CN109946477B - Liquid flow velocity measuring device and method based on electrochemical response of conductive electrode - Google Patents
Liquid flow velocity measuring device and method based on electrochemical response of conductive electrode Download PDFInfo
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Abstract
The invention discloses a liquid flow velocity measuring device and a liquid flow velocity measuring method based on electrochemical response of a conductive electrode. The liquid flow velocity measuring device disclosed by the invention is small in size and convenient to carry, has sensitivity which is nearly one order of magnitude higher than that of an ultrasonic flow velocity meter and an optical fiber flow velocity meter which are provided with higher sensitivity in the market at present, and can measure liquid with the flow velocity of 2.2 mm/s. In addition, the invention utilizes the metal mesh with very low price as the working electrode, not only has low price and wide applicability, but also has important scientific significance for expanding the application field of the electrochemical workstation and developing the flow rate monitoring technology of novel ultra-low flow rate liquid, and lays a foundation for the application of the invention in the fields of chemical synthesis, biological detection, nano materials and the like.
Description
Technical Field
The invention belongs to the field of liquid flow velocity measurement, relates to a liquid flow velocity measurement device and method based on metal grid open-circuit potential, and particularly relates to a liquid flow velocity measurement device and method based on conductive electrode electrochemical response.
Background
The development of low-flow-rate sensors in the biological, chemical and material frontier fields such as microfluidic chips and nanomaterial synthesis has clear demands, because too fast flow rate affects the analysis accuracy of chips and the current situation and performance of nanomaterials. Various flow velocity detection instruments are available in the market at present, and the flow velocity detection instruments are mainly divided into two types according to the working principle: flow rate sensors based on thermal principles and flow rate sensors based on non-thermal principles.
Although the flow velocity sensor based on the thermal principle has the advantages of easy process control and simpler detection, the flow velocity sensor has the defects of large measurement error, large working power consumption, long response time and the like. A flow rate sensor based on the non-thermal principle detects a mechanical quantity related to a fluid velocity and reflects the mechanical quantity by a machining means of a precision machine.
The common non-thermal liquid flow rate sensors include four types, namely an electromagnetic sensor, an ultrasonic sensor, a vortex street sensor and a turbine sensor. The electromagnetic sensor has low measurement precision and is unreliable; although the vortex street sensor has higher measurement accuracy, the vortex street sensor cannot measure the liquid flow velocity with higher speed or lower speed and more impurities; the turbine flow meter has high precision and good repeatability, and has a wide measurement range, but is not sensitive enough to ultra-low flow liquid. Therefore, the flow rate measurement of low-flow liquid is always a difficult problem, and due to the low flow rate, the signal generated by the sensor is weak, the signal-to-noise ratio is low, and the measurement signal is often submerged in noise and cannot be accurately measured.
At present, two non-thermal liquid flow rate sensors are mainly adopted for measuring the flow rate of low-flow-rate liquid: ultrasonic sensors and fiber optic sensors. The ultrasonic flow meter measures the flow rate mainly by detecting the speed difference generated by ultrasonic waves caused by the flow of the fluid. The optical fiber flowmeter is characterized in that when the optical fiber is placed in flowing liquid, the characteristics (such as intensity, phase, frequency and the like) of light transmitted in the optical fiber are influenced by the flow rate, and the change of the light detected by a proper light detection method can be used for reversely deducing the flow rate of the liquid. The flow velocity range which can be detected by the two flow velocity detectors in the market is respectively 0.01-12 m/s and 0.01-5 m/s. New measurement methods and instruments are also being developed for lower flow rates.
Disclosure of Invention
In view of the above, the present invention provides a liquid flow rate measuring device and a liquid flow rate measuring method based on electrochemical response of a conductive electrode. The inventor finds that the open-circuit potential and the current of the working electrode of the electrochemical workstation have a rule of increasing with the increase of the flowing speed of the liquid through the research on the electrochemical properties of the electrode material in the flowing liquid. The invention develops a new liquid flow rate sensor by measuring the open circuit potential difference of the metal grid working electrode.
