A centrifugal nozzle, device and method for measuring the pulsating flow of a liquid flow

Abstract

A centrifugal nozzle, an apparatus, and a method for measuring the pulsating flow rate of a liquid are provided. The centrifugal nozzle includes: a centrifugal nozzle housing with a swirling channel for liquid flow; a first measuring electrode and a second measuring electrode, symmetrically arranged and fixed to the inner wall of the swirling channel, wherein the inner surface arc diameter of the first and second measuring electrodes is equal to the diameter of the swirling channel; wherein the first and second measuring electrodes constitute a capacitive sensor, and the thickness of the annular adherent liquid film formed when the liquid flow enters the swirling channel is indirectly obtained by measuring the capacitance signal of the annular adherent liquid film. This application first measures the liquid film thickness based on the capacitance method, and then determines the pulsating flow rate of the liquid flow through the mapping relationship between the liquid film thickness and the pulsating flow rate, thereby achieving accurate measurement of the pulsating flow rate of non-conductive cryogenic liquids.

Description

Technical Field

[0001] This application relates to the field of fluid measurement technology, and in particular to a centrifugal nozzle, an apparatus and method for measuring the pulsating flow rate of a liquid. Background Technology

[0002] New-generation high-thrust rockets and heavy-lift launch vehicles all use cryogenic propellants, such as liquid oxygen / methane and liquid hydrogen / liquid oxygen. The injection dynamics of these cryogenic liquid streams are a significant cause of unstable combustion at medium and low frequencies. As a crucial unit for cryogenic propellant atomization and mixing, the centrifugal nozzle experiences high-frequency flow pulsations due to pressure fluctuations. These pulsations are important parameters of the injection dynamics and are crucial for assessing and resolving unstable combustion at medium and low frequencies. Therefore, measuring the high-frequency pulsating flow rate of the cryogenic liquid stream within the centrifugal nozzle is a key aspect of experimental research on nozzle dynamics and a challenging aspect of monitoring operating parameters during liquid rocket engine operation.

[0003] In existing technologies, the mainstream method for measuring high-frequency pulsating flow rate within centrifugal nozzles is the conductivity method. This method is based on the conductivity of liquids, indirectly calculating the flow pulsation characteristics by arranging electrodes in a conductive liquid and detecting the current changes caused by changes in liquid flow. To enhance signal strength, electrolytes such as sodium chloride are sometimes added to the liquid to improve conductivity. However, this method has significant limitations: cryogenic liquids (such as liquid nitrogen, liquid oxygen, and liquid methane) have extremely low conductivity due to their stable molecular structure and the absence of freely moving charged particles, making it difficult to generate a detectable current signal using the conductivity method. Therefore, existing conductivity methods cannot be directly applied to the measurement of high-frequency pulsating flow rate of cryogenic liquids. Therefore, how to measure the high-frequency pulsating flow rate of non-conductive cryogenic liquids within centrifugal nozzles is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the technical problem that existing technologies cannot measure the high-frequency pulsating flow rate of non-conductive cryogenic liquids within centrifugal nozzles, this application provides a centrifugal nozzle, an apparatus for measuring the pulsating flow rate of a liquid.

[0005] According to a first aspect of this application, a centrifugal nozzle is provided, comprising: a centrifugal nozzle housing having a swirling channel for liquid flow to pass through; a first measuring electrode and a second measuring electrode, symmetrically arranged and fixed to the inner wall of the swirling channel, wherein the inner surface arc diameter of the first measuring electrode and the second measuring electrode is equal to the diameter of the swirling channel; wherein the first measuring electrode and the second measuring electrode are used to form a capacitive sensor, and the thickness of the annular wall-attached liquid film is indirectly obtained by measuring the capacitance signal of the annular wall-attached liquid film formed when the liquid flow enters the swirling channel.

[0006] In some embodiments, the first measuring electrode and the second measuring electrode are fixed to the inner wall of the vortex channel by: providing an annular positioning groove on the inner wall of the vortex channel, the depth of the positioning groove matching the thickness of the first measuring electrode and the thickness of the second measuring electrode; after the measuring electrodes are embedded in the positioning groove, ultra-low temperature adhesive is used to make the inner surfaces of the first measuring electrode and the second measuring electrode fit tightly against the inner wall of the vortex channel.

[0007] In some embodiments, the first measuring electrode and the second measuring electrode are made of copper.

