Thermal liquid mass flowmeter suitable for micro flow

Abstract

The utility model discloses a thermal liquid mass flowmeter suitable for micro flow, which comprises a base, a regulating valve, a heating element, a temperature sensing module and a control module, a flow channel is arranged in the base, a liquid inlet and a liquid outlet which are communicated with the flow channel are respectively arranged at two ends of the base, and a cavity is arranged in the base. The cavity is communicated with the liquid inlet and the flow channel, the adjusting valve is arranged on the base and used for adjusting the flow of liquid flowing through the cavity, the cross section of the flow channel is of a rectangular structure, a bypass channel communicated with the flow channel is further arranged in the base, and the heating element is arranged on the bypass channel and used for heating the pipe wall of the bypass channel. The temperature sensing module is arranged on the bypass channel and used for detecting the temperature change of the pipe wall near the heating element, and the adjusting valve, the heating element and the temperature sensing module are all electrically connected with the control module; the device has the advantages of realizing high-precision measurement and keeping stability.

Description

Technical Field

[0001] The utility model relates to a flowmeter, in particular to a thermal liquid mass flowmeter suitable for micro-flows. Background Art

[0002] As an important flow measurement tool, the thermal flowmeter plays a key role in many industries such as chemical industry, petroleum, pharmaceutical, and food processing. Its basic principle is to measure the flow rate of the fluid by detecting the heat exchange between the heating module and the fluid. The heating module (such as a resistance wire or a hot film) is installed on the inner wall of the pipeline or close to the inner wall. When the fluid flows through, the temperature of the heating module will change. By measuring this change or the change in power required to maintain a constant temperature, the flow rate of the fluid can be indirectly calculated.

[0003] Existing thermal flowmeters exhibit good measurement performance over a wide range of flow rates, especially under medium and high flow rate conditions. However, under micro-flow conditions, that is, when the flow rate is extremely low (usually referring to a flow rate less than a few milliliters per minute (mL / min), or even lower to microliters per minute (μL / min)), traditional thermal flowmeters face many challenges. Under micro-flow conditions, the Reynolds number of the fluid is low, and the fluid flow characteristics are more sensitive, being easily affected by the surface roughness of the pipeline, fluid temperature fluctuations, and external disturbances. These factors will cause an increase in the noise of the measurement signal, thereby affecting the measurement accuracy.

[0004] In addition, fluids under micro-flow conditions usually have a high viscosity or are in a laminar flow state, which makes the distribution of the fluid in the pipeline more uniform, but at the same time, it will also cause more subtle changes in the temperature gradient around the heating module. Therefore, for micro-flow measurement, the flowmeter must have higher sensitivity and better anti-interference ability to accurately capture these subtle changes.

[0005] In summary, although existing thermal flowmeters perform excellently in conventional flow measurement, their limitations still exist under micro-flow conditions (such as below a few milliliters per minute). Therefore, it is very necessary to develop a thermal liquid mass flowmeter suitable for micro-flow conditions to improve the measurement accuracy and reliability under low flow rate conditions. Summary of the Utility Model

[0006] The purpose of the utility model is to provide a thermal liquid mass flowmeter suitable for micro-flows, which can achieve high-precision measurement and maintain stability.

[0007] To achieve the above object, the present utility model provides the following technical solutions: A thermal liquid mass flowmeter applicable to micro flow rates, comprising a base. A flow channel is provided in the base. A liquid inlet and a liquid outlet respectively communicating with the flow channel are further provided at both ends of the base. It is characterized in that: It further comprises a regulating valve, a heating element, a temperature sensing module and a control module. A cavity is provided in the base, and the cavity communicates with the liquid inlet and the flow channel respectively. The regulating valve is provided on the base and is used to regulate the liquid flow rate flowing through the cavity. The cross-section of the flow channel is in a rectangular structure. A bypass channel communicating with the flow channel is further provided in the base. The heating element is provided on the bypass channel and is used to heat the pipe wall of the bypass channel. The temperature sensing module is provided on the bypass channel and is used to detect the temperature change of the pipe wall near the heating element. Among them, the regulating valve, the heating element and the temperature sensing module are all electrically connected to the control module.

[0008] Preferably, the base comprises a top plate and a bottom plate. The top plate is closely attached to and fixed on the bottom plate. The flow channel is provided on the lower end surface of the top plate.