In order to achieve the above purpose, the invention provides the following technical scheme:
a liquid flow velocity measuring device based on electrochemical response of a conductive electrode comprises a shell, a connecting frame, a sliding block, a sliding way, three electrodes and three leads;
the connecting frame and the three electrodes are both arranged in the shell; the three electrodes correspond to the three leads, and the three electrodes comprise a reference electrode, a working electrode and a counter electrode;
the slideway is fixedly arranged on the shell, and one end of the slideway is provided with a clamping groove;
the sliding block is arranged in the slideway and is in sliding connection with the slideway; the sliding block is fixedly connected with the connecting frame.
By adopting the technical scheme, the invention has the following beneficial effects:
the sensitivity of the liquid flow velocity measuring device disclosed by the invention is 5 times higher than that of the portable ultrasonic flow velocity meter and the optical fiber flow velocity meter which have higher sensitivity in the market at present, and the liquid with the flow velocity as low as 2.2mm/s can be measured.
In addition, the invention utilizes the metal mesh with very low price as the working electrode, not only has low price and wide applicability, but also has important scientific significance for expanding the application field of the electrochemical workstation and developing the flow rate monitoring technology of novel ultra-low flow rate liquid, and lays a foundation for the application of the invention in the fields of chemical synthesis, biological detection, nano materials and the like.
Preferably, the liquid flow rate measuring device further comprises a support column and a cover plate; the cover plate is arranged at one end of the shell and seals the shell; one end of the supporting column is connected with the cover plate, and the other end of the supporting column is connected with the connecting piece.
It should be noted that, the measuring device of the present invention is inserted into the liquid of the flow rate to be measured, the liquid enters the cavity formed by the housing and the cover plate through the gap between the cover plate and the housing, and the open-circuit potential and current when the electrode retracts are measured by the electrochemical workstation as the static open-circuit potential and current, and the cover plate is designed to avoid the influence of the liquid flow on the static open-circuit potential and current to reduce the detection accuracy.
Preferably, the connecting frame is made of an organic material with a three-hole structure, and the three holes are used for inserting the reference electrode, the working electrode and the counter electrode respectively.
Preferably, the clamping groove is matched with the sliding block, and the sliding of the sliding block in the sliding way is limited through the clamping groove.
Preferably, the working electrode is made of a copper mesh, a nickel-chromium alloy wire mesh, a stainless steel mesh, FTO glass or any conductive electrode material.
It is worth to say that the invention discloses the corresponding connection of three electrodes and electrochemical workstation, specifically: cutting a 150-mesh conductive electrode such as a copper mesh, a nickel-chromium alloy wire mesh, a stainless steel mesh or FTO glass into a rectangle of 1 x 2cm to be used as a working electrode, cleaning surface oil stains by using alcohol, acetone or deionized water, and connecting the working electrode with a green connector lug of an electrochemical workstation; connecting a platinum wire electrode with a red connector lug of an electrochemical workstation to serve as a counter electrode; the silver/silver chloride electrode is connected with a white connector lug of an electrochemical workstation to be used as a reference electrode.
The invention also provides a liquid flow rate measuring method based on the electrochemical response of the conductive electrode.
In order to achieve the above purpose, the invention provides the following technical scheme:
a liquid flow rate measuring method based on electrochemical response of a conductive electrode specifically comprises the following steps:
(1) washing the liquid flow rate measuring device by using deionized water, correspondingly connecting the three leads with an electrochemical workstation, vertically placing the measuring device in liquid with the flow rate to be measured, and standing for 1-10 minutes;
(2) the three electrodes are in a retraction state in the shell by adjusting the sliding block to slide to the clamping groove position in the sliding way, the cover plate is closed, and after the three electrodes are stabilized for 10-300 seconds, the open-circuit potential and the current of the electrodes in the retraction process are measured by using an electrochemical workstation and are used as static open-circuit potential and current;
(3) sliding the adjusting slide block to the lowest end to enable the three electrodes to completely extend out of the shell, and measuring open-circuit potential and current of the electrodes when the electrodes extend out by using an electrochemical workstation after the three electrodes are stabilized for 10-300 seconds to serve as dynamic open-circuit potential and current;
(4) calculating the open circuit potential difference and the current difference of the working electrode in the dynamic liquid state and the static liquid state, and obtaining the flow rate of the liquid according to the calibration curve of the open circuit potential difference, the current difference and the flow rate.