[0008] According to a second aspect of this application, an apparatus for measuring the pulsating flow rate of a liquid is provided, comprising the centrifugal nozzle, data acquisition card, and computing device described above; the data acquisition card is used to convert the analog capacitance signal measured by the first and second measuring electrodes of the centrifugal nozzle into a digital capacitance signal; the computing device is used to determine the liquid film thickness corresponding to the digital capacitance signal based on a first relationship model between the measured digital signal and the liquid film thickness; and to determine the pulsating flow rate of the liquid corresponding to the liquid film thickness based on a second relationship model between the amplitude of the liquid film thickness and the pulsating flow rate of the liquid.

[0009] In some implementations, a capacitance conversion circuit is further included, disposed between the centrifugal nozzle and the data acquisition card; the capacitance conversion circuit is connected to the leads of the first measuring electrode and the second measuring electrode, and is used to convert the capacitance analog signal into other measurement analog signals, the other measurement analog signals being voltage analog signals, current analog signals, or frequency signals; the data acquisition card is used to convert the other measurement analog signals into other measurement digital signals.

[0010] In some implementations, a signal processing circuit is also included, disposed between the capacitor conversion circuit and the data acquisition card, for amplifying the other measurement analog signals; the data acquisition card is used to convert the amplified other measurement analog signals into other measurement digital signals.

[0011] In some implementations, when the other measurement analog signal is a voltage analog signal, the signal processing circuit is a two-phase lock-in amplifier used to perform interference removal and amplification processing on the voltage analog signal.

[0012] In some implementations, the first relational model can be established according to the following steps: obtaining a first data range obtained by digital signal measurement when there is no liquid flow in the centrifugal nozzle, and a second data range obtained by digital signal measurement when the centrifugal nozzle is filled with liquid flow; determining a final data range covering various operating conditions based on the first data range and the first data range; determining the minimum value of the final data range as the measured digital signal when there is no liquid flow in the centrifugal nozzle; determining the maximum value of the final data range as the measured digital signal when the centrifugal nozzle is filled with liquid flow; determining the liquid film thickness when there is no liquid flow in the centrifugal nozzle as 0, and determining the liquid film thickness when the centrifugal nozzle is filled with liquid flow as half the diameter of the vortex channel; and establishing a first relational model between the liquid film thickness and the measured digital signal using a two-point linear calibration method.

[0013] In some implementations, the second relational model is: in, The amplitude represents the liquid film thickness; This refers to the pulsating flow rate of the liquid. W a The velocity of the liquid flowing along the axial direction of the centrifugal nozzle; W in The velocity of the liquid as it enters the swirling flow channel through the tangential orifice of the centrifugal nozzle; D k The diameter of the swirling channel of the centrifugal nozzle; D t The diameter of the tangential orifice of the centrifugal nozzle. r m Let be the radius of the gas vortex.

[0014] According to a third aspect of this application, a method for measuring the pulsating flow rate of a liquid is provided, wherein the measurement is performed using the apparatus described above.

[0015] Compared with the prior art, the beneficial effects of this application include: By setting a first measuring electrode and a second measuring electrode on the inner wall of the swirling channel of a centrifugal nozzle to form a capacitive sensor, the thickness of the annular wall-attached liquid film inside the centrifugal nozzle can be measured by utilizing the correspondence between the capacitance characteristics of the liquid film and the thickness of the liquid film.

[0016] Furthermore, by establishing a mathematical relationship model between the amplitude of the liquid film thickness and the pulsating flow rate, combined with the measured liquid film thickness, accurate measurement of the pulsating flow rate of non-conductive cryogenic liquid can be achieved. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a centrifugal nozzle according to one embodiment of this application; Figure 2 This is a schematic diagram and cross-sectional view of the injection of a centrifugal nozzle according to the first embodiment of this application; Figure 3 This is a schematic diagram of a device for measuring the pulsating flow rate of a liquid according to one embodiment of this application; Figure 4 This is a schematic diagram of a device for measuring the pulsating flow rate of a liquid according to the second embodiment of this application; Figure 5 This is a schematic diagram of the C / V conversion circuit according to one embodiment of this application; Figure 6 This is a circuit diagram of a circuit board in a C / V conversion circuit according to one embodiment of this application; Figure 7 This is a schematic diagram of a device for measuring the pulsating flow rate of a liquid according to the third embodiment of this application; Figure 8 This is a circuit diagram of a dual-phase lock-in amplifier according to one embodiment of this application; Figure 9 This is a schematic diagram of the voltage signal between the measuring electrodes when the centrifuge nozzle is empty of liquid nitrogen and when it is filled with liquid nitrogen, according to one embodiment of this application; Figure 10 This is a schematic diagram of a calibration curve between liquid film thickness and voltage value according to one embodiment of this application; Figure 11 It is a timing diagram of the collected voltage values ​​according to one embodiment of this application; Figure 12 This is a time-series diagram of liquid film thickness collected according to one embodiment of this application; Figure 13 This is a schematic diagram of the Fourier transform result of the collected liquid film thickness time-series signal according to one embodiment of this application. Detailed Implementation

