Capillary tube sensor based on MEMS technology

Abstract

The invention relates to the technical field of micro-electro-mechanical sensors, in particular to a capillary sensor based on an MEMS (micro-electro-mechanical system) technology, which is used for high-precision measurement of micro-flow gas. The problems of fluid distortion and flow field stability in micro-flow measurement are mainly solved, and accurate and stable micro-flow measurement is achieved through the MEMS technology. According to the technical scheme, the device comprises a main flow channel, a flow adjuster, a laminar flow element and two branch flow channels, and gas flow sensors are installed in the branch flow channels. The flow regulator adopts a porous plate type structure, and the flow field stability is improved. The laminar flow element is designed to be a differential laminar flow element, and a porous rectifier is additionally arranged on a main pipeline in a shunting mode to ensure laminar flow of fluid. The flow sensor adopts a thermal distribution type mass flow meter, and the mass flow is calculated by measuring the temperature difference. The device has the technical advantages of improving the measurement precision, expanding the measurement range, simplifying the structural design, reducing the production cost and the like, and is suitable for the field of micro-flow gas measurement.

Description

Technical Field

[0001] The invention relates to the technical field of micro-electromechanical sensors, and in particular to a capillary sensor based on MEMS technology. Background Art

[0002] In industrial production, every process from raw material acquisition to processing to finished products cannot be separated from the role of measurement. Measurement plays a vital role in the development of industrial production and science and technology. Among them, flow sensors are an indispensable part of measurement and are closely related to all walks of life. At a time when energy is becoming increasingly exhausted, the level of industrialization is increasing, and the trend of production automation is rising, the development and update of flow meters in the development of economic production is particularly important.

[0003] There are many ways to measure flow sensors, and thermal flow sensors are widely used due to their simple structure, no moving parts, and mature technology.

[0004] The existing application scenario of MEMS technology is to measure flow range, and its application scope is relatively small. In order to expand the application of MEMS thermal sensors and improve accuracy requirements, it is necessary to design a pipeline structure that can measure gas flow in a small space. Summary of the invention

[0005] The present invention aims to solve the problems of fluid distortion and flow field stability in micro-flow high-precision gas flow measurement, and realize accurate and stable micro-flow measurement through MEMS technology.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a capillary sensor based on MEMS technology, comprising: a main flow channel for inlet and outlet, a flow regulator placed in the middle of the main channel, a laminar flow element, and two branch flow channels connected to the main flow channel located upstream and downstream of the laminar flow element, and a gas flow sensor installed in the middle of the branch flow channels.

[0008] In the above solution, the flow regulator is a symmetrical multi-through-hole structure.

[0009] In the above scheme, the laminar flow element includes two first laminar flow generators and a second laminar flow generator of different lengths and the same other data structure, which are connected in series in the same laminar flow element, and a rectifier is arranged a distance before the inlet of the first laminar flow generator.

[0010] In the above scheme, the rectifier is arranged at a distance before the inlet of the first laminar flow generator, and the distance is the same as the distance from the outlet of the first laminar flow generator to the inlet of the second laminar flow generator.

[0011] In the above scheme, the multi-through-hole structure of the first laminar flow generator and the second laminar flow generator has a smaller aperture than that of the flow regulator, and has more through-holes than the flow regulator.

[0012] In the above solution, the entrance of the main channel is a trumpet-shaped entrance.

[0013] In the above scheme, the flow sensor is arranged near the inner wall of the tube of the two branch flow channels. The flow sensor includes a constant current power supply, thermistor 1 and thermistor 2, which provide heat at a constant power. Thermistor 1 and thermistor 2 are symmetrically distributed upstream and downstream of the constant current power supply.

[0014] In the above scheme, the main channel flow is:

[0015]

[0016] Here, the two capillaries are exactly the same, d is the inner diameter of the capillary, and λ is m represents the resistance coefficient along the capillary tube, ∑ζ m The sum of the local resistance coefficients of the capillary, D is the inner diameter of the main channel, λ Z represents the resistance coefficient along the main pipeline, ζ Z is the resistance coefficient of the laminar flow element, L is the length of the main channel, A is the heat transfer coefficient of the heat exchange between the temperature sensing element and the surrounding environment, C p is the constant-pressure specific heat capacity of the measured gas; K is the instrument constant, and ΔT represents the temperature difference between thermistor 1 and thermistor 2.

