A method, system and apparatus for fluid microflow rate determination

Abstract

This invention relates to the technical field of fluid microvelocity measurement, and proposes a method, system, and apparatus for fluid microvelocity measurement. The method includes the following steps: two microneedles are fixed in the fluid to be measured, and droplets or bubbles are injected into the microneedles under controlled conditions, with the droplets or bubbles suspended at the intersection of the tops of the two microneedles; images are acquired to obtain the morphological parameters of the droplets or bubbles in the fluid to be measured; a flow velocity calculation formula is constructed based on the energy relationship between the surface tension of the droplets or bubbles and the fluid resistance; the flow velocity of the fluid to be measured is obtained and output based on the morphological parameters of the droplets or bubbles and the flow velocity calculation formula. This invention relies on the energy relationship between the surface tension of the droplets or bubbles and the fluid resistance to convert the flow velocity change into observable droplet or bubble interface displacement deformation, thereby obtaining the fluid flow velocity. It has a simple structure, low cost, and high stability.

Description

Technical Field

[0001] This invention relates to the technical field of fluid microvelocity measurement, and in particular to a method, system, and apparatus for fluid microvelocity measurement. Background Technology

[0002] Precise measurement of fluid microvelocities is a core technological requirement in fields such as microfluidic chips, biomedical detection, precision chemicals, environmental microfluidic monitoring, and microelectromechanical systems (MEMS) flow sensing. It plays a crucial supporting role in characterizing microscale fluid behavior, process control, and quantitative analysis. Traditional microvelocity detection methods mainly include differential pressure velocimetry, thermal velocimetry, laser Doppler velocimetry, and particle image velocimetry. Among them, differential pressure sensors require sensitive structures to be set in the flow channel, which can easily cause flow field disturbances and have insufficient sensitivity to low flow velocities. Thermal velocimetry relies on temperature field changes, which can easily damage biological samples and heat-sensitive fluids, and the measurement accuracy is significantly affected by ambient temperature. Optical velocimetry methods require the introduction of tracer particles, which are complex to operate, costly, difficult to miniaturize and integrate, and unsuitable for in-situ detection of transparent or highly scattering fluids.

[0003] Current microflow velocity measurements mainly rely on technologies such as particle imaging velocimetry (PIV / PTV), laser Doppler velocimetry (LDV), thermal microsensors, differential pressure microflowmeters, and MEMS flow sensors. Particle imaging and laser Doppler methods require introducing tracer particles into the fluid, which can easily alter flow field properties, interfere with the activity of biological samples, and rely on expensive optical systems and complex image algorithms, resulting in insufficient stability for measurements at ultra-low flow velocities and in small spaces. Thermal microsensors achieve flow velocity conversion through heat transfer between a heating element and the fluid, but suffer from problems such as direct heating damage to the measured fluid, significant noise, and large errors in the low-sensitivity region. The detection of microfluidics and thermosensitive media is significantly limited; mechanical sensing methods such as differential pressure and turbine sensors are prone to clogging, excessive pressure loss, and lag in dynamic response within microchannels, and it is difficult to guarantee linearity and repeatability in low flow rate ranges; although MEMS flow sensors have high integration, their manufacturing process is complex and costly, and it is difficult to directly establish a stable correlation between flow velocity and sensitive signal in microdroplet or micro-suspension droplet systems dominated by interfacial tension. Therefore, developing a simple, non-destructive, and highly sensitive method for measuring fluid microvelocities is of great practical significance and application value for improving the control accuracy and application range of microfluidic systems. Summary of the Invention

[0004] To address the aforementioned shortcomings, the present invention aims to provide a method, system, and apparatus for measuring fluid microvelocities, thereby solving the problems of high cost, insufficient stability, and poor adaptability of existing technologies.

[0005] To achieve this objective, the present invention adopts the following technical solution: A method for measuring fluid microvelocities includes the following steps: S1, the tips of two microneedles are crossed and fixed in the fluid being measured, and droplets or bubbles are injected into the microneedles. The droplets or bubbles are suspended at the intersection of the tips of the two microneedles. S2, acquire images to obtain the morphological parameters of droplets or bubbles in the fluid under test; S3, a flow velocity calculation formula is constructed based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance; S4, based on the morphological parameters of droplets or bubbles and the velocity calculation formula, obtains and outputs the velocity of the fluid being measured.