[0019] To make the above and other features and advantages of this application clearer, the application is further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explanation to those skilled in the art, and are exemplary only, not restrictive.

[0020] In the following description, numerous specific details are set forth to provide a thorough understanding of this application. However, it will be apparent to those skilled in the art that the specific details are not required to practice this application. In other instances, well-known steps or operations have not been described in detail to avoid obscuring this application.

[0021] The following, in conjunction with the accompanying drawings, provides a detailed description of the centrifugal nozzle, the device and method for measuring the pulsating flow rate of liquid provided in this application, through specific implementation schemes and application scenarios.

[0022] As attached Figure 1 As shown, an embodiment of the present invention provides a centrifugal nozzle 10, including a centrifugal nozzle housing 11, a first measuring electrode 12, and a second measuring electrode 13.

[0023] The centrifugal nozzle housing 11 can be 3D printed from non-conductive and low-temperature resistant alumina ceramic material, and its interior forms a swirling channel for liquid flow. A first measuring electrode 12 and a second measuring electrode 13 are fixedly attached to the inner wall of the swirling channel. The inner surface arc diameters of the first measuring electrode 12 and the second measuring electrode 13 are equal to the diameter of the swirling channel, and their structures are completely identical. The first measuring electrode 12 and the second measuring electrode 13 are fixed in a symmetrical arrangement, that is, they are located symmetrically on the inner wall of the swirling channel. Preferably, the first measuring electrode 12 and the second measuring electrode 13 are respectively positioned at 180-degree symmetrical locations on the inner wall of the swirling channel.

[0024] The first measuring electrode 12 and the second measuring electrode 13 constitute a capacitive sensor. When a cryogenic liquid flow accompanied by pulsating inflow enters the vortex channel from the tangential orifice of the centrifugal nozzle, a hollow annular adherent liquid film is formed on the inner wall of the vortex channel. The thickness of the liquid film changes with the pulsating inflow. The liquid film located on the surfaces of the first measuring electrode 12 and the second measuring electrode 13, together with the two electrodes, constitutes the two plates of the capacitive sensor. When the thickness of the liquid film changes, the capacitance value of the capacitive sensor also changes accordingly. By measuring this capacitance signal, the thickness of the annular adherent liquid film can be indirectly obtained.

[0025] The injection schematic diagram and cross-sectional view of the centrifugal nozzle 10 are as follows: Figure 2 As shown, where R b D is the swirl radius. k D is the diameter of the centrifugal nozzle swirl channel. t L is the diameter of the tangential hole. kThe length of the centrifugal nozzle swirl channel. r is the amplitude of the liquid film thickness. m Let be the radius of the gas vortex.

[0026] In this embodiment, the first measuring electrode 12 and the second measuring electrode 13 can be fixed to the inner wall of the vortex channel in the following manner: First, an annular positioning groove is provided on the inner wall of the vortex channel. The depth of the annular positioning groove matches the thickness of the first measuring electrode 12 and the thickness of the second measuring electrode 13, so that the inner surface of the measuring electrode is flush with the inner wall of the vortex channel after it is embedded. Then, after the measuring electrode is embedded in the annular positioning groove, it is bonded and fixed using ultra-low temperature adhesive. Ultra-low temperature adhesive refers to a special adhesive that can be used in ultra-low temperature environments (typically below -100℃, or even as low as -269℃) and maintain sufficient bonding strength and toughness. After curing, the ultra-low temperature adhesive has extremely high bonding strength and low temperature resistance, ensuring that the inner surfaces of the first measuring electrode 12 and the second measuring electrode 13 are tightly fitted to the inner wall of the vortex channel, guaranteeing pressure resistance, no leakage, and no gaps between the measuring electrode and the inner wall of the vortex channel.

