Photo-thermal conversion phase change thermal insulation flexible composite pipe and preparation method thereof

Abstract

This invention provides a photothermal conversion phase change insulation flexible composite pipe and its preparation method, comprising a base pipe layer and, from the inside out, an adhesive transition layer, a phase change insulation layer, a photothermal conversion layer, and a protective layer. The base pipe layer consists of an inner lining layer, a double-layer fiber reinforcement layer, and an outer protective layer. The adhesive transition layer is a mixture of ethylene-vinyl acetate copolymer and silane coupling agent. The phase change insulation layer uses modified melamine foam as a skeleton, loaded with erythritol phase change material and nano-silica. The photothermal conversion layer is a composite layer of polydopamine and waterborne polyurethane. The protective layer is a polyvinyl fluoride layer. The preparation method includes extrusion winding of the base pipe layer, thermal spraying of the adhesive transition layer, vacuum impregnation and hot pressing of the phase change insulation layer, spraying and drying of the photothermal conversion layer, and extrusion cooling and shaping of the protective layer. This invention achieves a combination of photothermal conversion energy storage and flexible insulation, with strong layer bonding, good flexibility, high mechanical strength, low heat loss, energy saving and environmental protection, and is suitable for various scenarios such as centralized heating and industrial steam transportation.

Description

Technical Field

[0001] This invention belongs to the field of composite tube technology, specifically relating to a photothermal conversion phase change heat-insulating flexible composite tube. Background Technology

[0002] Long-distance heating pipelines, as the core transmission and distribution link of urban centralized heating systems, are often laid overhead or on the ground due to terrain limitations, resulting in significant heat loss due to long-term exposure to the natural environment. Traditional insulation materials such as aluminum silicate wool, rock wool, and rubber-plastic sponge have certain thermal insulation properties, but they have drawbacks such as inability to utilize renewable energy sources, high rigidity and poor adaptability, and easy aging after long-term use, making it difficult to meet the actual needs of energy conservation and emission reduction.

[0003] The current insulation technologies used for long-distance heating pipelines have the following main shortcomings: 1) Structural aspects: Traditional insulation measures generally involve directly wrapping the insulation material onto the base pipe. This split design results in a weak bond between the insulation layer and the pipe substrate, making it prone to detachment and delamination over long-term operation, forming thermal bridges and severely weakening the insulation effect; 2) Material aspects: Traditional materials such as aluminum silicate and rock wool have poor flexibility and are difficult to tightly wrap complex pipe fittings such as elbows and valves, making them prone to cracking under thermal stress or mechanical displacement; their inherent hydrophilicity makes them easy to absorb moisture in humid environments, leading to a sharp and irreversible increase in thermal conductivity; long-term exposure to outdoor environments... 3) Functionally: Existing materials can only provide passive insulation, which is a static loss control and cannot be coupled with intermittent energy sources such as solar energy and off-peak electricity. They also cannot dynamically adjust thermal resistance according to demand, and have obvious shortcomings in terms of intelligence and energy interconnection. 4) Economically: In order to meet higher insulation requirements, it is often necessary to significantly increase the thickness of the insulation layer, which brings challenges in terms of space, load and cost. Although the initial investment is low, the economic efficiency of the whole life cycle is often insufficient due to its poor durability, frequent maintenance and large heat loss. Therefore, it is necessary to make improvements in order to solve the above technical problems. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a photothermal conversion phase change insulation flexible composite pipe and its preparation method. Outside the base pipe layer, which consists of an inner lining layer, a double-layer fiber reinforcement layer, and an outer protective layer, an adhesive transition layer consisting of a mixture of ethylene-vinyl acetate copolymer and silane coupling agent is sequentially arranged from the inside out. This includes a phase change insulation layer with modified melamine foam as the skeleton, loaded with erythritol phase change material and nano-silica; a photothermal conversion layer formed by a composite layer of polydopamine and waterborne polyurethane; and a protective layer formed by a polyvinyl fluoride layer. This achieves a combination of photothermal conversion energy storage and flexible insulation, improves the bonding strength between the insulation layer and the base pipe, reduces pipe heat loss, enhances the pipe's adaptability to complex fittings and terrain, and utilizes renewable solar energy to improve the energy efficiency and intelligence level of the heating system.