Preferably, in the step (1), the liquid flow rate measuring device is inserted into the liquid to be measured to a depth of not less than 3 cm.
By adopting the technical scheme, the invention has the following beneficial effects:
the invention builds a new liquid flow velocity sensor on the basis that the open circuit potential difference between flowing liquid and static liquid is in direct proportion to the liquid flow velocity, and finds that the minimum flow velocity as low as 2.2mm/s can be measured by utilizing the open circuit potential difference of a metal grid electrode under the flowing and static conditions of the liquid, and is about 5 times lower than the minimum limit flow velocity which can be measured by the most sensitive optical fiber flow velocity sensor in the market.
According to the technical scheme, compared with the prior art, the liquid flow velocity measuring device and the liquid flow velocity measuring method based on the electrochemical response of the conductive electrode provided by the invention have the advantages that the electrochemical workstation is connected with the liquid flow velocity measuring device, the current difference and the open-circuit potential difference of the working electrode in the dynamic and static liquid environments are measured, and the flow velocity of the liquid can be calculated according to the calibration curve. The liquid flow velocity measuring device is small in size and convenient to carry, and the sensitivity of the liquid flow velocity measuring device is 5 times higher than that of an ultrasonic flow velocity meter and an optical fiber flow velocity meter which are provided with high sensitivity on the market at present, so that the liquid with the lowest flow velocity of 2.2mm/s can be measured. The liquid flow velocity measuring method disclosed by the invention has good universality, can be used for measuring the flow velocity of various liquids by adopting different electrodes, and has wide application prospect in the aspect of monitoring the flow velocity of low-flow-velocity liquid.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a liquid flow rate measuring device.
FIG. 2 is a graph showing the voltage-current response of a NiCr alloy mesh in ionized water to the rotation speed of a rotor.
Figure 3 the figure is an open circuit potential response of different electrode materials in flowing deionized water.
FIG. 4 is a flow rate calibration device.
Fig. 5 is a schematic structural diagram of an open slot.
FIG. 6 is a graph showing the flow rate calibration results of the metal mesh electrode.
Figure 7 is a graph of open circuit potential versus time for a stainless steel mesh electrode in deionized water.
FIG. 8 is a graph showing the open circuit potential versus time of an NiCr alloy mesh electrode in NaCl solution.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention discloses a liquid flow velocity measuring device and a liquid flow velocity measuring method based on conductive electrode electrochemical response, which have wide applicability and higher sensitivity, and the measuring device can measure liquid with lower flow velocity (the flow velocity is less than or equal to 2.2 mm/s).
The present invention will be further specifically illustrated by the following examples for better understanding, but the present invention is not to be construed as being limited thereto, and certain insubstantial modifications and adaptations of the invention by those skilled in the art based on the foregoing disclosure are intended to be included within the scope of the invention.
Referring to the attached figure 1 in combination, the invention discloses a liquid flow rate measuring device based on electrochemical response of a conductive electrode, which comprises a shell 1, a connecting frame 2, a sliding block 3, a slideway 4, three electrodes, three leads, a supporting column 9 and a cover plate 10, wherein the shell is provided with a plurality of grooves;
the connecting frame 2 and the three electrodes are both arranged in the shell 1; the three electrodes correspond to the three leads and comprise a reference electrode 5, a working electrode 6 and a counter electrode 7;
the slideway 4 is fixedly arranged on the shell 1, and one end of the slideway 4 is provided with a clamping groove 8;
the sliding block 3 is arranged inside the slideway 4 and is connected with the slideway 4 in a sliding way; the sliding block 3 is fixed with the connecting frame 2;
the cover plate 10 is fixed with the connecting frame 2 through 4 supporting columns 9.