[0006] Preferably, in step S3, the energy relationship is: ,in ， Indicates the surface tension of a droplet or bubble. This represents the surface area of ​​a spherical droplet or bubble. This represents the length of the semi-major axis of the ellipsoid. Indicates the drag coefficient. This indicates the density of the fluid being measured. ， ， This indicates the length of the minor axis of the ellipsoid; Obtain flow rate Calculation formula: ,in Indicates the volume of a droplet or bubble. A represents the derivative of the ellipsoid's surface area with respect to its major axis.

[0007] Where e represents the eccentricity of the ellipsoid, ; .

[0008] Preferably, step S1 specifically includes: By controlling the valve opening time, the solution is injected through the microchannel inside the microneedle, so that the solution is injected into the intersection of the two microneedles to form droplets or bubbles; Control the solution injection volume at 1 .

[0009] Preferably, step S2 specifically includes: A clear image of the droplet or bubble is obtained by capturing a top view of the droplet or bubble using a camera and performing edge detection on the image under test. Obtain the droplet or bubble contour information from the clear image to obtain the droplet or bubble morphology parameters: the length of the minor semi-axis of the droplet or bubble ellipsoid. The length c of the semi-major axis of the droplet or bubble ellipsoid.

[0010] This invention proposes a system for measuring fluid microvelocities, comprising: The solution control module is used to control the injection of solution into the microneedles and keep the droplets or bubbles suspended at the intersection of the tops of the two microneedles; The image acquisition module acquires the morphological parameters of droplets or bubbles in the fluid being measured. The formula construction module constructs a flow velocity calculation formula based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance. The calculation output module is used to calculate the flow velocity of the measured fluid flowing through droplets or bubbles.

[0011] This invention proposes a device for measuring fluid microflow rate, characterized in that it includes two sets of microneedles, a camera, a solution injection mechanism, and a processor, wherein the processor is used to execute the method for measuring fluid microflow rate; The two sets of microneedles are fixed in the fluid being measured, and the tips of the two sets of microneedles are close together to form droplet or bubble suspension points; The camera is positioned directly above the microneedle and is used to capture images of droplets or bubbles.

[0012] Preferably, the microneedle has a through-channel inside, and the solution injection mechanism is connected to the microchannel at the bottom of the microneedle to inject the solution from the bottom of the microchannel and output it as droplets or bubbles from the top of the microchannel.

[0013] Preferably, the microneedles are made of stainless steel, tungsten, nickel-titanium alloy, titanium, copper, platinum, gold, glass, or ceramic. The surface of the microneedle is provided with a micro-nano etched layer or coated with an inorganic coating to enhance the adhesion of droplets or bubbles and prevent droplets or bubbles from falling off under the impact of fluid.

[0014] Preferably, the device further includes a light source assembly for irradiating droplets or bubbles on the microneedles.

[0015] Preferably, the output end of the solution injection mechanism is equipped with a solenoid valve and a flow meter. The solenoid valve is used to control the opening and closing of the solution injection, and the flow meter is used to control the solution injection volume.

[0016] One of the above technical solutions has the following advantages or beneficial effects: This invention utilizes the energy relationship between the surface tension of droplets or bubbles and fluid resistance to transform changes in flow velocity into observable displacement deformation at the droplet or bubble interface. It offers advantages such as simple structure, high integration, fast response, and applicability to low flow rates and low velocity ranges. It overcomes the shortcomings of existing technologies in detecting trace biological samples, volatile liquids, and low-viscosity fluids. It requires no insertable probes, no heating, no tracers, and does not alter the flow field or fluid composition. It only requires two microneedles for imaging and acquisition, eliminating the need for complex microfabrication sensors and precision drives. The device is simple, low-cost, highly stable, and easily integrated into microfluidic chips and piping systems. Using the energy balance of droplet or bubble surface tension and fluid resistance as its core physical model, it directly calculates flow velocity through morphological parameters, resulting in clear physical meaning, simple calibration, and minimal susceptibility to environmental interference. Attached Figure Description

[0017] Figure 1 This is a flowchart of one embodiment of the method proposed in this invention; Figure 2 This is a schematic diagram of the structure of one embodiment of the system proposed in this invention; Figure 3 This is an overall schematic diagram of one embodiment of the device proposed in this invention; Figure 4 This is a schematic diagram of the internal structure of a microneedle in one embodiment of the device proposed in this invention.

[0018] The components include: microneedles 1, droplets or bubbles 100, the fluid to be measured 200, microchannels 11, cameras 2, solution injection mechanisms 3, processors 4, light source components 5, solenoid valves 6, and flow meters 7. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] In the description of this invention, it should be understood that the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, features defined with "first" and "second" may explicitly or implicitly include one or more of these features, used to distinguish and describe features, without any order or emphasis.