[0005] The technical solution adopted in this invention is a photothermal conversion phase change insulation flexible composite pipe, comprising a base pipe layer and, from the inside out, an adhesive transition layer, a phase change insulation layer, a photothermal conversion layer, and a protective layer disposed outside the base pipe layer. The adhesive transition layer is a mixed layer composed of ethylene-vinyl acetate copolymer and silane coupling agent, and the phase change insulation layer, used for energy storage and heat conduction insulation, is bonded and fixed to the outer wall of the base pipe layer through the adhesive transition layer. The photothermal conversion layer is a composite layer formed by polydopamine and waterborne polyurethane to absorb solar radiation and convert it into heat energy, and the photothermal conversion layer is fixed to the outer wall of the phase change insulation layer. The protective layer is made of polyvinyl fluoride material with weather resistance, wear resistance, and corrosion resistance.

[0006] The base tube layer comprises, from the inside out, an inner liner, a reinforcing layer I, a reinforcing layer II, and an outer protective layer. The inner liner is formed by extruding molten polymer particles. The reinforcing layers I and II are both made by cross-winding one or more of polyester fibers, aramid fibers, glass fibers, and carbon fibers. The outer protective layer is made of HDPE or PERT, which is extruded in a molten state and encapsulates the reinforcing layer II inside it.

[0007] Furthermore, the polymer is one or more of PE, PERT, PVDF, and PA.

[0008] Furthermore, the mass ratio of polydopamine in the photothermal conversion layer is 30% to 40%.

[0009] A method for preparing a photothermal conversion phase change insulated flexible composite tube, comprising the following steps: 1) Preparation of the base pipe layer: First, one or more high molecular weight polymer granules selected from PE, PERT, PVDF, and PA are melted and extruded at 200°C to form an inner liner layer; then, one of polyester fiber, glass fiber, and carbon fiber is cross-wound to the outside of the inner liner layer using a winding device, and after two layers are wound, reinforcement layer I and reinforcement layer II are formed respectively; finally, HDPE or PERT granules are melted and extruded again at 200°C using an extruder to coat the outer wall of reinforcement layer II to form an outer protective layer, thus completing the preparation of the base pipe layer; 2) Coating of the adhesive transition layer: The mixture of ethylene-vinyl acetate copolymer and silane coupling agent in a certain proportion is coated on the outer wall of the outer protective layer at a temperature of 120℃~140℃ to form an adhesive transition layer; 3) Composite phase change insulation layer: Modified melamine foam is used as the supporting skeleton, erythritol phase change material is used and nano-silica is added as an auxiliary modifier, and a phase change insulation preform is formed by vacuum impregnation. Then, the phase change insulation preform is wrapped around the outer surface of the bonding transition layer and hot-pressed at a temperature of 80℃~100℃ and a pressure of 0.3~0.5MPa to make it tightly bonded to the bonding transition layer to form a phase change insulation layer; 4) Coating of the photothermal conversion layer: The composite emulsion of polydopamine and waterborne polyurethane is uniformly sprayed onto the outer surface of the phase change insulation layer under a pressure of 0.2-0.4 MPa and a spray distance of 15-25 cm. After curing, a photothermal conversion layer is formed, wherein the mass ratio of polydopamine is 30%-40%. Then, it is dried at a temperature of 60-80℃ for 3-4 hours to form a photothermal conversion layer with a thickness of 1-3 mm. 5) Forming of the protective layer: Polyvinyl fluoride particles are melted and extruded at 200-220℃ to uniformly coat the outer surface of the photothermal conversion layer. After cooling and shaping, a protective layer with a thickness of 0.8-2mm is formed, resulting in a flexible composite tube for solar photothermal conversion.

[0010] In step 2) above, the thickness of the adhesive transition layer is 0.5mm to 2mm.

[0011] In step 3) above, the purity of the erythritol is ≥99%, the particle size of the nano-silica is 30-80nm, the mass ratio of the erythritol to the nano-silica is 98:2, and the thickness of the phase change insulation layer is 10-15mm.

[0012] In step 3) above, the vacuum impregnation method is as follows: melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.4-0.6 kPa and maintained for 10-15 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 20-45 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation preform.

