A defrosting device and method for removing liquid bridges between fins of a microchannel heat exchanger

Abstract

A defrosting device and method for removing liquid bridges between fins of a microchannel heat exchanger is disclosed. The device includes ultrasonic transducers, several of which are vertically fixed on the fins of the microchannel heat exchanger; a piezoelectric ceramic array, composed of several piezoelectric ceramics, with one array fixed on each ultrasonic transducer, the piezoelectric ceramics arranged in a predetermined order and spacing; and an ultrasonic control module that converts mains power into a high-frequency AC signal matching the piezoelectric ceramics via an ultrasonic generator. The piezoelectric ceramics then convert the high-frequency AC signal into high-frequency mechanical vibration, which is transmitted to the microchannel heat exchanger fins via the ultrasonic transducers. The liquid bridge is atomized at the edge of the fins and then migrates directionally within the fins. This invention can achieve efficient removal of liquid bridges using variable frequency / variable voltage / variable array methods, and can automatically remove liquid bridges between the fins of a microchannel heat exchanger.

Description

Technical Field

[0001] This invention belongs to the field of microchannel heat exchanger technology, specifically relating to an anti-frost device and method for removing liquid bridges between fins of a microchannel heat exchanger. Background Technology

[0002] Heat exchangers are a crucial component of air conditioning systems. Compared to traditional finned tube heat exchangers, microchannel heat exchangers offer advantages such as lighter weight, higher heat exchange efficiency, lower refrigerant charge, and more compact structure, attracting widespread attention and leading to their widespread application in automotive air conditioning. However, microchannel heat exchangers face several challenges when used as evaporators under frosting and humid conditions. First, when operating under cyclical frosting and defrosting conditions, microchannel heat exchangers experience faster frosting rates compared to traditional finned tube heat exchangers. Studies show that the frosting time for microchannel heat exchangers is 20% to 50% shorter than that of traditional finned tube heat exchangers. Second, the smaller fins and pitch of microchannel heat exchangers cause more defrosting water to remain trapped in the fin gaps due to surface tension, exacerbating the formation of liquid bridges between adjacent fins. These trapped liquid bridges then freeze in the next frosting cycle, restricting free airflow and reducing the thermal performance of the microchannel heat exchanger. Therefore, developing an effective defrosting technology and improving drainage performance are crucial for ensuring the efficient operation of microchannel heat exchangers. Summary of the Invention

[0003] The purpose of this invention is to address the problems in the prior art by providing a defrosting device and method for removing liquid bridges between fins of a microchannel heat exchanger. While ensuring the efficient and stable operation of the microchannel heat exchanger, the device and method perform zoned control of the condensate bridges in the early stage of frosting and the residual liquid bridges after defrosting, and adopt a directional driving and atomization removal strategy to achieve the purpose of defrosting.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A defrosting device for removing liquid bridges between fins of a microchannel heat exchanger includes:

[0006] Ultrasonic transducer plates, several of which are vertically fixed on the fins of the microchannel heat exchanger.

[0007] The piezoelectric ceramic array consists of several piezoelectric ceramics. Each ultrasonic transducer plate has a set of piezoelectric ceramic arrays fixed on it. The piezoelectric ceramics are arranged on the ultrasonic transducer plate in a set order and spacing.

[0008] The ultrasonic control module includes an ultrasonic generator connected to a piezoelectric ceramic. The ultrasonic generator converts the mains power into a high-frequency AC signal that matches the piezoelectric ceramic. The piezoelectric ceramic then converts the high-frequency AC signal into high-frequency mechanical vibration. The high-frequency mechanical vibration is transmitted to the microchannel heat exchanger fins through an ultrasonic transmission plate. The liquid bridge is atomized at the edge of the microchannel heat exchanger fins and migrates directionally inside the microchannel heat exchanger fins.

[0009] As a preferred embodiment, the piezoelectric ceramic is of type PZT-4, with a length of 10mm to 40mm, a width of 2mm to 20mm, a thickness of 0.3mm to 1.25mm, and a power of 20W to 60W.

