A method and device for measuring the residence time distribution in a colorless and transparent microchannel

Abstract

The present invention discloses a method and device for measuring the residence time distribution in a colorless and transparent microchannel. The method includes: arranging a measuring device; a liquid supply assembly injects dyes and water with different concentrations into the microchannel at a fixed flow rate. After the flow state is stable, the image acquisition device is started to record a video of a fixed time length at an observation point and transmit it to an image and data processing system. After processing, the gray values at the observation point under different dye concentrations are obtained, and the absorbance is calculated to obtain the relationship between the absorbance and the concentration; the microchannel is filled with water, and the liquid supply assembly injects a certain concentration of dye into the microchannel at a fixed flow rate. At the same time, the image acquisition device is started, and the video is transmitted to the image and data processing system to obtain the gray values and absorbance at the observation point changing with time; furthermore, the concentration change at the observation point at different times is obtained to analyze the residence time distribution. The measuring device and method of the present invention are simple and easy to operate, greatly reducing the measurement time and cost.

Description

Technical Field

[0001] The present invention relates to the field of reaction engineering, and particularly to a method and device for measuring the residence time distribution in a colorless and transparent microchannel. Background Art

[0002] The degree of completion of a chemical reaction is related to the residence time of the reactants in the reactor. Generally speaking, the longer the residence time, the more complete the reaction. Studying the residence time distribution in the reactor is crucial for understanding the flow of materials in the reactor and the yield and selectivity of the final reaction. The reactions carried out in a microreactor have higher conversion rates and selectivities. As a typical microreactor, the measurement of the residence time distribution inside the microchannel is beneficial to deepen the understanding of microreactions. However, the current measurement of the residence time distribution often requires the use of complex and costly instrument equipment such as ultraviolet-visible spectrometers and fluorescence microscopes. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention proposes a method and device for measuring the residence time distribution in a colorless and transparent microchannel, which simplifies the measurement device and steps and reduces the measurement cost. The specific technical solutions are as follows:

[0004] A method for measuring the residence time distribution in a colorless and transparent microchannel, which is realized based on a measurement device. The measurement device includes: a liquid supply component, an illumination component, a microchannel, an image acquisition device, and an image and data processing system; the liquid supply component is communicated with the microchannel, and the illumination component is used for emitting visible light; the microchannel is colorless and transparent and is fixedly connected to the illumination component; one end of the microchannel communicated with the liquid supply component is the inlet, and the other end is the outlet. The image acquisition device is arranged directly above the outlet of the microchannel; the image acquisition device transmits the collected image information to the image and data processing system;

[0005] The method for measuring the residence time distribution in the colorless and transparent microchannel includes the following steps:

[0006] Step 1: Arrange the measurement device;

[0007] Step 2: The liquid supply component injects different concentrations of dye solutions and water into the microchannel at a fixed flow rate respectively. After the flow state is stable, the image acquisition device is turned on. After recording a video with a fixed time length, it is transmitted to the image and data processing system, and the center point of the shooting area of the image acquisition device is used as the observation point; the image and data processing system processes to obtain the gray values of the observation point under different dye concentrations, calculates the absorbance according to the gray values, and thus obtains the fitting relationship between the absorbance and the concentration;

[0008] Step 3: Fill the microchannel with water, load a dye solution of a certain concentration into the liquid supply component, and inject it into the microchannel at the same flow rate as in Step 2. At the same time, turn on the image acquisition device to record a video. When the microchannel is filled with the dye solution and the color in the microchannel no longer changes, stop recording and transmit the video to the image and data processing system to obtain the gray values of the observation points changing with time, and then obtain the absorbance of the observation points at different times. According to the fitting relationship between absorbance and concentration, obtain the concentration changes of the observation points at different times, and then analyze the residence time distribution.

[0009] Further, in Step 2, use water as a solvent to prepare dye solutions with concentrations of C0, 0.75C0, 0.5C0, 0.25C0, 0.1C0, 0.05C0, 0.025C0, and 0.01C0 respectively. The liquid supply component injects these dye solutions of different concentrations and water into the microchannel at a fixed flow rate.