[0013] Advantages of this invention compared to existing technologies: 1. This technical solution combines a phase change insulation layer with a photothermal conversion layer. The photothermal conversion layer converts solar energy into thermal energy and transfers it to the phase change insulation layer for storage. The phase change insulation layer utilizes the energy storage characteristics of erythritol phase change material to achieve the slow release of thermal energy. Combined with passive insulation, it achieves a combination of active heat storage and passive insulation, significantly reducing pipeline heat loss. At the same time, the phase change insulation layer uses modified melamine foam as a skeleton, which is both lightweight and has high thermal insulation properties, further improving the insulation effect. 2. This technical solution uses an adhesive transition layer composed of ethylene-vinyl acetate copolymer and silane coupling agent. Through interface modification, the bonding strength between the phase change insulation layer and the base pipe layer is improved, avoiding the problems of traditional insulation layer detachment and delamination, eliminating the formation of thermal bridges, and ensuring stable long-term insulation effect. 3. This technical solution combines a flexible phase change insulation layer, a photothermal conversion layer, and a protective layer on the basis of the base pipe layer to improve the overall flexibility. It can tightly wrap complex pipe fittings such as elbows and valves, adapt to the thermal stress deformation and mechanical displacement of the pipeline, avoid cracking and damage, and is suitable for long-distance laying needs in various terrains such as overhead and ground laying. 4. The base pipe layer of this technical solution is equipped with a double fiber reinforcement layer, which greatly improves the pressure resistance and tensile mechanical properties of the composite pipe and meets the mechanical requirements of long-distance heating. The outer protective layer is made of polyvinyl fluoride, which has excellent weather resistance, wear resistance and corrosion resistance, resists outdoor ultraviolet rays, high and low temperatures, acid and alkali media and other erosion. The layers are tightly bonded, without powdering or aging problems, thus extending the service life of the composite pipe. 5. This technical solution utilizes the high-efficiency photothermal conversion performance of polydopamine to convert solar renewable energy into thermal energy, achieving energy coupling with the heating system, reducing traditional energy consumption, and meeting the requirements of energy conservation and consumption reduction; the composite pipe has stable insulation effect and low maintenance frequency throughout its entire life cycle, without the need to significantly increase the insulation layer thickness, reducing space occupation and construction costs, extending the service life, and significantly improving economic performance. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the photothermal conversion phase change heat-insulating flexible composite tube of the present invention; Figure 2 This is a cross-sectional view of the end face of the photothermal conversion phase change insulating flexible composite tube of the present invention. Detailed Implementation

[0015] The following will be based on embodiments of the present invention. Figure 1-2 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] It should be noted that, unless otherwise stated herein, the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0017] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0018] The photothermal conversion phase change insulation flexible composite tube includes a base tube layer 1 and, from the inside out, an adhesive transition layer 2, a phase change insulation layer 3, a photothermal conversion layer 4, and a protective layer 5, all disposed outside the base tube layer 1. The adhesive transition layer 2 is a mixed layer composed of ethylene-vinyl acetate copolymer and a silane coupling agent. Utilizing the high adhesion of the ethylene-vinyl acetate copolymer and the interfacial modification effect of the silane coupling agent, a strong bond is achieved between the phase change insulation layer 3 and the base tube layer 1, preventing delamination. Furthermore, the phase change insulation layer 3, used for energy storage and heat conduction insulation, is bonded and fixed to the outer wall of the base tube layer 1 through the adhesive transition layer 2, achieving heat storage and slow release, and dynamic regulation. To control pipeline temperature, the photothermal conversion layer 4 is a composite layer formed by polydopamine and water-based polyurethane to absorb solar radiation and convert it into heat energy. The mass ratio of polydopamine is 30% to 40%. Polydopamine has excellent solar radiation absorption performance, while water-based polyurethane is used to improve the flexibility and adhesion of the layer. The photothermal conversion layer 4 is fixed to the outer wall of the phase change insulation layer 3, converting solar energy into heat energy and transferring it to the phase change insulation layer 3 for storage and utilization. The protective layer 5 is made of polyvinyl fluoride material with weather resistance, wear resistance and corrosion resistance, providing an outer layer of protection for the composite pipe and resisting the erosion of the outdoor natural environment. The specific structure of the base pipe layer 1 is as follows: The base pipe layer 1 includes, from the inside out, an inner liner layer 1-1, a reinforcing layer I 1-2, a reinforcing layer II 1-3, and an outer protective layer 1-4. The inner liner layer 1-1 is formed by extruding molten polymer particles to ensure the corrosion resistance and media compatibility of the base pipe. The reinforcing layers I 1-2 and II 1-3 are both made of one or more of polyester fibers, aramid fibers, glass fibers, and carbon fibers, which are cross-wound to improve the mechanical strength and pressure resistance of the base pipe layer and meet the mechanical requirements of long-distance laying. The outer protective layer 1-4 is made of HDPE or PERT, which is extruded in a molten state and encapsulates the reinforcing layer II 1-3 inside it, to provide protection for the reinforcing layer II 1-3 and prevent the fiber layer from being eroded by the outside. The polymer of the base pipe layer 1 is one or more of PE, PERT, PVDF, and PA.

