Piezoelectrically excited injector and method for quantitatively designing resonance structure of injection chamber thereof

Abstract

A piezoelectric excitation injector and a quantitative design method of its spray cavity resonance structure, the piezoelectric excitation injector comprises a shell, a spray panel, an excitation panel, a piezoelectric ceramic and a liquid inlet. The spray cavity is formed by the shell and the spray panel. When the injector works, the liquid working medium enters the spray cavity from the liquid inlet, and then is sprayed out to form a jet by the spray hole on the spray panel. The liquid working medium in the spray cavity resonates to form a larger pressure disturbance under the excitation of the piezoelectric ceramic driving the excitation panel, so as to promote the jet to break to form droplets. The present application increases the active disturbance amplitude under the condition that the piezoelectric excitation energy is unchanged, so as to realize uniform droplet generation in a wide frequency range, overcome the shortcomings of the conventional piezoelectric excitation injector in the uniformity and consistency of droplet generation under the condition of large flow, and promote the batch generation of droplets in engineering application.

Description

Technical Field

[0001] This invention relates to a piezoelectrically excited injector and a quantitative design method for the resonant structure of its nozzle cavity, which is applied to the design of piezoelectrically excited injectors. Background Technology

[0002] Droplet generators, used for efficient droplet generation, are core components of space droplet radiators, additive manufacturing equipment, and other granulation devices. While extensive research has been conducted on the uniform droplet generation characteristics of droplet generators, most of this work focuses on micro-jet flow from a single orifice. For engineering applications of droplet radiators, the number of droplets generated per second needs to reach millions or even tens of millions, with a jet flow rate of 1 kg / s. Single-orifice, low-flow-rate injectors cannot meet these requirements. To meet the engineering application demands for mass droplet generation, the injector needs to spray a large liquid flow rate. Under high-flow-rate conditions, problems such as uneven droplet size and inconsistent jet velocity arise, severely degrading equipment performance and even posing safety risks for space applications.

[0003] Droplet generators primarily employ piezoelectrically excited nozzles to form uniform droplets. Their effective operation depends on the dominance of piezoelectric excitation disturbances within the nozzle, causing surface waves in the jet to develop and break up into ordered droplets under the applied excitation. For single-stream micro-jet nozzles, the liquid flow rate is relatively small, the flow Reynolds number is low, and the flow field is relatively stable, making artificially applied piezoelectric disturbances dominant. However, when the flow rate of the piezoelectrically excited nozzle is large, the flow impact within the nozzle is stronger, the flow Reynolds number increases, and the amount of disordered pulsation in the flow field becomes larger. This may overwhelm the artificially applied excitation disturbances, preventing the jet from breaking up into ordered droplets under the applied excitation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and solve the problem of insufficient uniformity and consistency of droplet generation under high flow conditions.

[0005] The objective of this invention is achieved through the following technical solutions:

[0006] A quantitative design method for the resonant structure of the nozzle cavity of a piezoelectrically excited injector includes:

[0007] Obtain the liquid working fluid density ρ, viscosity μ, surface tension coefficient σ, and sound velocity c; determine the droplet size D, injection velocity u, and injection flow rate q required for the task, and further determine the nozzle orifice diameter d of the injector. out And the number of nozzles n; further, based on the jet instability theory, the operating frequency f of the piezoelectric excitation is obtained;

[0008] Based on the liquid resonance formula, determine the effective volume V of the injector cavity and the nozzle length l. out The product;

[0009] According to d out The effective cross-sectional size of the injection panel is determined by n, so that all nozzles are evenly distributed on the injection panel and do not interfere with each other;

[0010] Determine l based on the injector's working pressure and droplet generation requirements. out Then determine V; based on the injector's external structure, piezoelectric ceramic, excitation panel, and injector panel size constraints, adjust the nozzle cavity configuration and nozzle cavity length to keep V constant.

[0011] The throttling size of the liquid working fluid inlet is determined based on the liquid supply pressure and the injector working pressure, so that the equivalent impedance of the liquid working fluid inlet is maximized.