[0009] Preferably, the bypass channel comprises a first branch channel, a second branch channel and a capillary tube. The first branch channel and the second branch channel are respectively and vertically arranged at intervals in the bottom plate and both communicate with the flow channel. The capillary tube is connected between the first branch channel and the second branch channel.

[0010] Preferably, a support plate is fixed to the lower end of the bottom plate. A first adapter and a second adapter are provided in the support plate. One end of the first adapter communicates with the first branch channel, and the other end of the first adapter communicates with one end of the capillary tube. One end of the second adapter communicates with the second branch channel, and the other end of the second adapter communicates with the other end of the capillary tube.

[0011] Preferably, a first sealing member is provided between the first adapter and the bottom plate, and a second sealing member is provided between the second adapter and the bottom plate.

[0012] Preferably, the temperature sensing module comprises a first temperature measuring element and a second temperature measuring element. The first temperature measuring element and the second temperature measuring element are both provided on the capillary tube and are respectively located at the upstream and downstream positions of the heating element. The first temperature measuring element is used to detect the temperature of the pipe wall at the upstream position of the heating element, and the second temperature measuring element is used to detect the temperature of the pipe wall at the downstream position of the heating element. The first temperature measuring element and the second temperature measuring element are respectively electrically connected to the control module.

[0013] Preferably, the heating element is a heating resistance wire, and the heating element is fixedly wound on the outer wall of the capillary tube.

[0014] Preferably, the regulating valve is a piezoelectric ceramic valve.

[0015] Compared with the prior art, the advantages of the present utility model are as follows: The rectangular flow channel is easier to process than the circular flow channel, and a larger flow area can be formed in a relatively compact space, which is conducive to the generation of laminar flow, reduces the turbulence phenomenon at the same time, improves the stability of measurement under low Reynolds number conditions, and can also adjust the flow rate of a single channel by changing the aspect ratio of the rectangular channel to make it meet the maximum designed Reynolds number. At the same time, the overall size of the flowmeter is also easier to adjust; A bypass channel is provided in the base and is connected to the main flow channel. A heating element and a temperature sensing module are installed in the bypass channel. The heating element heats the tube wall of the bypass channel. When there is fluid flowing through the bypass, the heat from the upstream is carried to the downstream by the fluid, thus forming a temperature difference. The temperature sensing module then detects the temperatures of the upstream and downstream tube walls. According to the specific linear relationship between the flow rate and the temperature, the flow rate of the bypass can be calculated. And in a flowmeter of a certain specification, the ratio of the bypass flow rate to the main flow rate is a constant. The control module can obtain the total flow rate of the flowmeter by detecting the flow rate of the bypass according to the relationship between the bypass flow rate and the main flow rate. The bypass channel structure is adopted in this design scheme, so that the actual flow rate measurement occurs in the bypass channel, completely avoiding the disturbance of the measurement to the flow field of the main flow channel, which helps to improve the measurement accuracy. At the same time, the opening degree of the regulating valve is controlled by the control module to control the flow rate in the flow channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0017] Figure 1 It is a three-dimensional structure schematic diagram of the present utility model;

[0018] Figure 2 It is a cross-sectional view of the present utility model;

[0019] Figure 3 It is a three-dimensional structure schematic diagram of the top plate in the present utility model;

[0020] Figure 4 It is a three-dimensional structure schematic diagram when the support plate cooperates with the capillary tube in the present utility model;

[0021] Figure 5 It is a principle block diagram of the circuit part in the present utility model;

[0022] In the figure, 1 is the base; 2 is the flow channel; 3 is the liquid inlet; 4 is the liquid outlet; 5 is the regulating valve; 6 is the heating element; 7 is the temperature sensing module; 8 is the control module; 9 is the cavity; 10 is the bypass channel; 11 is the top plate; 12 is the bottom plate; 13 is the first branch channel; 14 is the second branch channel; 15 is the capillary; 16 is the support plate; 17 is the first adapter; 18 is the second adapter; 19 is the first seal; 20 is the second seal; 21 is the first temperature measuring element; 22 is the second temperature measuring element. Specific embodiments