[0010] As a preferred option, the ultrasonic intensity at different locations on the microchannel heat exchanger fins is ranked as follows: double edge > single edge > no edge;

[0011] Double edge refers to the liquid bridge being located at the right angle where the vertical edges of the fin intersect, and the liquid bridge contact line simultaneously contacts the adjacent edge;

[0012] Single edge means that the liquid bridge is located on the side or upper and lower edges of the fin, and the liquid bridge contact line only contacts one edge of the fin.

[0013] "Edgeless" means that the liquid bridge is located inside the fin, and the liquid bridge contact line does not contact the edge of the fin.

[0014] As a preferred embodiment, the system also includes a liquid bridge positioning module. The liquid bridge positioning module emits ultrasonic pulses to the air gap between the fins of the microchannel heat exchanger via a sensor. If a liquid bridge exists, the pulses are reflected back to the sensor after passing through the liquid surface of the liquid bridge. The time required for the ultrasonic pulse to travel from emission to reception is measured, and the distance between the sensor and the liquid surface is obtained based on the speed of sound in the medium, thereby determining the position of the liquid bridge.

[0015] As a preferred embodiment, a signal feedback module is also included. The signal feedback module compares the liquid bridge detection value collected by the liquid bridge positioning module with the set value. If the liquid bridge detection value is less than the set value, it indicates that the liquid removal condition has not been met, and the liquid bridge positioning module continues to collect signals. If the feedback value reaches the set value, the signal feedback module issues a corresponding working command to the ultrasonic control module based on the liquid bridge distribution characteristics. The signal feedback module combines the liquid bridge information with the ambient temperature and humidity information to determine the ultrasonic working parameters.

[0016] As a preferred embodiment, the microchannel heat exchanger fins are divided into n regions, each of which is equipped with an ultrasonic transducer plate. The signal feedback module performs zoned control based on the differences in the number and distribution characteristics of liquid bridges in different regions. That is, it formulates the optimal working mode according to the liquid bridge information of each region and starts the ultrasonic transducer plate of each region to work independently.

[0017] As a preferred solution, the signal feedback module adopts an ultrasonic frequency conversion working mode during the zoned control process. The ultrasonic transducer plate performs frequency sweeping operation within the working frequency range of 30kHz to 40kHz.

[0018] A method for preventing defrosting by removing liquid bridges between fins of a microchannel heat exchanger includes:

[0019] When ultrasonic waves are applied to the fins of a microchannel heat exchanger, the ultrasonic waves generate acoustic flow force and acoustic radiation force inside the liquid bridge. The directional driving effect of the ultrasonic waves on the liquid bridge depends on the vibration characteristics of the microchannel heat exchanger fins. The propagation of ultrasonic waves on the microchannel heat exchanger fins and the superposition of reflected waves form antinodes and nodes on the microchannel heat exchanger fins. Under the action of ultrasonic waves, the liquid bridge migrates directionally towards the antinodes, thereby directionally driving the liquid bridge inside the microchannel heat exchanger fins to migrate to the edge of the microchannel heat exchanger fins for atomization, so that the atomized droplets are discharged into the air for evaporation.

[0020] As a preferred embodiment, when ultrasound is applied, atomized droplets are generated on the liquid bridge, and the atomized droplet particles are generated by the surface decomposition of the main droplet;

[0021] The size of the ultrasonically excited atomized droplets is calculated using the following formula:

[0022]

[0023] In the formula, d is the average diameter of the atomized droplets, σ ​​is the surface tension of the liquid, ρ is the liquid density, and f is the excitation frequency.

