Nondestructive testing system and method for membrane interface temperature distribution

Abstract

The invention discloses a nondestructive testing system and method for membrane interface temperature distribution, relates to the field of membrane distillation, and is used for detecting the membrane interface temperature field distribution condition in a real-time, nondestructive and visual manner. Fluorescent tracer particles sensitive to temperature are added into a water inlet solution of a membrane distillation device, under irradiation of laser beams, a high-speed camera is used for shooting a detected area on the surface of a membrane, an image is analyzed, and the water environment temperature is measured based on the linear relation between the fluorescence intensity of the fluorescent tracer particles and the water environment temperature. And the membrane interface temperature distribution condition can be calculated. According to the method, the specific condition of the membrane surface temperature field can be instantaneously, visually and quantitatively represented, and the distribution of the membrane surface temperature field is indirectly detected by using the fluorescent tracer particles, so that the damage to the membrane surface and the influence on system operation are reduced. In addition, the operation state of the main membrane assembly is monitored in real time, and related devices are convenient to repair and replace.

Description

Technical Field

[0001] The present invention relates to the technical field of thin film distillation, in particular to a non-destructive detection system and method for membrane interface temperature distribution in membrane distillation. Background Art

[0002] Membrane distillation (also known as membrane separation) is a modern, emerging technology used for the separation, concentration, and purification of substances. It focuses on the semipermeable membranes used for separation. Currently, membrane separation technology is widely used in the petrochemical industry, food industry, medical industry, biotechnology, environmental engineering, and seawater desalination.

[0003] Some membrane separation technologies, such as membrane distillation, utilize the vapor pressure differential across a porous, hydrophobic membrane as the driving force. Steam molecules permeate the membrane pores, condensing and concentrating, achieving efficient separation of water and solutes. During the separation process, the membrane surface temperature on the feed side is lower than that of the feed solution, while the membrane surface temperature on the permeate side is higher than that of the cooling water. This leads to temperature polarization, a phenomenon in which a temperature boundary layer forms between the membrane surface and the temperature change point on both sides of the membrane. The thicker this layer, the greater the temperature difference between the membrane and the feed, and the more pronounced the temperature polarization.

[0004] However, temperature polarization on the membrane surface can reduce the mass transfer driving force by 40% to 65%, which in turn reduces permeate flux and increases energy consumption, severely impacting the membrane separation process. Therefore, during membrane separation, we need technical means to characterize the membrane surface temperature field, observe the membrane surface in real time, quantitatively characterize temperature polarization, and promptly implement effective measures to minimize its impact on the entire membrane separation process.

[0005] Currently, the technical approaches for characterizing membrane surface temperature polarization include traditional characterization methods and visualization methods. Traditional characterization methods often use temperature sensors installed in membrane distillation units (also known as membrane separation units). Visualization software is then used to observe the membrane surface temperature field in real time and monitor temperature polarization. This method requires modification of the membrane separation unit and may damage the hydrophobic membrane, potentially affecting the entire membrane separation process.

[0006] The most widely used visualization characterization method is to establish a computational fluid dynamics (CFD) model to study temperature polarization. Scholar Aikaterini Katsandri used ANSYS CFX to develop a three-dimensional CFD model and verified the CFD model on a flat plate direct contact membrane distillation device to analyze the temperature polarization coefficient at different contact angles. However, the CFD model requires the use of a large number of equations and algorithms, setting appropriate boundary conditions, and using UDF and FLUENT solvers to obtain a unique solution to the control equation and ultimately obtain the temperature polarization coefficient. In the entire process of building the model, the complex situation in the membrane separation process cannot be fully taken into account, and the selection of algorithms and the setting of boundary conditions will lead to different results. Therefore, the numerical simulation results of the model need to be further verified and calibrated with the help of experimental results.

[0007] Therefore, there is an urgent need for a solution that can timely and non-destructively observe the temperature field of the membrane interface and clearly, accurately and quantitatively characterize the temperature polarization phenomenon of the membrane interface to facilitate subsequent analysis. Summary of the Invention

[0008] The object of the present invention is to provide a non-destructive detection system and method for membrane interface temperature distribution in order to solve all or part of the above problems.