In order to further achieve the technical effect of the present invention, the connecting frame 2 is an organic material block provided with a three-hole structure, and the three holes are used for inserting the reference electrode 5, the working electrode 6 and the counter electrode 7 respectively.
In order to further achieve the technical effect of the invention, the clamping groove 8 is matched with the sliding block 3, and the sliding of the sliding block 3 in the sliding way 4 under the condition that the cover plate is closed is limited by the clamping groove 8.
In order to further realize the technical effect of the invention, the working electrode 6 is made of copper mesh, nickel-chromium alloy wire mesh, stainless steel mesh, FTO glass or any other electrode material.
It is still another object of the present invention to provide a method for measuring a flow rate of a liquid based on an electrochemical response of a conductive electrode, the method comprising the steps of:
(1) washing the liquid flow rate measuring device by using deionized water, and correspondingly connecting the three leads with an electrochemical workstation;
(2) the telescopic state of the three electrodes in the shell is controlled by adjusting the sliding of the sliding block in the slide way, the current response of the working electrode is detected by using an electrochemical workstation so as to measure the current and the open-circuit potential difference of the working electrode in the dynamic and static liquid environments, and the ultralow flow rate of the liquid is calculated according to a calibration curve.
The technical solution of the present invention will be further described with reference to the following specific examples.
Example 1: flow rate response experiment
(1) Reagent and laboratory apparatus
Deionized water is self-made by a laboratory, and the resistivity is 12M omega cm; NaCl (analytically pure) was purchased from Sjogren science, Inc.; the stirrer, the glass sealed electrolytic cell and the iron support are purchased from chemical instruments of Beijing; platinum wire electrodes, silver/silver chloride electrodes were purchased from yozhou, positive and electronic technologies; the meshes of stainless steel, copper and nickel-chromium alloy grids are all 150 meshes, and are purchased from Lei kou metals. The electrochemical workstation adopts CHI660E model manufactured by Shanghai Chenghua instruments; the digital display constant temperature magnetic stirrer adopts a model 90-2 produced by Town Xinrui instruments company of gold Tan city.
(2) Content of the experiment
The glass-sealed cell was rinsed with deionized water and the three electrodes were placed in the cell. Cutting 150-mesh copper mesh, nickel-chromium alloy wire mesh, stainless steel mesh and FTO glass into a rectangle of 1 x 2cm to be used as a working electrode, cleaning surface oil stains by using alcohol, acetone and deionized water, and connecting with a green connector lug of an electrochemical workstation. And selecting a platinum wire electrode connected with a red connector lug of the electrochemical workstation as a counter electrode. The silver/silver chloride electrode is selected to be connected with a white connector lug of the electrochemical workstation to be used as a reference electrode.
Different liquids are added to partially immerse the electrodes in the liquid and ensure that none of the three electrodes touch the wall of the container and the stirrer. And opening a switch of the electrochemical workstation for preheating for 5min, opening corresponding software on a computer, and detecting the electrochemical response of the work through the electrochemical workstation by utilizing the built three-electrode system. In the experiment, a current-time mode or an open circuit potential-time mode is selected, and the system current is detected for 30s in a standing state to obtain a static I-t or V-t curve. The water was then passed through the wire mesh for 30s by rotating the stirrer and repeating the cycle for several cycles to obtain either an I-t or V-t curve.
In order to explore the qualitative relationship between voltage/current and different flow rates, measurements were performed at three rotation speeds, low, medium and high, respectively. And taking out the metal wire mesh after the measurement is finished, and measuring different samples and different solutions in the same way to obtain a flow rate response curve of open-circuit voltage or current.