[0024] As a preferred embodiment, if the microchannel heat exchanger fins are subjected to ultrasonic excitation, the forces balanced on the liquid surface include:

[0025] hydrostatic pressure:

[0026] P h =-ρgz

[0027] Capillary force:

[0028] P2-P1=σ(1 / R x +1 / R y )

[0029] Acoustic radiation pressure:

[0030]

[0031] In the formula, A and B are nonlinear effect constants, u(x) is the acoustic displacement, ρ is the liquid density, σ is the liquid surface tension, c is the sound velocity in the liquid, and R... x Let R be the radius of curvature at any point along the x-direction.y Let be the radius of curvature at any point along the y-direction, g be the gravitational acceleration, z be the liquid depth, P2 be the pressure inside the liquid layer, and P1 be the pressure outside the liquid layer.

[0032] Acoustic pressure:

[0033]

[0034]

[0035] Where z0 is the water thickness, l u Where A is the absorption length, f is a constant for the given liquid, f is the excitation frequency, f1 = 1MHz, and P is the absorption length. r This refers to acoustic radiation pressure;

[0036] The forces generated by acoustic radiation pressure and acoustic flow pressure cause the droplet to move by changing the position of the antinodes.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] On the one hand, ultrasonic vibrations generate acoustic radiation force in the liquid bridge, using relatively small energy to directionally drive away the liquid bridges on the surface of the working equipment. On the other hand, ultrasonic atomization effect is used to atomize the liquid bridges into small droplets, which are then released into the air to evaporate, ultimately forming a "liquid-free" or even "liquid-free" working surface, fundamentally achieving the purpose of defrosting. This invention adopts an "internal drive + edge atomization" strategy, which can completely remove all liquid bridges between the fins of a microchannel heat exchanger, achieving a dry and liquid-free state. This invention can achieve fully automated control for efficient removal of liquid bridges / droplets using variable frequency / variable voltage / variable array methods. It can effectively remove liquid bridges formed by condensation between the fins of a microchannel heat exchanger and residual liquid after defrosting, saving energy while ensuring efficient system operation. It has the advantages of high liquid removal efficiency and good defrosting effect.

[0039] Furthermore, the present invention employs a liquid bridge positioning module based on ultrasonic positioning technology, which can quickly acquire liquid bridge information and effectively remove liquid bridges / droplets using the acoustic flow effect and atomization effect of ultrasound. Through the synergistic action of the liquid bridge positioning module, signal feedback module, and ultrasonic control module, reasonable ultrasonic operating parameters are formulated based on the current liquid bridge information between the microchannel heat exchanger fins and the ambient temperature and humidity information. While saving energy, it automatically and efficiently completes defrosting, ensuring the efficient and stable operation of the microchannel heat exchanger without damaging the heat exchanger components.

[0040] Furthermore, this invention divides the microchannel heat exchanger fins into n regions, each of which is equipped with an ultrasonic transducer plate. In response to the differences in the number and distribution characteristics of liquid bridges in different regions, the signal feedback module performs "zonal control," that is, it formulates the optimal working mode based on the liquid bridge information of each region and starts the ultrasonic transducer plate of each region to work independently. In this way, energy consumption is saved while avoiding interference from the ultrasonic waves in other regions on the vibration characteristics of the target region. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in this application, the drawings used in the application description will be briefly introduced below. The drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the overall structure of the anti-frost device for removing liquid bridges between fins of a microchannel heat exchanger according to an embodiment of the present invention;

[0043] Figure 2 This is a flowchart of the anti-frost method for removing liquid bridges between fins of a microchannel heat exchanger according to an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the droplet movement in the anti-frost device according to an embodiment of the present invention;

[0045] Figure 4 This is a comparison diagram of the vibration displacement between the fin edge and the fin center in the anti-frost device of this embodiment of the invention;