[0023] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0024] Embodiment 1: As Figures 1 to 5 shown, a thermal liquid mass flowmeter applicable to a micro flow rate includes a base 1. A flow channel 2 is provided in the base 1. A liquid inlet 3 and a liquid outlet 4 communicating with the flow channel 2 are respectively provided at both ends of the base 1. It further includes a regulating valve 5, a heating element 6, a temperature sensing module 7 and a control module 8. A cavity 9 is provided in the base 1. The cavity 9 communicates with the liquid inlet 3 and the flow channel 2 respectively. The regulating valve 5 is provided on the base 1 and is used to regulate the liquid flow rate flowing through the cavity 9. The cross section of the flow channel 2 is in a rectangular structure. A bypass channel 10 communicating with the flow channel 2 is further provided in the base 1. The heating element 6 is provided on the bypass channel 10 and is used to heat the tube wall of the bypass channel 10. The temperature sensing module 7 is provided on the bypass channel 10 and is used to detect the temperature change of the tube wall near the heating element 6. Among them, the regulating valve 5, the heating element 6 and the temperature sensing module 7 are all electrically connected to the control module 8.

[0025] The cross section of the main channel of the device is a rectangular structure. Compared with the traditional circular channel, the rectangular channel is easier to process in terms of processing technology. By adjusting the aspect ratio of the rectangular channel, the effective flow area of ​​the channel can be changed. A narrower width will increase the flow velocity of the fluid, thereby increasing the Reynolds number, and a wider width will reduce the flow velocity, thereby reducing the Reynolds number. In this way, the flow rate of a single channel can be optimized by changing the aspect ratio to ensure that it operates within the optimal Reynolds number range. In addition, the rectangular channel has a larger surface area than the circular channel, so that the boundary layer effect of the fluid in the channel 2 is stronger. The boundary layer effect causes the velocity of the fluid to gradually decrease near the wall, thereby reducing the turbulent tendency in the central area of ​​the fluid. The fluid distribution in the rectangular channel will also be more uniform, especially under low Reynolds number conditions. The flow of the fluid in the rectangular channel is smoother, reducing the turbulence caused by uneven fluid velocity. Most importantly, in the rectangular channel, the fluid is easier to maintain a laminar state, and the fluid flow in the laminar state is more orderly, reducing the formation of vortices, thereby reducing the impact of turbulence on measurement accuracy.

[0026] Embodiment 2: Figures 1 to 5 As shown, different from the first embodiment, the base 1 includes a top plate 11 and a bottom plate 12 , the top plate 11 is tightly attached to and fixed on the bottom plate 12 , and the flow channel 2 is arranged on the lower end surface of the top plate 11 .

[0027] In the above structure, the flow channel 2 is opened on the lower surface of the top plate 11, which can minimize the heat exchange area between the flow channel 2 and the external environment, thereby avoiding the influence of ambient temperature fluctuations as much as possible, which helps to improve the accuracy and repeatability of temperature measurement.

[0028] The fitting design of the top plate 11 and the bottom plate 12 completely encloses the flow channel 2 and the internal structure, avoiding the risk of fluid leakage and the entry of external impurities, thereby ensuring the cleanliness and airtightness of the measurement environment and making the measurement data more reliable. The top plate 11 and the bottom plate 12 can be connected by bolts, adhesives or welding to achieve a close fit between the two.

[0029] In this embodiment, the bypass channel 10 includes a first branch channel 13, a second branch channel 14 and a capillary 15. The first branch channel 13 and the second branch channel 14 are respectively arranged vertically at intervals in the bottom plate 12 and are both connected to the flow channel 2. The capillary 15 is connected between the first branch channel 13 and the second branch channel 14.

[0030] In the above structure, arranging the first branch channel 13 and the second branch channel 14 vertically within the bottom plate 12 can effectively utilize the space, achieve compact integration of the device, and make the total bypass length relatively short, reducing the fluid flow resistance and pressure loss. A capillary 15 is provided between the first branch and the second branch. The capillary 15 has a relatively small flow cross-sectional area and a relatively high flow velocity, which is beneficial to improving the measurement sensitivity of the temperature field and the measurement accuracy. At the same time, when the flow rate is large, the capillary 15 can also play a certain throttling role.

[0031] In addition, with such an arrangement, the fluid passes through the processes of vertical downward flow and vertical upward flow successively, and an obvious convection effect will naturally form under the action of gravity, which is beneficial to improving the heat exchange efficiency between the fluid and the wall surface, thereby improving the sensitivity and accuracy of temperature measurement.

