Micro-flow sensor flow channel structure

Abstract

The invention relates to a flow channel structure of a micro-flow sensor, which relates to the field of micro-flow channel sensors and comprises a tapered inlet rectification section arranged at the top of one side of a base, a straight measurement section arranged at the top end of the middle part of the base and a divergent outlet section arranged at the other side of the base, the base is fixedly connected with a sensor main body, so that the inlet rectifying section, the measuring section and the outlet section form a flow channel and are communicated with one another; the position, located in the middle of the measuring section, of the base is fixedly connected with a sensitive element so as to detect temperature field change or heat loss caused when fluid flows through the measuring section, and the flow speed and flow of the fluid in the measuring section can be calculated. The fluid is jointly guided to form a stable laminar flow field, the vortex and flow separation phenomenon is greatly reduced, and it is ensured that the state of the fluid flowing through the sensitive element is uniform and stable.

Description

Technical Field

[0001] This invention relates to the field of microfluidic sensor technology, and more particularly to a flow channel structure for a microflow sensor. Background Technology

[0002] Thermal flow sensors, especially MEMS-based thermal micro-flow sensors, are widely used in the field of micro-flow measurement due to their advantages such as fast response, high accuracy, and small size. Their working principle typically involves measuring the temperature field change or heat loss caused by fluid flowing through a thermally sensitive element to infer the flow velocity and flow rate.

[0003] However, when measuring minute flow rates, traditional sensor structures face two major technical challenges: 1) Flow stability issues: Due to the tiny size of microchannels, fluid inertia is weakened, while the effects of surface tension and viscous forces are relatively prominent. If the channel design is unreasonable, turbulent phenomena such as flow separation, eddies, or uneven velocity distribution can easily occur upstream and downstream of the sensor element. The sensing element is extremely sensitive to the surrounding flow field distribution; any tiny flow fluctuation will directly interfere with its thermal field distribution, introducing significant measurement noise and errors, severely affecting the signal-to-noise ratio and measurement accuracy at low flow rates.

[0004] 2) System sealing issues: Micro-flow measurement means that the absolute leakage requirement is extremely high. Even a tiny leak (e.g., a few bubbles per second) is not negligible relative to the measured flow rate and will directly lead to serious distortion of the measurement results. Traditional adhesive or mechanical compression sealing methods are prone to aging, creep, or gaps under long-term use, temperature cycling, or pressure shocks, making it difficult to meet the stringent requirements of long-term stability and high sealing performance in aerospace, military, and other fields.

[0005] While existing technologies have attempted to alleviate these problems by improving the flow channel shape or sealing methods, they often fail to simultaneously ensure sufficient flow stability and high-reliability sealing at the joints, or result in complex structures and high manufacturing costs.

[0006] Therefore, to address the above shortcomings, a flow channel structure for a micro-flow sensor is needed. Summary of the Invention

[0007] (a) Technical problems to be solved The technical problem to be solved by the present invention is to address the issue of decreased measurement accuracy of existing thermal microflow sensors under low flow measurement conditions due to fluid flow turbulence and insufficient system sealing.

[0008] (II) Technical Solution To address the aforementioned technical problems, this invention provides a micro-flow sensor channel structure, comprising a tapered inlet rectifying section located at the top of one side of a base, a straight measuring section located at the top of the middle of the base, and a tapered outlet section located on the other side of the base. A sensor body is fixedly connected to the base so that the inlet rectifying section, the measuring section, and the outlet section form a flow channel and are interconnected. A sensitive element is fixedly connected to the base in the middle of the measuring section to detect temperature field changes or heat loss caused by fluid flowing through the measuring section and to calculate the fluid velocity and flow rate within the measuring section.

[0009] As a further explanation of the present invention, preferably, the inlet rectifying section is in the shape of a triangular frustum or a cone, the end of the inlet rectifying section with the smaller opening is connected to the measuring section, and the length of the inlet rectifying section is greater than five times the hydraulic diameter.

[0010] As a further explanation of the present invention, preferably, the inlet rectifier section tapering ratio is 1.2 to 2.0.

[0011] As a further explanation of the present invention, preferably, the measuring segment has a rectangular cross-section, a width of 1 to 5 mm, a height of 0.3 to 1.5 mm, and a length of 25 to 100 mm.

[0012] As a further explanation of the present invention, preferably, the outlet section structure is the same as the inlet rectifier section structure and the end with the smaller opening is connected to the measurement section; the sensor body has an inlet connection end and an outlet connection end respectively opened at both ends along the axial direction for connecting to external pipes, the inlet connection end has a flow channel opened radially and is connected to the end with the larger opening of the inlet rectifier section, and the outlet connection end has a flow channel opened radially and is connected to the end with the larger opening of the outlet section.

[0013] As a further explanation of the present invention, preferably, a stepped groove is provided in the middle of the base, the groove passes through the measuring section, the shape of the groove is the same as the shape of the sensitive element, the sensitive element is embedded in the groove so that the measuring end extends into the measuring section and coincides with the inner wall surface of the measuring section.