[0046] In the attached diagram: 1-Refrigerant outlet; 2-Refrigerant inlet; 3-Microchannel heat exchanger fins; 4-Piezoelectric ceramic array; 5-Ultrasonic transmission plate; 6-Liquid bridge positioning module; 7-Signal feedback module; 8-Ultrasonic control module; 9-Cable; 10-Initial droplet position; 11-Ultrasonic position. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0048] In recent years, active defrosting methods utilizing external physical fields (such as electric fields, magnetic fields, and acoustic fields) have attracted considerable attention. These methods not only inhibit the growth of condensation nuclei but also eliminate liquid bridges / droplets during condensation and freezing processes. Ultrasonic defrosting technology, in particular, has garnered significant attention due to the advantages of short wavelength, high frequency, and highly concentrated energy of ultrasound. The core idea of ​​ultrasonic defrosting technology is twofold: firstly, it utilizes the mechanical vibration of ultrasound to generate acoustic radiation force within the liquid bridge, thereby directionally dispersing the liquid bridge from the surface of the working equipment by applying relatively small amounts of energy; secondly, it utilizes the ultrasonic atomization effect to atomize the liquid bridge into small droplets, which are then released into the air to evaporate, ultimately forming a "low-liquid" or even "liquid-free" working surface, fundamentally achieving the purpose of defrosting. Based on this, this invention proposes a defrosting device for removing liquid bridges between the fins of a microchannel heat exchanger.

[0049] Please see Figure 1 The defrosting device for removing liquid bridges between fins of a microchannel heat exchanger according to an embodiment of the present invention includes a liquid bridge positioning module 6, a signal feedback module 7, an ultrasonic control module 8, a piezoelectric ceramic array 4, and an ultrasonic transmission plate 5.

[0050] The main component of the ultrasonic control module 8 is an ultrasonic generator. The piezoelectric ceramic array 4 is composed of several piezoelectric ceramics. The ultrasonic generator converts the mains power into a high-frequency AC signal that matches the piezoelectric ceramics. The piezoelectric ceramics convert the high-frequency current into high-frequency mechanical vibration, and then the high-frequency mechanical vibration is transmitted to the microchannel heat exchanger fins 3 through the ultrasonic transmission plate 5.

[0051] Several ultrasonic transducer plates 5 are provided, all vertically fixed to the microchannel heat exchanger fins 3. Piezoelectric ceramics are attached to the ultrasonic transducer plates 5 in a certain order and at certain intervals. Ultrasonic vibrations are effectively propagated on the fins, allowing more ultrasonic energy to be transferred to the fins. The liquid bridges located between the fins undergo severe deformation, migration, and atomization under the action of ultrasonic waves.

[0052] In one possible implementation, the piezoelectric ceramic is of type PZT-4, with a length of 10mm to 40mm, a width of 2mm to 20mm, a thickness of 0.3mm to 1.25mm, and a power of 20W to 60W. The ultrasonic amplitude is extremely small and will not damage the heat exchanger components.

[0053] Due to the end reflection effect, the ultrasonic intensity at the fin edge is much greater than that inside the fin, such as... Figure 4 As shown, liquid bridges tend to atomize at the fin edges, while directional migration occurs inside the fins. The intensity of ultrasonic action at different locations on the fins is ranked as follows: double-edge > single-edge > no-edge.

[0054] Double edge refers to the liquid bridge being located at the right angle where the vertical edges of the fin intersect, and the liquid bridge contact line simultaneously contacts the adjacent edge.

[0055] Single edge means that the liquid bridge is located on the side or upper and lower edges of the fin, and the liquid bridge contact line only contacts one edge of the fin.

[0056] "Edgeless" means that the liquid bridge is located inside the fin, and the liquid bridge contact line does not contact the edge of the fin.

[0057] The anti-frost method for removing interfined liquid bridges in microchannel heat exchangers according to embodiments of the present invention is as follows: Figure 2 As shown: Based on considerations of energy consumption, fin vibration response differences, and the need for residue removal of liquid bridges, the liquid bridge inside the fin adopts an "internal drive + edge atomization" strategy. Ultrasonic waves generate acoustic flow force and acoustic radiation force inside the liquid bridge, thereby directionally driving the liquid bridge inside the fin to migrate to the edge of the fin for atomization, so that the atomized droplets are discharged into the air to evaporate, thereby achieving the purpose of completely removing the liquid bridge.