[0032] Embodiment 3: As Figures 1 to 5 shown, different from Embodiment 2, a support plate 16 is fixed to the lower end of the bottom plate 12. A first adapter 17 and a second adapter 18 are arranged within the support plate 16. One end of the first adapter 17 is communicated with the first branch channel 13, and the other end of the first adapter 17 is communicated with one end of the capillary 15. One end of the second adapter 18 is communicated with the second branch channel 14, and the other end of the second adapter 18 is communicated with the other end of the capillary 15.

[0033] In the above structure, by using the support plate 16 and the adapters, the first branch channel, the second branch channel are connected to the thin capillary 15, which can greatly reduce the dead space and leakage points caused by assembly errors, avoid fluid short-circuiting and leakage, and ensure the integrity and tightness of the flow in the entire bypass channel 10. The adapter provides a reliable physical interface, facilitating the separate assembly of the two parts of the capillary 15 and the support plate 16.

[0034] The connection between the adapter and the capillary 15 usually adopts threaded connection or snap connection, which not only simplifies the overall assembly process, but also is beneficial to improving the assembly accuracy, reducing the relative displacement between components, thereby improving the measurement sensitivity, and can also effectively prevent liquid leakage, ensure the tightness of the device, and ensure the normal operation of the device.

[0035] In this embodiment, a first sealing member 19 is provided between the first adapter 17 and the bottom plate 12, and a second sealing member 20 is provided between the second adapter 18 and the bottom plate 12.

[0036] The two seals can effectively isolate the tiny gap at the connection interface between the adapter and the base plate 12, eliminating the risk of fluid leakage from this location, ensuring the tightness of the entire flow path of the bypass channel 10, avoiding interference or deviation in the flow measurement data. In addition, the seals can block the heat exchange between the base plate 12 and the external environment, enabling the temperature measurement to be only affected by the temperature change of the fluid within the bypass channel 10 and not being interfered by external temperature fluctuations, significantly improving the temperature measurement accuracy and repeatability.

[0037] The seals are made of high-temperature, high-pressure, and corrosion-resistant metal rings or non-metallic materials, which can withstand the high-temperature, high-pressure, and other environments under harsh working conditions and will not age or leak during long-term use, ensuring that the whole machine maintains good sealing performance and measurement accuracy for a long time.

[0038] In this embodiment, the temperature sensing module 7 includes a first temperature measuring element 21 and a second temperature measuring element 22. Both the first temperature measuring element 21 and the second temperature measuring element 22 are arranged on the capillary 15 and are located upstream and downstream of the heating element 6 respectively. The first temperature measuring element 21 is used to detect the wall temperature at the upstream position of the heating element 6, and the second temperature measuring element 22 is used to detect the wall temperature at the downstream position of the heating element 6. The first temperature measuring element 21 and the second temperature measuring element 22 are electrically connected to the control module 8 respectively.

[0039] The temperature sensing module 7 of this thermal liquid mass flowmeter consists of a first temperature measuring element 21 and a second temperature measuring element 22, which are respectively arranged at the upstream and downstream positions of the heating element 6 on the thin capillary 15 and are electrically connected to the control module 8. This arrangement can minimize the delay of temperature measurement, improve the fast response ability and sensitivity. At the same time, by measuring the wall temperature before and after heating respectively and calculating the temperature rise value, the influence of the initial temperature fluctuation of the fluid can be effectively eliminated, greatly improving the accuracy and reliability of flow conversion.

[0040] In the environment of high flow rate and strong convection in the capillary 15, the temperature difference measurement further enhances the measurement resolution of the temperature field. The temperature measuring element is directly connected to the control module 8, realizing high-speed data transmission, high-precision A / D conversion, and real-time digital temperature compensation and other processes, further improving the temperature measurement and operation accuracy, and thus further enhancing the sensitivity and reliability of the entire temperature measurement system.

[0041] In this embodiment, the heating element 6 is a heating resistance wire, and the heating element 6 is fixed on the outer wall of the capillary 15 by winding.

[0042] In the above structure, the heating wire itself has uniform heat generation and high heating efficiency, and can quickly convert electrical energy into heat input to the fluid, providing an efficient and stable heating source. At the same time, it is wound around the outer wall of the capillary 15, minimizing the distance between the heat source and the fluid, which is beneficial to improving the heat transfer efficiency. The winding arrangement enables the heating element 6 to closely adhere to the outer surface of the capillary 15, increasing the heating area and further improving the heat transfer efficiency. Meanwhile, the winding form also provides a certain elastic buffering effect, helping to absorb the stress of thermal expansion and contraction and extending the service life of the heating element 6. The manufacture and installation of the externally wound heating element 6 are extremely simple. It only needs to wind the heating wire around the capillary 15 without complex processing such as grooving or drilling the capillary 15, significantly reducing the manufacturing difficulty and cost.