[0021] In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] The following is combined Figure 1 A method for measuring microfluidic velocity according to an embodiment of the present invention includes the following steps: S1, the tips of two microneedles are crossed and fixed in the fluid being measured, and droplets or bubbles are injected into the microneedles. The droplets or bubbles are suspended at the intersection of the tips of the two microneedles. S2, acquire images to obtain the morphological parameters of droplets or bubbles in the fluid under test; S3, a flow velocity calculation formula is constructed based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance; S4, based on the morphological parameters of droplets or bubbles and the velocity calculation formula, obtains and outputs the velocity of the fluid being measured.

[0024] The present invention provides a method for measuring microfluidic velocity. It utilizes the inherent surface tension property of liquids to stabilize the interface morphology of droplets or bubbles at the suspension point of a microneedle, establishing a quantifiable mechanical relationship between the morphology and the flow velocity. This method requires no external drive, introduces no tracer, and causes no disturbance to the fluid. A flow velocity calculation formula is constructed based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance. The flow velocity can be directly calculated using the morphological parameters of the droplet or bubble deformation. The required structure is simple and low-cost. The morphological parameters of droplets or bubbles are obtained by capturing images of their changes, thereby analyzing the flow velocity of the measured fluid. Stability is maintained even for measurements at ultra-low flow velocities and in small spaces, demonstrating strong adaptability.

[0025] This type of method relies on the energy relationship between the surface tension of droplets or bubbles and fluid resistance to convert changes in flow velocity into observable displacement deformation at the droplet or bubble interface. It has advantages such as simple structure, high integration, fast response, and applicability to small flow rates and low flow velocity ranges. It can make up for the shortcomings of existing technologies in detection scenarios such as trace biological samples, volatile liquids, and low viscosity fluids. It does not require an insertable probe, heating, or tracers, and does not change the flow field or fluid composition. It only requires two microneedles for imaging and acquisition, without the need for complex microfabrication sensors and precision drives. The device is simple, low-cost, highly stable, and easy to integrate into microfluidic chips and pipeline systems. It uses the energy balance of droplet or bubble surface tension and fluid resistance as the core physical model, and directly calculates the flow velocity through morphological parameters. The physical meaning is clear, the calibration is simple, and it is less affected by environmental interference.

[0026] It is compatible with flow rate monitoring and calibration in microfluidic laboratory-on-a-chip (LOC), point-of-care testing (POCT) equipment, and micro-drug delivery systems. This includes real-time microchannel fluid control in microfluidic biochemical analysis systems such as protein analysis and cell sorting; precise dose infusion calibration for micro-injection pumps and implantable drug delivery devices; and basic scientific research measurements in biological microcirculation fluid dynamics and ex vivo tissue permeation characteristics, providing reliable microflow rate measurement support for biomedical research and development and precision clinical diagnosis and treatment. It can also be used for micro-volume delivery flow rate control of photoresist, etching solution, and cleaning solution in semiconductor wafer manufacturing; micro-leakage detection and performance calibration of micro-hydraulic / pneumatic components and precision solenoid valves; micro-flow rate characterization of inks / coatings in industrial inkjet printing, micro-nano spraying, and 3D printing equipment; and micro-lubricant supply monitoring in precision bearings and aerospace micro-transmission mechanisms, ensuring the process accuracy and operational reliability of high-end equipment.

[0027] Furthermore, in step S3, the energy relationship is: ,in ， Indicates the surface tension of a droplet or bubble. This represents the surface area of ​​a spherical droplet or bubble. This represents the length of the semi-major axis of the ellipsoid. Indicates the drag coefficient. This indicates the density of the fluid being measured. ， ， This indicates the length of the minor axis of the ellipsoid; Obtain flow rate Calculation formula: ,in Indicates the volume of a droplet or bubble. A represents the derivative of the ellipsoid's surface area with respect to its major axis.

[0028] Where e represents the eccentricity of the ellipsoid, ; .

[0029] Furthermore, step S1 specifically includes: By controlling the valve opening time, the solution is injected through the microchannel inside the microneedle, so that the solution is injected into the intersection of the two microneedles to form droplets or bubbles; Control the solution injection volume at 1 .

