Magnetic control phase change high-efficiency heat transfer copper pipe and preparation process thereof

Abstract

The application discloses a high-efficiency heat transfer copper pipe with magnetic control phase change and a preparation process thereof, and relates to the technical field of heat exchange devices.The copper pipe comprises a copper pipe base body and a magnetic phase change composite slurry.The application utilizes a gradient magnetic field to dynamically control slurry filling, and through an axial / radial gradient magnetic field, the directional migration of magnetic nano-particles is guided, so that the high-heat-conducting particle concentration at the inlet end of the copper pipe is significantly higher than that at the outlet end.A magnetic force difference generated by the gradient magnetic field is utilized to drive the magnetic particles to gather in the direction of increasing magnetic field intensity, so as to form a functional gradient structure matched with the heat flow distribution.The structure enables the inlet end to quickly absorb and concentrate heat flow, and through the heat conduction network between the particles, heat is efficiently transferred to the outlet end, so that a self-adapting heat flow distribution mechanism is formed in the heat transfer process of the whole copper pipe, and the heat transfer capacity and heat load demand of different regions are accurately matched.

Description

Technical Field

[0001] This invention relates to the field of heat exchange device technology, specifically to a magnetically controlled phase change high-efficiency heat transfer copper tube and its manufacturing process. Background Technology

[0002] With the rapid development of new energy, cold chain logistics, and industrial waste heat recovery, higher requirements are being placed on the efficiency, stability, and controllability of heat transfer elements. Copper tubes, due to their excellent thermal conductivity, corrosion resistance, and processing performance, have become the core component of phase change heat transfer systems and are widely used in equipment such as heat pumps, condensers, and thermal storage devices. In the phase change heat transfer process, the synergistic effect of copper tubes and phase change materials (PCMs) directly determines the system's energy efficiency. Especially in high power density and variable operating conditions, it is necessary to achieve dynamic control of the heat transfer rate and efficient and stable output.

[0003] In the existing technology, the preparation of phase change copper tubes has many limitations: In terms of filling process, traditional static filling or homogeneous filling methods cannot achieve the functional gradient distribution of PCM, resulting in an imbalance in the heat transfer capacity of different areas of the copper tube. The inlet end is prone to overheating due to heat flow concentration, while the outlet end forms a temperature difference due to insufficient heat transfer. In the encapsulation and curing stage, relying solely on mechanical stirring to disperse magnetic particles can easily lead to agglomeration residue, while static curing is difficult to ensure the directional arrangement of particles, making the heat transfer path messy. For impregnation of porous matrix, high viscosity PCM is prone to forming a "bottleneck effect" in micropores, resulting in incomplete filling and air bubbles, which significantly reduces the effective heat transfer area.

[0004] In summary, the existing phase change copper tube manufacturing process suffers from the core problems of gradient distribution and particle dispersion, resulting in large fluctuations in heat transfer efficiency and poor long-term stability under varying operating conditions. This makes it impossible to meet the precision heat transfer requirements of high-end fields. Therefore, developing a manufacturing process that can precisely control the material distribution and structural properties through a magnetic field is the key to breaking through the existing technological bottlenecks. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-efficiency heat transfer copper tube with magnetically controlled phase change and its manufacturing process. It utilizes a gradient magnetic field to dynamically control the slurry filling and guides the directional migration of magnetic nanoparticles through axial / radial gradient magnetic fields, resulting in a significantly higher concentration of high thermal conductivity particles at the inlet end of the copper tube compared to the outlet end. By utilizing the magnetic force difference generated by the magnetic field gradient, the magnetic particles are driven to aggregate along the direction of increasing magnetic field strength, forming a functional gradient structure that matches the heat flow distribution. This structure allows the inlet end to quickly absorb concentrated heat flow and efficiently transfer heat to the outlet end through the heat conduction network between particles. This enables the entire copper tube to form an adaptive heat flow distribution mechanism during the heat transfer process, ensuring a precise match between the heat transfer capacity of different areas and the heat load requirements.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On the one hand, a high-efficiency heat transfer copper tube with magnetic phase change, the copper tube comprising: a copper tube substrate and a magnetic phase change composite slurry;

[0007] The copper tube substrate is made of oxygen-free copper with a purity of ≥99.9%, with a tube diameter of 5-50mm and a wall thickness of 0.5-3mm, and has an axially through inner cavity;

[0008] The inner wall of the copper tube substrate is provided with a gradient porous microstructure, the pore size of which increases from the inner wall to the outer wall in a gradient of 50nm-2μm, and the porosity is 30%-60%.