[0010] Further, the image and data processing system includes a video processing module and a gray value extraction module. For any dye concentration, the video processing module intercepts a video picture at fixed intervals. The video picture is an RGB three-channel picture. The gray value extraction module divides the RGB three-channel video picture into single-channel pictures and uses the picture of a certain channel to extract the gray value of the observation point. Take the average of the gray values obtained by processing all the video pictures obtained by the video processing module through the gray value extraction module to obtain the gray value of the observation point at this dye concentration.

[0011] Further, in Step 2, the expression for calculating absorbance based on the gray value is as follows:

[0012]

[0013] In the formula, Abs is the absorbance, I is the transmitted light intensity, that is, the gray value of the observation point at a certain dye concentration; I0 is the incident light intensity, that is, the gray value of the observation point when the dye concentration is 0.

[0014] Further, in Step 3, after obtaining the concentration changes of the observation points at different times, plot the F-t image of the specific concentration changing with time and perform filtering processing on it. Based on the moving average principle, take a certain number of data points near a certain data point and calculate the average value of these data points, and use this average value as the new value of this data point. After all data points are averaged to obtain new data points, connect the new data points to obtain the filtered F-t curve;

[0015] Convert the relationship between the specific concentration and time into the relationship between the residence time distribution density and time. The specific expression is:

[0016]

[0017] Wherein, t i is the time corresponding to the i-th data point, F i is the specific concentration corresponding to the i-th data point, E i is the residence time distribution density corresponding to the i-th data point;

[0018] According to the relationship between the residence time distribution density and time, an E-t image is plotted; according to the relationship between the residence time distribution density and time, the average residence time t m of the dye in the microchannel in the dye solution is calculated, that is, the average flow time from the inlet of the microchannel to the observation point, and the calculation expression is:

[0019]

[0020] Wherein, n is the total number of data points in the E-t image.

[0021] Furthermore, in the second step, the liquid supply assembly injects dye solutions with different concentrations into the microchannel at a flow rate of 0.01-1 mL / min.

[0022] Furthermore, in the second step, the image acquisition device records a 30s video, and the video processing module of the image and data processing system intercepts a video picture every 1 second.

[0023] A measuring device for the residence time distribution in a colorless and transparent microchannel, comprising: an injection pump, a syringe, a liquid guide tube, a microchannel, an LED backlight, an image acquisition device, and an image and data processing system;

[0024] The injection pump, the syringe, and the liquid guide tube form the liquid supply assembly. The syringe is pressed on the injection pump, and the syringe is filled with a dye solution. The injection pump is used to control the flow rate output by the syringe; one end of the liquid guide tube is communicated with the syringe, and the other end is communicated with the microchannel;

[0025] The LED backlight is an illumination assembly. The microchannel is horizontally placed on the LED backlight so that the visible light emitted by the LED backlight can penetrate the microchannel; the image acquisition device is arranged directly above the outlet of the microchannel and is connected to the image and data processing system; the image and data processing system can process and obtain the gray value of the observation point.

[0026] Furthermore, the injection pump is used to control the flow rate output by the syringe to be adjusted within the range of 0.001-20 mL / min.

[0027] Furthermore, the channel diameter range of the microchannel is 100-1000 μm.

[0028] The beneficial effects of the present invention are:

[0029] (1) The present invention has low requirements for the tracer. It only needs to present a certain color under visible light and be soluble in water, and does not need to use materials such as fluorescent particles that require specific light sources to emit light. The light source of the present invention does not need to use high-energy light sources such as ultraviolet light, and only using a visible light source can achieve the measurement of the residence time distribution in a colorless and transparent microchannel.

[0030] (2) The present invention does not need to use devices such as optical fiber probes. The image acquisition device only needs to be able to clearly record the video of the liquid flow in the microchannel, and the image acquisition device occupies a small space.

[0031] (3) The present invention sets the image acquisition frequency according to the flow rate of the liquid in the microchannel, which can ensure the sampling accuracy. The steps are simple and easy to operate, greatly reducing the measurement time and cost. Description of the Drawings

[0032] Figure 1 is a schematic structural diagram of the device of the present invention.

[0033] Figure 2 is a schematic flow diagram of the method of the present invention.

