A frost suppression device and method for removing droplets using pulsed ultrasonic waves

Abstract

A frost suppression device and method for removing droplets using pulsed ultrasonic waves. The frost suppression device includes an ultrasonic generator connected via a cable to a sandwich-type longitudinal vibration transducer, which is connected to a circular vibrating plate via an horn. The ultrasonic generator generates a voltage signal, which is converted by the sandwich-type longitudinal vibration transducer into an ultrasonic mechanical vibration signal. The amplitude of the mechanical vibration is increased by the horn. The horn is mounted at the center of the circular vibrating plate. Under the action of the ultrasonic mechanical vibration, the ultrasonic amplitude on the working surface of the circular vibrating plate is gradiently distributed. The leading and trailing contact lines of the condensed droplets vibrate to varying degrees, causing the leading and trailing contact angles of the droplets to change to varying degrees. This causes the condensed droplets to experience an imbalance in force, causing them to move, and thus move away from the cold surface before freezing into frost. The present invention controls the direction and speed of the condensed droplet movement, and the device has a simple structure and stable operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of frost suppression, and in particular relates to a frost suppression device and a frost suppression method for removing liquid droplets using pulsed ultrasonic waves. Background Art

[0002] Frost formation is a common phenomenon in daily life and has a significant impact on engineering fields such as refrigeration, cryogenics, and aerospace. Frost layers can cause a continuous increase in heat transfer resistance and a decrease in heat transfer coefficient. For example, air coolers operating in low-temperature, high-humidity environments and air-source heat pumps used for winter heating are susceptible to deteriorating heat transfer performance due to frost, resulting in performance degradation and increased energy consumption. In severe cases, frost can damage component structures, leading to complete failure of mechanical equipment, resulting in a series of serious accidents and significant operating and maintenance costs.

[0003] There are many defrosting methods, the most common of which is thermal defrosting, including natural defrost, electric defrost, reverse cycle defrost, and hot gas defrost. Currently, these defrosting methods consume additional heat energy, reducing system efficiency. They also cause varying degrees of temperature rise and increased load in the refrigeration system, leading to unstable operating conditions. Therefore, exploring effective frost suppression methods is particularly important. Summary of the Invention

[0004] The purpose of the present invention is to address the problems in the above-mentioned prior art and provide a frost suppression device and a frost suppression method for removing droplets using pulsed ultrasonic waves, which can completely drive and remove wide-scale condensed droplets before they freeze while saving energy, thereby suppressing frost from the root without affecting the stable operation of the system.

[0005] In order to achieve the above object, the present invention has the following technical solutions:

[0006] A frost suppression device for removing droplets using pulsed ultrasonic waves comprises an ultrasonic generator, which is connected to a sandwich-type longitudinal vibration transducer via a cable, and the sandwich-type longitudinal vibration transducer is connected to a circular vibration plate via an horn; the ultrasonic generator generates a voltage signal, the sandwich-type longitudinal vibration transducer converts the voltage signal into an ultrasonic mechanical vibration signal, and the amplitude of the mechanical vibration is increased by the horn; the horn is installed at the center of the circular vibration plate, and condensed droplets on the surface of the circular vibration plate move in a directional manner under the mechanical vibration of the ultrasonic wave, so that the condensed droplets leave the cold surface before freezing into frost.

[0007] As a preferred solution, the sandwich longitudinal vibration transducer, horn and circular vibration plate operate in a resonant state, and the resonant impedance between the sandwich longitudinal vibration transducer and the circular vibration plate is reduced by adjusting the load matching.

[0008] As a preferred solution, the resonant frequency f of the circular vibration plate is n The following relationship is satisfied:

[0009]

[0010] Where R(n)=k n a, n are positive integers, representing the vibration order of the circular vibration plate's bending vibration; h is the thickness of the circular vibration plate; a is the diameter of the circular vibration plate; E is Young's modulus; ρ v is the density of the circular vibrating plate; σ is the Poisson coefficient.

[0011] As a preferred solution, the calculation expression for the radiated sound pressure of the circular vibration plate is as follows:

[0012]

[0013] Where (r, θ) are polar coordinate parameters, t is time, k0 = ω / c0, ω is the angular frequency, c0 is the propagation velocity in air, ρ0 is the air density, H is the distance between the central point source and the calculation point, A and B are unknown constants; J0(kρ) is the first kind of zero-order Bessel function, I0(kρ) is the first kind of zero-order modified Bessel function, and dS is the area of the point source.