[0009] The gradient porous microstructure is filled with a magnetic phase change composite slurry, which is composed of magnetic nanoparticles and phase change materials. The magnetic nanoparticles are distributed in a gradient along the axial direction of the copper tube. The particle mass concentration at the inlet end is ≥15% higher than that at the outlet end, the overall porosity is <0.5%, and the axial heat transfer temperature difference is ≤2.0℃ at a heat flux density of 50kW / m².

[0010] Furthermore, in the magnetic phase change composite slurry, the organic phase change material matrix is ​​at least one of paraffin, fatty acid or eutectic salt, accounting for 70% to 94% of the magnetic phase change composite slurry, and the magnetic nanoparticles are at least one of Fe3O4, Co or NiFe2O4, with a particle size of 10-100 nm, accounting for 15% to 35% of the magnetic phase change composite slurry.

[0011] On the other hand, a process for fabricating a high-efficiency heat transfer copper tube with magneto-controlled phase change is described, and the specific steps of this process are as follows:

[0012] S100, Gradient Porous Matrix Preparation: Oxygen-free copper powder is loaded into a mold, an axial gradient magnetic field is applied, and gradient sintering is carried out in a hydrogen atmosphere to form a porous structure with a pore size increasing from 50nm to 2μm.

[0013] S200, Magnetic Dynamic Filling Slurry: The magnetic phase change composite slurry is heated to 60-80℃ and the viscosity is reduced to 30-100mPa.s. It is then injected into the copper tube at a speed of 3-8mm / s under an axial gradient magnetic field, and the magnetic particles migrate directionally toward the inlet end.

[0014] S300, Dual-station magnetic field switching curing: The copper tube is transferred to the first station by a mechanical conveying device, and a high-frequency alternating magnetic field is applied to make the magnetic nanoparticles generate vortex motion to break up the agglomerates. The copper tube is then transferred to the second station, where an axial static magnetic field is applied to drive the copper tube to rotate around the axis and simultaneously heat up to the curing point of the phase change material.

[0015] S400, Magnetically Controlled Vacuum-Centrifugal Composite Impregnation: Place the copper tube in the vacuum chamber, ensuring complete immersion in the injected molten slurry. Apply a radial gradient magnetic field and maintain for 5 minutes to remove residual air bubbles.

[0016] Furthermore, in S100, the intensity configuration of the axial gradient magnetic field must satisfy:

[0017] The magnetic field strength at the entrance is 0.5T to 1.0T;

[0018] The magnetic field strength at the exit end is 0.1T to 0.5T;

[0019] The slope of the magnetic field gradient is from 0.3T / m to 0.8T / m.

[0020] Furthermore, in S300, the parameters of the high-frequency alternating magnetic field are:

[0021] Frequency range: 50Hz to 200Hz;

[0022] Magnetic field strength ranges from 0.3 T to 0.8 T;

[0023] The duration of action is 30 to 120 seconds.

[0024] Furthermore, the processing temperature is controlled at 5-15℃ below the melting point of the phase change material.

[0025] Furthermore, in S300, the parameters for the rotation of the axis are:

[0026] Rotation speed from 1000 rpm to 6000 rpm;

[0027] The direction of centrifugal acceleration is parallel to the direction of the axial static magnetic field.

[0028] The static magnetic field strength ranges from 0.2T to 0.6T.

[0029] Furthermore, in S400, the porous copper tube substrate is placed in a vacuum chamber, evacuated to a pressure of 10-100 Pa, and held for 15-30 minutes to extract pore gas.

[0030] Furthermore, in the S300, the first station integrates an alternating magnetic field generator and a temperature control device, and the second station integrates a static magnetic field coil and a centrifugal rotary table.

[0031] Compared with existing technologies, this magneto-controlled phase change high-efficiency heat transfer copper tube and its manufacturing process have the following advantages:

[0032] I. This invention utilizes a gradient magnetic field to dynamically control slurry filling. By guiding the directional migration of magnetic nanoparticles through an axial / radial gradient magnetic field, the concentration of high thermal conductivity particles at the inlet end of the copper tube is significantly higher than that at the outlet end. Utilizing the magnetic force difference generated by the magnetic field gradient, the magnetic particles are driven to aggregate along the direction of increasing magnetic field strength, forming a functional gradient structure that matches the heat flow distribution. This structure allows the inlet end to quickly absorb concentrated heat flow, and the heat is efficiently transferred to the outlet end through the heat conduction network between particles. This enables the entire copper tube to form an adaptive heat flow distribution mechanism during the heat transfer process, ensuring a precise match between the heat transfer capacity of different areas and the heat load requirements.