[0058] Furthermore, during ultrasonic treatment, capillary waves generated by surface instabilities are produced on the liquid bridge, and small droplet particles are observed around the liquid bridge. These small droplet particles are generated by the surface decomposition of the main droplet. The size of the small droplet particles ejected from the surface is related to the wavelength of the least unstable capillary. The size of the ultrasonically excited atomized droplets is calculated according to the following formula:

[0059]

[0060] Where d is the average diameter of the atomized droplets, σ ​​is the surface tension of the liquid, ρ is the liquid density, and f is the excitation frequency.

[0061] The directional driving effect of ultrasound on the liquid bridge depends on the vibration characteristics of the fins. The propagation of ultrasound waves on the fins and the superposition of reflected waves create antinodes and nodes on the metal fins. Under the action of ultrasound, the liquid bridge migrates directionally from its initial position 9 towards the antinode position 10, as shown below. Figure 3 As shown. If the metal fins are subjected to ultrasonic excitation, permanent deformation of the liquid surface can be observed. The forces considered in the liquid surface equilibrium include:

[0062] hydrostatic pressure:

[0063] P h =-ρgz

[0064] Capillary force:

[0065] P2-P1=σ(1 / R x +1 / R y )

[0066] Acoustic radiation pressure:

[0067]

[0068] The expression for acoustic radiation pressure gives the time-independent second-order terms in the acoustic pressure expression. Terms A and B are nonlinear effect constants, u(x) is the acoustic displacement, ρ is the liquid density, σ is the liquid surface tension, c is the velocity of sound in the liquid, and R... x Let R be the radius of curvature at any point along the x-direction. y Let be the radius of curvature at any point along the y-direction, g be the gravitational acceleration, z be the liquid depth, P2 be the pressure inside the liquid layer, and P1 be the pressure outside the liquid layer.

[0069] The acoustic pressure can be approximated as:

[0070]

[0071]

[0072] Where z0 is the water thickness, l u Where A is the absorption length, f is a constant for the given liquid, f is the excitation frequency, f1 = 1MHz, and P is the absorption length. r This refers to acoustic radiation pressure.

[0073] The forces generated by acoustic radiation pressure and acoustic flow pressure cause droplets to move. If the ultrasonic vibration amplitude is high enough, droplets deposited on the substrate will move towards the nearest ultrasonic antinode, i.e., the maximum radiation pressure, such as... Figure 2 As shown. Therefore, the droplet can be moved by changing the position of the antinodes. Since the boundary conditions of the fins determine the position of the antinodes for each bending mode, multiple modes must be excited consecutively to achieve displacement.

[0074] The anti-frost device of this invention uses the coordinated operation of the liquid bridge positioning module 6, the signal feedback module 7, and the ultrasonic control module 8 to precisely locate and remove the liquid bridge. The specific working steps are as follows:

[0075] Step 1: The liquid bridge positioning module 6 mainly uses ultrasonic positioning technology. The transmitting sensor sends ultrasonic pulses to the air gap between the fins of the microchannel heat exchanger. If a liquid bridge exists, the pulses are transmitted to the liquid surface of the liquid bridge, reflected, and returned to the receiving sensor. The time required for the ultrasonic pulse to travel from transmission to reception is measured. Based on the speed of sound in the medium, the distance between the sensor and the liquid surface is obtained, thereby determining the position of the liquid bridge.

[0076] Step 2: The signal feedback module 7 compares the detected value with the set value. If the feedback value is less than the set value, it indicates that the liquid removal conditions have not been met, and the liquid bridge positioning module continues to collect signals. If the feedback value reaches the set value, the signal feedback module 7 issues a corresponding working command to the ultrasonic control module 8 based on the liquid bridge distribution characteristics. Furthermore, the signal feedback module 7 combines liquid bridge information with ambient temperature and humidity information to determine reasonable ultrasonic operating parameters. If the total number of liquid bridges is small and the ambient temperature is high, low-power ultrasonic waves are emitted. If the total number of liquid bridges is large and the ambient temperature is low, the liquid bridges are prone to freezing, requiring rapid removal, and high-power ultrasonic waves are emitted.