[0017] The capillary sensor technology solution based on MEMS technology provided by the present invention has significant technical advantages in the field of micro-flow gas measurement. The following is a specific technical effect analysis:

[0018] 1. Application of vertical flow regulators Vertical flow regulators: By installing flow regulators in the pipeline, problems such as uneven flow velocity distribution and vortex mixing before the fluid enters the sensor can be effectively improved. This design can accelerate the stabilization of abnormal fluid flow, eliminate or significantly reduce vortices, thereby improving measurement accuracy and operational stability.

[0019] 2. Design of vertical shaft porous plate flow conditioner Vertical shaft: The porous plate flow conditioner is used. Its symmetrical porous structure can balance the flow field and reduce vortices, etc., and improve the stability of the flow field. Compared with the traditional throttling device, its linearity is improved by 5-10 times, and the straight pipe section length requirement is low, which shortens the straight pipe section requirement and has a wide range ratio.

[0020] 3. Design of vertical parallel pipelines: Through the design of parallel pipelines, the flow loss of each branch is equal, thus simplifying the flow calculation. This design not only improves the measurement accuracy, but also expands the measurement range of the sensor.

[0021] 4. Constant power measurement method of vertical thermal mass flowmeter Vertical: The constant power measurement method is used to calculate the mass flow by measuring the temperature difference. This method improves the accuracy and reliability of the measurement.

[0022] 5. Design of vertical laminar flow element Vertical: The design of differential laminar flow element is based on the theory that the pressure loss of fluid flowing through the pipeline is proportional to the fluid flow rate. This design can ensure the laminar flow of fluid in the main pipeline and capillary, thereby further improving the measurement accuracy. The design of the first laminar flow and the second laminar flow generator in series can effectively avoid the influence of local loss at the inlet and outlet of the capillary and reduce the flow resistance. The design of long tube and small inner diameter makes the wall boundary layer effect dominant, and can maintain the laminar state in a wider range of flow rates.

[0023] 6. Vertical capillary and laminar flow element parallel vertical well: By connecting the capillary and laminar flow element in parallel, the amount of gas flowing into the capillary is increased, so that a fixed proportion of the fluid flowing through the main channel flows to the capillary. This design not only improves the measurement accuracy, but also expands the application range of the sensor.

[0024] 7. Design of vertical U-shaped capillary: The U-shaped capillary is easy to install, and the laminar flow element is a small hole type, with a simple structure, flexible and changeable measurement range, and a small volume. These design features make the sensor simple in structure, reasonable in design, easy to use, and low in production cost.

[0025] In summary, the capillary sensor based on MEMS technology has significant advantages in improving measurement accuracy, expanding measurement range, simplifying structural design and reducing production costs. These technical features make it have broad application prospects in the field of micro-flow gas measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a Wheatstone circuit schematic diagram of the sensor of the present invention;

[0027] Figure 2 It is a position structure diagram of the capillary and the sensor of the present invention;

[0028] Figure 3 is a cross-sectional view of a rectifier of the present invention;

[0029] Figure 4 It is a schematic diagram of the channel structure of the flow sensor of the present invention;

[0030] Figure 5 It is a schematic diagram of the structure of the laminar flow element of the present invention.

[0031] In the figure: 1. Wheatstone bridge; 2. operational amplifier; 3. fixed resistor; 4. thermistor; 5. variable resistor; 6. bipolar adjustment voltage; 7. main fluid channel; 8. capillary channel; 9. rectifier; 10. laminar flow element; 10-1. first laminar flow generator; 10-2. second laminar flow generator; 11. flow sensor. DETAILED DESCRIPTION

[0032] The following is a detailed description of the embodiments of the present invention. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, modifications or equivalent substitutions made to the present invention should all be included in the scope of the claims of the present invention.

[0033] In addition, in order to better illustrate the present invention, numerous specific details are given in the following specific embodiments. It will be understood by those skilled in the art that the present invention can also be implemented without these specific details.