[0033] II. The dual-station magnetic field switching high-frequency alternating magnetic field of this invention disperses the agglomeration of magnetic particles through high-frequency alternating magnetic force, so that the particles are uniformly dispersed in the magnetic phase change composite slurry. The axial static magnetic field guides the dispersed particles to oriented along the magnetic field direction, forming an ordered heat transfer channel. The shear force of the alternating magnetic field overcomes the van der Waals force between particles, and the magnetic dipole moment of the steady magnetic field makes the particles oriented. The uniformly dispersed particles ensure the isotropic basis of the thermal conductivity of the phase change material, and the oriented channels enhance the axial heat transfer rate, so that heat is efficiently transferred along the preset path, avoiding local thermal resistance differences caused by uneven particle distribution.

[0034] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of a high-efficiency heat transfer copper tube fabrication process using magnetron-controlled phase change. Detailed Implementation

[0037] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0038] Example 1

[0039] This embodiment uses a magnetic phase change composite slurry composed of Fe3O4 nanoparticles and paraffin as the core. By controlling the particle distribution through a gradient magnetic field and combining it with a dual-station magnetic field switching curing process, a magnetically controlled phase change copper tube suitable for high power density heat transfer scenarios is prepared. The copper tube has an axial heat transfer temperature difference of only 1.8℃ at a heat flux density of 50kW / m², the magnetic particle concentration at the inlet end is 20% higher than that at the outlet end, and the porosity is controlled below 0.3%, which solves the problems of uneven heat transfer and particle agglomeration in phase change copper tubes.

[0040] (1) Raw material selection and parameter setting

[0041] Copper tube substrate material: 99.95% pure oxygen-free copper is selected. The tube diameter is determined to be 20mm and the wall thickness is 1.5mm according to the target application scenario (industrial waste heat recovery condenser). The inner cavity is axially connected to ensure the flow of working fluid. The high purity of oxygen-free copper can reduce the thermal resistance of the substrate. Its thermal conductivity reaches 401W / (mk), which provides a basis for efficient heat transfer.

[0042] Magnetic phase change composite slurry formulation:

[0043] Organic phase change material matrix: Industrial-grade paraffin wax (99% purity) with a melting point of 58℃ is selected, accounting for 80% of the total mass of the slurry. Paraffin wax has the characteristics of high latent heat of phase change (205kJ / kg) and good chemical stability, making it suitable for medium and low temperature heat transfer scenarios.

[0044] Magnetic nanoparticles: Fe3O4 particles with an average particle size of 50 nm (the surface is modified with oleic acid to enhance dispersibility) account for 20% of the total mass of the slurry. Fe3O4 has superparamagnetism with a saturation magnetization of 80 emu / g. It can achieve directional migration under the action of a magnetic field, and its thermal conductivity (40 W / (mk)) is much higher than that of paraffin (0.2 W / (mk)), which can enhance the thermal conductivity of the slurry.

[0045] Slurry mixing: The paraffin wax is heated to 70℃ to melt, and Fe3O4 particles are added. The mixture is then pretreated with an ultrasonic disperser (300W power, 30min time) to initially break up the particle agglomerates and form a uniform suspension.

[0046] (2) Preparation of gradient porous matrix

[0047] Mold and raw material filling: Custom-made cylindrical graphite mold with smooth inner wall (diameter 20mm, length 500mm) is used to fill oxygen-free copper powder (purity 99.9%) with a particle size of 5-10μm into the mold. The bulk density of the copper powder is controlled at 4.2g / cm³. The selection of copper powder particle size must match the pore size range of the target porous structure (50nm-2μm). If it is too small, it will easily lead to pore blockage after sintering. If it is too large, it will be impossible to form a gradient increasing pore size distribution.

[0048] Axial gradient magnetic field application: An axial gradient magnetic field is generated using a Helmholtz coil. The magnetic field strength at the inlet end (heat flow input side) is set to 0.8T, and at the outlet end (heat flow output side) it is set to 0.3T. The magnetic field gradient slope is 0.5T / m (the magnetic field strength changes by 0.5T per meter along the length of the copper tube). The function of the gradient magnetic field is to guide the copper powder particles to oriented alignment during sintering, laying the foundation for the subsequent pore size gradient distribution.