[0014] As a preferred solution, the ultrasonic generator operates periodically to generate pulsed ultrasonic waves to drive the sandwich-type longitudinal vibration transducer.

[0015] As a preferred solution, the ultrasonic generator is used to achieve adjustable ultrasonic power of 0-1000W. When the size of the condensed droplets is small, the ultrasonic generator generates ultrasonic waves with higher power. When the size of the condensed droplets is large, the ultrasonic generator generates ultrasonic waves with lower power. Alternatively, the ultrasonic generator uses high-power ultrasonic waves to drive small-sized condensed droplets to move and gather to form large-sized condensed droplets, and then converts them into low-power ultrasonic waves to drive the movement of large-sized condensed droplets.

[0016] As a preferred solution, the circular vibration plate is an aluminum plate with a working surface diameter of 100 mm and a thickness of 9.2 mm.

[0017] As a preferred solution, the node circles and antinode circles generated by the bending vibration state of the circular vibration plate collect condensed liquid droplets in a concentrated manner.

[0018] A frost suppression method based on the frost suppression device for removing droplets using pulsed ultrasonic waves, comprising:

[0019] Turn on the ultrasonic generator to drive the sandwich-type longitudinal vibration transducer to generate ultrasonic mechanical vibration;

[0020] Under the mechanical vibration of ultrasound, the ultrasonic amplitude on the working surface of the circular vibrating plate is distributed in a gradient, and the leading and trailing contact lines of the condensate droplets vibrate to varying degrees, causing the leading and trailing contact angles of the condensate droplets to change to varying degrees, causing the condensate droplets to move due to unbalanced force.

[0021] The ultrasonic power of the ultrasonic generator is adjusted to adjust the speed and direction of the condensation droplets, so as to drive the condensation droplets to move in a directional manner away from the cold surface and completely remove the condensation droplets before they freeze.

[0022] Preferably, the ultrasonic generator is turned on each time and works for 10 seconds, and then rests for 10 seconds, alternating in sequence to generate pulsed ultrasonic waves.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] The sandwich-type longitudinal vibration transducer is connected to the circular vibration plate through the horn, and the amplitude of the mechanical vibration is increased by the horn. The horn is installed at the center of the circular vibration plate, which can cause the circular vibration plate to generate bending vibration. The present invention utilizes the condensed liquid droplets on the surface of the circular vibration plate to produce directional movement under the mechanical vibration of ultrasound, so that the condensed liquid droplets leave the cold surface before freezing to form frost and are completely removed, so that there are no droplets on the working surface, fundamentally achieving the purpose of frost suppression. The ultrasonic-driven droplet effect of the present invention is obvious and has a wide range of scales. Ultrasonic waves with a power of 200W can drive condensed liquid droplets with a diameter of 3mm and above. When the ultrasonic power is increased to 500W, the average movement speed of droplets with a diameter of 5mm can reach 28mm / s. The ultrasonic-driven droplets of the present invention are directional, and the preset vibration strategy of the working surface can be realized by adjusting the input signal, thereby realizing the controllability of the direction and speed of the droplet movement. The ultrasonic amplitude generated by the ultrasonic wave on the surface of the circular vibration plate in the present invention is at the micron level, and the operation is stable. The frost suppression device of the present invention also has the advantages of simple structure, easy installation and use.

[0025] Furthermore, the use of pulsed ultrasound can achieve high efficiency and energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic structural diagram of a frost suppression device for removing droplets using pulsed ultrasonic waves according to an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the distribution of vibration circles and the movement of liquid droplets on the working surface of a circular vibration plate according to an embodiment of the present invention;

[0028] Figure 3 Schematic diagram of the longitudinal vibration velocity of the working surface of the frost suppression device according to an embodiment of the present invention;

[0029] Figure 4 Figure 3 Evolution characteristics of the average droplet velocity at midpoint II under different ultrasonic powers and droplet sizes;

[0030] In the accompanying drawings: 1-ultrasonic generator; 2-cable; 3-sandwich longitudinal vibration transducer; 4-horn; 5-circular vibration plate; 6-condensation droplets. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can also derive other embodiments without making any creative work.

[0032] See also Figure 1 A pulse ultrasonic frost suppression device for removing droplets according to an embodiment of the present invention includes an ultrasonic generator 1, a cable 2, a sandwich longitudinal vibration transducer 3, a horn 4 and a circular vibration plate 5.