[0034] In order to achieve the above object, the present application provides a capillary sensor based on MEMS technology, comprising:

[0035] The main flow channel of the inlet and outlet, the flow regulator placed in the middle of the main channel, the laminar flow element, and two branch flow channels connected to the main flow channel located upstream and downstream of the laminar flow element, the gas flow sensor installed in the middle of the branch flow channel, and the branch pipeline is a capillary.

[0036] In the above technical solution, the rectifier is combined with the branch pipeline. In the pipeline, since there are often various flow-disturbing elements such as elbows or valves upstream of most inlet pipelines, the fluid will produce fluid distortion, and uneven velocity distribution and vortex mixing will occur before the fluid enters the measurement range of the sensor. The non-ideal fluid flow is the main reason for the poor measurement accuracy and operation stability of the flow meter. The flow regulator can improve the above problems well, accelerate the abnormal fluid flow to stabilize, redistribute the flow velocity of the fluid to achieve an allowable flow state, eliminate or significantly reduce vortices, and produce a completely normal flow velocity distribution profile while eliminating the influence of the rotating flow.

[0037] The flow conditioner adopts a porous plate type. The porous plate is a porous structure symmetrically arranged on a plate substrate. It can balance the flow field and reduce vortices, etc. The flow field stability is improved, and the linearity is improved by 5-10 times compared with the traditional throttling device. It has low requirements on the length of the straight pipe section, shortening the requirements for the straight pipe section; it has a wide range ratio.

[0038] The two branch capillary channels in parallel are referred to as parallel pipelines. The calculation method of the total current in parallel pipelines is similar to that in parallel circuits. The flow loss characteristics in parallel pipelines are:

[0039] The flow loss of each branch in the parallel pipeline is equal, that is:

[0040] h w =h wi (m).

[0041] Flow characteristics of parallel pipelines: The flow rate of parallel pipelines is equal to the sum of the flow rates of each branch, that is:

[0042]

[0043] In the formula, q v is the main line flow, q vi is the flow rate of the parallel pipeline, m 3 / s.

[0044] The pressure loss of each pipeline in parallel pipeline is equal, h f =h fi For the pressure loss of a circular pipe, the calculation formula (Darcy's formula) is:

[0045]

[0046] In the formula, l is the length of the tube, d is the diameter of the tube, l / d is the aspect ratio, v is the average flow velocity of the fluid, and h is f is the pressure loss, and λ is the resistance coefficient along the path.

[0047] The thermal mass flow meter uses a constant power measurement method, such as Figure 2 As shown, the flow sensor is placed close to the inner wall of the tube, and the temperature measuring resistors 1 and 2 are symmetrically distributed upstream and downstream of the capillary channel.

[0048] By measuring the temperature difference, the mass flow rate can be calculated as: Where A is the heat transfer coefficient between the temperature sensing element and the surrounding environment; C p is the constant-pressure specific heat capacity of the measured gas; K is the instrument constant.

[0049] In order to be applied to large-diameter pipe measurement and ensure the laminar flow of gas in the pipe, the split flow mode is adopted. A porous rectifier is installed in the main pipe to rectify the irregular fluid. The flow through the branch pipe is increased by the laminar flow element. The flow q of the split flow channel is measured. m After that, the total flow rate Q can be calculated by the flow rate ratio of the branch channel to the main channel. m .

[0050] In the above technical solution, the relationship between the branch flow and the main flow is:

[0051]

[0052] Where V, V1, and V2 are the average flow velocities of the fluid in the main channel and the upper and lower capillaries, and λZ , m1 , m2 is the resistance coefficient along the main channel and the upper and lower capillaries, L, l1, l2 are the calculated lengths of the main channel and capillaries, D, d1, 2 are the inner diameters of the main channel and capillaries, ζ Z is the drag coefficient of the laminar flow element, ∑ζ m1 ,∑ζ m2 is the sum of the capillary local resistance coefficients.