[0077] Step 3: After receiving the working instruction from the signal feedback module, the ultrasonic control module 8 starts the ultrasonic device to begin the liquid removal process. Pulsed ultrasound is used, operating for 1 minute followed by a 1-minute interval. After the ultrasonic control module completes the set working time, it switches to the liquid bridge positioning module 6, repeating steps 1 through 3 until the final detection result shows no liquid bridge exists in the area.

[0078] In one possible implementation, the microchannel heat exchanger is divided into n regions, each equipped with an ultrasonic transducer plate 8, on which piezoelectric ceramics 4 are arranged in an array. To address the differences in the number and distribution characteristics of liquid bridges in different regions, the signal feedback module 7 performs "regional control," determining the optimal operating mode based on the liquid bridge information for each region and activating the ultrasonic components of each region independently. This saves energy while preventing interference from ultrasonic waves from other regions on the vibration characteristics of the affected region.

[0079] In one possible implementation, for cases where there are many liquid bridges in various regions, an ultrasonic frequency conversion working mode is adopted to perform frequency sweeping within the working frequency range of 30 to 40 kHz. The frequency conversion working mode can switch the optimal working point on the fins in real time, so that the ultrasonic waves can be effectively transmitted to all positions of the fins in that region, resulting in the large-scale removal of liquid bridges.

[0080] In this embodiment of the invention, the liquid bridge undergoes four processes under ultrasonic waves: spreading, necking, breaking, and atomization. The stronger the ultrasonic wave, the more pronounced the spreading and the more intense the atomization. Under a fixed frequency of ultrasonic waves, due to the complex propagation and mutual influence of vibrations between the fins, the vibration characteristics between fins in the same area differ, resulting in different optimal operating frequencies for fins at different locations. Therefore, the ultrasonic vibrations experienced by the fins attached to both sides of the liquid bridge vary. Furthermore, atomization occurs simultaneously with the necking and breaking processes to reduce the mass of the liquid bridge. The shape of the liquid bridge changes as the atomization process progresses, ultimately leading to a change in the optimal atomization frequency. As the atomization process continues, the optimal atomization frequency of the liquid bridge fluctuates within the range of ±0.5 kHz.

[0081] Furthermore, the longer the necking-atomization coexistence stage, the smaller the throat diameter at the time of liquid bridge breakage. Most of the liquid is atomized and removed on the more vibrating fins, while the residual droplets adhering to the liquid bridge on the less vibrating fins are smaller, which is beneficial for improving the removal efficiency of the liquid bridge. Therefore, in practical applications, real-time control of frequency and power is used to extend the necking-atomization coexistence stage of the liquid bridge.

[0082] Furthermore, the atomization effect of ultrasound is positively correlated with the ultrasound power; that is, the higher the ultrasound power, the more intense the atomization of the liquid bridge and the shorter the time. There is a critical power for liquid bridge atomization. When the power is low, the liquid bridge only undergoes spreading and directional migration. When the ultrasound power exceeds the critical power, the liquid bridge will experience breakage and atomization. Therefore, the liquid bridge can be placed in a specified state, such as stationary, spreading, migrating, necking, or atomized, by adjusting the power.

[0083] Furthermore, under the same ultrasonic vibration, the smaller the volume of the liquid bridge, the shorter the response time of the liquid bridge to the ultrasonic wave, and the faster the liquid bridge is atomized and removed. However, because the necking-fracture process of small-volume liquid bridges is completed rapidly during removal, larger-volume droplets will remain on adjacent attached fins, and these droplets need to be removed a second time using ultrasonic action.