[0027] In one embodiment of this application, the first measuring electrode 12 and the second measuring electrode 13 may be made of copper. Copper has good electrical conductivity, and its relative permittivity is approximately 8.9 × 10⁻⁶. 4 F / m (a multiple of the vacuum dielectric constant) can generate a significant capacitance change signal. Furthermore, copper is easy to process and shape, allowing for the manufacture of electrode shapes with precise dimensions.

[0028] In one embodiment of this application, the high-frequency pulsating flow rate of the liquid at the centrifugal nozzle outlet causes periodic changes in the liquid flow distribution, specifically manifested as dynamic fluctuations in the thickness of the annular wall-attached centrifugal liquid film. Since the change in liquid film thickness is directly related to the amplitude of the flow pulsation, the high-frequency pulsating flow characteristics can be indirectly deduced by measuring the liquid film thickness in real time. Therefore, to achieve this measurement objective, the first measuring electrode 12 and the second measuring electrode 13 can be symmetrically arranged in the annular liquid film region at the centrifugal nozzle outlet, thereby achieving accurate capture of the flow pulsation parameters.

[0029] In one embodiment of this application, the pulsating flow rate of the liquid flow may include the high-frequency pulsating flow rate of a cryogenic liquid flow. Cryogenic liquid flow typically refers to liquefied gas with a boiling point below -150 degrees Celsius. The high-frequency pulsating flow rate can be a pulsating flow rate higher than 1000 Hz.

[0030] In the above embodiments, when the high-frequency pulsating flow rate of the cryogenic liquid causes periodic changes in the liquid film thickness, the liquid film thickness of the dielectric layer between the first measuring electrode 12 and the second measuring electrode 13 is dynamically adjusted accordingly, resulting in changes in the value of the capacitance signal between the electrodes. In this way, the capacitance signal provides a quantitative basis for the dynamic characterization of the cryogenic liquid flow rate pulsation.

[0031] As attached Figure 3 As shown, one embodiment of this application provides an apparatus for measuring the pulsating flow rate of a liquid, including the centrifugal nozzle 10, data acquisition card 20, and computing device 30 described above.

[0032] The data acquisition card 20 is used to convert the analog capacitance signal measured by the first measuring electrode 12 and the second measuring electrode 13 of the centrifugal nozzle into a digital capacitance signal. The data acquisition card 20 may have multiple analog input channels and analog-to-digital conversion function, and can digitally acquire the analog capacitance signal at a high sampling rate.

[0033] The computing device 30 is used to determine the liquid film thickness corresponding to the capacitance digital signal based on a first relationship model established between the measured digital signal and the liquid film thickness; and to determine the pulsating flow rate of the liquid flow corresponding to the liquid film thickness based on a second relationship model established between the amplitude of the liquid film thickness and the pulsating flow rate of the liquid flow. The computing device 30 may be a personal computer, an industrial control computer, or an embedded system.

[0034] The measurement digital signals involved in one embodiment of this application may include, but are not limited to, capacitance signals, voltage signals, current signals, and frequency signals.

[0035] The device provided in this application forms a capacitive sensor by setting a measuring electrode on the inner wall of the swirling channel of the centrifugal nozzle. By utilizing the correspondence between the liquid film thickness and the capacitance signal, non-contact measurement of the liquid film thickness can be achieved. By establishing a mathematical relationship model between the amplitude of the liquid film thickness and the pulsating flow rate, accurate measurement of the pulsating flow rate can be achieved, which has the advantages of fast response speed and high measurement accuracy.

[0036] As attached Figure 4 As shown, the device for measuring the pulsating flow rate of a liquid is... Figure 3 The structure shown can also include a capacitor conversion circuit 40.

[0037] A capacitance conversion circuit 40 is disposed between the centrifuge nozzle and the data acquisition card 20, and is connected to the electrode leads of the first measuring electrode 12 and the second measuring electrode 13. It is used to convert the capacitance analog signal into other measurement analog signals. These other measurement analog signals can be voltage analog signals, current analog signals, or frequency signals. The capacitance conversion circuit 40 can be a capacitance-to-voltage conversion circuit, a capacitance-to-current conversion circuit, or other circuit structures besides the capacitor in an oscillation circuit.

[0038] In one embodiment of this application, when other measurement analog signals are voltage analog signals, a capacitor-to-voltage conversion circuit can be used to convert the capacitor analog signal output by the centrifugal nozzle into a voltage analog signal.

[0039] In one embodiment of this application, when other measurement analog signals are current analog signals, a capacitor-to-current conversion circuit can be used to convert the capacitor analog signal output by the centrifugal nozzle into a current analog signal.