[0012] The parameters of the piezoelectric ceramic and the excitation panel are determined, a jetting experiment is carried out, the pulsating pressure of the fluid in the jet chamber is measured, the actual resonant frequency is obtained, and the volume of the jet chamber is corrected according to the difference between the actual resonant frequency and the working frequency.

[0013] A piezoelectrically excited injector determined based on the aforementioned quantitative design method includes a housing, an injection panel, an excitation panel, and piezoelectric ceramics.

[0014] The housing and the injection panel surround to form the injection chamber. The housing has a liquid inlet and a notch for accommodating the excitation panel. A piezoelectric ceramic is placed outside the housing to excite the excitation panel. When the injector is working, the liquid working medium enters the injection chamber from the liquid inlet and is then ejected from the nozzle on the injection panel to form a jet. Under the excitation effect of the piezoelectric ceramic driving the excitation panel, the liquid working medium in the injection chamber resonates and forms pressure disturbance, which causes the jet to break into droplets.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) This invention increases the active disturbance amplitude under the condition of constant piezoelectric excitation energy, thereby achieving uniform droplet generation in a wider frequency range, overcoming the shortcomings of conventional piezoelectric excitation injectors in terms of droplet generation uniformity and consistency under high flow conditions, and promoting the engineering application development of batch droplet generation.

[0017] (2) By matching structural design parameters, the present invention increases the active disturbance energy in the spray cavity under the same piezoelectric excitation conditions, so that it dominates the jet breakup process, thereby improving the controllability of droplet generation.

[0018] (3) This invention proposes a quantitative design method for the resonance of the nozzle cavity of a piezoelectrically excited injector, which can quantitatively design the injector structure according to the mission requirements, thereby greatly reducing the number of structural optimization and improvement and ground test tests in the injector design process.

[0019] (4) The piezoelectric excitation injector resonance structure proposed in this invention takes into account the influence of nozzle size and number, and establishes the correspondence between nozzle cavity volume and nozzle size and number, which can serve as the basis for large flow injector scaling verification and modular design.

[0020] (5) The piezoelectric excitation injector resonance structure proposed in this invention takes into account the natural frequency of the piezoelectric ceramic during operation, so that the excitation frequency of the piezoelectric ceramic deviates from its natural frequency, thus avoiding the resonance damage of the piezoelectric ceramic structure. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the piezoelectrically excited injector structure of the present invention.

[0022] Figure 2 The droplet generation effect of the microdroplet generator designed using the design method of this invention.

[0023] Figure 3 The droplet generation effect of a millimeter-scale droplet generator designed using the design method of this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] A quantitative design method for the resonant structure of the nozzle cavity of a piezoelectrically excited injector includes the following steps:

[0026] Determine the liquid working medium to be sprayed, as well as the droplet size D, spray velocity u, and spray flow rate q, based on the task requirements. Obtain the physical properties of the liquid working medium, including density ρ, viscosity μ, surface tension coefficient σ, and sound velocity c; design the nozzle orifice diameter d of the injector based on the droplet size, spray velocity, and spray flow rate. out The number of nozzles, n, is determined based on the physical properties of the liquid working fluid, such as density ρ, viscosity μ, and surface tension coefficient σ, as well as the nozzle diameter d. out The working parameters, such as injection speed u, are used to obtain the working frequency f of piezoelectric excitation by utilizing jet instability theory;

[0027] According to the nozzle diameter d out The number of nozzles n, the sound velocity c of the liquid working fluid, and the operating frequency f of the piezoelectric excitation determine the effective volume V of the injector cavity and the nozzle length l. out The product satisfies the following resonance relationship: This allows the liquid acoustic vibration system inside the spray chamber to resonate.

[0028] Based on the jet Weber number We and the Euler number Oh, the minimum spacing s between adjacent nozzles is calculated to ensure that all nozzles distributed on the injection panel do not interfere with each other; based on the minimum spacing s between adjacent nozzles, the number of nozzles n, and the nozzle diameter d... out Determine the effective cross-sectional dimensions of the injection panel.

[0029] The injector's operating pressure is determined based on the flow rate relationship of the nozzle. The nozzle's length-to-diameter ratio is selected based on the injector's operating pressure and droplet generation requirements, thus determining the nozzle length l. out Based on the resonance relationship, the effective volume V of the spray chamber is calculated according to the thickness of the spray panel and the thickness of the spray plate.