[0019] A method for preparing a photothermal conversion phase change insulated flexible composite tube, comprising the following steps: 1) Preparation of the base tube layer 1: First, one or more high molecular weight polymer granules selected from PE, PERT, PVDF, and PA are melted and extruded at 200℃ to form the inner liner layer 1-1, ensuring that the wall thickness of the inner liner layer 1-1 is uniform; then, one of polyester fiber, glass fiber, and carbon fiber is cross-wound to the outside of the inner liner layer 1-1 using a winding device. After winding two layers, reinforcement layer I1-2 and reinforcement layer II1-3 are formed respectively. During the winding process, the tension is controlled to ensure tight adhesion; finally, HDPE or PERT granules are melted and extruded again at 200℃ using an extruder, so that they cover the outer wall of reinforcement layer II1-3 to form the outer protective layer 1-4, completing the preparation of the base tube layer 1; the inner diameter of the base tube layer 1 ranges from 50 to 2000 mm, and the wall thickness is 5 to 20 mm; 2) Coating of adhesive transition layer 2: The mixture of ethylene-vinyl acetate copolymer and silane coupling agent at a ratio of 98.8:1.2 is coated on the outer wall of outer protective layer 1-4 at a temperature of 120℃~140℃ and allowed to cool naturally to room temperature to form adhesive transition layer 2 with a thickness of 0.5mm~2mm. 3) Composite of phase change insulation layer 3: Modified melamine foam is used as the supporting skeleton, erythritol phase change material is used and nano-silica is added as an auxiliary modifier, and a phase change insulation preform is formed by vacuum impregnation. The purity of the erythritol is ≥99%, the particle size of the nano-silica is 30-80nm, the mass ratio of erythritol to nano-silica is 98:2, and the thickness of the phase change insulation layer 3 is 10-15mm. Then, the phase change insulation preform is wound around the outer surface of the bonding transition layer 2 and hot-pressed at a temperature of 80℃~100℃ and a pressure of 0.3~0.5MPa to make it tightly bonded to the bonding transition layer 2, forming a phase change insulation layer 3 with a thickness of 10-15mm. The vacuum impregnation method is as follows: Melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.4-0.6 kPa and maintained for 10-15 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 20-45 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation prefabricated body. 4) Coating of photothermal conversion layer 4: Polydopamine and waterborne polyurethane composite emulsion are uniformly sprayed onto the outer surface of phase change insulation layer 3 under a pressure of 0.2-0.4 MPa and a spray distance of 15-25 cm. After curing, a photothermal conversion layer is formed, wherein the mass ratio of polydopamine is 30%-40%. Then, it is dried at a temperature of 60-80℃ for 3-4 hours to form a photothermal conversion layer 4 with a thickness of 1-3 mm. 5) Forming of protective layer 5: Polyvinyl fluoride particles are melted and extruded at 200-220℃ to uniformly coat the outer surface of the photothermal conversion layer 4. After cooling and shaping, a protective layer 5 with a thickness of 0.8-2mm is formed, resulting in a flexible composite tube for solar photothermal conversion.

[0020] Example 1 A method for preparing a photothermal conversion phase change insulated flexible composite tube, comprising the following steps: 1) Preparation of the base pipe layer 1: First, PE granules are melted and extruded at 200℃ to form the inner lining layer 1-1, ensuring that the wall thickness of the inner lining layer 1-1 is uniform; then, one of polyester fiber, glass fiber, and carbon fiber is cross-wound to the outside of the inner lining layer 1-1 using a winding device. After two layers are wound, reinforcement layer I1-2 and reinforcement layer II1-3 are formed respectively. During the winding process, the tension is controlled to ensure tight adhesion; finally, HDPE granules are melted and extruded again at 200℃ using an extruder, so that they cover the outer wall of reinforcement layer II1-3 to form the outer protective layer 1-4, completing the preparation of the base pipe layer 1; the inner diameter of the base pipe layer 1 is 200mm and the wall thickness is 6mm; 2) Coating of adhesive transition layer 2: The mixture of ethylene-vinyl acetate copolymer and silane coupling agent at a ratio of 98.8:1.2 is coated on the outer wall of outer protective layer 1-4 at a temperature of 120°C and allowed to cool naturally to room temperature to form adhesive transition layer 2 with a thickness of 0.8 mm. 3) Composite of phase change insulation layer 3: Modified melamine foam is used as the supporting skeleton, erythritol phase change material is used and nano-silica is added as an auxiliary modifier, and a phase change insulation preform is formed by vacuum impregnation. The purity of the erythritol is ≥99%, the particle size of the nano-silica is 30nm, the mass ratio of erythritol to nano-silica is 98:2, and the thickness of the phase change insulation layer 3 is 10mm. Then, the phase change insulation preform is wound around the outer surface of the bonding transition layer 2 and hot-pressed at a temperature of 80℃~100℃ and a pressure of 0.3MPa to make it tightly bonded to the bonding transition layer 2, forming a phase change insulation layer 3 with a thickness of 10mm. The vacuum impregnation method is as follows: Melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.4 kPa and maintained for 10 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 20 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation prefabricated body. 4) Coating of photothermal conversion layer 4: Polydopamine and waterborne polyurethane composite emulsion are uniformly sprayed onto the outer surface of phase change insulation layer 3 under a pressure of 0.2 MPa and a spray distance of 18 cm. After curing, a photothermal conversion layer is formed. The mass ratio of polydopamine is 30% to 40%. Then, it is dried at a temperature of 60 to 80°C for 3 hours to form a photothermal conversion layer 4 with a thickness of 1 mm. 5) Forming of protective layer 5: Polyvinyl fluoride particles are melted and extruded at 200°C to uniformly coat the outer surface of the photothermal conversion layer 4. After cooling and shaping, a protective layer 5 with a thickness of 1mm is formed, resulting in a flexible composite tube for solar photothermal conversion.