[0053] The two branch capillaries are exactly the same, where l1 = l2, d1 = d2, ∑ζ m1 =∑ζ m2 , from the above relationship we can get:

[0054]

[0055] The capillary channels are symmetrically distributed, and V and V1 in the formula can be replaced by the flow rate Q of the main channel and a single capillary. m ,q m Instead, it can be simplified to:

[0056]

[0057] Where k is the ratio of the main channel to the capillary, S Z , S m are the resistance parameters of the main channel and capillary, λ m is m1 , m2 The average value, ∑ζ m ∑ζ m1 ,∑ζ m2 The average value of

[0058] In the above scheme, the main channel flow is:

[0059]

[0060] The fluid branch pipe is a capillary tube, and most of the gas flows through the main channel, and there is almost no gas flow through the capillary tube. The capillary tube is connected in parallel with the laminar flow element, which has resistance to the fluid. Increasing the amount of gas flowing into the capillary tube can make a fixed proportion of the fluid flowing through the main channel flow to the capillary tube.

[0061] The pressure loss of fluid flowing through a pipeline is proportional to the fluid flow rate, and the design of the laminar flow element is based on this theory. This invention uses a differential laminar flow element, which consists of two first laminar flow generators with different lengths and the same other data structures connected in series in the same laminar flow element. The distance before the inlet of the first laminar flow generator (the distance is the same as the distance from the outlet of the first laminar flow generator to the inlet of the second laminar flow generator) prevents the rectifier, so as to make the flow states at the inlets of the two laminar flow generators close.

[0062] The entrance of the main channel is a trumpet-shaped entrance, which ensures the stability of the airflow at the entrance. By setting the capillary into a U shape, the capillary can be easily installed. The laminar flow element is a small hole type, which has a simple structure, a flexible measurement range, and a small size. The channel housing is made of stainless steel, which can effectively extend the service life of the equipment.

[0063] Example 1

[0064] The invention provides a capillary sensor based on MEMS technology, which is used for improving the measurement accuracy and expanding the measurement range of the sensor.

[0065] In order to achieve the above object, the present application provides a capillary sensor based on MEMS technology, comprising:

[0066] The main flow channel of the inlet and outlet, the flow regulator placed in the middle of the main channel, the laminar flow element, and two branch flow channels connected to the main flow channel located upstream and downstream of the laminar flow element, and the gas flow sensor installed in the middle of the branch flow channel.

[0067] In the above technical solution, its main feature is the combination of a rectifier and a branch pipeline. In the pipeline, since there are often various flow-disturbing elements such as elbows or valves upstream of most inlet pipelines, the fluid will produce fluid distortion, and uneven velocity distribution and vortex mixing will occur before the fluid enters the measurement range of the sensor. The non-ideal fluid flow is the main reason for the poor measurement accuracy and operation stability of the flow meter. The flow regulator can improve the above problems well, accelerate the abnormal fluid flow to stabilize, redistribute the flow velocity of the fluid to achieve an allowable flow state, eliminate or significantly reduce vortices, and produce a completely normal flow velocity distribution profile while eliminating the influence of the rotating flow.

[0068] The flow conditioner adopts a porous plate type. The orifice plate has a symmetrical porous structure, which can balance the flow field and reduce vortices, etc. The flow field stability is improved, and the linearity is improved by 5-10 times compared with the traditional throttling device; it has low requirements on the length of the straight pipe section, shortening the requirements for the straight pipe section; it has a wide range ratio.

[0069] The calculation method of total current in parallel pipelines is similar to that in parallel circuits. The flow loss characteristics in parallel pipelines are: the flow loss of each branch in the parallel pipeline is equal, that is:

[0070] h w =h wi (m).

[0071] Flow characteristics of parallel pipelines: The flow rate of parallel pipelines is equal to the sum of the flow rates of each branch, that is:

[0072]

[0073] In the formula, q v is the main line flow, q vi is the flow rate of the parallel pipeline, m 3 / s.

[0074] The pressure loss of each pipeline in parallel pipeline is equal, h f =h fi For the pressure loss of a circular pipe, the calculation formula (Darcy's formula) is:

[0075] In the formula, l is the length of the tube, d is the diameter of the tube, l / d is the aspect ratio, v is the average flow velocity of the fluid, and h is f is the pressure loss, and λ is the resistance coefficient along the path.