[0030] Specifically, micro-injection of liquid is achieved through microchannels within microneedles, combined with valve opening time to precisely control the droplet or bubble formation process. This allows for reliable and repeatable formation of stable suspended droplets or bubbles at the intersection of two microneedles, preventing premature droplet or bubble detachment or unstable morphology, thus ensuring measurement consistency and accuracy. The droplet or bubble volume is controlled within 1... The range can ensure that the droplets or bubbles have sufficient structural stability and are not easily damaged by small disturbances, and also enable the droplet or bubble morphology to respond with high sensitivity to micro-flow rate changes. It is particularly suitable for the precise measurement of droplets or bubbles under microscale and low flow rate conditions. This method can flexibly adapt to different flow rate ranges by adjusting the volume and surface tension of droplets or bubbles: when measuring high flow rates, the volume of droplets or bubbles is reduced and a liquid with higher surface tension is selected to improve the droplet or bubble's resistance to erosion and expand the upper limit of measurable flow rates; when measuring low flow rates, the volume of droplets or bubbles is appropriately increased and a liquid with moderate surface tension is selected to enhance the morphological response to low-speed flow fields and improve the detection accuracy at low flow rates; thus, high-sensitivity measurement can be achieved with the same measuring device over a wide flow rate range, making it highly versatile and applicable to a wide range of scenarios.

[0031] Furthermore, step S2 specifically includes: A clear image of the droplet or bubble is obtained by capturing a top view of the droplet or bubble using a camera and performing edge detection on the image under test. Obtain the droplet or bubble contour information from the clear image to obtain the droplet or bubble morphology parameters: the length of the minor semi-axis of the droplet or bubble ellipsoid. and the length of the semi-major axis of the droplet or bubble ellipsoid c .

[0032] Specifically, photographing droplets or bubbles from a top-down perspective avoids interference from structures such as microneedles and flow channels, clearly capturing the overall contour of the droplets or bubbles under the influence of the flow field. Edge detection of the acquired images effectively suppresses interference from background noise and uneven illumination, highlighting the boundary features of the droplets or bubbles and obtaining high-contrast, high-definition droplet or bubble contour images. This significantly improves the accuracy and stability of morphological parameter extraction. By treating the droplets or bubbles as equivalent to an ellipsoidal model, only the length of the minor semi-axis needs to be obtained. and length of semi-axis c It can characterize the deformation state of droplets or bubbles after being scoured by fluid. It has few characteristic parameters, low computational load, and is easy to process in real time, which is conducive to realizing rapid flow velocity calculation and online measurement. The entire acquisition and detection process is realized only through optical imaging, without contacting or interfering with the droplet or bubble morphology and the measured flow field, ensuring the in-situ nature and authenticity of the measurement process. It is particularly suitable for measurement scenarios that are sensitive to disturbances, such as microfluidics, weak fluids, and biological samples.

[0033] This invention proposes a system for measuring fluid microvelocities, characterized in that it comprises: The solution control module is used to control the injection of solution into the microneedles and keep the droplets or bubbles suspended at the intersection of the tops of the two microneedles; The image acquisition module acquires the morphological parameters of droplets or bubbles in the fluid being measured. The formula construction module constructs a flow velocity calculation formula based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance. The calculation output module is used to calculate the flow velocity of the measured fluid flowing through droplets or bubbles.

[0034] This invention proposes a device for measuring fluid microflow rate, comprising two sets of microneedles 1, a camera 2, a solution injection mechanism 3, and a processor 4, wherein the processor 4 is used to execute the method for measuring fluid microflow rate. The two sets of microneedles 1 are fixed in the fluid 200 to be measured, and the tips of the two sets of microneedles 1 are close together to form droplet or bubble suspension points; The camera 2 is positioned directly above the microneedle 1 and is used to capture images of the droplets or bubbles 100.