[0014] As a further explanation of the present invention, preferably, the sensing element is a plate-type MEMS thermal flow chip, and the contact surface between the sensing element and the base is electron beam welded to ensure that the leakage rate at the contact point between the sensing element and the base is less than 1×10⁻⁶. -9 Pa. m 3 / s.

[0015] (III) Beneficial Effects The above-described technical solution of the present invention has the following advantages: 1. High measurement accuracy: Through a carefully designed laminar flow channel, the interference of flow turbulence on sensitive elements is fundamentally eliminated, ensuring the stability of the flow signal and the signal-to-noise ratio, making it particularly suitable for the accurate measurement of extremely low flow rates; 2. Ultra-high sealing performance: The metal sealing joint formed by electron beam welding has extremely high airtightness and long-term stability, and is resistant to high temperature, corrosion and aging, solving the leakage problem of micro-flow measurement; 3. Compact and reliable structure: It integrates flow channel optimization with high-reliability sealing technology, has a simple structure, requires no additional seals or complicated assembly steps, has good overall rigidity, and strong resistance to impact and vibration. 4. Broad application prospects: This structure is not only suitable for propellant flow control in aerospace electric propulsion systems, but can also be widely used in many high-precision measurement fields such as special gas monitoring in semiconductor manufacturing, environmental monitoring instruments, and laboratory analytical instruments. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the flow channel structure of the present invention; Figure 2 This is a schematic diagram of the installation structure of the present invention; Figure 3 This is a schematic diagram of the interaction between the sensitive element and the base of the present invention; Figure 4 This is a structural diagram of the sensitive element of the present invention.

[0017] In the diagram: 1. Sensor body; 11. Inlet connection end; 12. Outlet connection end; 2. Base; 21. Groove; 3. Inlet rectifier section; 4. Measurement section; 5. Sensitive element; 51. Weld; 6. Outlet section. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A micro-flow sensor channel structure, combined with Figure 1 , Figure 2 It includes a tapered inlet rectifier section 3 located at the top of one side of the base 2, a straight measuring section 3 located at the top of the middle of the base 2, and a tapered outlet section 6 located on the other side of the base 1. The sensor body 1 is fixedly connected to the base 2 so that the inlet rectifier section 3, the measuring section 4, and the outlet section 5 form a flow channel and are connected.

[0020] Combination Figure 1 , Figure 2Both the sensor body 1 and the base 2 are precision-machined from stainless steel or Kovar alloy and other metal materials. The sensor body 1 has an inlet connection end 11 and an outlet connection end 12 at its two ends along the axial direction for connecting to external pipes. The inlet connection end 11 has a radially formed flow channel that connects to the larger opening end of the inlet rectifying section 3, and the outlet connection end 12 has a radially formed flow channel that connects to the larger opening end of the outlet section 6. This allows the fluid to flow through the pipe, through the inlet connection end 11, into the inlet rectifying section 3, then through the measuring section 4 to the outlet section 6, and finally out through the outlet connection end 12. The base 2 has a sensing element 5 fixedly connected in the middle of the measuring section. The sensing element 5 detects the temperature field changes or heat loss caused by the fluid flowing through the measuring section 4, and the computer calculates the fluid velocity and flow rate within the measuring section 4 based on the data changes obtained from the sensing element 5.

[0021] Combination Figure 1 , Figure 2 The inlet rectifying section 3 is truncated triangular or conical in shape. The smaller opening end of the inlet rectifying section 3 connects to the measuring section 4. The tapering ratio of the inlet rectifying section 3 is 1.2–2.0. It is used to stabilize the fluid from upstream, eliminating any large-scale eddies or uneven velocity distributions, allowing the fluid to smoothly transition to the measuring section 4 with a stable and uniform velocity profile. The length of this section needs to be calculated using fluid dynamics and is typically no less than 5 times the hydraulic diameter of the flow channel to ensure sufficient flow formation.

[0022] Combination Figure 2 , Figure 3 The measuring section 4 has a circular or rectangular cross-section, preferably rectangular, to match the sensing element 5. The measuring section 4 has a width of 1–5 mm, a height of 0.3–1.5 mm, a length of 25–100 mm, and a surface roughness of less than or equal to 0.05 μm. This ensures that within the target flow rate range of 0.1–1000 sccm, the Reynolds number of the fluid remains well below the critical value (less than 2300) for the transition from laminar to turbulent flow, thus guaranteeing a stable laminar flow state.