[0076] The thermal mass flow meter uses a constant power measurement method, such as Figure 2 As shown, the flow sensor is placed close to the inner wall of the pipe, the heat source heats at a constant power, and the temperature measuring resistors 1 and 2 are symmetrically distributed upstream and downstream of the heat source.

[0077] By measuring the temperature difference, the mass flow rate can be calculated as: Where A is the heat transfer coefficient between the temperature sensing element and the surrounding environment; C p is the constant-pressure specific heat capacity of the measured gas; K is the instrument constant.

[0078] In order to be applied to large-diameter pipe measurement and ensure the laminar flow of gas in the pipe, the split flow mode is adopted. A porous rectifier is installed in the main pipe to rectify the irregular fluid. The flow through the branch pipe is increased by the laminar flow element. The flow q of the split flow channel is measured. m After that, the total flow rate Q can be calculated by the flow rate ratio of the branch channel to the main channel. m .

[0079] In the above technical solution, the relationship between the branch flow and the main flow is:

[0080]

[0081] Where V, V1, and V2 are the average flow velocities of the fluid in the main channel and the upper and lower capillaries, and λ Z , m1 , m2is the resistance coefficient along the main channel and the upper and lower capillaries, L, l1, l2 are the calculated lengths of the main channel and the capillary, D, d1, d2 are the inner diameters of the main channel and the capillary, ζ Z is the drag coefficient of the laminar flow element, ∑ζ m1 ,∑ζ m2 is the sum of the capillary local resistance coefficients.

[0082] The two branch capillaries are exactly the same, where l1 = l2, d1 = d2, ∑ζ m1 =∑ζ m2 , from the above relationship we can get:

[0083]

[0084] The capillary channels are symmetrically distributed, and V and V1 in the formula can be replaced by the flow rate Q of the main channel and a single capillary. m ,q m Instead, it can be simplified to:

[0085]

[0086] Where K is the ratio of the main channel to the capillary, S Z , S m are the resistance parameters of the main channel and capillary, λ m is m1 , m2 The average value, ∑ζ m ∑ζ m1 ,∑ζ m2 The average value of

[0087] In the above scheme, the main channel flow is:

[0088]

[0089]

[0090] Where k is the flow rate ratio between the main channel and the capillary, S Z , S m are the resistance parameters of the main channel and capillary, respectively.

[0091] The fluid branch pipe is a capillary tube, and most of the gas flows through the main channel, and there is almost no gas flow through the capillary tube. The capillary tube is connected in parallel with the laminar flow element, which has resistance to the fluid. Increasing the amount of gas flowing into the capillary tube can make a fixed proportion of the fluid flowing through the main channel flow to the capillary tube.

[0092] The pressure loss of fluid flowing through a pipeline is proportional to the fluid flow rate, and the design of the laminar flow element is based on this theory. This invention uses a differential laminar flow element, which consists of two first laminar flow generators with different lengths and the same other data structures connected in series in the same laminar flow element. A rectifier is placed a distance before the inlet of the first laminar flow generator (the distance is the same as the distance from the outlet of the first laminar flow generator to the inlet of the second laminar flow generator) to make the flow states at the inlets of the two laminar flow generators close.

[0093] The entrance of the main channel is a trumpet-shaped entrance, which ensures the stability of the airflow at the entrance. By setting the capillary into a U shape, the capillary can be easily installed. The laminar flow element is a small hole type, which has a simple structure, a flexible measurement range, and a small size. The channel housing is made of stainless steel, which can effectively extend the service life of the equipment.

[0094] Example

[0095] like Figure 1-Figure 4 As shown, an embodiment of the present invention provides a capillary flow sensor, comprising a main pipe 7, symmetrically distributed bypass pipe capillary channels 8, a flow conditioner 9 and a laminar flow element 10. Before describing the flow sensor in more detail, it should be pointed out that the sensor can be used in a variety of systems in which the measurement of the desired flow velocity is performed.