[0034] Figure 3 is a schematic diagram of the principle of calculating the absorbance according to the gray value of the present invention.

[0035] Figure 4 is the calibration curve of absorbance - specific concentration in the embodiment of the present invention.

[0036] Figure 5 is the F - t image of the concentration changing with time in the embodiment of the present invention.

[0037] Figure 6 is the E - t image of the residence time distribution density changing with time in the embodiment of the present invention.

[0038] In the figure, injection pump 1, syringe 2, liquid guide tube 3, microchannel 4, LED backlight 5, image acquisition device 6, beaker 7. Detailed Embodiments

[0039] The present invention will be described in detail below according to the drawings and preferred embodiments. The purpose and effect of the present invention will become more clear. The present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] As Figure 1 shown, the device for measuring the residence time distribution in a colorless and transparent microchannel includes: a liquid supply assembly, an illumination assembly, a microchannel 4, an image acquisition device 6, and an image and data processing system.

[0041] Among them, the liquid supply assembly includes: an injection pump 1, a syringe 2, and a liquid guide tube 3. The injection pump 1 is placed horizontally, the syringe 2 is pressed tightly on the injection pump 1, the syringe 2 is filled with the liquid to be measured, one end of the liquid guide tube 3 is communicated with the syringe 2, and the other end is communicated with the microchannel 4; the injection pump 1 is used to control the flow rate output by the syringe 2, and the flow rate can be adjusted between 0.001 - 20 mL / min.

[0042] The lighting assembly selects an LED backlight 5 for emitting white light. The microchannel 4 is colorless and has good transparency, and the channel diameter is between 100 - 1000 μm. The microchannel 4 is placed horizontally on the LED backlight 5 so that the white light emitted by the LED backlight 5 can penetrate the microchannel 4. One end of the microchannel 4 communicated with the liquid guide tube 3 is the inlet, and the other end is the outlet; the image acquisition device 6 is located directly above the outlet of the microchannel 4 for taking images inside the microchannel 4, and the image acquisition device 6 needs to be able to magnify 3 times or more; the image acquisition device 6 transmits the acquired image information to the image and data processing system. The image and data processing system includes a video processing module and a grayscale extraction module. Among them, the video processing module is used to intercept a frame of picture from the image information at regular intervals, and the grayscale extraction module is used to convert the RGB three-channel picture obtained by the video processing module into a single-channel picture, and calculate its grayscale value according to the color of the dye solution by selecting a certain channel picture.

[0043] As Figure 2 shown, the method for measuring the residence time distribution in a colorless and transparent microchannel specifically includes the following steps:

[0044] Step 1: Arrange the measuring device for the residence time distribution in the colorless and transparent microchannel, specifically: fix the syringe 2 on the injection pump 1, fix the microchannel 4 flat on the LED backlight 5, align the image acquisition device 6 with the observation position, which is close to the outlet of the microchannel 4, and adjust the magnification to make the image inside the microchannel 4 captured clear.

[0045] Step 2: Calibrate the absorbance - specific concentration curve, which is specifically realized through the following sub-steps:

[0046] (2.1) Configure dye solutions with different concentrations. If the concentration of the undiluted dye solution is C0, use water as the solvent to configure dye solutions with concentrations of 0.75C0, 0.5C0, 0.25C0, 0.1C0, 0.05C0, 0.025C0, and 0.01C0 respectively; in this embodiment, methylene blue is used as the dye solution.

[0047] (2.2) Fill the syringes 2 with staining solutions having concentrations of C0, 0.75C0, 0.5C0, 0.25C0, 0.1C0, 0.05C0, 0.025C0, 0.01C0, and 0 (a concentration of 0 means water). Set the propulsion speed of the syringe pump 1 and inject the staining solution into the microchannel 4 at a fixed flow rate of 0.01 - 1 mL / min. For any staining solution concentration, after its flow state stabilizes, turn on the image acquisition device 6, record a video for a certain period of time, and use the center point of the shooting area of the image acquisition device 6 as the observation point. In this embodiment, the propulsion speed of the syringe pump 1 is 0.01 mL / min, and the duration of the video recorded by the image acquisition device 6 is 30 s.