[0009] The technical solution adopted in the present invention is as follows:

[0010] A nondestructive detection system for membrane interface temperature distribution, comprising a membrane distillation device, a hydrophobic membrane, a laser source module, a high-speed camera, and a data processing system;

[0011] The hydrophobic membrane is disposed in the membrane distillation device, and the membrane distillation device is separated by the hydrophobic membrane into two cavities, one cavity being a hot material solution cavity, and the other cavity being a condensate solution cavity. Fluorescent tracer particles are distributed in the solutions of the two cavities, and the fluorescence intensity of the fluorescent tracer particles is linearly related to the water environment temperature. The fluorescent tracer particles are evenly distributed in the inlet water of the hot material solution cavity and the condensate solution cavity;

[0012] When triggered, the laser source module irradiates the surface of the measured area of ​​the hydrophobic membrane in the form of a sheet light source;

[0013] The high-speed camera is arranged at a position where at least a part of the field of view can observe the surface of the membrane in the measured area, and collects the image of the membrane surface when triggered;

[0014] The high-speed camera is connected to the data processing system to transmit the collected membrane surface image to the data processing system;

[0015] The data processing system calculates the hydrophobic membrane interface temperature distribution data based on the linear relationship between the fluorescence intensity of the configured fluorescent tracer particles and the water environment temperature.

[0016] Furthermore, the laser source module includes a laser source, a cylindrical lens and at least one prism; the laser emitted by the laser source is reflected by each prism to the cylindrical lens, and the cylindrical lens converts the laser into a sheet light source to irradiate the surface of the film in the measured area.

[0017] Furthermore, the system also includes an energy detector and a spectroscope; the spectroscope is located on the optical path of the laser source and branches the laser light emitted by the laser source to the energy detector for energy detection.

[0018] Furthermore, the system also includes a synchronous triggering device, which is connected to the high-speed camera and the laser source module respectively to synchronously trigger the high-speed camera and the laser source module.

[0019] Furthermore, the membrane distillation device consists of an upper part and a lower part, and the connection between the upper part and the lower part is sealed; the upper part and the lower part are both provided with water flow cavities, and the hydrophobic membrane is arranged in the middle position of the water flow cavities on both sides.

[0020] Furthermore, one of the upper part and the lower part is connected to a low-temperature water tank via a first circulating water pump, and the other is connected to a high-temperature constant-temperature water tank via a second circulating water pump.

[0021] Furthermore, the low-temperature water tank is located on a balance, and the balance is connected to a data recording device.

[0022] Furthermore, the high-speed camera is equipped with a fluorescent filter.

[0023] The present invention also provides a non-destructive testing method for membrane interface temperature distribution, which is based on the above-mentioned non-destructive testing system for membrane interface temperature distribution and includes:

[0024] During the membrane distillation process, under stable cross-flow velocity and transmembrane temperature difference, fluorescent tracer particles are evenly distributed into the inlet water of the hot material solution chamber and the condensate solution chamber, and the inlet water on both sides is pumped into the hot material solution chamber and the condensate solution chamber of the membrane distillation device respectively;

[0025] Trigger the laser source module and high-speed camera to work synchronously;

[0026] The data analysis system analyzes the membrane surface images collected by the high-speed camera based on the linear relationship between the fluorescence intensity of the configured fluorescent tracer particles and the water environment temperature, and calculates the hydrophobic membrane interface temperature distribution data.

[0027] Furthermore, the hydrophobic membrane interface temperature distribution data calculated by the data analysis system is an average value calculated after analyzing a plurality of consecutive membrane surface images.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. The present invention uses a high-speed camera to observe the changes of temperature-sensitive fluorescent tracer particles under laser excitation, and transmits the data to a data processing system for processing, thereby achieving instantaneous and visual characterization of the specific conditions of the membrane surface temperature field.

[0030] 2. The present invention uses tiny fluorescent tracer particles, such as rhodamine B, to observe the different intensities of fluorescence emitted by them under laser according to the temperature, indirectly indicating the temperature field on the membrane surface, and using non-interfering methods to observe the membrane surface, thereby reducing the damage to the membrane surface and the impact on the test results caused by interfering observation methods.