[0040] In one embodiment of this application, when other measured analog signals are frequency signals, an oscillation circuit consisting of a capacitor formed by the first measuring electrode 12 and the second measuring electrode 13 and the liquid film, and a capacitance conversion circuit 40, can be used to convert the analog capacitance signal output from the centrifugal nozzle into a frequency signal. When the value of the capacitance signal changes, the value of the frequency signal output by the capacitance conversion circuit 40 will also change accordingly. By measuring the change in the frequency signal, the change in the capacitance signal can be calculated, and thus the liquid film thickness can be obtained.

[0041] As a specific embodiment, taking a capacitance-to-voltage (C / V) conversion circuit as an example, see [link to relevant documentation]. Figure 5 The C / V conversion circuit includes a circuit board 21, a first input port 22, a second input port 23, a first output port 24, and a second output port 25. The first input port 22 and the second input port 23 are connected to the first measuring electrode 12 and the second measuring electrode 13 of the centrifugal nozzle via a first wire and a second wire, respectively. The circuit diagram of the circuit board 21 is shown below. Figure 6 As shown, where C s1 and C s2 A1 is a differential capacitor used to reduce noise interference and the effects of power supply noise; C is an operational amplifier. f and R f This forms a parallel feedback network, where C f = 10 pF and R f = 20 kΩ; V i (t) represents the input voltage, with an effective value of V. i = 1 V, angular frequency ω = 100kHz; V o (t) represents the output voltage.

[0042] The data acquisition card 20 is also used to convert other measurement analog signals into other measurement digital signals.

[0043] In some of the above embodiments, by converting the capacitance analog signal into other easily processed measurement analog signals by the capacitance conversion circuit 40, the device's anti-interference capability can be improved and the converted signal can be easily reprocessed.

[0044] Furthermore, the device provided in this application forms a capacitive sensor by setting a measuring electrode on the inner wall of the swirling channel of the centrifugal nozzle. By utilizing the correspondence between the liquid film thickness and the conversion signal, non-contact measurement of the liquid film thickness can be achieved. By establishing a mathematical relationship model between the amplitude of the liquid film thickness and the pulsating flow rate, accurate measurement of the pulsating flow rate can be achieved, which has the advantages of fast response speed and high measurement accuracy.

[0045] As attached Figure 7 As shown, the device for measuring the pulsating flow rate of a liquid is... Figure 4 The structure shown can also include a signal processing circuit 50.

[0046] The signal processing circuit 50 is located between the capacitor conversion circuit 40 and the data acquisition card 20, and is used to amplify the other measurement analog signals.

[0047] The data acquisition card 20 is used to convert amplified analog signals from other measurements into digital signals from other measurements.

[0048] In some of the above embodiments, the signal processing circuit 50 can amplify other measurement analog signals to improve the accuracy of calculating liquid film thickness and flow pulsation flow rate.

[0049] In one embodiment of this application, the signal processing circuit 50 may include a signal amplification circuit and / or a filtering circuit corresponding to other measurement signals.

[0050] In one embodiment of this application, when the other measured analog signal is a voltage analog signal, the signal processing circuit 50 is preferably a two-phase lock-in amplifier. The two-phase lock-in amplifier has excellent noise suppression capabilities and can perform interference removal and amplification processing on the voltage analog signal.

[0051] Specifically, see Figure 8 This is the circuit diagram of a two-phase lock-in amplifier. PSD is a phase-sensitive detector. V p1 (t), V p2 (t) represents the voltage after passing through two PSDs; V r (t) is the reference signal; LPF is the low-pass filter; X=V Output 1 Y=V Output 2 R is the voltage after passing through two LPFs; R is the output amplitude; θ represents the measured signal V. o (t) and reference signal V r Phase difference of (t); A r Reference signal V r The magnitude of (t).

[0052] The device provided in this application uses a two-phase lock-in amplifier to perform interference removal and amplification processing on other measurement analog signals, thereby further improving the accuracy of calculating liquid film thickness and flow pulsation flow rate.

[0053] In one embodiment of this application, a first relational model is used to establish the relationship between the measured digital signal and the liquid film thickness, and a second relational model is used to establish the relationship between the liquid film thickness and the liquid flow pulsation flow rate.