[0049] Hydrogen atmosphere gradient sintering: The mold is placed in a tube furnace, and 99.99% pure hydrogen gas (flow rate 500 mL / min) is introduced to purge air and prevent copper powder oxidation. The sintering process uses gradient heating.

[0050] From room temperature to 300℃: heating rate 5℃ / min, to remove moisture and impurities adsorbed on the surface of copper powder;

[0051] 300℃ to 700℃: heating rate 2℃ / min. During this stage, the gradient magnetic field is simultaneously strengthened, and the copper powder particles begin to form sintering necks under the action of magnetic force and surface tension.

[0052] Holding at 700℃ for 2 hours: This achieves a gradient increase in pore size from 50nm on the inner wall to 2μm on the outer wall, with the final porosity controlled at 45%.

[0053] Cooling stage: After the furnace is cooled to 100°C, the hydrogen gas is turned off and nitrogen gas is introduced to protect the porous structure until it reaches room temperature, thus preventing oxidation of the porous structure.

[0054] (3) Magnetic field dynamic filling slurry

[0055] Slurry pretreatment: Pour the prepared Fe3O4-paraffin slurry into a constant temperature stirring vessel and heat it to 70℃ (12℃ higher than the melting point of paraffin). At this time, the viscosity of the slurry is measured to be 60 mPa·s by a rotational viscometer. During the heating process, stir continuously (200 rpm) to prevent Fe3O4 particles from settling.

[0056] Axial gradient magnetic field parameter settings: An axial gradient magnetic field is generated using an electromagnet, with a magnetic field strength of 0.6T at the inlet end and 0.2T at the outlet end, and a gradient slope of 0.4T / m, which matches the gradient distribution of the porous matrix. The direction of the magnetic field is consistent with the axis of the copper tube, ensuring that the magnetic particles migrate directionally towards the inlet end.

[0057] Dynamic injection process: Molten slurry is injected from the outlet end of the copper tube using a precision injection pump (reverse injection can reduce air bubble entrapment). The injection speed is controlled at 5 mm / s. During the injection process, the pressure inside the tube is monitored in real time (maintained at 0.12 MPa). The injection speed is adjusted by the pressure sensor to ensure that the slurry is uniformly filled into the micropores of the gradient porous structure. After injection, the tube is allowed to stand for 5 minutes. The magnetic field force is used to further drive the Fe3O4 particles to gather towards the inlet end. Finally, the particle concentration at the inlet end (25 wt%) is verified by sampling analysis to be 20% higher than that at the outlet end (5 wt%), which meets the design requirement of ≥15%.

[0058] (4) Dual-station magnetic field switching curing

[0059] First station: A mechanical conveyor (positioning accuracy ±0.1mm) transfers the copper tube to the first station, which integrates a 10kHz high-frequency alternating magnetic field generator and an infrared temperature control device. An alternating magnetic field with a strength of 0.5T and a frequency of 100Hz is applied for 60 seconds. During this time, the copper tube temperature is controlled at 55℃ (3℃ below the paraffin melting point to prevent the slurry from remelting and flowing) using an infrared thermometer. The Lorentz force generated by the alternating magnetic field causes the magnetic particles to vortex, colliding and breaking up agglomerates (original agglomerate particle size approximately 5μm, reduced to below 200nm after processing, verified by transmission electron microscopy). Second station: The conveyor transfers the copper tube to the second station, which integrates an axial static magnetic field coil (maximum magnetic field strength...). A 0.4T axial static magnetic field (direction consistent with the copper tube axis) was applied to a centrifugal rotating table (speed range 0-8000rpm). The rotating table was started simultaneously, causing the copper tube to rotate around the axis at 3000rpm (centrifugal acceleration of about 500g, direction parallel to the magnetic field direction, enhancing the particle orientation effect). The temperature was simultaneously raised to 45℃ (13℃ below the paraffin curing point) at a rate of 2℃ / min. The temperature was precisely controlled by a programmable temperature controller to ensure that the phase change material was slowly cured, providing sufficient time for the particle orientation. During the curing process, the crystal orientation of the Fe3O4 particles was monitored in real time by an X-ray diffractometer. It was found that the particles formed an ordered "thermal conductive chain" along the magnetic field direction, with a chain spacing of about 1μm, which significantly reduced the axial thermal resistance.