[0031] 3. The present invention connects the laser to an energy detector to detect and evaluate its energy attenuation and service life, making it easier to repair and replace the machine.

[0032] 4. The present invention changes the direction of the laser through the prism in the laser arm and the viewing angle of the high-speed camera through the reflector, thereby realizing flexible arrangement of the laser source and the high-speed camera position, thereby enhancing the flexibility of the system arrangement. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 This is a simplified model diagram of the nondestructive testing system for membrane interface temperature distribution.

[0035] Figure 2 The invention is an embodiment of the overall design of a nondestructive detection system for membrane interface temperature distribution.

[0036] Figure 3 This is an embodiment of membrane distillation interface temperature field detection.

[0037] Figure 4 It is an embodiment of a nondestructive testing system combined with a membrane distillation system.

[0038] 101-laser source; 102-first prism; 103-second prism; 104-cylindrical lens; 201-high-speed camera; 301-membrane distillation device; 302-hydrophobic membrane; 401-synchronous trigger device; 402-data processing system; 501-beam splitter; 502-light-guiding arm; 503-energy detector; 601-first circulating water pump; 602-second circulating water pump; 603-low-temperature water tank; 604-high-temperature constant-temperature water tank; 605-balance; 606-data recording device; 607-heating stirrer; 608-low-temperature constant-temperature source. DETAILED DESCRIPTION

[0039] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0040] Any feature disclosed in this specification (including any appended claims and abstract), unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0041] Example 1

[0042] A nondestructive detection system for membrane interface temperature distribution includes a membrane distillation device 301, a hydrophobic membrane 302, a laser source module, a high-speed camera 201 and a data processing system 402.

[0043] A hydrophobic membrane 302 is installed in a membrane distillation apparatus 301. The membrane 302 separates two cavities within the apparatus 301: one cavity for the hot feed solution and the other for the condensate solution. Fluorescent tracer particles are evenly distributed in the influent solutions of the hot feed solution and condensate solution chambers. The influent solution of the hot feed solution chamber passes through the hydrophobic membrane 302 as water vapor and condenses and enriches as condensate in the condensate solution chamber, achieving water separation.

[0044] In the flow field, the fluorescent dye Rhodamine B is commonly used to measure the temperature field, and Rhodamine 6G is commonly used to measure the concentration field. The excitation wavelength of Rhodamine B is 500-550nm, and it can emit strong fluorescence within the characteristic wavelength.

[0045] When triggered, the laser source module irradiates the surface of the measured area of ​​the hydrophobic membrane 302 in the form of a sheet light source. Under the action of the laser, the fluorescent tracer particles absorb the laser energy and are excited from a lower energy state to a higher energy state, and then release fluorescence in the form of long-wave light when returning to the lower energy state. The fluorescence intensity of the fluorescent tracer particles is linearly related to the water environment temperature, so the temperature field distribution can be indirectly detected by detecting the fluorescent tracer particles. Figure 1 As shown, in some embodiments, the laser source module does not directly generate the original light sheet, but converts the line light source through a series of optical elements to form a light sheet. Figure 2 As shown, in some specific embodiments, the laser source module includes a laser source 101, a first prism 102, a second prism 103, and a cylindrical lens 104. The laser light emitted by the laser source 101 is reflected by each prism to the cylindrical lens 104. The cylindrical lens 104 is located above the membrane distillation apparatus 301, which then converts the laser light into a sheet light source and irradiates the membrane surface in the measured area. Reflecting the laser light through the two prisms can change its optical path direction, thereby removing the restriction on the position of the laser source 101. In other cases, other numbers of prisms can be designed, which can be flexibly determined according to specific needs.

[0046] The high-speed camera 201 is set at a position where at least part of the field of view can observe the surface of the film in the measured area, and collects the image of the film surface when it is triggered. Figure 3 As shown, the field of view of the high-speed camera 201 is usually directed toward the surface of the film in the test area to maximize the detection range of the test area.

