compensation mechanism to ensure the quality of the interference fringes.

[0007] (2) The temperature control accuracy and stability requirements are high in low temperature environments, and it is necessary to be able to flexibly simulate different cooling boundary conditions.

[0008] (3) It is essential to effectively suppress the interference of intense radiative heat transfer on the sample temperature field under low-temperature conditions to ensure that the measurement results reflect the heat transfer characteristics of the phase change itself. Currently, there is a lack of a dedicated experimental platform that integrates the above-mentioned key technologies. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry. It can not only realize full-field, dynamic, and high-precision measurement of the internal temperature field of PCM phase change process at low temperature, but also solve key technical problems such as boundary condition simulation, thermal interference suppression, and measurement accuracy assurance in low-temperature optical measurement through innovative replaceable cold head, cold screen, and optical path compensation design.

[0010] A visualization measurement device for the temperature field of low-temperature phase change materials based on Mach-Zehnder interferometry, comprising a Mach-Zehnder optical interferometer system, a low-temperature Dewar, and an image acquisition and processing system; The Mach-Zehnder optical interferometer system includes: a laser generator, a beam expander, a beam splitter, a first mirror, a second mirror, a beam combiner, a high-speed camera, and an optical path compensator. The laser generated by the laser generator is expanded and collimated by the beam expander and then enters the beam splitter, which splits it into a reference optical path and a test optical path. The reference optical path is reflected by the optical path compensator and the first mirror in sequence and then enters the beam combiner. The test optical path passes through the second mirror and the sample cavity in the low temperature Dewar and then enters the beam combiner. The two beams are superimposed at the beam combiner to form interference light and enter the high-speed camera to record the interference fringes. The image acquisition and processing system is connected to a high-speed camera and is used for interference fringe extraction, phase calculation, temperature field reconstruction, and dynamic display.

[0011] Furthermore, the optical path compensator is used to adjust the optical path of the reference optical path to match the optical path of the test optical path in the initial state, ensuring that high-contrast initial interference fringes are obtained.

[0012] Furthermore, the image acquisition and processing system employs one or more of the following methods—Fourier transform, phase shift, or digital holographic phase inversion—to perform phase calculation on the interference fringes acquired by the high-speed camera, and reconstructs the temperature field of the low-temperature phase change material within the sample cavity based on the phase-refractive index-temperature relationship.

[0013] Furthermore, the phase-refractive index-temperature relationship is obtained through pre-calibration. The calibration method involves arranging standard temperature measuring elements in the sample cavity and establishing a mapping relationship between the interference phase and temperature at multiple temperature points.

[0014] Furthermore, the low-temperature Dewar includes a Dewar container and a cold source, a cold stage, a heater, a replaceable cold head, a sample chamber, and a cold screen disposed inside the Dewar container; The cold source, cold stage, and heater constitute the temperature control system. The cold source is thermally connected to the cold stage to provide low-temperature cooling to the cold stage. The replaceable cold head is detachably connected to the cold stage, and the lower end of the replaceable cold head is thermally connected to the sample chamber. The heater is thermally connected to the cold stage and achieves constant temperature or programmed temperature control through a PID controller. The cold screen surrounds the sample chamber and is at the same or nearly the same temperature as the cold stage. Optical windows are opened at relative positions on the Dewar flask and the cold screen to allow the test light path to be transmitted.

[0015] Alternatively, the cold source may be provided by a refrigeration unit or a cryogenic liquid cold source.

[0016] Furthermore, by replacing replaceable cold heads with different shapes or connection methods, the position, area, and geometry of the cold source surface of the replaceable cold head can be changed, thereby simulating different boundary heat transfer conditions.

[0017] Alternatively, the cold source surface of the replaceable cold head can be one or more of a plane, cylindrical surface, spherical surface, wedge-shaped surface or stepped surface to form boundary conditions of constant temperature, constant heat flow, local cooling or stepped cooling.

[0018] Preferably, the sample chamber is made of a transparent low-temperature heat-resistant material, wherein the transparent low-temperature heat-resistant material is one of quartz glass, borosilicate glass or sapphire; the side of the sample chamber is provided with thermocouple or resistance thermometer sockets for local temperature calibration and monitoring.