(3) Influence of rotor speed on electrode open circuit potential and current
FIG. 2 is a graph of the voltage current response of a NiCr alloy mesh in deionized water to the rotational speed of a magnetic stirring rotor. And FIG. 2(A) is an open circuit potential versus time curve; FIG. 2(B) is a current-time curve; FIG. 2(C) is the open circuit potential difference versus rotational speed; fig. 2(D) shows the current difference-rotation speed relationship.
It can be seen from fig. 2 that there is a clear response to liquid flow rate whether it is open circuit potential or current flow between the NiCr alloy mesh and the counter electrode.
Open circuit potential refers to the electrode potential at zero current density, i.e., the potential difference between the working electrode and the reference electrode without a load. Current refers to the baseline current between the working electrode and the counter electrode. At the instant the magnetic rotor is turning/stopped, the open circuit potential and current also show significant changes. The change has good repeatability and is in one-to-one correspondence with the starting and stopping of the magnetic stirring rotor in the liquid.
As can be seen from fig. 2: at a moderate rotational speed of 330r/min, the open circuit potential produces a voltage variation of around 20mV (FIG. 2A); while the current produced an average change of 0.58 mua (fig. 2B). The open circuit potential and current change in opposite directions, similar to the charging process of a battery.
At three rotational speeds of 162r/min, 330r/min and 495r/min, the average values of the open circuit potential differences were 18mV, 20.6mV and 23mV, respectively, and good linearity was exhibited, as shown in FIG. 2C. The current difference averages were 0.44 μ A, 0.58 μ A, and 0.779 μ A, respectively, and a positive correlation was also shown, as shown in FIG. 2D. Although there is some error in representing the flow rate by the rotational speed, these results qualitatively reflect the positive correlation between the open circuit potential difference and the current difference and the liquid flow rate. From these measurements it can be seen that: along with the change of the flow velocity, the change quantity of the open circuit potential difference is larger, and the data is more stable in the measuring process. But the change in current difference is small, on the order of microamperes.
(4) Influence of electrode materials on open circuit potential
It is a common phenomenon that conductive electrodes have an open circuit potential in a flowing liquid. Due to the different potentials of the different electrode materials, their open circuit potential responses differ in the same solution at the same flow rate. The invention carries out corresponding researches on copper mesh, FTO glass, stainless steel mesh and nickel-chromium alloy mesh. Fig. 3 shows the open-circuit potential response of different conductive electrodes when the magnetic rotor is started and stopped every 30 seconds, and the rotor speed is 330 r/min. And FIG. 3(A) is a graph of NiCr alloy mesh open circuit potential versus time; FIG. 3(B) is a plot of open circuit potential versus time for a stainless steel mesh; FIG. 3(C) is a FTO glass open circuit potential versus time curve; FIG. 3(D) is a graph of open circuit potential versus time for a copper mesh.
As can be seen in fig. 3: as the liquid flows, the open circuit potentials of all electrode materials increase, but the average amount of change in open circuit potential varies from electrode material to electrode material. NiCr alloy mesh was 20.6mV (FIG. 3A), stainless steel mesh was 24.5mV (FIG. 3B), FTO glass was 2.1mV (FIG. 3C), and copper mesh was 10mV (FIG. 3D). During the starting and stopping of the magnetic stirring rotor, the change of the open-circuit potential is related to factors such as the surface potential, the surface area and the surface liquid flow rate of the electrode material. However, the physicochemical mechanism of the open circuit potential change is caused by the change of the double layer structure on the surface of the material due to the liquid flow. According to the Stern double layer model, the double layer of the metal surface comprises a compact layer and a diffusion layer, and the capacitances are CH and CD, respectively. The total capacitance of the electric double layer is equal to the capacitance after the two capacitances are connected in series
As the liquid flow rate increases, ions in the diffusion layer are carried away, CD decreases, and the total capacitance C also decreases. And at relatively low flow rates, the interaction force between the ions in the compact layer and the metal surface is strong and is not affected by the flow of the liquid. The charge density in the compact layer is not changed. Capacitance due to double electric layers
C＝δ/V (2)
Where δ is the metal-side charge density and V is the Zeta potential. As the capacitance decreases, the electrode potential at the surface of the material increases.