[0033] In this embodiment, the circular vibration plate 5 is made of aluminum. The ultrasonic generator 1 is connected to the lower end of the sandwich longitudinal vibration transducer 3 via a cable 2. The upper end of the sandwich longitudinal vibration transducer 3 is connected to the lower end of the horn 4 via a screw. The upper end of the horn 4 is threadedly connected to the circular vibration plate 5. The horn 4 is mounted at the center of the surface of the circular vibration plate 5.

[0034] The ultrasonic generator 1 of the present invention is used to generate a voltage signal. The sandwich-type longitudinal vibration transducer 3 is an energy conversion device that converts electrical signals into acoustic signals. The amplitude of the mechanical vibration is increased by the horn 4, which is threadedly connected to the circular vibrating plate 5, transmitting the mechanical vibration to the working surface of the circular vibrating plate 5. The sandwich-type longitudinal vibration transducer 3, the horn 4, and the circular vibrating plate 5, which vibrates in bending, form a longitudinal-bending vibration-ultrasonic radiation system. When the frost suppression device of the present invention is in operation, the sandwich-type longitudinal vibration transducer 3, the horn 4, and the circular vibrating plate 5 must be in a resonant state. The load matching between the sandwich-type longitudinal vibration transducer 3 and the circular vibrating plate 5 is adjusted to reduce the resonant impedance. The resonant frequency of the frost suppression device of the present invention is 35kHz, and the ultrasonic power can be adjusted from 0 to 1000W by the ultrasonic generator 1. Pulsed ultrasonic waves are used for periodic operation, i.e., the ultrasonic wave is turned on for 10 seconds and then rested for 10 seconds, to achieve energy conservation.

[0035] The sandwich-type longitudinal vibration transducer 3 of the present invention converts a voltage signal into an ultrasonic mechanical vibration signal. The resonant frequency and radiated sound pressure of the flexurally vibrating aluminum disc plate require theoretical calculations. The output end of the sandwich-type longitudinal vibration transducer 3 is perpendicularly connected to the aluminum disc plate, causing the plate to generate flexural vibration. Based on the flexural vibration theory of the aluminum disc plate, the eigenfunction is:

[0036] y(ρ,t)=[AJ0(kρ)+BI0(kρ)]exp(jωt) (1)

[0037] Where A and B are unknown constants, J0(kρ) is the first kind zero-order Bessel function, and I0(kρ) is the first kind zero-order modified Bessel function.

[0038] k 4 =ρ v hω 2 / D (2)

[0039]

[0040]

[0041] Where, ρ v is the density of the aluminum plate, h is the thickness of the aluminum plate, ω is the angular frequency, D is the bending stiffness of the aluminum plate, E is the Young's modulus, and σ is the Poisson's coefficient.

[0042] For the nth-order vibration of the circular aluminum plate, its displacement is expressed by the following formula:

[0043] y n (ρ,t)=[A n J0(k n ρ)+B n I0(k n ρ)]exp(jω n t) (5)

[0044] Since it is a fixed boundary, the lateral displacement and derivative at the boundary of the disk aluminum plate with a diameter of a are 0, and the following formula can be obtained:

[0045] -AJ0(ka)=BI0(ka) (6)

[0046] AJ1(ka)=BI1(ka) (7)

[0047] Therefore, the equation for the resonant frequency of the flexural vibration disk aluminum plate is expressed as follows:

[0048] J0(ka)I1(ka)+I0(ka)J1(ka)=0 (8)

[0049] k n a=R(n) (9)

[0050] Where R(n) is the root of equation (8), and n is a positive integer representing the nth-order vibration of the circular aluminum plate.

[0051] The resonant frequency f of the aluminum disk is n for:

[0052]

[0053] The radiated sound pressure of the circular aluminum plate is calculated by the following formula:

[0054]

[0055] Where (r, θ) is the polar coordinate parameter, t is the time, k0 = ω / c0, c0 is the propagation speed in the air, ρ0 is the air density, H is the distance between the central point source and the calculation point, and dS is the area of the point source.

[0056] Under the mechanical vibration of ultrasonic waves, the circular aluminum plate's surface exhibits a gradient of ultrasonic amplitude distribution, creating a velocity gradient. Consequently, the leading and trailing contact lines of the condensate droplet 6 vibrate to varying degrees, causing the leading and trailing contact angles of the condensate droplet 6 to change to varying degrees. This causes the droplet 6 to move due to unbalanced forces, and the speed and direction of this movement are controllable. Consequently, the ultrasonic waves drive the condensate droplet 6 in a directional motion away from the cold surface, completely removing it before it freezes, leaving the work surface free of droplets and fundamentally suppressing the formation of frost crystals.