[0047] In some embodiments, the high-speed camera 201 observes the membrane surface of the measured area through a reflector. Specifically, the high-speed camera 201 captures an image of the membrane surface of the measured area (i.e., a membrane surface image) through the reflector. Thus, even if the membrane distillation apparatus 301 limits the viewing window for the membrane surface of the measured area, the reflector can still capture membrane surface images from different directions, greatly increasing the flexibility of the system layout. As a preferred embodiment, the reflector and the hydrophobic membrane 302 can be positioned at the same level, i.e., at the same level as the membrane surface of the measured area. By adjusting the positions of the high-speed camera 201 and the reflector, an optimal observation orientation can be determined.

[0048] In some embodiments, high-speed camera 201 can utilize a CMOS high-speed camera equipped with a 105mm f / 2.8 macro lens. By precisely adjusting the focus distance, the film surface area illuminated by the light sheet can be observed. Furthermore, an expansion ring is installed on high-speed camera 201 to achieve a corresponding magnification effect. Furthermore, the camera lens of high-speed camera 201 is equipped with a long-wavelength filter, which allows the passage of long wavelengths of light and blocks short-wavelength light, reducing background light interference and improving image contrast and clarity, thereby increasing measurement accuracy and reliability.

[0049] High-speed camera 201 is connected to data processing system 402 to transmit captured membrane surface images to the system for analysis. Data processing system 402 includes the necessary data processor and software, which is configured with a linear relationship between the fluorescence intensity of fluorescent tracer particles and the ambient water temperature. Based on this relationship, specific software is used to analyze membrane surface images and calculate the hydrophobic membrane interface temperature distribution data in a very short time.

[0050] As mentioned above, fluorescent tracer particles emit light under the excitation of lasers. Obviously, those skilled in the art will understand that fluorescent tracer particles are matched to the wavelength of the laser. For example, laser source 101 is a dual-wavelength frequency-doubled laser (Nano-L-50-100PV by Litron Lasers), which can excite fluorescent substances at a frequency of 100 Hz to cause them to fluoresce. The laser wavelength is 532 nm. Correspondingly, rhodamine B is selected as the fluorescent reagent and tracer particle. The laser excitation wavelength is 532 nm, which is also a characteristic wavelength of rhodamine B. At 532 nm, rhodamine B can emit strong fluorescence.

[0051] In addition, the high-speed camera 201 captures the fluorescent tracer particles in the luminous state, which is obviously in the laser excitation state. Therefore, in order to ensure the synchronization between the high-speed camera 201 and the laser source module and reduce the slight errors caused by inconsistent machine usage time, a synchronization trigger device 401 is designed in the system. The synchronization trigger device 401 is respectively connected to the high-speed camera 201 and the laser source module to synchronously trigger the high-speed camera 201 and the laser source module.

[0052] The most frequently used and highest-powered component in the system is the laser source 101, which plays a crucial role in the detection results. Therefore, its operational stability must be ensured at all times, and timely maintenance or repairs must be performed in the event of a malfunction. To this end, an energy detector 503 is designed to detect the energy of the laser source 101. In some embodiments, the laser light emitted by the laser source 101 is transmitted by a light guide arm 502. A beam splitter 501 is provided on the optical path transmitted by the light guide arm 502. The beam splitter 501 diverts the laser light emitted by the laser source 101 to the energy detector 503 for energy detection. This allows the use of the laser source 101 to be monitored, facilitating timely maintenance and replacement.

[0053] Membrane distillation apparatus 301 must be transparent to light in order to meet the requirements of high-speed camera 201. In some embodiments, membrane distillation apparatus 301 is made of transparent acrylic and has a small opening on the side of membrane distillation apparatus 301 for the high-speed camera 201 to enter and exit, enabling observation and real-time characterization of the temperature field.

[0054] In some embodiments, the membrane distillation device 301 is made of an acrylic organic glass material with a light transmittance of 92%, and its exterior is concave. The membrane distillation device 301 consists of an upper half and a lower half, and a hydrophobic membrane 302 is arranged in the middle of the two parts, with an effective area of ​​8cm×3cm (only as an example). The upper half and the lower half both include a water inlet and a reflux hole with a pore diameter of 0.5cm and a membrane cavity height of 3.5mm. The upper half and the lower half are both provided with a water flow cavity of a certain size (for example, a length, width and height of about 8cm×3cm×1cm). The upper and lower halves are sealed with a sealing ring and fixed with screws to achieve the purpose of sealing and high pressure resistance. As an example, the upper half is used as a hot material solution chamber, and the lower half is used as a condensate solution chamber.