[0043] In this embodiment, the regulating valve 5 is a piezoelectric ceramic valve.

[0044] The working principle of the piezoelectric ceramic valve is to utilize the piezoelectric effect of piezoelectric ceramic materials. Piezoelectric ceramic materials have unique properties. When a voltage is applied to them, they will deform. Conversely, when pressure is applied to them, they will generate voltage. In the piezoelectric ceramic valve, the piezoelectric ceramic sheet is installed on the valve body. When the control module 8 issues a control signal, the piezoelectric ceramic sheet will deform according to the signal, thereby changing the opening of the valve and further regulating the liquid flow rate through the cavity 9. Thus, it can achieve micron-level precision control, can very precisely regulate the liquid flow rate, improve the measurement accuracy, and has a very fast response speed. It can quickly change the valve opening according to the control signal to achieve rapid flow control.

[0045] The above is only the implementation mode of this application, and it does not limit the patent scope of this application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied in other related technical fields, is similarly included in the patent protection scope of this application.

Claims

1. A thermal liquid mass flowmeter suitable for small flow rates, comprising a base, a flow channel is provided in the base, and a liquid inlet and a liquid outlet connected to the flow channel are provided at both ends of the base, characterized in that: It also includes a regulating valve, a heating element, a temperature sensing module and a control module. A cavity is provided in the base, and the cavity is respectively connected with the liquid inlet and the flow channel. The regulating valve is arranged on the base and is used to adjust the liquid flow through the cavity. The cross-section of the flow channel is a rectangular structure. A bypass channel connected with the flow channel is also arranged in the base. The heating element is arranged on the bypass channel and is used to heat the pipe wall of the bypass channel. The temperature sensing module is arranged on the bypass channel and is used to detect the temperature change of the pipe wall near the heating element. The regulating valve, the heating element and the temperature sensing module are all electrically connected to the control module.

2. A thermal liquid mass flowmeter suitable for small flow rates according to claim 1, characterized in that: The base comprises a top plate and a bottom plate, the top plate is closely attached to and fixed on the bottom plate, and the flow channel is arranged on the lower end surface of the top plate.

3. A thermal liquid mass flowmeter suitable for small flow rates according to claim 2, characterized in that: The bypass channel includes a first branch channel, a second branch channel and a capillary tube. The first branch channel and the second branch channel are respectively arranged vertically in the bottom plate at intervals and are both connected to the flow channel. The capillary tube is connected between the first branch channel and the second branch channel.

4. A thermal liquid mass flowmeter suitable for small flow rates according to claim 3, characterized in that: A support plate is fixed to the lower end of the base plate, and a first adapter and a second adapter are arranged in the support plate, one end of the first adapter is connected to the first branch channel, the other end of the first adapter is connected to one end of the capillary, one end of the second adapter is connected to the second branch channel, and the other end of the second adapter is connected to the other end of the capillary.

5. A thermal liquid mass flowmeter suitable for small flow rates according to claim 4, characterized in that: A first sealing member is provided between the first adapter and the bottom plate, and a second sealing member is provided between the second adapter and the bottom plate.

6. A thermal liquid mass flowmeter suitable for small flow rates according to claim 3, characterized in that: The temperature sensing module includes a first temperature measuring element and a second temperature measuring element. The first temperature measuring element and the second temperature measuring element are both arranged on the capillary tube and are respectively located at the upstream and downstream positions of the heating element. The first temperature measuring element is used to detect the tube wall temperature at the upstream position of the heating element, and the second temperature measuring element is used to detect the tube wall temperature at the downstream position of the heating element. The first temperature measuring element and the second temperature measuring element are respectively electrically connected to the control module.

7. A thermal liquid mass flowmeter suitable for small flow rates according to claim 6, characterized in that: The heating element is a heating resistance wire, and the heating element is wound and fixed on the outer wall of the capillary.

8. A thermal liquid mass flowmeter suitable for small flow rates according to claim 1, characterized in that: The regulating valve is a piezoelectric ceramic valve.

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