[0057] Figure 4 Shown Figure 3 The evolution of the average droplet velocity at midpoint II under different ultrasonic powers and droplet sizes shows that as the ultrasonic power and the size of condensed droplets 6 increase, the velocity of condensed droplets 6 also increases, making them easier to drive and remove. At an ultrasonic power of 200W, condensed droplets 6 with a diameter of 3mm or greater can be completely removed. When the ultrasonic power is increased to 500W, the average velocity of condensed droplets 6 with a diameter of 5mm can reach 28mm / s. Therefore, when the size of condensed droplets 6 is small, higher-power ultrasonic driving is used, while when the size of condensed droplets 6 is large, lower-power ultrasonic driving is used. High-power ultrasonic driving can also be used to rapidly drive small-sized condensed droplets 6 to coalesce and form large-sized condensed droplets 6, and then switch to low-power ultrasonic driving to drive the movement of large-sized condensed droplets 6, thereby achieving energy conservation.

[0058] See also Figure 2The working surface is a circular aluminum plate with a diameter of 100mm and a thickness of 9.2mm. The horn 4 is threaded to apply the sound source to the center of the circular aluminum plate. Due to the problem of end reflection, a standing wave is generated on the circular aluminum plate. Due to the existence of the velocity gradient on the aluminum plate surface, the droplet moves towards the vibration antinode under the coupling of adhesion, surface tension, and acoustic fluid force. When the mechanical effect of ultrasound acts on the surface of the aluminum plate, due to the standing wave, nodes appear on the surface of the aluminum plate, that is, points with zero velocity. Figure 2 The dotted circles b and d are node circles. The droplet velocity at this position is 0 and will not move. Figure 2 The center point a and solid coil c in the figure represent the antinodes, where the velocity is maximum. Points I, II, and III are the center points of the distances between adjacent node coils and antinodes, respectively. Due to the limited size of the aluminum plate, solid coil e represents the edge of the plate, and point IV is the center point of the distance between coils d and e. The distances of coils a, b, c, d, and e from the central sound source are 0 mm, 14.8 mm, 26.6 mm, 38 mm, and 45 mm, respectively. Figure 2 The arrows in the figure indicate the movement directions of the droplets at points Ⅰ-Ⅳ under ultrasonic driving. Figure 3 The longitudinal velocity distribution of the aluminum plate particles in the radial direction is shown. The direction from the node to the antinode is the direction of increasing velocity, that is, the direction of acceleration. Therefore, the droplet moves toward the antinode. However, when the droplet reaches the antinode, the acceleration of the front and rear contact lines of the droplet is the same but in opposite directions. The ultrasonic driving force cancels out the droplet, so the droplet stops after reaching the antinode. Droplets can be collected in the node and antinode circles.

[0059] Active frost suppression using external physical fields (such as electric, magnetic, and acoustic fields) to eliminate condensed droplets in the early stages of frost formation has attracted considerable attention. Surface ultrasound, with its excellent mechanical and cavitation effects, generates acoustic radiation forces and acoustic streaming within droplets on cold surfaces, causing them to slide and roll, driving them in a directional manner away from the cold surface and removing them before they freeze, ultimately reducing or even eliminating frost crystals.

[0060] The frost suppression device proposed in the present invention can not only drive large droplets with a diameter of 3 mm or more, but also has the advantages of simple structure, easy installation and use, stable operation, obvious droplet removal effect, and energy saving.

[0061] By making the circular vibration plate 5 of the present invention into other shapes, according to the same technical principle, the frost suppression device proposed in the present invention can be applied to various components that produce droplets or frost due to low temperature conditions or the operation of the refrigeration system, including air conditioners, refrigerators, air coolers, car windshield raindrop removal, air source heat pumps, spacecraft air-breathing engines, gas turbines, liquid oxygen vaporizers, rockets, microfluidics, transmission lines, wind turbine blades, etc.