[0030] Based on the specific dimensional constraints of the injector's external structure, piezoelectric ceramic, excitation panel, and injection panel, the nozzle configuration and length are adjusted to keep the effective volume of the nozzle constant.

[0031] The throttling size of the liquid working fluid inlet is designed based on the liquid supply pressure and the injector working pressure to maximize the equivalent impedance of the liquid working fluid inlet.

[0032] The weight of the excitation panel is determined based on the load-carrying capacity of the piezoelectric ceramic, ensuring that the natural frequency of the piezoelectric ceramic under load is not less than three times the piezoelectric excitation operating frequency, thus avoiding resonance damage to the piezoelectric ceramic. Lightweight materials, including aluminum alloys, titanium alloys, and composite materials, are selected for the excitation panel to maximize the effective excitation area of ​​the excitation panel under the same weight and structural constraints.

[0033] Based on the quantitative design method of the resonant structure of the piezoelectric excitation nozzle cavity, an experimental nozzle was designed. Liquid jetting experiments were carried out to measure the pulsating pressure of the fluid in the nozzle cavity and obtain the actual resonant frequency. The nozzle cavity volume was corrected according to the difference between the actual resonant frequency and the working frequency.

[0034] Preferably, the nozzle diameter ranges from 0.15 mm to 3 mm, the number of nozzles ranges from 1 to 1000, the injection velocity ranges from 5 m / s to 30 m / s, and the viscosity of the liquid working fluid ranges from 20 mPa·s to 200 mPa·s. The jet Reynolds number is achieved through matching these basic operating parameters. No more than 1000.

[0035] Preferably, the piezoelectric excitation of the injector is applied to the fluid through the vibration of the excitation panel. The vibration displacement range of the piezoelectric ceramic is 0.5 μm to 5 μm. Based on the equivalent stiffness K of the piezoelectric ceramic, the piezoelectric excitation operating frequency f, and pi, the effective mass of the excitation panel is determined to meet the following requirements. The mass and size of the excitation panel are determined based on the coupling constraints of the piezoelectric ceramic parameters and the spray cavity structure parameters. The preferred effective mass of the excitation panel is 2g to 50g, and the diameter of the excitation panel is 5mm to 20mm.

[0036] Preferably, the aspect ratio of the nozzles is in the range of 2 to 8, and the nozzle length is in the range of 0.5 mm to 5 mm; the minimum spacing between the nozzles to prevent mutual interference satisfies the following conditions. The ratio of nozzle spacing to nozzle diameter is 1 to 20, and the minimum nozzle spacing is not less than 0.5 mm; the throttling diameter of the liquid working fluid inlet is in the range of 0.2 mm to 10 mm.

[0037] like Figure 1 As shown, the piezoelectrically excited injector of the present invention includes a housing 1, an injection panel 2, an excitation panel 3, a piezoelectric ceramic 4, and a liquid inlet 5. The injector housing 1 and the injection panel 2 surround and form an injection cavity. When the injector is working, the liquid working medium enters the injection cavity from the liquid inlet 5 and is then ejected from the nozzle on the injection panel 3 to form a jet. Under the excitation effect of the piezoelectric ceramic 4 driving the excitation panel 3, the liquid working medium in the injection cavity resonates and forms a large pressure disturbance, which causes the jet to break up and form droplets. Figure 2 To illustrate the droplet generation effect of the microdroplet generator designed using the method of this invention, Figure 3 The droplet generation effect of a millimeter-scale droplet generator designed using the design method of this invention.

[0038] Example 1:

[0039] A quantitative design method for the resonant structure of the nozzle cavity of a piezoelectrically excited injector includes:

[0040] (1) A liquid working medium was prepared according to the requirements of a certain experiment, and the density of the liquid working medium was measured to be 1020 kg / m³. 3 The viscosity is 50 mPa·s, the surface tension coefficient is 0.07 N / m, and the sound velocity is 1580 m / s. The experimental task requires a droplet size of 0.4 mm, a jet velocity of 20 m / s, and a jet flow rate of 283 g / s. Based on the droplet size, jet velocity, and flow rate parameters, the relationship between droplet diameter and nozzle diameter (d) is established. out =0.53D), and the nozzle diameter is taken as 0.2mm; the number of nozzles is calculated to be 450 according to the flow rate formula, and the optimal operating frequency is obtained by converting the formula for the most easily broken wavelength of the jet. The calculated piezoelectric excitation operating frequency is 15kHz.