[0048] (2.3) The image acquisition device 6 transmits the recorded video to the image and data processing system. The video processing module of the image and data processing system intercepts a video picture at fixed intervals. This video picture is an RGB three-channel picture. The grayscale extraction module divides the RGB three-channel video picture into single-channel pictures and extracts the grayscale value of the observation point from a certain channel picture according to the color of the staining solution. In this embodiment, since the staining solution methylene blue is blue, the picture of the green channel is selected to extract the grayscale value of the observation point. Take the average of the grayscale values obtained by processing all the video pictures obtained by the video processing module through the grayscale extraction module to obtain the grayscale value of the observation point at this staining solution concentration, so as to reduce errors. In this embodiment, the video processing module intercepts a video picture every 1 s, and takes the average of the grayscale values obtained by processing the 30 pictures through the grayscale extraction module.

[0049] (2.4) Calculate the absorbance based on the grayscale values of the observation points at different staining solution concentrations, thereby calibrating the absorbance - specific concentration curve.

[0050] Calculating the absorbance based on the grayscale value is achieved based on the Lambert - Beer law. The expression of the Lambert - Beer law is:

[0051]

[0052] In the formula, Abs is the absorbance, T is the transmittance, K is the absorption coefficient of the sample, C is the sample concentration, and L is the length of the sample in the optical path.

[0053] As Figure 3 shown, it can be seen from the Lambert - Beer law that the absorbance has a linear relationship with the sample concentration. When calculating the absorbance according to the grayscale value of the observation point corresponding to the staining solution concentration in the present invention, the following expression is used:

[0054]

[0055] Wherein, I is the intensity of transmitted light, i.e., the gray value of the observation point; I0 is the intensity of incident light, i.e., the gray value of the observation point when the dye concentration is 0.

[0056] The relational expression between absorbance and concentration is obtained:

[0057] Abs = k × C

[0058] Wherein, k is the proportionality coefficient, which is calculated from the corresponding relationships of multiple groups of absorbance and concentration.

[0059] The calibrated absorbance-specific concentration curve is as Figure 4 shown. Taking the specific concentration as the abscissa and the absorbance as the ordinate, the specific concentration is the ratio of the current dye concentration to the original dye concentration, that is, the concentration is normalized to make it dimensionless. Since the original concentration is determined for a certain research system, the relationship between Abs and the specific concentration is also a proportional relationship. From Figure 4 it can be seen that the relationship between the absorbance Abs and the specific concentration C′ is Abs = 0.39′, and the R 2 value of its fitting formula is as high as 0.9975, indicating that the linear relationship between absorbance and specific concentration is good.

[0060] Step 3: Experimental data is collected and processed to obtain the residence time distribution. It is specifically realized through the following sub-steps:

[0061] (3.1) Fill the microchannel 4 with water, load the undiluted (i.e., concentration C0) dye solution into the syringe 2, set the propulsion speed of the syringe pump 1 and start it, inject the dye solution into the microchannel 4 at the same flow rate as in step 2.2, and at the same time turn on the image acquisition device 6 to start recording the video. When the microchannel 4 is filled with the dye solution and the color in the microchannel no longer changes, end the video recording.

[0062] (3.2) The image acquisition device 6 transmits the captured video to the image and data processing system, and the image and data processing system processes to obtain the gray value of the observation point changing with time, and obtains the absorbance at different times from formula (2).

[0063] (3.3) According to the relational expression between absorbance and concentration obtained in step two, calculate the concentration values at different times.

[0064] Analyze the obtained concentration values at different times to obtain the residence time distribution in the microchannel, specifically:

[0065] According to the concentration values at different times, draw an F-t image of the specific concentration changing with time as Figure 5 shown, wherein, t is the time elapsed since the syringe 2 started to introduce the dye solution into the microchannel 4, and F is the value of the specific concentration. From Figure 5It can be seen that the specific concentration values obtained from the experiment fluctuate greatly. Therefore, it is necessary to filter them. The filtering process is based on the principle of moving average. For a certain data point, a certain number of data points near it are taken and the average value of these data points is calculated. This average value is used as the new value of this data point. This processing can reduce the fluctuation degree of the data points. After filtering, connecting each data point to obtain a curve, that is, the F-t curve, which is the curve of the experimental data after filtering in Figure 5

[0066] Let t i be the time corresponding to the i-th data point, and F i be the specific concentration corresponding to the i-th data point. The relationship between the specific concentration and time is converted into the relationship between the residence time distribution density and time. The specific expression is:

[0067]

[0068] In the formula, E i is the residence time distribution density corresponding to the i-th data point.