[0023] Combination Figure 3 , Figure 4The base 2 has a stepped groove 21 in the middle, which extends through the measuring section 4. The shape of the groove 21 is the same as that of the sensing element 5. The sensing element 5 is a plate-type MEMS thermal flow chip. The sensing element 5 is embedded in the groove 21 so that the measuring end extends into the measuring section 4 and coincides with or forms a smooth transition with the inner wall of the measuring section 4, avoiding the formation of steps that would cause flow disturbance. The contact surface between the sensing element 5 and the base 2 is welded by electron beam. Before welding, the fit gap between the groove 21 and the sensing element 5 must be extremely small to achieve preliminary positioning and mechanical fixation, preparing for subsequent welding and sealing. During welding, in a high vacuum environment, a high-energy-density electron beam is precisely controlled to scan the junction between the metallized edge of the sensing element 51 and the edge of the groove 21. The energy of the electron beam causes the local metal material at the junction to melt and fuse instantly, forming a continuous, dense, and narrow weld 51 after cooling. This weld 51 achieves a metallurgical-level bond, and its sealing performance is far superior to traditional methods, with a leakage rate easily reaching less than 1×10⁻⁶. -9 Pa. m 3 With a flow rate on the order of / s, leakage at the micro-flow level can be completely eliminated. Furthermore, this method has the advantages of a small heat-affected zone and minimal deformation.

[0024] Combination Figure 1 , Figure 2 The outlet section 6 has the same structure as the inlet rectifier section 3, but the smaller opening end is connected to the measurement section 4. This allows the measured fluid to gradually reduce its velocity and restore some pressure, thereby reducing the pressure loss of the entire flow channel structure and avoiding backflow and other interference at the outlet.

[0025] In summary, this invention utilizes a flow-rectifying design at the inlet section to create a stable laminar flow of fluid into the measuring section 4. The matching profile between the measuring section 4 and the sensing element 5 allows the laminar fluid to flow smoothly over the surface of the sensing element 5, which is mounted flush with the channel wall. The sensing element 5 detects changes in fluid flow rate using thermodynamic principles and converts them into an electrical signal. Subsequently, the fluid flows smoothly out through the outlet section 6. The sensing element 5 is positioned using a high-precision embedded mounting slot and achieves a full-circumferential, seamless metal-sealed connection with the channel base 2 using electron beam welding, thus solving the leakage problem at the micro-flow level. This invention is particularly suitable for fields with extremely high requirements for accuracy and reliability in measuring minute flow rates, such as propellant flow control in aerospace electric propulsion systems and gas monitoring in semiconductor processes.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flow channel structure for a micro-flow sensor, characterized in that: It includes a tapered inlet rectifying section (3) located at the top of one side of the base (2), a straight measuring section (4) located at the top of the middle of the base (2), and a tapered outlet section (6) located on the other side of the base (2). A sensor body (1) is fixedly connected to the base (2) so that the inlet rectifying section (3), the measuring section (4), and the outlet section (6) form a flow channel and are connected. A sensitive element (5) is fixedly connected to the base (2) in the middle of the measuring section (4) to detect the temperature field change or heat loss caused by the fluid flowing through the measuring section (4) and calculate the fluid velocity and flow rate in the measuring section (4).

2. The micro-flow sensor channel structure according to claim 1, characterized in that: The inlet rectifying section (3) is truncated triangular or conical. The end of the inlet rectifying section (3) with the smaller opening is connected to the measuring section (4). The length of the inlet rectifying section (3) is greater than five times the hydraulic diameter.

3. The micro-flow sensor channel structure according to claim 2, characterized in that: The inlet rectifier section (3) has a tapering ratio of 1.2 to 2.

0.

4. The micro-flow sensor channel structure according to claim 3, characterized in that: The cross section of the measuring segment (4) is rectangular. The width of the measuring segment (4) is 1-5 mm, the height is 0.3-1.5 mm, and the length is 25-100 mm.

5. The micro-flow sensor channel structure according to claim 4, characterized in that: The outlet section (6) has the same structure as the inlet rectifier section (3), and the end with the smaller opening is connected to the measuring section (4); the sensor body (1) has an inlet connection end (11) and an outlet connection end (12) at both ends of the axial direction for connecting to external pipes. The inlet connection end (11) has a flow channel in the radial direction that is connected to the end with the larger opening of the inlet rectifier section (3), and the outlet connection end (12) has a flow channel in the radial direction that is connected to the end with the larger opening of the outlet section (6).

6. The micro-flow sensor channel structure according to claim 5, characterized in that: The base (2) has a stepped groove (21) in the middle. The groove (21) passes through the measuring section (4). The shape of the groove (21) is the same as that of the sensitive element (5). The sensitive element (5) is embedded in the groove (21) so that the measuring end extends into the measuring section (4) and coincides with the inner wall of the measuring section (4).

7. The micro-flow sensor channel structure according to claim 6, characterized in that: The sensing element (5) adopts a plate-type MEMS thermal flow chip. The contact surface between the sensing element (5) and the base (1) is welded by electron beam to ensure that the leakage rate at the contact point between the sensing element (5) and the base (2) is less than 1×10. -9 Pa. m 3 / s.

Images