[0041] (2) According to the liquid resonance formula The product of the spray chamber volume and the spray orifice length was calculated to be 3994 mm. 4 ;

[0042] (3) Select an average nozzle spacing of 1mm and arrange 450 nozzles evenly on the injection panel. Based on this, design the injection panel diameter to be 27mm.

[0043] (4) Based on the droplet ejection requirements, the length-to-diameter ratio of the nozzle is selected as 3, and the nozzle length is determined to be 0.6 mm. Based on the liquid resonance formula, the volume of the nozzle cavity is determined to be 6.7 mL and the effective length is 11.6 mm.

[0044] (5) Based on the system pressure drop matching relationship, the equivalent diameter of the liquid working fluid inlet is selected as 4 mm;

[0045] (6) Select a piezoelectric ceramic suitable for high-frequency operation with a vibration displacement of 2μm, an excitation panel diameter of 5mm, and an excitation panel mass of 2g. Design an experimental piece to carry out a jetting experiment, measure the pulsating pressure of the fluid in the jet chamber, and obtain the actual resonance frequency.

[0046] (7) Correct the volume of the nozzle cavity. When the measured resonance frequency is lower than (or higher than) the working frequency, reduce (or increase) the volume of the nozzle cavity according to the proportional relationship of the resonance formula, and retest the resonance frequency.

[0047] (8) Design the injector based on the quantitative parameters and conduct injection characteristic tests to obtain the experimental results as follows: Figure 2 As shown.

[0048] Example 2:

[0049] A quantitative design method for the resonant structure of the nozzle cavity of a piezoelectrically excited injector includes:

[0050] (1) A liquid working medium was prepared according to the requirements of a certain experiment, and the density of the liquid working medium was measured to be 1020 kg / m³. 3 The viscosity is 100 mPa·s, the surface tension coefficient is 0.07 N / m, and the sound velocity is 1580 m / s. The experimental task requires a droplet size of 2 mm, a jet velocity of 20 m / s, and a jet flow rate of 256 g / s. Based on the droplet size, jet velocity, and flow rate parameters, the nozzle diameter is designed to be 1 mm, the number of nozzles is 16, and the piezoelectric excitation frequency is 3.1 kHz.

[0051] (2) The product of the effective volume of the nozzle cavity and the nozzle length was calculated to be 83127 mm based on the liquid resonance formula. 4 ;

[0052] (3) Select an average nozzle spacing of 6mm and arrange 16 nozzles evenly on the injection panel. Based on this, design the injection panel diameter to be 25mm.

[0053] (4) The nozzle length is determined to be 3 mm according to the droplet ejection requirements, the nozzle volume is determined to be 27.7 mL according to the liquid resonance formula, and the effective length of the nozzle is 56.4 mm.

[0054] (5) Based on the system pressure drop matching relationship, the equivalent diameter of the liquid working fluid inlet is selected as 5mm;

[0055] (6) Select a piezoelectric ceramic suitable for high-frequency operation with a vibration displacement of 5μm, an excitation panel diameter of 10mm, and an excitation panel mass of 8g. Design a test piece to carry out a jetting experiment, measure the pulsating pressure of the fluid in the jet chamber, and obtain the actual resonance frequency.

[0056] (7) Correct the volume of the nozzle cavity. When the measured resonance frequency is lower than (or higher than) the working frequency, reduce (or increase) the volume of the nozzle cavity according to the proportional relationship of the resonance formula, and retest the resonance frequency.

[0057] (8) Design the injector based on the quantitative parameters and conduct injection characteristic tests to obtain the experimental results as follows: Figure 3 As shown.