[0054] Specifically, the first relationship model between the measured digital signal and the liquid film thickness can be established as follows: First, a first data range is obtained by digital signal measurement when there is no liquid flow inside the centrifugal nozzle. In the absence of liquid flow, the liquid film thickness is 0, and the capacitance value of the capacitive sensor is at its minimum. The measured data may fluctuate, forming a data range. The minimum value of this data range is taken as the measured digital signal S0 when there is no liquid flow inside the centrifugal nozzle.

[0055] Then, a second data range was obtained by digital signal measurement when the centrifugal nozzle was filled with liquid flow. The liquid film thickness reaches its maximum value, which is half the diameter of the swirling channel (D), when the swirling channel is completely filled with liquid flow. k / 2). At this time, the capacitance value of the capacitive sensor is at its maximum. The measured data also fluctuates, forming a data range. The maximum value of this data range is taken as the measured digital signal S1 when the centrifugal nozzle is filled with liquid.

[0056] Based on the above measurement results, a first relationship model between the liquid film thickness and the measured digital signal is established using the two-point linear calibration method: Equation (1) Where δ is the liquid film thickness, D k Where is the diameter of the vortex channel, and S is the actual measured digital capacitance signal or other measured digital signal.

[0057] In one embodiment of this application, taking liquid nitrogen as an example, the relationship between the measured digital signal (e.g., voltage signal) and the corresponding liquid film thickness is specifically determined using a two-point linear calibration method. Figure 9 (a) shows the voltage signals collected under cryogenic conditions when there is no liquid nitrogen in the nozzle (but gaseous nitrogen is still continuously ejected, solid line) and when the nozzle is filled with liquid nitrogen (the entire nozzle is immersed in liquid nitrogen, dashed line). Figure 9 In (a), U n This is the voltage between the two measuring electrodes when there is no liquid nitrogen in the nozzle. U f This is the voltage between the two measuring electrodes when the nozzle is filled with liquid nitrogen. Figure 9(b) shows the FFT analysis results of the voltage signals under two operating conditions. It can be seen that the acquired voltage signals did not show significant power frequency interference or electromagnetic interference noise.

[0058] like Figure 9 As shown in (a), when there is no liquid nitrogen in the nozzle (but gaseous nitrogen is continuously emitted), the recorded voltage signal ranges from 404.30 to 404.44 mV. When liquid nitrogen is injected, a hollow vortex-shaped liquid film forms on the inner wall of the nozzle, with a gas nucleus (gaseous nitrogen) appearing in its central region. It is this liquid nitrogen / gaseous nitrogen distribution that affects the dielectric constant detected by the two measuring electrodes within the nozzle. When the nozzle is filled with liquid nitrogen, the measured voltage ranges from 440.06 to 440.16 mV. The effect of the liquid film (liquid nitrogen) on the dielectric constant must be considered during the experiment. Therefore, the voltage calibration range is approximately 404.30–440.16 mV, which covers all voltage values ​​collected under various operating conditions.

[0059] In cryogenic environments, when the nozzle is empty of liquid nitrogen, the liquid film thickness corresponds to 0. When the nozzle is completely filled with liquid nitrogen, the liquid film thickness corresponds to the nozzle diameter. D k Half of that, which is 1.24 mm. For example... Figure 10 As shown, the relationship between the thickness of the cryogenic liquid film (liquid nitrogen) and the measured voltage signal is determined using the two-point linear calibration method, namely: Equation (2) in, h The liquid film thickness is expressed in mm. U This represents voltage, measured in mV.

[0060] When the injection pressure drop is 0.3 MPa, the voltage signal during injection collected by the measuring electrode under different inflow pulsation frequencies is as follows: Figure 11 As shown, the voltage distribution range corresponding to each incoming flow pulsation frequency is 419.1–421.8 mV. The voltage signals collected under all operating conditions fall within... Figure 10 Within the voltage range shown.

[0061] According to the formula The collected voltage signal ( Figure 11 After further processing, it is converted into liquid film thickness data, such as... Figure 12 As shown, at a pressure drop of 0.30 MPa, the larger pressure difference leads to an increase in nozzle flow rate, which in turn increases the liquid film thickness at the nozzle outlet. Furthermore, the overall trend of liquid film thickness variation with pulsation frequency is as follows: as the pulsation frequency increases, the liquid film thickness gradually decreases.