[0084] The anti-frost device for removing liquid bridges between fins of microchannel heat exchangers proposed in this embodiment of the invention is not only applicable to liquid bridges, but also to droplets and other liquid substances present between fins, with a working liquid volume range of 5-30 μL.

[0085] Compared with existing technologies, the defrosting device and method for removing liquid bridges between fins of microchannel heat exchangers of the present invention have the following advantages:

[0086] (1) By adopting the strategy of “internal drive + edge atomization”, it is possible to completely remove all liquid bridges / droplets between the fins of the microchannel heat exchanger and achieve a dry and liquid-free state.

[0087] (2) On the one hand, the liquid bridge positioning module based on ultrasonic positioning technology can quickly collect liquid bridge information. On the other hand, the acoustic flow effect and atomization effect of ultrasonic waves can effectively remove liquid bridges / droplets. Both of these parts can be integrated into the ultrasonic device. Therefore, the device has the advantages of simple structure and easy operation.

[0088] (3) Through the synergistic effect of the liquid bridge positioning module, signal feedback module, and ultrasonic control module, and by using frequency conversion / voltage conversion / array conversion, fully automated control for efficient removal of liquid bridges / droplets is achieved.

[0089] (4) The present invention can effectively remove the liquid bridge formed by condensation between the fins of the microchannel heat exchanger and the residual liquid after defrosting. It saves energy while ensuring the efficient operation of the system and has the advantages of high liquid removal efficiency and good defrosting effect.

[0090] The above-described 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preventing frost formation by removing liquid bridges between fins of a microchannel heat exchanger, characterized in that, This is achieved using a defrosting device to remove liquid bridges between the fins of a microchannel heat exchanger. The defrosting device includes: An ultrasonic transducer plate (5) is vertically fixed on the microchannel heat exchanger fins (3). The piezoelectric ceramic array (4) is composed of several piezoelectric ceramics. Each ultrasonic transducer plate (5) has a set of piezoelectric ceramic arrays (4) fixed on it. The piezoelectric ceramics are arranged on the ultrasonic transducer plate (5) in a set order and spacing. The ultrasonic control module (8) includes an ultrasonic generator connected to the piezoelectric ceramic. The ultrasonic generator converts the mains power into a high-frequency AC signal that matches the piezoelectric ceramic. The piezoelectric ceramic then converts the high-frequency AC signal into high-frequency mechanical vibration. The high-frequency mechanical vibration is transmitted to the microchannel heat exchanger fins (3) through the ultrasonic transmission plate (5). The liquid bridge is atomized at the edge of the microchannel heat exchanger fins (3) and migrates directionally inside the microchannel heat exchanger fins (3). The intensity of ultrasonic action at different locations on the microchannel heat exchanger fins (3) is ranked as follows: double edge > single edge > no edge; Double edge refers to the liquid bridge being located at the right angle where the vertical edges of the fin intersect, and the liquid bridge contact line simultaneously contacts the adjacent edge; Single edge refers to the liquid bridge being located on the side or upper and lower edges of the fin, with the liquid bridge contact line only contacting one fin edge. "Edgeless" means that the liquid bridge is located inside the fin, and the liquid bridge contact line does not contact the edge of the fin. The defrosting method for removing interfined liquid bridges in microchannel heat exchangers includes: Ultrasonic waves are applied to the microchannel heat exchanger fins (3). The ultrasonic waves generate acoustic flow force and acoustic radiation force inside the liquid bridge. The directional driving effect of the ultrasonic waves on the liquid bridge depends on the vibration characteristics of the microchannel heat exchanger fins (3). The propagation of ultrasonic waves on the microchannel heat exchanger fins (3) and the superposition of reflected waves form antinodes and nodes on the microchannel heat exchanger fins (3). Under the action of ultrasonic waves, the liquid bridge migrates directionally towards the antinodes, thereby directionally driving the liquid bridge inside the microchannel heat exchanger fins (3) to migrate to the edge of the microchannel heat exchanger fins (3) for atomization, so that the atomized droplets are discharged into the air for evaporation.