[0060] (5) Magnetically controlled vacuum-centrifugal composite impregnation

[0061] Vacuum pretreatment: Place the cured copper tube in a vacuum chamber, close the chamber, and start the vacuum pump to reduce the pressure to 50 Pa (within the process range of 10-100 Pa). Maintain this pressure for 20 minutes to remove residual air bubbles in the micropores (insufficient vacuum will cause residual air bubbles, reducing the heat transfer area; excessive vacuum may cause paraffin to evaporate, so 50 Pa is chosen as the equilibrium point). Inject molten paraffin (temperature 70℃) into the vacuum chamber to completely immerse the copper tube (liquid level 50 mm above the top of the copper tube). Apply a radial gradient magnetic field (0.3T on the inner side and 0.1T on the outer side) to drive the Fe3O4 particles in the incompletely filled area to migrate into the depth of the micropores. At the same time, start the centrifuge to rotate the chamber around the copper tube axis (speed 800 rpm). Use centrifugal force to press the slurry into the micropores to eliminate the "bottleneck effect". Continue treatment for 15 minutes, then stop the magnetic field and centrifugation. Allow the tube to cool naturally to room temperature. Then remove the copper tube and wipe the surface with alcohol to remove any residual slurry. The preparation is now complete.

[0062] (6) Performance testing and result analysis

[0063] Structural characterization: Scanning electron microscopy showed that the pore size of the gradient porous structure smoothly increased from 50 nm on the inner wall to 2 μm on the outer wall. The Fe3O4 particles were distributed in a gradient along the axial direction and formed oriented thermally conductive channels under the action of a static magnetic field. There were no obvious agglomerates. The overall porosity measured by mercury porosimetry was 0.3% (<0.5%), and the bubble residual rate was less than 0.1%, indicating excellent filling effect.

[0064] Heat transfer performance test: Under the test conditions of heat flux density of 50kW / m² (simulating industrial waste heat recovery scenario), the temperature at different positions along the axis of the copper tube was measured using a thermocouple array (accuracy ±0.1℃). The temperature difference between the inlet end (100℃) and the outlet end (98.2℃) was only 1.8℃, which meets the design requirement of ≤2.0℃.

[0065] Comparative experiments show that the temperature difference of traditional homogeneous filled copper tubes reaches 4.5℃ under the same conditions. The heat transfer efficiency of the product in this embodiment is improved by more than 50%, which is attributed to the synergistic effect of gradient particle distribution and directional heat conduction channels.

[0066] Long-term stability test: After 1000 cycles of hot and cold (-20℃ to 80℃), the heat transfer temperature difference was tested again and found to be 1.9℃, an increase of only 0.1℃, indicating that the magnetic particles did not have obvious sedimentation or agglomeration and the structure was stable.

[0067] This embodiment successfully fabricated a high-performance magnetron-controlled phase-change copper tube by precisely controlling the gradient magnetic field parameters and the slurry filling process. Its core advantages lie in: utilizing the axial gradient magnetic field to achieve a functional gradient distribution of magnetic particles, thus solving the inlet overheating problem; and through the synergistic effect of the high-frequency alternating magnetic field and the static magnetic field, both particle agglomeration is broken up and an ordered heat transfer channel is constructed, significantly reducing axial thermal resistance. The vacuum-centrifugal composite impregnation process ensures complete filling of the porous structure and eliminates the influence of air bubbles. This fabrication method provides a reliable technical solution for high power density heat transfer scenarios.

[0068] Example 2

[0069] This embodiment addresses the variable operating conditions required by cold chain logistics refrigeration systems by using NiFe2O4 nanoparticles and fatty acid eutectics to prepare a magnetic phase change composite slurry. By optimizing the magnetic field parameters and curing process, a magnetically controlled phase change copper tube with wide temperature range adaptability is prepared. This copper tube exhibits axial heat transfer temperature difference fluctuations of ≤0.5℃ within a heat flux density range of 30-70kW / m², with an inlet particle concentration 18% higher than the outlet. It demonstrates excellent stability in cyclic testing from -20℃ to 60℃, solving the problem of large fluctuations in heat transfer efficiency of traditional copper tubes under variable operating conditions.

[0070] (1) Raw material selection and parameter setting

[0071] Copper tube base material: 99.92% pure oxygen-free copper is selected. To meet the compact requirements of cold chain logistics evaporators, the tube diameter is determined to be 10mm, wall thickness 1.0mm, and length 300mm. The small diameter design reduces system volume while enhancing the magnetic field's control over particles inside the tube.

[0072] Magnetic phase change composite slurry formulation:

[0073] Organic phase change material matrix: It is a eutectic salt composed of stearic acid (60wt%) and palmitic acid (40wt%), with a phase change temperature of 32℃ and a latent heat of phase change of 210kJ / kg, which is suitable for the temperature range of cold chain systems (-20℃ to 40℃).