[0062] In addition, such as Figure 13As shown, the amplitude-frequency curve was obtained by performing a Fast Fourier Transform on the liquid film thickness signal under a pressure drop of 0.30 MPa. At a pressure drop of 0.30 MPa, low-frequency oscillations caused by KH instability still occurred under all pulsation frequency conditions. Furthermore, low-amplitude high-frequency oscillations appeared in multiple frequency bands. However, most of these oscillation frequencies did not correspond to the inflow pulsation frequency; only when the pulsation frequency was 310 Hz and 400 Hz did the amplitude-frequency curve show peaks at these frequencies. This reflects the influence of inflow pulsation on the liquid film thickness oscillation within the nozzle.

[0063] The above-mentioned device can be used to measure the thickness of a high-frequency pulsating annular cryogenic liquid film inside a micro-channel.

[0064] Furthermore, a second relationship model between the amplitude of the liquid film thickness and the pulsating flow rate of the liquid can be established as follows: According to fluid mechanics theory, there is a mathematical relationship between the pulsating flow rate of a liquid and the amplitude of the liquid film thickness. The instantaneous flow rate at the centrifugal nozzle outlet... Q Amplitude of liquid film thickness The relationship is: Equation (3) in, The steady-state flow rate measured by the flow meter; The amplitude of the flow oscillation within the nozzle; W a The velocity of the liquid flowing along the nozzle axis; W in The velocity at which the liquid enters the vortex channel through the tangential orifice of the centrifugal nozzle.

[0065] The instantaneous value of the pulsating flow rate when the incoming flow condition is given. Q It is the amplitude of the liquid film thickness. A single-valued function, i.e., the pulsating flow rate of the fluid. Amplitude relative to liquid film thickness The conversion relationship between them is as follows: Equation (4) in, The amplitude represents the liquid film thickness; This refers to the pulsating flow rate of the liquid. W a The velocity of the liquid flowing along the axial direction of the centrifugal nozzle; W in The velocity of the liquid as it enters the swirling flow channel through the tangential orifice of the centrifugal nozzle; D k The diameter of the swirling channel of the centrifugal nozzle; D t The diameter of the tangential orifice of the centrifugal nozzle. rm Let be the radius of the gas vortex.

[0066] This application constructs a capacitive sensor by setting measuring electrodes on the inner wall of the swirling channel of a centrifugal nozzle. Utilizing the correlation between liquid film thickness and capacitance value, it achieves non-contact measurement of liquid film thickness. Furthermore, by establishing a mathematical model relating liquid film thickness to pulsating flow rate, it achieves accurate measurement of pulsating flow rate. This application offers advantages such as fast response speed and high measurement accuracy.

[0067] One embodiment of this application provides a method for measuring the pulsating flow rate of a liquid, using the apparatus described in any embodiment of this application.

[0068] To further illustrate the method for measuring the pulsating flow rate of a liquid, this application also provides another embodiment. Specifically, based on the aforementioned apparatus for measuring the pulsating flow rate of a liquid, the method for measuring the high-frequency pulsating flow rate of a cryogenic liquid may include: Step 1: Establish the relationship between the high-frequency pulsating flow rate and the liquid film thickness in the centrifugal nozzle, including the first relationship model and the second relationship model; Step 2: Detect the change in capacitance signal between the first measuring electrode 12 and the second measuring electrode 13 caused by the change in the thickness of the liquid film inside the centrifugal nozzle; Step 3: Convert the acquired capacitance analog signal into other measurement analog signals through capacitance conversion circuit 40; Step 4: Use signal processing circuit 50 to remove interference and amplify the other converted analog measurement signals; Step 5: After removing interference and amplifying, the other analog measurement signals are acquired by the data acquisition card 20 and converted into other digital measurement signals; Step 6: Input the other measured digital signals after acquisition into the computing device 30 for calculation and display.

[0069] In this embodiment, a centrifugal nozzle is 3D printed using non-conductive and low-temperature resistant alumina ceramic material. Two symmetrically arranged, copper-machined fittings are embedded within the nozzle's internal flow channel, serving as measuring electrodes. When a pulsating cryogenic liquid flow enters the nozzle flow channel through a tangential orifice, it forms a hollow, annular, wall-attached liquid film. The film thickness changes with the pulsating flow, causing a change in the capacitance value of the liquid film passing between the two measuring electrodes. Therefore, by setting a first and second measuring electrode on the inner wall of the centrifugal nozzle's swirling channel to form a capacitance sensor, the thickness of the annular wall-attached liquid film inside the centrifugal nozzle can be measured using the correspondence between the liquid film's capacitance characteristics and its thickness. By establishing a mathematical model of the relationship between the liquid film thickness and the pulsating flow rate, combined with capacitance signal measurement, accurate measurement of the pulsating flow rate of the non-conductive cryogenic liquid flow can be achieved.