[0055] like Figure 4As shown, the membrane distillation system also includes a corresponding circulating water pump, water tank, heat source, and cold source. Specifically, it includes a first circulating water pump 601 (corresponding to the low-temperature side), a second circulating water pump 602 (corresponding to the high-temperature side), a low-temperature water tank 603, a high-temperature constant-temperature water tank 604, a balance 605, a data recording device 606, a heating stirrer 607, and a low-temperature constant-temperature source 608. Regarding the water circulation portion, in some embodiments, the upper half of the membrane distillation apparatus 301 is connected to the high-temperature constant-temperature water tank 604 via the second circulating water pump 602, and the lower half is connected to the low-temperature water tank 603 via the first circulating water pump 601. The heating stirrer 607 heats and stirs the feed liquid in the high-temperature constant-temperature water tank 604, while also acting as a heat source to provide heat to the high-temperature constant-temperature water tank 604. The low-temperature constant-temperature source 608 provides a cold source for the low-temperature water tank 603. Of course, the upper and lower halves can also be connected in reverse. The portion connected to the low-temperature water tank 603 collects condensed water. The low-temperature water tank 603 is placed on a balance 605, which is connected to a data recording device 606. Water in the high-temperature constant-temperature water tank 604 and the low-temperature water tank 603 is pumped into the solution chambers on both sides of the surface of the hydrophobic membrane 302 in the membrane distillation apparatus 301 by corresponding circulating water pumps. This creates a vapor pressure difference between the two sides, driving water molecules through the hydrophobic membrane 302 and concentrating on the condensate solution chamber side. The water is then collected in the low-temperature water tank 603 placed on the balance 605. The reading of the balance 605 is recorded in real time by the data recording device 606, realizing a record of the flux.

[0056] Example 2

[0057] After the system layout is completed, the temperature field detection can be started. The non-destructive detection method of the membrane interface temperature distribution in this embodiment includes:

[0058] When the cross-flow velocity and trans-membrane temperature difference of the membrane distillation device reach stability, fluorescent tracer particles are added to the inlet water solution of the solution chambers on both sides, and a magnetic stirrer is used to quickly stir them evenly to achieve uniform distribution of the fluorescent tracer particles in the inlet water solution of the hot material solution chamber and the condensate solution chamber. The fluorescent tracer particles enter the hot material solution chamber and the condensate solution chamber of the membrane distillation device 301 through the circulating water pump along with the inlet water solution.

[0059] The laser source module and high-speed camera 201 are triggered to work synchronously. Fluorescent tracer particles emit fluorescence under the excitation of laser. At this time, the high-speed camera is used to capture the fluorescent tracer particles evenly distributed on the surface of the membrane in the measured area, and obtain an image of the membrane surface, which is automatically transmitted to the data analysis system.

[0060] The data analysis system analyzes the membrane surface image captured by the high-speed camera 201 according to the linear relationship between the fluorescence intensity of the configured fluorescent tracer particles and the water environment temperature, calculates the hydrophobic membrane interface temperature distribution data, and realizes the quantitative characterization of temperature polarization.

[0061] Preferably, in this embodiment, the images captured by the high-speed camera 201 can be transmitted to a data processor equipped with analysis software such as Matlab. By setting an appropriate capture frequency, multiple membrane surface images are obtained, and the analysis results of the resulting continuous membrane surface images are averaged. In post-processing, image processing algorithms are used to subtract interference from the initial images, thereby determining the changes in the temperature polarization layer on both sides of the membrane distillation membrane. In some specific embodiments, after the membrane distillation experiment begins, the software is set to image acquisition mode, the frequency is set to 10 Hz, and the interval between two consecutive frames is approximately 0.1 s. The high-speed camera 201 is used to capture images every 5 minutes to determine the changes in the concentration of the retained substance on the membrane surface. The formation and changes of the temperature polarization layer are then determined based on the particle distribution and fluorescence intensity.