[0096] like Figure 1 As shown, the entire circuit consists of a Wheatstone bridge 1, an operational amplifier loop 2, and a constant current power supply DC. The Wheatstone bridge includes two fixed resistors 3 and two thermistors 4, wherein two sets of copper wire coils with equal lengths, coil turns, and resistance values ​​are wound around the two symmetrical ends of the middle of the outer wall of the fluid pipeline as two temperature-sensitive resistors. Since the flow sensor of the present invention has a measurement range of micro-flow and the generated electrical signal is weak, in order to accurately measure, it needs to be processed by an operational amplifier to realize the digitization, storage, and control of the signal, so the operational amplifier needs to be configured with a high gain. Ap

[0097] Figure 1 In the operational amplifier loop, V OS is the amplifier input offset differential, with the following relationship.

[0098] V OS = ±V DC T OL / 100(%)

[0099] Among them, V DC is the bridge voltage, T OL is the resistance tolerance, which has the following relationship: R is the initial resistance of the thermistor and the fixed resistor, and ΔR is the maximum difference in the resistance change of the thermistor.

[0100] T OL =ΔR / R(%)

[0101] When the voltage at the input terminal is equal to the voltage between the feedback terminal (FB) and the reference terminal (REF), the feedback of the operational amplifier needs to be satisfied. In addition, the Wheatstone bridge of the present invention needs to determine the resistance value R of a variable resistor 5. A , so that the operational amplifier meets the maximum offset V expected by the sensor IN (MAX), when the given bipolar adjustment voltage 6 is V A (MAX), the output voltage is 0, that is, V OUT = 0. The above relationship is as follows, R1 and R2 are fixed resistors.

[0102] R A =(R1R2 / R1+R2)V A (MAX) / V IN (MAX)

[0103] V OUT =(R1+R2) / R2V IN -R1 / R A V A

[0104] The gain G of the operational amplifier is thus obtained

[0105] G=(1+R1 / R2+R1 / R A )

[0106] like Figure 2-Figure 4 As shown, the outer end faces of the two symmetrical capillary channels 8 are provided with inwardly recessed grooves, and the sensor chip 11 is placed in the grooves. The circuit structure of the sensor chip is as shown above. The main flow channel can be divided into three sections, and the three sections are connected by a flow regulator 9 and a laminar flow element 10. A flow regulator is placed in the middle of the main channel 7, and the rectifier adopts a porous channel. The laminar flow element 10 connects the second and third sections of the main channel. The capillary channel 8 is U-shaped, and the structure is a branch of the main channel 7 upstream of the laminar flow element 10, and is connected to the main channel 7 downstream of the laminar flow element 10.

[0107] After the fluid flows in from the upper port of the first section structure of the main channel 7, the fluid flows out from the lower port of the first section structure of the main channel and flows into the fluid regulator 9. The fluid regulator realizes the rectification of irregular fluid, and the fluid enters the second section structure of the main pipeline 7 in a good development state. Under the action of the laminar flow element 10, the fluid flows into the two branch capillary channels 8 at a certain flow rate, and the remaining fluid flows into the next stage through the laminar flow element 10. The sensor chip 11 in the groove of the capillary channel 8 measures the flow rate in the tube. The flow rate out of the capillary channel 8 merges with the flow rate out of the laminar flow element and flows out of the main pipeline from the lower section of the third stage structure.

[0108] Figure 5 The laminar flow elements from left to right are the first laminar flow generator and the second laminar flow generator. The two generators with different lengths but otherwise identical are connected in series in the same laminar flow element, overcoming the nonlinearity of the capillary flow loss at the inlet and outlet of the flowmeter and the flow loss at the inlet section. The pressure difference of the first laminar flow generator includes the loss along the way from the first pressure port to the inlet of the first laminar flow generator; the local loss at the inlet of the first laminar flow generator; the loss along the way from the fluid flowing through the first laminar flow generator; the local loss at the outlet of the first laminar flow generator; the loss along the way from the outlet of the first laminar flow generator to the second pressure port. The pressure difference of the second laminar flow generator includes the loss along the way from the second pressure port to the inlet of the second laminar flow generator; the local loss at the inlet of the second laminar flow generator; the loss along the way from the fluid flowing through the first part of the second laminar flow generator; the loss along the way from the fluid flowing through the second part of the second laminar flow generator; the local loss at the outlet of the second laminar flow generator; the loss along the way from the outlet of the second laminar flow generator to the third pressure port. A rectifier is placed at a distance before the inlet of the first laminar flow generator (the distance should be equal to the distance from the outlet of the first laminar flow generator to the inlet of the second laminar flow generator) to make the flow conditions at the inlets of the two laminar flow generators closer.