Example 2: calibration of alloy mesh flow velocity sensor
The flow rate calibration device disclosed by the invention comprises a circulating water pump 1, an open slot 2 and an electrochemical workstation 3, wherein the circulating water pump 1 and the open slot 2 are connected into a liquid circulation loop through a pipeline, as shown in figure 4. A water valve 4 and a liquid flow sensor 5 are sequentially arranged between the water outlet of the circulating water pump 1 and the open slot 2; the water inlet of the circulating water pump 1 is directly connected with the open slot 2.
The electrochemical workstation 3 is correspondingly connected with three electrodes of a liquid flow velocity measuring device (shown in figure 1) and is used for detecting the current and open-circuit potential response of the working electrode at different flow velocities, and calibrating the ultralow flow velocity corresponding to the current difference and the open-circuit potential difference of the working electrode according to the indication of the current and liquid flow sensor 5.
In addition, the liquid flow sensor disclosed by the invention adopts a Chinese Koutou DN10 type flowmeter which is convenient to process and connect and has the measurement precision as high as 0.5%. In order to obtain smaller water flow velocity, an open slot with a larger cross section area is designed to be connected with the liquid flow sensor, and in order to make the calibration result as accurate as possible, the water flow in the flow velocity detection system needs to be designed into laminar flow. An aluminum open slot 2 with the inner diameter of 100mm is connected with a stainless steel pipeline with the inner diameter of 10mm in the calibration device. The open groove 2 acts as a fluid retarder and is structured as shown in fig. 5, and the inventor uses the Reynolds equation of the fluid in the circular aluminum groove
(wherein v is a liquid flow rate, d is a circular tube diameter, and v is a kinematic viscosity coefficient of the liquid), and the kinematic viscosity coefficient of water at 25 ℃ is 0.8937 x 10-6m2The Reynolds number of the water flow in the aluminum open slot is far less than Re through calculationc2320, which satisfies the condition of laminar flow.
Through controlling the liquid inlet valve and the liquid outlet valve, the depth of the deionized water in the flow speed detection tank is stabilized at 6.3cm, and the cross sectional area S of the water flow passing through the open tank can be calculated to be 53.83cm2. The liquid used in the present invention is incompressible and therefore the indication of the flow sensor is the instantaneous flow of liquid in the tank. Therefore, the water flow speed in the groove and the reading of the flow sensor satisfy the relation:
where Q is the turbine liquid flow meter reading.
And continuously acquiring open-circuit potential data by using an electrochemical workstation, adjusting a water valve at the water outlet of the circulating water pump to change the water flow speed in the tank, and reading and recording after the flow sensor is stable. The water valve is continuously adjusted to change the water yield so as to obtain a plurality of flow rates. Due to the limitations of the water pump power and the measurement range of the flow sensor, the flow meter of the turbine liquid can display the flow range of 40-390L/h, and obvious open-circuit potential changes on the working electrode can be observed in the range. According to the obtained instantaneous average flow and the obtained open circuit potential signals recorded by experiments, an origin software is used for making a scatter diagram of the open circuit potential difference and the water flow velocity, and a curve is fitted to obtain the relation between the open circuit potential difference and the water flow velocity.
The invention selects the NiCr alloy net and the stainless steel net which have stable chemical properties and high rigidity to calibrate the flow rate, and the calibration result is shown in figure 6.
FIG. 6(A) shows the calibration results of the open circuit potential of the NiCr alloy mesh in deionized water; FIG. 6(B) is the open circuit potential calibration result of stainless steel mesh in deionized water; FIG. 6(C) is the open circuit potential calibration result of NiCr alloy net in tap water; FIG. 6(D) shows the calibration result of the open circuit potential of the stainless steel net in tap water; FIG. 6(E) shows the calibration results of the open circuit potential of the NiCr alloy mesh in a 0.1M NaCl solution; FIG. 6(F) is the open circuit potential calibration result of the stainless steel net in 0.1M NaCl solution; FIG. 6(G) is the current calibration result of NiCr alloy mesh in deionized water.