[0058] Example 3:

[0059] A piezoelectrically excited injector determined based on a quantitative design method includes a housing, an injection panel, an excitation panel, and piezoelectric ceramics;

[0060] The housing and the injection panel surround to form the injection chamber. The housing has a liquid inlet and a notch for accommodating the excitation panel. A piezoelectric ceramic is placed outside the housing to excite the excitation panel. When the injector is working, the liquid working medium enters the injection chamber from the liquid inlet and is then ejected from the nozzle on the injection panel to form a jet. Under the excitation effect of the piezoelectric ceramic driving the excitation panel, the liquid working medium in the injection chamber resonates and forms pressure disturbance, which causes the jet to break into droplets.

[0061] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0062] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A quantitative design method for the resonant structure of the nozzle cavity of a piezoelectrically excited injector, characterized in that, include: Obtaining the density of the liquid working fluid ρ Viscosity μ Surface tension coefficient σ、 Speed ​​of sound c Determine the droplet size required for the task. D jet speed u and jet flow rate q To further determine the nozzle diameter of the injector d out and number of nozzles n Furthermore, the operating frequency of the piezoelectric excitation is obtained based on the jet instability theory. f ; Determine the effective volume of the injector cavity based on the liquid resonance formula. V and nozzle length l out The product; according to d out and n Determine the effective cross-sectional dimensions of the injection panel to ensure all nozzles are evenly distributed on the panel and do not interfere with each other; the minimum nozzle spacing to prevent interference between nozzles. Satisfy the following formula: in, We For the jet Weber number, Oh It is the Euclid number; Determine based on the injector's operating pressure and droplet generation requirements. l out Then determine V Based on the constraints of the injector's external structure, piezoelectric ceramic, excitation panel, and injection panel dimensions, adjust the nozzle cavity configuration and length to achieve the desired effect. V Remain unchanged; The throttling size of the liquid working fluid inlet is determined based on the liquid supply pressure and the injector working pressure, so that the equivalent impedance of the liquid working fluid inlet is maximized. The parameters of the piezoelectric ceramic and the excitation panel are determined, a jetting experiment is carried out, the pulsating pressure of the fluid in the jet chamber is measured, the actual resonant frequency is obtained, and the volume of the jet chamber is corrected according to the difference between the actual resonant frequency and the working frequency.

2. The quantitative design method according to claim 1, characterized in that, The viscosity range of the liquid working fluid is 20 mPa. s~200mPa The jet velocity ranges from 5 m / s to 30 m / s, and the Reynolds number of the jet is kept below 1000 by matching the operating parameters.

3. The quantitative design method according to claim 1, characterized in that, Nozzle hole diameter d out The range is 0.15mm~3mm, and the number of nozzles... n The range is 1 to 1000.

4. The quantitative design method according to claim 1, characterized in that, The injector applies the vibration of its own excitation panel to the fluid. The diameter of the excitation panel ranges from 5mm to 20mm, the vibration displacement ranges from 0.5μm to 5μm, and the effective mass of the excitation panel ranges from 2g to 50g.

5. The quantitative design method according to claim 1, characterized in that, The nozzle length ranges from 0.5mm to 5mm, and the nozzle length-to-diameter ratio ranges from 2 to 8.

6. The quantitative design method according to claim 1, characterized in that, The ratio of nozzle spacing to nozzle diameter that prevents mutual interference is 1 to 20, and the minimum nozzle spacing is not less than 0.5 mm.

7. The quantitative design method according to claim 1, characterized in that, The inlet diameter of the liquid working medium ranges from 2mm to 10mm.

8. The quantitative design method according to claim 1, characterized in that, The specific formula for liquid resonance is as follows: 。 9. A piezoelectrically excited injector determined based on the quantitative design method according to any one of claims 1 to 8, characterized in that, Includes housing, injection panel, excitation panel, and piezoelectric ceramics; The housing and the injection panel surround to form the injection chamber. The housing has a liquid inlet and a notch for accommodating the excitation panel. A piezoelectric ceramic is placed outside the housing to excite the excitation panel. When the injector is working, the liquid working medium enters the injection chamber from the liquid inlet and is then ejected from the nozzle on the injection panel to form a jet. Under the excitation effect of the piezoelectric ceramic driving the excitation panel, the liquid working medium in the injection chamber resonates and forms pressure disturbance, which causes the jet to break into droplets.

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