[0074] Magnetic nanoparticles: NiFe2O4 particles with an average particle size of 30nm (saturation magnetization of 65 emu / g) are selected, accounting for 25% of the total mass of the slurry. NiFe2O4 has good chemical stability and is not easily corroded in acidic or humid environments, making it suitable for the working conditions of cold chain systems.

[0075] Slurry preparation: The fatty acid eutectic was heated to 50°C to melt, and NiFe2O4 particles were added. The mixture was then processed in a planetary ball mill (300 rpm, ball-to-material ratio 5:1) for 1 hour to further refine the particles and improve dispersibility.

[0076] (2) Preparation of gradient porous matrix

[0077] Mold and copper powder selection: Stainless steel mold (with titanium nitride plating on the inner wall to reduce adhesion) is used, and oxygen-free copper powder with a particle size of 3-8μm (bulk density of 4.0g / cm³) is loaded into it. The target porosity is 50% (higher than Example 1, to enhance the storage capacity of the phase change material).

[0078] Axial gradient magnetic field and sintering process:

[0079] Magnetic field parameters: Magnetic field strength at the inlet is 1.0T, at the outlet is 0.2T, and the gradient slope is 0.8T / m (a higher gradient slope can enhance the aperture increase effect).

[0080] Sintering in a hydrogen atmosphere: Heat to 650℃ (lower than in Example 1 to avoid excessive deformation of small-diameter copper tubes), hold for 3 hours, and control the pore size to increase gradually from 50nm on the inner wall to 1.8μm on the outer wall.

[0081] Cooling process: Step-by-step cooling (holding temperature for 30 minutes at every 100℃) is adopted to reduce cracking of porous structures caused by thermal stress.

[0082] (3) Magnetic field dynamic filling slurry

[0083] Slurry pretreatment: The NiFe2O4-fatty acid slurry is heated to 65℃ (the viscosity is reduced to 40mPa.s), and the viscosity is further reduced by ultrasonic vibration (power 200W) to ensure flowability in small diameter pipes.

[0084] Magnetic field and injection parameters:

[0085] Axial gradient magnetic field: 0.7T at the inlet and 0.2T at the outlet, with a gradient slope of 0.5T / m, matching the diameter of the copper tube.

[0086] Injection speed: 3 mm / s (injection pressure controlled at 0.15 MPa to ensure the slurry is evenly filled into the micropores of the 10 mm diameter pipe.)

[0087] Filling effect verification: Energy dispersive X-ray spectroscopy analysis showed that the NiFe2O4 concentration at the inlet (24wt%) was 18% higher than that at the outlet (6wt%), which met the design requirements.

[0088] (4) Dual-station magnetic field switching curing

[0089] First station: High-frequency alternating magnetic field:

[0090] The frequency was increased to 200Hz (higher than in Example 1, because NiFe2O4 particles are smaller and require a higher frequency to effectively break up the agglomerates), the magnetic field strength was 0.6T, and the action time was 40s (shorter than in Example 1, to avoid overheating and decomposition of fatty acids).

[0091] Temperature control target: 40℃ (8℃ above the melting point of fatty acid eutectic to prevent premature curing).

[0092] Second station: Axial static magnetic field and rotation:

[0093] The static magnetic field strength is 0.5T (higher strength can enhance the orientation effect of small particles), and the rotation speed is 6000rpm (centrifugal acceleration is about 1200g, which can meet the filling requirements of small diameter tubes).

[0094] Curing temperature: 25℃ (7℃ below the eutectic point), heating rate 1℃ / min (a slower rate ensures uniform curing of small-diameter tubes and avoids stress cracking caused by internal and external temperature differences).

[0095] (5) Magnetically controlled vacuum-centrifugal composite impregnation

[0096] Vacuum parameters: Pressure is reduced to 30 Pa (lower vacuum to address the difficulty of venting micropores in small-diameter tubes), and maintained for 30 minutes (extended time to ensure complete removal of air bubbles).

[0097] Radial magnetic field and centrifugation: 0.4T on the inner side and 0.1T on the outer side of the radial magnetic field (to enhance the radial magnetic field gradient and drive the particles to migrate to the micropores of the tube wall), centrifugation speed of 1000 rpm, and processing time of 20 min (longer than Example 1, to ensure that the micropores of the small-diameter tube are completely filled).