2. The defrosting method for removing liquid bridges between fins of a microchannel heat exchanger according to claim 1, characterized in that, The piezoelectric ceramic is of type PZT-4, with a length of 10mm to 40mm, a width of 2mm to 20mm, a thickness of 0.3mm to 1.25mm, and a power of 20W to 60W.

3. The defrosting method for removing interfined liquid bridges in a microchannel heat exchanger according to claim 1, characterized in that, It also includes a liquid bridge positioning module (6), which sends ultrasonic pulses to the air gap between the microchannel heat exchanger fins (3) through a sensor. If a liquid bridge exists, the pulses are reflected back to the sensor after being reflected by the liquid surface of the liquid bridge. The time required for the ultrasonic pulse to travel from emission to reception is measured. Based on the speed of sound in the medium, the distance between the sensor and the liquid surface is obtained, thereby determining the position of the liquid bridge.

4. The defrosting method for removing interfined liquid bridges in a microchannel heat exchanger according to claim 3, characterized in that, It also includes a signal feedback module (7), which compares the liquid bridge detection value collected by the liquid bridge positioning module (6) with the set value. If the liquid bridge detection value is less than the set value, it means that the liquid removal condition has not been met, and the liquid bridge positioning module (6) continues to collect signals. If the feedback value reaches the set value, the signal feedback module (7) issues a corresponding working instruction to the ultrasonic control module (8) according to the liquid bridge distribution characteristics. The signal feedback module (7) combines the liquid bridge information with the ambient temperature and humidity information to formulate ultrasonic working parameters.

5. The defrosting method for removing interfined liquid bridges in a microchannel heat exchanger according to claim 4, characterized in that, The microchannel heat exchanger fins (3) are divided into n regions, and each region is equipped with an ultrasonic transducer plate (5). In response to the differences in the number and distribution characteristics of liquid bridges in different regions, the signal feedback module (7) performs zoned control, that is, it formulates the best working mode according to the liquid bridge information of each region and starts the ultrasonic transducer plate (5) of each region to work independently.

6. The defrosting method for removing interfined liquid bridges in a microchannel heat exchanger according to claim 5, characterized in that, During the partition control process of the signal feedback module (7), the ultrasonic frequency conversion working mode is adopted, and the ultrasonic transducer plate (5) performs frequency sweeping work in the working frequency range. The working frequency range of the ultrasonic transducer plate (5) is 30kHz~40kHz.

7. The defrosting method for removing liquid bridges between fins of a microchannel heat exchanger according to claim 1, characterized in that, When ultrasound is applied, atomized droplets are generated on the liquid bridge. The atomized droplet particles are generated by the surface decomposition of the main droplet. The size of the ultrasonically excited atomized droplets is calculated using the following formula: In the formula, The average diameter of the atomized droplets. For liquid surface tension, For the density of the liquid, The excitation frequency.

8. The defrosting method for removing interfined liquid bridges in a microchannel heat exchanger according to claim 1, characterized in that, If the microchannel heat exchanger fins (3) are excited by ultrasound, the forces in equilibrium on the liquid surface include: hydrostatic pressure: z Capillary force: Acoustic radiation pressure: In the formula, and The term is the nonlinear effect constant. It is acoustic displacement. It is the density of the liquid. It is the surface tension of the liquid. It is the speed of sound in a liquid. For along The radius of curvature at any point in the direction. For along The radius of curvature at any point in the direction. Let z be the acceleration due to gravity and z be the depth of the liquid. The pressure within the liquid layer, The pressure outside the liquid layer; Acoustic pressure: in, It's the thickness of the water. It is the absorption length. It is a constant for a given liquid. For the excitation frequency, , This refers to acoustic radiation pressure; The forces generated by acoustic radiation pressure and acoustic flow pressure cause the droplet to move by changing the position of the antinodes.

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