[0062] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A frost suppression device for removing droplets using pulsed ultrasonic waves, characterized in that: The ultrasonic generator (1) comprises an ultrasonic generator (1), the ultrasonic generator (1) is connected to a sandwich-type longitudinal vibration transducer (3) via a cable (2), and the sandwich-type longitudinal vibration transducer (3) is connected to a circular vibration plate (5) via an horn (4); the ultrasonic generator (1) generates a voltage signal, the sandwich-type longitudinal vibration transducer (3) converts the voltage signal into an ultrasonic mechanical vibration signal, and the amplitude of the mechanical vibration is increased by the horn (4); the horn (4) is installed at the center of the circular vibration plate (5), and condensed liquid droplets (6) on the surface of the circular vibration plate (5) generate directional movement under the mechanical vibration of the ultrasonic wave, so that the condensed liquid droplets (6) leave the cold surface before freezing into frost; the ultrasonic generator (1) performs a periodic The ultrasonic generator (1) can work in a pulsed manner to generate ultrasonic waves that drive a sandwich longitudinal vibration transducer (3); the ultrasonic power can be adjusted from 0 to 1000W by using the ultrasonic generator (1); when the size of the condensed liquid droplets (6) is small, the ultrasonic generator (1) generates ultrasonic waves with a relatively high power; when the size of the condensed liquid droplets (6) is large, the ultrasonic generator (1) generates ultrasonic waves with a relatively low power; or, the ultrasonic generator (1) uses high-power ultrasonic waves to drive the small-sized condensed liquid droplets (6) to move and gather to form large-sized condensed liquid droplets (6), and then converts them into low-power ultrasonic waves to drive the large-sized condensed liquid droplets (6) to move; the node rings and antinode rings generated by the circular vibration plate (5) in the bending vibration state collect the condensed liquid droplets (6) in a concentrated manner.

2. The frost suppression device for removing droplets using pulsed ultrasonic waves according to claim 1, characterized in that: The sandwich-type longitudinal vibration transducer (3), the amplitude transformer (4) and the circular vibration plate (5) operate in a resonant state, and the resonant impedance between the sandwich-type longitudinal vibration transducer (3) and the circular vibration plate (5) is reduced by adjusting the load matching.

3. The frost suppression device for removing droplets using pulsed ultrasonic waves according to claim 1, characterized in that: The resonant frequency f of the circular vibration plate (5) n The following relationship is satisfied: Where R(n)=k n a, n are positive integers, representing the vibration order of the bending vibration of the circular vibration plate (5); h is the thickness of the circular vibration plate (5); a is the diameter of the circular vibration plate (5); E is the Young's modulus; ρ v is the density of the circular vibrating plate (5); σ is the Poisson coefficient.

4. The frost suppression device for removing droplets using pulsed ultrasonic waves according to claim 1, characterized in that: The calculation expression of the radiation sound pressure of the circular vibration plate (5) is as follows: Where (r, θ) are polar coordinate parameters, t is time, k0 = ω / c0, ω is the angular frequency, c0 is the propagation velocity in air, ρ0 is the air density, H is the distance between the central point source and the calculation point, A and B are unknown constants; J0(kρ) is the first kind of zero-order Bessel function, I0(kρ) is the first kind of zero-order modified Bessel function, and dS is the area of the point source.

5. The frost suppression device for removing droplets using pulsed ultrasonic waves according to claim 1, characterized in that: The circular vibration plate (5) is an aluminum plate with a working surface diameter of 100 mm and a thickness of 9.2 mm.

6. A frost suppression method based on the frost suppression device for removing droplets by pulsed ultrasonic waves according to any one of claims 1 to 5, characterized in that: include: The ultrasonic generator (1) is turned on to drive the sandwich-type longitudinal vibration transducer (3) to generate ultrasonic mechanical vibration. Under the mechanical vibration of the ultrasonic wave, the ultrasonic amplitude on the working surface of the circular vibration plate (5) is distributed in a gradient, and the leading edge contact line and the trailing edge contact line of the condensed liquid droplet (6) vibrate to different degrees, causing the leading edge contact angle and the trailing edge contact angle of the condensed liquid droplet (6) to change to different degrees, so that the condensed liquid droplet (6) is subjected to an unbalanced force and moves. The ultrasonic power of the ultrasonic generator (1) is adjusted to adjust the speed and direction of the movement of the condensed liquid droplets (6), drive the condensed liquid droplets (6) to move in a direction away from the cold surface, and completely remove the condensed liquid droplets (6) before they freeze.

7. The frost suppression method according to claim 6, characterized in that: Each time the ultrasonic generator (1) is turned on, it works for 10 seconds and then rests for 10 seconds, alternating in sequence to generate pulsed ultrasonic waves.

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