[0019] The specific process of interference fringe extraction, phase calculation, and temperature field reconstruction in the image acquisition and processing system is as follows: S1. Interference Image Acquisition and Preprocessing: During the low-temperature phase change material melting / solidification experiment, a high-speed camera 7 synchronously acquired an interference fringe image sequence, and preprocessed the interference fringe image sequence by dark field / background subtraction and filtering noise reduction. S2, Phase Extraction: The wrapped phase field is extracted from the preprocessed interference fringe image using Fourier transform, phase shift, or digital holographic inversion methods. ; The spatial coordinates of the temperature location within the sample chamber on the cross section; S3 indicates the image acquisition time during the experiment; Phase unwrapping: For the wrapping phase field Perform a joint phase expansion of space or spacetime to obtain a continuous phase field. And based on the phase of the initial steady-state frame of the experiment Using this as a reference, calculate the phase difference: ; S4. Optical path difference and refractive index field inversion: The phase difference is converted into an optical path difference based on the laser wavelength λ, and this is applied to the equivalent thickness of the sample. Inversion of refractive index field under known conditions : ; ; in, This represents the optical path difference at different times and locations. This represents the refractive index of the sample at the initial moment; S5, Temperature Field Reconstruction: The refractive index field is converted into a temperature field by utilizing the thermo-optic relationship of low-temperature phase change materials. : ; Alternatively, the phase difference field can be converted into a temperature field using a calibration curve. : ; in, This indicates the sample temperature at the initial moment. This represents the thermo-optic coefficient of the phase change material. This represents the inversion mapping relationship from phase difference to temperature.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. Realize the visualization of the internal temperature field of low-temperature PCM: By replacing point temperature measurement with MZI full-field interferometry, non-invasive dynamic observation of the continuous temperature distribution inside the low-temperature phase transition process can be achieved.

[0021] 2. High measurement accuracy and high reliability: The optical path compensator ensures fringe contrast; the cold screen suppresses radiation interference; the sample cavity has a reserved jack for local temperature measurement calibration and verification, improving the reliability of temperature inversion.

[0022] 3. Flexible and adjustable boundary conditions: The replaceable cold head supports multiple cooling geometry / contact methods, which facilitates the systematic study of the impact of different boundary structures on phase change heat transfer.

[0023] 4. Wide and stable temperature control range: The cold source and heater form a wide temperature range active control system, which can cover experimental needs from about 77K to room temperature and above.

[0024] 5. High integration and good repeatability: The synergistic integration of optics, cryogenics and image processing simplifies the experimental setup and makes it repeatable; the synchronous acquisition and calibration process improves experimental efficiency. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the optical path of a low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry, according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the low-temperature Dewar structure in an embodiment of the present invention.

[0028] Figure 3 This is a flowchart illustrating the workflow of the image acquisition and processing system in an embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of a replaceable cold head in an embodiment of the present invention.

[0030] In the diagram: 1-Laser generator, 2-Beam expander, 3-Beam splitter, 4-Mirror No. 1, 5-Mirror No. 2, 6-Beam combiner, 7-High-speed camera, 8-Optical path compensator, 9-Cold source, 10-Cold stage, 11-Heater, 12-Replaceable cold head, 13-Sample chamber, 14-Cold screen, 15-Visualization window. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that, unless otherwise specified, the features in the following embodiments and implementation methods can be combined with each other.

[0033] like Figure 1 As shown, a low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry includes a Mach-Zehnder optical interferometer system, a low-temperature Dewar, and an image acquisition and processing system.

[0034] The Mach-Zehnder optical interferometer system comprises a laser generator 1, a beam expander 2, a beam splitter 3, a first mirror 4, a second mirror 5, a beam combiner 6, a high-speed camera 7, and an optical path compensator 8. The laser generator 1 produces a coherent laser beam, which is expanded and collimated by the beam expander 2 before being incident on the beam splitter 3. The beam is split into a reference beam and a test beam. The reference beam propagates within the reference path, and after the initial optical path difference is adjusted by the optical path compensator 8, it is reflected by the first mirror 4 to the beam combiner 6. The test beam passes through the second mirror 5, through the low-temperature Dewar sidewall and the visualization window 15 on the cold screen, and then through the PCM sample area within the sample cavity 13 before reaching the beam combiner 6. The two beams superimpose in the beam combiner 6 to form interference fringes, which are recorded as an interference image sequence by the high-speed camera 7. The optical path compensator 8 is used to adjust the optical path of the reference beam to match the initial optical path of the test beam, ensuring high-contrast initial fringes, which is the basis for subsequent phase extraction and temperature field inversion.

[0035] like Figure 2 As shown, the low-temperature Dewar provides stable and controllable low-temperature boundary conditions for PCM phase transition. It includes a Dewar canister and a cold source 9, a cold stage 10, a heater 11, a replaceable cold head 12, a sample chamber 13, and a cold screen 14 disposed inside the Dewar canister.