[0035] Specifically, two sets of microneedles 1 are fixed in the flow field to be measured, with their tips close together to form a stable droplet or bubble suspension point; the solution injection mechanism 3 delivers a quantitative solution to the suspension point through the microchannel 11 inside the microneedle 1, forming and suspending the droplet or bubble 100 to be measured at the tips of the two sets of microneedles 1; the camera 2 is located directly above the microneedle 1, and acquires the morphological image of the droplet or bubble 100 under the action of the flow field in real time from a top-down perspective and transmits it to the processor 4; the processor 4 performs edge detection and contour extraction on the image, obtains the morphological parameters such as the major and minor semi-axes of the droplet or bubble 100 ellipsoid, calculates and outputs the micro velocity of the fluid 200 to be measured according to the pre-established surface tension-fluid resistance energy relationship, thereby completing the non-disruptive, in-situ, high-precision micro velocity measurement of the microneedle 1; the cross suspension point of the two microneedles 1 can be changed by changing the length and tilt angle of the two microneedles 1, thereby realizing the velocity measurement at different height positions in the fluid. The device consists of only two sets of microneedles 1, a camera 2, a solution injection mechanism 3, and a processor 4. It has no complex sensing components or mechanical drive structure, making it easy to manufacture and assemble, and suitable for miniaturization, integration, and mass production. It uses visual imaging to acquire the morphology of droplets or bubbles 100. The entire process is non-invasive, heat-free, and does not involve the addition of tracer particles, thus not interfering with the original flow field and fluid properties. It is particularly suitable for the measurement of trace, biological, thermally sensitive, and chemically sensitive fluids. The processor 4 can automatically complete the injection of droplets or bubbles 100, image acquisition, edge detection, parameter extraction, and flow rate calculation without manual intervention. It has a fast response speed and can realize continuous, dynamic, and real-time online monitoring of microflow rates.

[0036] Furthermore, the microneedle 1 has a through-channel microchannel 11 inside, and the solution injection mechanism 3 is connected to the microchannel 11 at the bottom of the microneedle 1 to inject the solution from the bottom of the microchannel 11 and output it as droplets or bubbles 100 from the top of the microchannel 11.

[0037] Specifically, the solution is directly delivered using an internally connected microchannel 11, allowing droplets or bubbles 100 to be generated and suspended in situ at the tip of the microneedle 1 without the need for external transport or additional molding structures. This ensures that the droplets or bubbles 100 are in a fixed position and have a consistent shape. The solution is injected from the bottom and output from the top of the microneedle 1, with a straight and unobstructed path, ensuring that the volume of droplets or bubbles 100 is controllable and the generation process is stable. This improves the injection accuracy and measurement repeatability. The injection channel is integrated with the microneedle 1, eliminating the need for additional tubing connections and resulting in a compact structure.

[0038] Furthermore, the microneedle 1 is made of stainless steel, tungsten, nickel-titanium alloy, titanium, copper, platinum, gold, glass, or ceramic; the surface of the microneedle 1 is provided with a micro-nano etching layer or coated with an inorganic coating to enhance the adhesion of the droplets or bubbles 100 and prevent the droplets or bubbles 100 from falling off under the impact of fluid.

[0039] Specifically, the microneedle 1 can be made of materials such as stainless steel, tungsten, nickel-titanium alloy, metal, glass, and ceramics, taking into account mechanical strength, corrosion resistance, biocompatibility, and processing performance. It can be used in different scenarios such as aqueous solutions, organic solvents, weakly corrosive media, and biological samples. The device has strong versatility. The fluid being measured does not wet the microneedle, while the droplet or bubble 100 can wet the surface of the microneedle 1 without wetting the fluid being measured. The droplet or bubble 100 can be selected as pure liquid, oily liquid, conductive liquid, or liquid metal according to the characteristics of the fluid being measured 200. The microneedle 1 is modified by surface micro-nano structures or coatings to improve the adhesion of the droplet or bubble 100 to the tip of the microneedle 1, effectively inhibiting the droplet or bubble 100 from falling off under fluid impact and expanding the measurable flow rate range.

[0040] Furthermore, the device also includes a light source assembly 5, which is used to irradiate the droplets or bubbles 100 on the microneedles 1.

[0041] Specifically, the light source component 5 provides uniform and sufficient illumination for the droplet or bubble 100. Under the auxiliary illumination of the light source, the difference in brightness between the droplet or bubble 100 and the background and micro needle 1 is amplified, and the outline of the droplet or bubble 100 is clearer and more prominent. This makes up for the problem of insufficient ambient light or uneven light, so that the camera 2 can obtain droplet or bubble 100 images with appropriate brightness in various measurement environments, and avoids blurry images and information loss due to excessive light. Furthermore, the output end of the solution injection mechanism 3 is equipped with a solenoid valve 6 and a flow meter 7. The solenoid valve 6 is used to control the opening and closing of the solution injection, and the flow meter is used to control the amount of solution injected.

[0042] Specifically, the solenoid valve 6 enables rapid and precise control of solution injection on / off. In conjunction with the flow meter 7, it monitors and precisely regulates the injection flow rate and volume in real time. It can stably generate standard droplets or bubbles 100 with consistent volume and controllable shape at the intersection of the microneedles 1, avoiding instability of droplets or bubbles 100 due to fluctuations in the injection volume, and greatly improving the consistency and repeatability between different measurements.