As can be seen in fig. 6: the linearity of the solution is improved continuously with the increase of the ion concentration, from about 90% (fig. 6A, fig. 6B) to about 95% (fig. 6E, F). In addition to the open circuit potential difference, the NiCr alloy mesh electrode current difference calibration also yielded good linearity data (fig. 6G), which also illustrates the linear relationship of the base line current to the open circuit potential.
The open circuit potential differences between the two electrodes in deionized and tap water did not vary much, both in the 0-14mV range (FIGS. 6A-D). However, the open circuit potential difference increased sharply in the 0.1M NaCl solution to the 20-60mV range (FIG. 6E, F), and the sensitivity (which can be expressed as the slope of the open circuit potential-flow rate curve) in the measurement range increased by several times. This is because the increase in ion concentration reduces the capacitance of the diffusion layer, and the open circuit potential and its rate of change are both correspondingly improved according to equation 2. The sensitivity was better for the 304 stainless steel mesh in both deionized water and NaCl solution, with open circuit potential-flow rate slopes of 0.81 and 3.24 greater than the NiCr alloy mesh in both solutions, with open circuit potential-flow rate slopes of 0.48 and 2.71, respectively. However, the sensitivity of NiCr alloy mesh was higher in tap water, with an open circuit potential-flow rate curve slope of 0.68 greater than that of stainless steel, 0.30 (fig. 6C). This phenomenon is estimated to be related to the presence of certain ions in the tap water that interact strongly with the NiCr alloy.
In the two flow velocity measuring devices, open-circuit potential response of millivolt level can be measured on the NiCr alloy net and the stainless steel net electrodes, the change of the flow velocity can be reflected obviously, and the linear relation is formed between the flow velocity and the flow velocity. Due to the specification limit of laboratory water pumps and turbine flow meters, the invention mainly detects the liquid flow rate less than or equal to 2 cm/s. The minimum flow rate measured at the actual calibration was 2.2 mm/s. Even when the flowmeter cannot display the flow, the metal mesh electrode can still detect obvious current, so that the sensitivity of the flow velocity detection device is very high at low flow velocity, and the limit flow velocity capable of being measured is very small. The flowmeter purchased in the experiment is the highest sensitivity in the turbine flowmeter with the same specification on the market. The pore diameter is 10mm, and the measurement limit is 40L/h. According to the conversion of the cross section area proportion, the minimum measured flow rate is 14.15cm/s, and the minimum limit flow rate measured by the metal electrode flow measuring device adopted by the invention is reduced by 64 times compared with a turbine flow meter. The lowest flow rate limit that can be measured by the metal electrode flow measuring device is reduced by about 5 times compared to commercially available portable fiber optic sensors with higher sensitivity.
Example 3: measurement of liquid flow rate
In all tested solutions, an obvious linear relationship exists between the flow rate and the open circuit potential difference of the metal mesh electrode in the flow rate range of the tested liquid, which indicates that the metal mesh electrode has universal applicability for measuring the flow rate. The present invention measures the flow rates of deionized water and sodium chloride solution using the flow rate measuring device shown in fig. 1. The measurement steps are as follows:
(1) washing the liquid flow velocity measuring device by using deionized water, correspondingly connecting the three leads with an electrochemical workstation, vertically placing the measuring device in liquid with the flow velocity to be measured, enabling the device to penetrate into the liquid level to be not less than 3cm, and standing for 1 minute;
(2) the three electrodes are in a retraction state in the shell by adjusting the sliding of the sliding block in the sliding way, and after the three electrodes are stabilized for 60 seconds, an electrochemical workstation is used for measuring the open-circuit potential of the electrodes during retraction to serve as a static open-circuit potential;
(3) the three electrodes extend out of the shell through adjusting the sliding block, and after the three electrodes are stabilized for 60 seconds, the open-circuit potential when the electrodes extend out is measured by using an electrochemical workstation and is used as the dynamic open-circuit potential;
(4) adjusting the flow rate of the liquid, and measuring the change of the dynamic and static open-circuit potentials along with the flow rate of the liquid;
(5) the open circuit potential difference of the working electrode in the dynamic and static liquid environments is calculated, and the flow rate of the liquid can be obtained according to the calibration curve of the open circuit potential difference and the flow rate in the embodiment 2.