[0069] According to the relationship between the residence time distribution density and time, an E-t image as shown in Figure 6 is drawn. Similarly, filtering can be performed again according to actual needs. The peak of the E-t curve corresponds to the place where the slope of the F-t curve is the largest, indicating that most of the dyes in the dye solution flow through the observation point at this moment. Recording the proportion of dyes at different residence times, the residence time distribution in the microchannel can be obtained.

[0070] The average residence time t m of the dye in the microchannel 4 can also be calculated through the relationship between the residence time distribution density and time, that is, the average flow time from the inlet to the observation point. The calculation expression is:

[0071]

[0072] where n is the total number of data points in the E-t image.

[0073] According to the average residence time t m of the dye in different microchannels 4, the flow conditions of the dye in different microchannels 4 can be compared and analyzed, so as to optimize the shape and size of the microchannel 4. In this embodiment, the distance from the inlet of the microchannel 4 to the observation point is 240 mm, and the channel diameter of the microchannel 4 is 400 μm, thus obtaining t m = 188.3 s.

[0074] ​The present invention has low requirements for the tracer (i.e., the dye solution). It only needs to present a certain color under visible light and be soluble in water, and there is no need to use materials such as fluorescent particles that require specific light sources to emit light. The light source of the present invention does not need to use high-energy light sources such as ultraviolet light, and a visible light source can meet the requirements. The present invention does not need to use devices such as optical fiber probes. The image acquisition device only needs to be able to record videos and have a magnification of more than 3 times, and the image acquisition device occupies a small space. The present invention can ensure the sampling accuracy by setting the image acquisition frequency according to the flow rate of the liquid in the microchannel. In summary, the present invention uses a simple device and method to measure the residence time distribution in a colorless and transparent microchannel only using visible light. The steps are simple and easy to operate, greatly reducing the measurement time and cost.

[0075] Those of ordinary skill in the art can understand that the above are only preferred examples of the invention and are not used to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing examples or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principle of the invention shall be included in the protection scope of the invention.

Claims

1. A method for measuring the residence time distribution in a colorless and transparent microchannel, characterized in that Implemented based on a measuring device, which includes: a liquid supply component, an illumination component, a microchannel, an image acquisition device, and an image and data processing system; the liquid supply component is in communication with the microchannel, and the illumination component is used to emit visible light; the microchannel is colorless and transparent and is fixedly connected to the illumination component; one end of the microchannel in communication with the liquid supply component is the inlet, and the other end is the outlet, and the image acquisition device is arranged directly above the outlet of the microchannel; the image acquisition device transmits the acquired image information to the image and data processing system; The method for measuring the residence time distribution in the colorless and transparent microchannel includes the following steps: Step 1: Arrange the measuring device; Step 2: The liquid supply component injects dyed solutions with different concentrations and water into the microchannel at a fixed flow rate. After its flow state is stable, the image acquisition device is turned on. After recording a video with a fixed time length, it is transmitted to the image and data processing system, and the center point of the shooting area of the image acquisition device is used as the observation point; after processing by the image and data processing system, the gray values of the observation point at different dyed solution concentrations are obtained, and the absorbance is calculated based on the gray values, so as to obtain the fitting relationship between the absorbance and the concentration; Step 3: Fill the microchannel with water, load a dyed solution with a certain concentration into the liquid supply component, and inject it into the microchannel at the same flow rate as in Step 2. At the same time, turn on the image acquisition device to record the video. When the dyed solution fills the microchannel and the color in the microchannel no longer changes, stop recording and transmit the video to the image and data processing system to obtain the gray values of the observation point changing with time, and then obtain the absorbance of the observation point at different times; according to the fitting relationship between the absorbance and the concentration, obtain the concentration change of the observation point at different times, and then analyze the residence time distribution; In Step 3, after obtaining the concentration change of the observation point at different times, draw an F-t image of the specific concentration changing with time and perform filtering processing on it. Based on the moving average principle, take a certain number of data points near a certain data point and calculate the average value of these data points, and use this average value as the new value of this data point. When the average values of all data points are taken to obtain new data points, connect the new data points to obtain the filtered F-t curve; Convert the relationship between the specific concentration and time into the relationship between the residence time distribution density and time, and the specific expression is: where t i is the time corresponding to the i-th data point, F i is the specific concentration corresponding to the i-th data point, and E i is the residence time distribution density corresponding to the i-th data point; According to the relationship between the residence time distribution density and time, an E-t image is plotted; according to the relationship between the residence time distribution density and time, the average residence time t of the dye in the dye solution in the microchannel is calculated m , that is, the average flow time from the inlet of the microchannel to the observation point, and the calculation expression is as follows: In the formula, n is the total number of data points in the E-t image.