[0043] Other configurations and operations of the method, system, and apparatus for measuring fluid microvelocities according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0044] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0045] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus or device (such as a computer-based system, a system including a processing module or other system that can fetch and execute instructions from, an instruction execution system, apparatus or device).

[0046] In the description of this specification, references to terms such as "embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for measuring microfluidic velocity, characterized in that, Includes the following steps: S1, the tips of two microneedles are crossed and fixed in the fluid being measured, and droplets or bubbles are injected into the microneedles. The droplets or bubbles are suspended at the intersection of the tips of the two microneedles. S2, acquire images to obtain the morphological parameters of droplets or bubbles in the fluid under test; S3, a flow velocity calculation formula is constructed based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance; S4, based on the morphological parameters of droplets or bubbles and the velocity calculation formula, obtains and outputs the velocity of the fluid being measured.

2. The method for measuring microfluidic velocity according to claim 1, characterized in that, In step S3, the energy relationship is: ,in ， Indicates the surface tension of a droplet or bubble. This represents the surface area of ​​a spherical droplet or bubble. This represents the length of the semi-major axis of the ellipsoid. Indicates the drag coefficient. This indicates the density of the fluid being measured. ， ， This indicates the length of the minor axis of the ellipsoid; Obtain flow rate Calculation formula: ,in Indicates the volume of a droplet or bubble. ; A represents the derivative of the ellipsoid's surface area with respect to its major axis. Where e represents the eccentricity of the ellipsoid, ; .

3. The method for measuring microfluidic velocity according to claim 1, characterized in that, Step S1 specifically includes: By controlling the valve opening time, the solution is injected through the microchannel inside the microneedle, so that the solution is injected into the intersection of the two microneedles to form droplets or bubbles; Control the solution injection volume at 1 .

4. The method for measuring fluid microvelocities according to claim 1, characterized in that, Step S2 specifically includes: A clear image of the droplet or bubble is obtained by capturing a top view of the droplet or bubble using a camera and performing edge detection on the image under test. Obtain the droplet or bubble contour information from the clear image to obtain the droplet or bubble morphology parameters: the length of the minor semi-axis of the droplet or bubble ellipsoid. and the length of the semi-major axis of the droplet or bubble ellipsoid c .

5. A system for measuring fluid microvelocities, characterized in that, include: The solution control module is used to control the injection of solution into the microneedles and keep the droplets or bubbles suspended at the intersection of the tops of the two microneedles; The image acquisition module acquires the morphological parameters of droplets or bubbles in the fluid being measured. The formula construction module constructs a flow velocity calculation formula based on the energy relationship between the surface tension of droplets or bubbles and fluid resistance. The calculation output module is used to calculate the flow velocity of the measured fluid flowing through droplets or bubbles.

6. A device for measuring microfluidic velocity, characterized in that, It includes two sets of microneedles, a camera, a solution injection mechanism, and a processor, wherein the processor is used to perform the method as described in any one of claims 1-4; The two sets of microneedles are fixed in the fluid being measured, and the tips of the two sets of microneedles are close together to form droplet or bubble suspension points; The camera is positioned directly above the microneedle and is used to capture images of droplets or bubbles.

7. A device for measuring microfluidic velocity according to claim 6, characterized in that, The microneedle has a through-channel inside, and the solution injection mechanism is connected to the microchannel at the bottom of the microneedle to inject the solution from the bottom of the microchannel and output it as droplets or bubbles from the top of the microchannel.

8. A device for measuring microfluidic velocity according to claim 6, characterized in that, The microneedles are made of stainless steel, tungsten, nickel-titanium alloy, titanium, copper, platinum, gold, glass, or ceramic. The surface of the microneedle is provided with a micro-nano etched layer or coated with an inorganic coating to enhance the adhesion of droplets or bubbles and prevent droplets or bubbles from falling off under the impact of fluid.

9. A device for measuring microfluidic velocity according to claim 6, characterized in that, The device also includes a light source assembly for irradiating droplets or bubbles on the microneedles.

10. A device for measuring microfluidic velocity according to claim 6, characterized in that, The output end of the solution injection mechanism is equipped with a solenoid valve and a flow meter. The solenoid valve is used to control the opening and closing of the solution injection, and the flow meter is used to control the solution injection volume.

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