[0098] (6) Performance testing and variable operating condition verification

[0099] Structure and basic properties: Scanning electron microscopy shows that NiFe2O4 particles are distributed in a gradient along the axial direction and are arranged in an orderly manner along the magnetic field direction. The aggregate particle size is <100nm, the porosity is 0.4%, which meets the requirement of <0.5%, and the axial temperature difference is 1.9℃ at a heat flux density of 50kW / m².

[0100] Adaptability test under varying operating conditions: Under conditions of 30kW / m² (low load), 50kW / m² (design load), and 70kW / m² (high load), the axial heat transfer temperature differences were 1.5℃, 1.9℃, and 2.0℃, respectively, with a fluctuation range of only 0.5℃, indicating that it has stable heat transfer performance under varying operating conditions (the temperature difference fluctuation of traditional copper pipes under the same conditions reaches 2.3℃).

[0101] After 1000 cycles of thermal cycling (-20℃ to 60℃), the heat transfer temperature difference increased to 2.1℃, showing good stability, which is attributed to the chemical inertness of the fatty acid eutectic and the corrosion resistance of NiFe2O4.

[0102] This embodiment addresses the variable operating conditions required by cold chain logistics. By optimizing magnetic field parameters and process details, a small-diameter, highly stable magnetron-controlled phase change copper tube was successfully fabricated. A fatty acid eutectic was used to expand the phase change temperature range, matching the operating conditions of the cold chain system. By increasing the alternating magnetic field frequency and static magnetic field strength, the particle dispersion and orientation issues within the small-diameter tube were resolved. Variable operating condition testing verified the stability of the copper tube under fluctuating heat flux density, providing an ideal heat transfer solution for variable load scenarios such as cold chain logistics. Compared to Embodiment 1, this embodiment demonstrates superior wide-temperature adaptability and variable operating condition stability, showcasing the potential for scenario-based applications of magnetron-controlled phase change technology.

[0103] In summary, the two embodiments, targeting industrial waste heat recovery and cold chain logistics scenarios respectively, verified the universality of magnetically controlled phase change technology by adjusting copper tube parameters, slurry formulation, and magnetic field processes. Embodiment 1 focuses on efficient heat transfer under high power density, while Embodiment 2 emphasizes stability under varying operating conditions. Both demonstrate the core advantages of magnetic field control in the field of phase change heat transfer. To visually compare the performance of the two embodiments in different application scenarios, the specific performance test results are shown in the table below:

[0104] Performance indicators Copper pipe parameters (pipe diameter, wall thickness) Phase change material ratio Magnetic particle ratio Concentration difference between inlet and outlet Overall porosity Axial temperature difference at a heat flux density of 50 kW / m² Temperature difference after 1000 cycles of heating and cooling Example 1 20mm, 1.5mm 80% 20% 20% 0.3% 1.8℃ 1.9℃ Example 2 10mm, 1.0mm 75% 25% 18% 0.4% 1.9℃ 2.1℃