2. The method for measuring the residence time distribution in a colorless and transparent microchannel according to claim 1, wherein, In Step 2, use water as a solvent to prepare dyed solutions with concentrations of C0, 0.75C0, 0.5C0, 0.25C0, 0.1C0, 0.05C0, 0.025C0, and 0.01C0 respectively, and the liquid supply component injects these dyed solutions with different concentrations and water into the microchannel at a fixed flow rate.

3. The method for measuring the residence time distribution in a colorless and transparent microchannel according to claim 1, characterized in that, The described image and data processing system includes a video processing module and a grayscale extraction module. For any dye concentration, the video processing module captures a video picture every fixed time interval. The video picture is an RGB three-channel picture. The grayscale extraction module splits the RGB three-channel video picture into single-channel pictures and uses the picture of a certain channel to extract the grayscale value of the observation point. The average value of the grayscale values obtained after processing all the video pictures obtained by the video processing module through the grayscale extraction module is taken to obtain the grayscale value of the observation point at this dye concentration.

4. The method for measuring the residence time distribution in a colorless and transparent microchannel according to claim 1, characterized in that, In the second step, the expression for calculating the absorbance based on the grayscale value is as follows: In the formula, Abs is the absorbance, I is the transmitted light intensity, that is, the grayscale value of the observation point at a certain dye concentration; I0 is the incident light intensity, that is, the grayscale value of the observation point when the dye concentration is 0.

5. The method for measuring the residence time distribution in a colorless and transparent microchannel according to claim 1, characterized in that, In the second step, the liquid supply component injects dyes with different concentrations into the microchannel at a flow rate of 0.01 - 1 mL / min.

6. The method for measuring the residence time distribution in a colorless and transparent microchannel according to claim 3, wherein In the second step, the image acquisition device records a 30-s video, and the video processing module of the image and data processing system captures a video picture every 1 second.

7. A measuring device for the residence time distribution in a colorless and transparent microchannel, adopting the measuring method described in any one of claims 1-6, characterized in that It includes: an injection pump, a syringe, a liquid guiding tube, a microchannel, an LED backlight, an image acquisition device, and an image and data processing system; The injection pump, syringe, and liquid guiding tube form the liquid supply component. The syringe is pressed tightly on the injection pump. The syringe is filled with dye. The injection pump is used to control the flow rate output by the syringe. One end of the liquid guiding tube is connected to the syringe, and the other end is connected to the microchannel; The LED backlight is an illumination component. The microchannel is horizontally placed on the LED backlight so that the visible light emitted by the LED backlight can penetrate the microchannel. The image acquisition device is arranged directly above the outlet of the microchannel and is connected to the image and data processing system. The image and data processing system can process and obtain the grayscale value of the observation point.

8. The measuring device for the residence time distribution in a colorless and transparent microchannel according to claim 7, characterized in that, The injection pump is used to control the flow rate output by the syringe to be adjusted within the range of 0.001 - 20 mL / min.

9. The measuring device for the residence time distribution in a colorless and transparent microchannel according to claim 7, characterized in that The channel diameter range of the microchannel is 100 - 1000 μm.

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