[0109] The thermal distributed mass flowmeter is a flow measurement instrument based on the principle of heat diffusion, wherein the implementation conditions of the heat diffusion technology are relatively strict, but due to its good performance, high accuracy and reliability, it has been widely used. The thermal distributed flowmeter of the present invention includes a copper wire coil with variable resistance as a heating body and a temperature detection element, and two copper wire coils are evenly wound outside the fluid pipeline, placed on both sides of the pipeline, and form a Wheatstone bridge with two other resistors with equal resistance. The constant current power supply provides heat to the copper wire coil, and the heat passes through the copper wire coil and the outer wall of the pipeline, and then conducts the heat to the fluid in the pipe, and the signal is amplified by the operational amplifier and then output. When the fluid is stationary, the axial temperature distribution of the pipeline is symmetrical with respect to the upstream and downstream of the center of the measuring tube, and the bridge composed of the copper wire coil and the resistor is in a balanced state; when the fluid flows, the temperature field in the axial direction of the pipeline changes, and its symmetry is destroyed. The fluid brings part of the heat from the upstream to the downstream, resulting in the upstream temperature of the copper wire being lower than the downstream temperature, and the resistance value of the temperature measuring copper wire changes.

Claims

1. A capillary sensor based on MEMS technology, characterized in that: include: A main flow channel (7) for inlet and outlet, a flow regulator (9) placed in the middle of the main channel, a laminar flow element (10), and two branch flow channels (8) connected to the main flow channel located upstream and downstream of the laminar flow element (10), and a gas flow sensor (11) installed in the middle of the branch flow channels.

2. A capillary sensor based on MEMS technology according to claim 1, characterized in that: The flow regulator (9) is a symmetrical multi-through hole structure.

3. The capillary sensor based on MEMS technology according to claim 2, characterized in that: The laminar flow element (10) comprises a first laminar flow generator (10-1) and a second laminar flow generator (10-2) of different lengths but the same other data structures, which are connected in series in the same laminar flow element, and a rectifier is arranged at a distance before the entrance of the first laminar flow generator.

4. The capillary sensor based on MEMS technology according to claim 1, characterized in that: A distance before the inlet of the first laminar flow shedder is arranged in the rectifier, and the distance is the same as the distance from the outlet of the first laminar flow shedder to the inlet of the second laminar flow shedder.

5. The capillary sensor based on MEMS technology according to claim 3, characterized in that: The multi-through hole structure of the first laminar flow generator (10-1) and the second laminar flow generator (10-2) has a smaller hole diameter than the hole diameter of the flow regulator (9), and has more through holes than the flow regulator (9).

6. The capillary sensor based on MEMS technology according to claim 1, characterized in that: The entrance of the main channel (7) is a trumpet-shaped entrance.

7. The capillary sensor based on MEMS technology according to claim 1, characterized in that: The flow sensor is arranged at a position close to the inner wall of the tube of the two branch flow channels (8), and comprises a constant current power supply, a thermistor 1 and a thermistor 2, and provides heat at a constant power. The thermistor 1 and the thermistor 2 are symmetrically distributed upstream and downstream of the constant current power supply.

8. The capillary sensor based on MEMS technology according to claim 6, characterized in that: Main channel flow: The two capillaries are exactly the same, d represents the inner diameter of the capillary, λ m represents the resistance coefficient along the capillary tube, ∑ζ m The sum of the local resistance coefficients of the capillary, D is the inner diameter of the main channel, λ Z represents the resistance coefficient along the main pipeline, ζ Z is the resistance coefficient of the laminar flow element, L is the length of the main channel, A is the heat transfer coefficient of the heat exchange between the temperature sensing element and the surrounding environment, C p is the constant-pressure specific heat capacity of the measured gas; K is the instrument constant, and ΔT represents the temperature difference between thermistor 1 and thermistor 2.

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