FIG. 7 is the variation of the open circuit potential of the stainless steel wire mesh electrode surface in the flowing deionized water, and FIG. 8 is the variation curve of the open circuit potential of the NiCr alloy wire mesh electrode surface in the 0.1MNaCl solution. The real-time flow rate of the liquid can be obtained by substituting the dynamic and static open circuit potential differences into the linear fitting equations in fig. 6(B) and 6 (E). The deviation of the open circuit potential measurement is within 5% compared to the scaled results of the turbine meter. In addition, it can be seen that the open circuit potential-time curve in deionized water exhibits a spike-like waveform (fig. 7), while in NaCl solution a square wave waveform (fig. 8). It shows that the ion content in the deionized water is low, the time for the ions in the diffusion layer to return to the equilibrium concentration after the liquid stops flowing is long, and the return of the open-circuit potential is slow. The ions in the diffusion layer can quickly restore to the equilibrium concentration in tap water and ionic solution, which makes the measurement of the open circuit potential difference more accurate.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (2)
1. A liquid flow rate measuring method based on electrochemical response of a conductive electrode is characterized in that the measuring method is carried out by a liquid flow rate measuring device, and specifically comprises the following steps:
(1) cleaning a liquid flow velocity measuring device by using deionized water, correspondingly connecting three leads with an electrochemical workstation, vertically placing the measuring device in liquid with a flow velocity to be measured, and standing for 1-10 minutes;
(2) the three electrodes are in a retraction state in the shell by adjusting the sliding of the sliding block in the slideway, and after the three electrodes are stabilized for 10-300 seconds, an electrochemical workstation is used for measuring the open-circuit potential and current of the electrodes during retraction to serve as static open-circuit potential and current;
(3) enabling the three electrodes to extend out of the shell through adjusting the sliding block, and measuring open-circuit potential and current of the electrodes when the electrodes extend out by using an electrochemical workstation after the three electrodes are stabilized for 10-300 seconds to serve as dynamic open-circuit potential and current;
(4) calculating the open circuit potential difference and the current difference of the working electrode in the dynamic and static liquid environments, and obtaining the flow rate of the liquid according to the calibration curve of the open circuit potential difference, the current difference and the flow rate;
the liquid flow velocity measuring device comprises a shell, a connecting frame, a sliding block, a slideway, three electrodes and three leads; the connecting frame and the three electrodes are both arranged in the shell; the three electrodes correspond to the three leads, and the three electrodes comprise a reference electrode, a working electrode and a counter electrode; the slide way is positioned on the shell, the two ends of the slide way are provided with limit positions, and the end of the slide way, far away from the cover plate, is provided with a clamping groove; the sliding block is fixedly connected with the connecting frame and is in sliding connection with the slide way; the clamping groove is matched with the sliding block, and the sliding of the sliding block in the sliding way is limited through the clamping groove;
the liquid flow velocity measuring device also comprises a supporting column and a cover plate; the cover plate is arranged at one end of the shell and seals the shell; one end of the supporting column is connected with the cover plate, and the other end of the supporting column is connected with the connecting frame; the connecting frame is made of organic materials with a three-hole structure, and the three holes are used for inserting the reference electrode, the working electrode and the counter electrode respectively; the working electrode is made of copper mesh, nickel-chromium alloy wire mesh, stainless steel mesh or FTO glass.
2. The method for measuring the flow rate of liquid based on the electrochemical response of the conductive electrode as claimed in claim 1, wherein in the step (1), the liquid flow rate measuring device is inserted into the liquid to be measured to a depth of not less than 3 cm.
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