[0070] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A centrifugal nozzle, characterized in that, include: The centrifugal nozzle housing has an internal swirling channel through which the liquid flows. The first and second measuring electrodes are symmetrically arranged and fixed to the inner wall of the vortex channel, and the inner surface arc diameters of the first and second measuring electrodes are equal to the diameter of the vortex channel. The first and second measuring electrodes are used to form a capacitive sensor, which measures the capacitance signal of the annular adherent liquid film formed when the liquid flows into the swirling channel, so as to indirectly obtain the thickness of the annular adherent liquid film.

2. The centrifugal nozzle according to claim 1, characterized in that, The first measuring electrode and the second measuring electrode are fixed to the inner wall of the swirling channel in the following manner: An annular positioning groove is provided on the inner wall of the vortex channel, and the depth of the positioning groove matches the thickness of the first measuring electrode and the thickness of the second measuring electrode. After the measuring electrodes are embedded in the positioning groove, ultra-low temperature adhesive is used to make the inner surfaces of the first and second measuring electrodes fit tightly against the inner wall of the vortex channel.

3. The centrifugal nozzle according to claim 1 or 2, characterized in that, The first measuring electrode and the second measuring electrode are made of copper.

4. A device for measuring the pulsating flow rate of a liquid, characterized in that, Includes the centrifugal nozzle, data acquisition card, and computing device as described in any one of claims 1-3; The data acquisition card is used to convert the analog capacitance signal measured by the first and second measuring electrodes of the centrifugal nozzle into a digital capacitance signal. The computing device is used to determine the liquid film thickness corresponding to the capacitance digital signal based on the established first relationship model between the measured digital signal and the liquid film thickness. And based on the established second relationship model between the amplitude of the liquid film thickness and the pulsating flow rate of the liquid flow, the pulsating flow rate of the liquid flow corresponding to the liquid film thickness is determined.

5. The apparatus according to claim 4, characterized in that, It also includes a capacitor conversion circuit disposed between the centrifugal nozzle and the data acquisition card; The capacitance conversion circuit is connected to the leads of the first measuring electrode and the second measuring electrode, and is used to convert the capacitance analog signal into other measurement analog signals, which are voltage analog signals, current analog signals, or frequency signals. The data acquisition card is used to convert the other measurement analog signals into other measurement digital signals.

6. The apparatus according to claim 5, characterized in that, It also includes a signal processing circuit disposed between the capacitor conversion circuit and the data acquisition card, for amplifying the other measurement analog signals; The data acquisition card is used to convert amplified analog measurement signals into digital measurement signals.

7. The apparatus according to claim 6, characterized in that, When the other measured analog signals are voltage analog signals, the signal processing circuit is a two-phase lock-in amplifier, used to perform interference removal and amplification processing on the voltage analog signals.

8. The apparatus according to any one of claims 4-7, characterized in that, The first relational model can be established according to the following steps: The first data range obtained by digital signal measurement when there is no liquid flow in the centrifugal nozzle, and the second data range obtained by digital signal measurement when the centrifugal nozzle is full of liquid flow; Based on the first data range and the first data range, determine the final data range covering various working conditions; The minimum value of the final data range is determined as the measured digital signal when there is no liquid flow in the centrifugal nozzle; the maximum value of the final data range is determined as the measured digital signal when the centrifugal nozzle is filled with liquid flow; the liquid film thickness when there is no liquid flow in the centrifugal nozzle is determined as 0, and the liquid film thickness when the centrifugal nozzle is filled with liquid flow is determined as half the diameter of the vortex channel; a first relationship model between the liquid film thickness and the measured digital signal is established using the two-point linear calibration method.

9. The apparatus according to any one of claims 4-7, characterized in that, The second relational model is: in, The amplitude represents the liquid film thickness; This refers to the pulsating flow rate of the liquid. W a The velocity of the liquid flowing along the axial direction of the centrifugal nozzle; W in The velocity of the liquid as it enters the swirling flow channel through the tangential orifice of the centrifugal nozzle; D k The diameter of the swirling channel of the centrifugal nozzle; D t The diameter of the tangential orifice of the centrifugal nozzle. r m Let be the radius of the gas vortex.

10. A method for measuring the pulsating flow rate of a liquid, characterized in that, The measurement is performed using the apparatus as described in any one of claims 4-9.

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