[0036] The cold source 9 is a refrigerator cold head or a cryogenic liquid cold source (liquid nitrogen / liquid helium), which generates cooling and transfers it to the sample chamber 13 through the highly thermally conductive cold stage 10. The heater 11 is arranged on the cold stage 10 or the replaceable cold head 12, and realizes constant temperature, linear heating and cooling or stepped temperature program through a PID controller. The replaceable cold head 12 is detachably connected to the cold stage 10 through a standardized interface. The lower end of the cold head is in contact with or thermally connected to the sample chamber 13. Different cooling boundary conditions can be simulated by replacing cold heads with different geometries. The cold screen 14 surrounds the sample chamber 13 and is at the same or nearly the same temperature as the cold stage 10. It is used to block the influence of high temperature radiation from the Dewar wall on the PCM sample and reduce radiation heat leakage. Visualization windows 15 are opened at relative positions on the Dewar tank and the cold screen 14 to ensure low-loss transmission of the test optical path.

[0037] The image acquisition and processing system consists of a synchronization trigger module, a computer workstation, and image processing software. The high-speed camera 7 is synchronized with the temperature control system to achieve a one-to-one correspondence between the temperature program and the time of interferometric image acquisition. The image software is used to extract fringes, calculate phase, and expand phases of the interferometric image sequence, and to invert the internal temperature field of the PCM by combining the refractive index-temperature calibration relationship, thereby realizing dynamic visualization and data analysis of the temperature field.

[0038] The process of inverting the PCM temperature field using interference fringes will be introduced below.

[0039] like Figure 3As shown, the test light passes through the PCM region within the sample cavity 12. The temperature gradient within the PCM causes a non-uniform refractive index distribution, resulting in a spatial change in the optical phase. This leads to a shift or distortion in the fringes formed after interference with the reference light at the beam combiner 6. The interference fringe sequence is recorded using a high-speed camera 7, and the phase difference is obtained using image processing software. Combining the relationship between the refractive index of PCM and temperature and thermo-optic coefficient The temperature field can be obtained from the calibration curve. It includes the following steps: 1. Interference image acquisition and preprocessing.

[0040] During the low-temperature PCM melting / solidification experiment, a high-speed camera (7) synchronously acquired a sequence of interference fringe images. The image sequences were then subjected to dark field / background subtraction and filtering for noise reduction.

[0041] 2. Phase extraction.

[0042] The wrapped phase field is extracted from the preprocessed interference fringe image using Fourier transform, phase shift, or digital holographic inversion methods. .

[0043] 3. Phase expansion.

[0044] For the package phase Perform a joint phase expansion of space or spacetime to obtain a continuous phase field. And based on the phase of the initial steady-state frame of the experiment Using this as a reference, calculate the phase difference: ; 4. Optical path difference and refractive index field inversion.

[0045] The phase difference is converted into an optical path difference based on the laser wavelength λ, and the refractive index field is inverted under the condition that the equivalent thickness d of the sample is known: ; ; 5. Temperature field reconstruction.

[0046] The refractive index field / phase difference field is converted into a temperature field using the low-temperature PCM thermo-optic relationship or calibration curve: ; or, .

[0047] The phase transition test steps are as follows: 1. Inject low-temperature PCM into sample chamber 13 and seal it for fixation.

[0048] 2. Select a replaceable cold head 12 with a specific geometry to contact the sample chamber 13. For example... Figure 4 Figures (a) and (b) show schematic diagrams of two replaceable cold heads in embodiments of the present invention.

[0049] 3. The temperature is reduced by the cold source 9 and controlled by the heater 11.

[0050] 4. Simultaneously acquire interferometric image sequences during the melting or solidification process.

[0051] 5. Phase extraction and temperature field reconstruction are performed using software to obtain the evolution law of phase interface and temperature field.

[0052] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A visualization measurement device for the temperature field of low-temperature phase change materials based on Mach-Zehnder interferometry, characterized in that, This includes the Mach-Zehnder optical interferometer system, cryogenic Dewar, and image acquisition and processing system; The Mach-Zehnder optical interferometer system includes: a laser generator (1), a beam expander (2), a beam splitter (3), a first mirror (4), a second mirror (5), a beam combiner (6), a high-speed camera (7), and an optical path compensator (8). The laser generated by the laser generator (1) is expanded and collimated by the beam expander (2) and then enters the beam splitter (3), which divides it into a reference optical path and a test optical path. The reference optical path is reflected by the optical path compensator (8) and the first mirror (4) and then enters the beam combiner (6). The test optical path passes through the second mirror (5) and the sample cavity (13) inside the low-temperature Dewar and then enters the beam combiner (6). The two beams are superimposed at the beam combiner (6) to form interference light and enter the high-speed camera (7) to record the interference fringes. The image acquisition and processing system is connected to the high-speed camera (7) and is used for interference fringe extraction, phase calculation, temperature field reconstruction and dynamic display.

2. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 1, characterized in that, The optical path compensator (8) is used to adjust the optical path of the reference optical path to match the optical path of the test optical path in the initial state, so as to ensure that a high-contrast initial interference fringes are obtained.

3. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 1, characterized in that, The image acquisition and processing system uses one or more of the Fourier transform method, phase shift method or digital holographic phase inversion method to perform phase calculation on the interference fringes acquired by the high-speed camera (7), and reconstructs the temperature field of the low-temperature phase change material in the sample cavity (13) based on the phase-refractive index-temperature relationship.

4. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 3, characterized in that, The phase-refractive index-temperature relationship is obtained through pre-calibration. The calibration method is to arrange standard temperature measuring elements in the sample cavity (13) and establish the mapping relationship between interference phase and temperature at multiple temperature points.

5. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 1, characterized in that, The low-temperature Dewar includes a Dewar canister and a cold source (9), a cold stage (10), a heater (11), a replaceable cold head (12), a sample chamber (13), and a cold screen (14) disposed inside the Dewar canister. The cold source (9), the cold stage (10) and the heater (11) constitute a temperature control system. The cold source (9) is thermally connected to the cold stage (10) to provide low-temperature cooling to the cold stage (10). The replaceable cold head (12) is detachably connected to the cold stage (10), and the lower end of the replaceable cold head (12) is thermally connected to the sample chamber (13). The heater (11) is thermally connected to the cold stage (10) and achieves constant temperature or program temperature control through a PID controller. The cold screen (14) surrounds the sample chamber (13) and is at the same or nearly the same temperature as the cold stage (10). Optical windows (15) are opened at relative positions on the Dewar jar and the cold screen (14) for the transmission of test light.

6. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 5, characterized in that, The cold source (9) is provided by a refrigeration unit or a cryogenic liquid cold source.

7. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 5, characterized in that, By replacing the replaceable cold head (12) with different shapes or different connection methods, the position, area and geometry of the cold source surface of the replaceable cold head (12) can be changed, thereby simulating different boundary heat transfer conditions.

8. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 5, characterized in that, The cold source surface of the replaceable cold head (12) is one or more of a plane, cylindrical surface, spherical surface, wedge-shaped surface or stepped surface, so as to form boundary conditions of constant temperature, constant heat flow, local cooling or stepped cooling.

9. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 5, characterized in that, The sample chamber (13) is made of a transparent low-temperature heat-resistant material, wherein the transparent low-temperature heat-resistant material is one of quartz glass, borosilicate glass or sapphire; the side of the sample chamber (13) is provided with thermocouple or resistance thermometer sockets for local temperature calibration and monitoring.

10. The low-temperature phase change material temperature field visualization measurement device based on Mach-Zehnder interferometry according to claim 1, characterized in that, The specific process of interference fringe extraction, phase calculation, and temperature field reconstruction in the image acquisition and processing system is as follows: S1. Interference Image Acquisition and Preprocessing: During the low-temperature phase change material melting / solidification experiment, a high-speed camera 7 synchronously acquired an interference fringe image sequence, and preprocessed the interference fringe image sequence by dark field / background subtraction and filtering noise reduction. S2, Phase Extraction: The wrapped phase field is extracted from the preprocessed interference fringe image using Fourier transform, phase shift, or digital holographic inversion methods. ; The spatial coordinates of the temperature location within the sample chamber on the cross section; Indicates the time of image acquisition during the experiment; S3, Phase Unfolding: For the wrapping phase field Perform a joint phase expansion of space or spacetime to obtain a continuous phase field. And based on the phase of the initial steady-state frame of the experiment Using this as a reference, calculate the phase difference: ； S4. Optical path difference and refractive index field inversion: The phase difference is converted into an optical path difference based on the laser wavelength λ, and this is applied to the equivalent thickness of the sample. Inversion of refractive index field under known conditions : ； ； in, This represents the optical path difference at different times and locations. This represents the refractive index of the sample at the initial moment; S5, Temperature Field Reconstruction: The refractive index field is converted into a temperature field by utilizing the thermo-optic relationship of low-temperature phase change materials. : ； Alternatively, the phase difference field can be converted into a temperature field using a calibration curve. : ； in, This indicates the sample temperature at the initial moment. This represents the thermo-optic coefficient of the phase change material. This represents the inversion mapping relationship from phase difference to temperature.

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