[0062] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A nondestructive testing system for membrane interface temperature distribution, characterized in that: It includes membrane distillation device, hydrophobic membrane, laser source module, high-speed camera and data processing system; The hydrophobic membrane is disposed in the membrane distillation device, and the membrane distillation device is separated by the hydrophobic membrane into two cavities, one cavity being a hot material solution cavity, and the other cavity being a condensate solution cavity. Fluorescent tracer particles are distributed in the solutions of the two cavities, and the fluorescence intensity of the fluorescent tracer particles is linearly related to the water environment temperature. The fluorescent tracer particles are evenly distributed in the inlet water of the hot material solution cavity and the condensate solution cavity; When triggered, the laser source module irradiates the surface of the measured area of ​​the hydrophobic membrane in the form of a sheet light source; The high-speed camera is arranged at a position where at least a part of the field of view can observe the surface of the membrane in the measured area, and collects the image of the membrane surface when triggered; The high-speed camera is connected to the data processing system to transmit the collected membrane surface image to the data processing system; The data processing system calculates the hydrophobic membrane interface temperature distribution data based on the linear relationship between the fluorescence intensity of the configured fluorescent tracer particles and the water environment temperature.

2. The nondestructive testing system for membrane interface temperature distribution according to claim 1, characterized in that: The laser source module includes a laser source, a cylindrical lens and at least one prism; the laser light emitted by the laser source is reflected by each prism to the cylindrical lens, and the cylindrical lens converts the laser light into a sheet light source to irradiate the surface of the film in the measured area.

3. The nondestructive testing system for membrane interface temperature distribution according to claim 2, characterized in that: It also includes an energy detector and a spectroscope; the spectroscope is located on the optical path of the laser source and splits the laser light emitted by the laser source to the energy detector for energy detection.

4. The nondestructive testing system for membrane interface temperature distribution according to claim 1, characterized in that: It also includes a synchronous triggering device, which is connected to the high-speed camera and the laser source module respectively to synchronously trigger the high-speed camera and the laser source module.

5. The nondestructive testing system for membrane interface temperature distribution according to claim 1, characterized in that: The membrane distillation device consists of an upper part and a lower part, and the connection between the upper part and the lower part is sealed; the upper part and the lower part are both provided with water flow cavities, and the hydrophobic membrane is arranged in the middle of the water flow cavities on both sides.

6. The nondestructive testing system for membrane interface temperature distribution according to claim 5, characterized in that: One of the upper part and the lower part is connected to a low-temperature water tank through a first circulating water pump, and the other is connected to a high-temperature constant-temperature water tank through a second circulating water pump.

7. The nondestructive testing system for membrane interface temperature distribution according to claim 6, characterized in that: The low-temperature constant-temperature water tank is located on a balance, and the balance is connected to a data recording device.

8. The nondestructive testing system for membrane interface temperature distribution according to claim 1, characterized in that: The high-speed camera is equipped with a fluorescence filter.

9. A non-destructive testing method for membrane interface temperature distribution, the method being based on the non-destructive testing system for membrane interface temperature distribution according to claim 1, characterized in that: include: During the membrane distillation process, under stable cross-flow velocity and transmembrane temperature difference, fluorescent tracer particles are evenly distributed into the inlet water of the hot material solution chamber and the condensate solution chamber, and the inlet water on both sides is pumped into the hot material solution chamber and the condensate solution chamber of the membrane distillation device respectively; Trigger the laser source module and high-speed camera to work synchronously; The data analysis system analyzes the membrane surface images collected by the high-speed camera based on the linear relationship between the fluorescence intensity of the configured fluorescent tracer particles and the water environment temperature, and calculates the hydrophobic membrane interface temperature distribution data.

10. The non-destructive testing method for membrane interface temperature distribution according to claim 9, characterized in that: The hydrophobic membrane interface temperature distribution data calculated by the data analysis system is an average value calculated after analyzing a plurality of consecutive membrane surface images.

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