[0105] In summary, the magnetic particle concentration difference between the inlet and outlet ends of both embodiments (20% and 18%) is higher than the threshold of ≥15%, the overall porosity (0.3% and 0.4%) is less than 0.5%, and the axial temperature difference (1.8℃ and 1.9℃) at a heat flux density of 50kW / m² is less than 2.0℃, verifying the feasibility of the magnetically controlled phase change copper tube design. Embodiment 1 uses high latent heat paraffin and moderately magnetic Fe3O4, which is suitable for medium-temperature stable heat transfer scenarios in industrial waste heat recovery. Embodiment 2 uses low-melting-point fatty acid eutectic and small-particle-size NiFe2O4, which is more suitable for the low-temperature variable operating conditions required in cold chain logistics, demonstrating the material's superior performance. The selection and application scenarios were targeted. Through 1000 cycles of hot and cold cycling tests, the temperature difference change of both examples was ≤0.3℃ (1.8℃→1.9℃, 1.9℃→2.1℃), indicating that the dual-station magnetic field switching curing and vacuum-centrifugal impregnation process can effectively suppress particle agglomeration and structural deterioration, ensuring long-term stability. Example 1 achieved efficient heat transfer in a large pipe diameter (20mm), which is suitable for high power density steady-state scenarios. Example 2 showed excellent adaptability to changing operating conditions (temperature difference fluctuation of 0.5℃) in a small pipe diameter (10mm), verifying the universality of the magnetron sputtering process under different sizes and operating conditions.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. 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 some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. 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 scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for manufacturing a high-efficiency heat transfer copper tube with magnetically controlled phase change, applicable to a high-efficiency heat transfer copper tube with magnetically controlled phase change, characterized in that, The copper tube comprises: a copper tube matrix and a magnetic phase change composite slurry; The copper tube substrate is made of oxygen-free copper with a purity of ≥99.9%, with a tube diameter of 5-50mm and a wall thickness of 0.5-3mm, and has an axially through inner cavity; The inner wall of the copper tube substrate is provided with a gradient porous microstructure, the pore size of which increases from the inner wall to the outer wall in a gradient of 50nm-2μm, and the porosity is 30%-60%. The gradient porous microstructure is filled with a magnetic phase change composite slurry, which is composed of magnetic nanoparticles and phase change materials. The magnetic nanoparticles are distributed in a gradient along the axial direction of the copper tube. The particle mass concentration at the inlet end is ≥15% higher than that at the outlet end. The overall porosity is <0.5%. The axial heat transfer temperature difference is ≤2.0℃ at a heat flux density of 50kW / m². The specific steps of this preparation process are as follows: S100, Gradient Porous Matrix Preparation: Oxygen-free copper powder is loaded into a mold, an axial gradient magnetic field is applied, and gradient sintering is carried out in a hydrogen atmosphere to form a porous structure with a pore size increasing from 50nm to 2μm. S200, Magnetic Dynamic Filling Slurry: The magnetic phase change composite slurry is heated to 60-80℃ and the viscosity is reduced to 30-100mPa.s. It is then injected into the copper tube at a speed of 3-8mm / s under an axial gradient magnetic field, and the magnetic particles migrate directionally toward the inlet end. S300, Dual-station magnetic field switching curing: The copper tube is transferred to the first station by a mechanical conveying device, and a high-frequency alternating magnetic field is applied to make the magnetic nanoparticles generate vortex motion to break up the agglomerates. The copper tube is then transferred to the second station, where an axial static magnetic field is applied to drive the copper tube to rotate around the axis and simultaneously heat up to the curing point of the phase change material. S400, Magnetically Controlled Vacuum-Centrifugal Composite Impregnation: Place the copper tube in the vacuum chamber to completely immerse it in the injected molten slurry, apply a radial gradient magnetic field, maintain for 5 minutes, and remove residual air bubbles.

2. The process for preparing a high-efficiency heat transfer copper tube with magnetically controlled phase transition according to claim 1, characterized in that, In S100, the intensity configuration of the axial gradient magnetic field must satisfy the following: The magnetic field strength at the entrance is 0.5T to 1.0T; The magnetic field strength at the exit end is 0.1T to 0.5T; The slope of the magnetic field gradient is from 0.3T / m to 0.8T / m.

3. The process for preparing a high-efficiency heat transfer copper tube with magnetically controlled phase transition according to claim 1, characterized in that, In S300, the parameters of the high-frequency alternating magnetic field are: Frequency range: 50Hz to 200Hz; Magnetic field strength ranges from 0.3 T to 0.8 T; The duration of action is 30 to 120 seconds. Furthermore, the processing temperature is controlled at 5-15℃ below the melting point of the phase change material.

4. The process for manufacturing a high-efficiency heat transfer copper tube with magnetized phase change according to claim 1, characterized in that, In S300, the parameters for the rotation of the axis are: Rotation speed from 1000 rpm to 6000 rpm; The direction of centrifugal acceleration is parallel to the direction of the axial static magnetic field. The static magnetic field strength ranges from 0.2T to 0.6T.

5. The process for preparing a high-efficiency heat transfer copper tube with a magnetically controlled phase change according to claim 1, characterized in that, In the S400 process, a porous copper tube substrate is placed in a vacuum chamber, and the pressure is evacuated to 10-100 Pa for 15-30 minutes to extract pore gas.

6. The process for preparing a high-efficiency heat transfer copper tube with a magnetically controlled phase transition according to claim 1, characterized in that, In the S300, the first station integrates an alternating magnetic field generator and a temperature control device, and the second station integrates a static magnetic field coil and a centrifugal rotary table.

7. The process for preparing a high-efficiency heat transfer copper tube with a magnetically controlled phase transition according to claim 1, characterized in that, In the magnetic phase change composite slurry, the organic phase change material matrix is ​​at least one of paraffin, fatty acid or eutectic salt, accounting for 70% to 94% of the magnetic phase change composite slurry, and the magnetic nanoparticles are at least one of Fe3O4, Co or NiFe2O4, with a particle size of 10-100 nm, accounting for 15% to 35% of the magnetic phase change composite slurry.

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