[0021] Example 2 A method for preparing a photothermal conversion phase change insulated flexible composite tube, comprising the following steps: 1) Preparation of the base tube layer 1: First, the PERT and PVDF mixed granules are melted and extruded at 200℃ to form the inner liner layer 1-1, ensuring that the wall thickness of the inner liner layer 1-1 is uniform; then, one of polyester fiber, glass fiber, and carbon fiber is cross-wound to the outside of the inner liner layer 1-1 using a winding device. After winding two layers, reinforcement layer I1-2 and reinforcement layer II1-3 are formed respectively. During the winding process, the tension is controlled to ensure tight adhesion; finally, the PERT granules are melted and extruded again at 200℃ through an extruder to coat the outer wall of reinforcement layer II1-3 to form the outer protective layer 1-4, completing the preparation of the base tube layer 1; the inner diameter of the base tube layer 1 is 1000mm and the wall thickness is 12mm; 2) Coating of adhesive transition layer 2: The mixture of ethylene-vinyl acetate copolymer and silane coupling agent at a ratio of 98.8:1.2 is coated on the outer wall of outer protective layer 1-4 at a temperature of 130°C and allowed to cool naturally to room temperature to form adhesive transition layer 2 with a thickness of 1 mm. 3) Composite of phase change insulation layer 3: Modified melamine foam is used as the supporting skeleton, erythritol phase change material is used and nano-silica is added as an auxiliary modifier, and a phase change insulation preform is formed by vacuum impregnation. The purity of the erythritol is ≥99%, the particle size of the nano-silica is 50nm, the mass ratio of erythritol to nano-silica is 98:2, and the thickness of the phase change insulation layer 3 is 12mm. Then, the phase change insulation preform is wound around the outer surface of the bonding transition layer 2 and hot-pressed at a temperature of 80℃~100℃ and a pressure of 0.4MPa to make it tightly bonded to the bonding transition layer 2, forming a phase change insulation layer 3 with a thickness of 12mm. The vacuum impregnation method is as follows: Melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.5 kPa and maintained for 12 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 30 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation prefabricated body. 4) Coating of photothermal conversion layer 4: Polydopamine and waterborne polyurethane composite emulsion are uniformly sprayed onto the outer surface of phase change insulation layer 3 under a pressure of 0.3 MPa and a spray distance of 20 cm. After curing, a photothermal conversion layer is formed. The mass ratio of polydopamine is 30% to 40%. Then, it is dried at a temperature of 60 to 80°C for 3.5 hours to form a photothermal conversion layer 4 with a thickness of 2 mm. 5) Forming of protective layer 5: Polyvinyl fluoride particles are melted and extruded at 210°C to uniformly coat the outer surface of the photothermal conversion layer 4. After cooling and shaping, a protective layer 5 with a thickness of 1.5 mm is formed, resulting in a flexible composite tube for solar photothermal conversion.

[0022] Example 3 A method for preparing a photothermal conversion phase change insulated flexible composite tube, comprising the following steps: 1) Preparation of the base tube layer 1: First, one or more high molecular weight polymer granules in PA are melted and extruded at 200℃ to form the inner liner layer 1-1, ensuring that the wall thickness of the inner liner layer 1-1 is uniform; then, one of polyester fiber, glass fiber, and carbon fiber is cross-wound to the outside of the inner liner layer 1-1 using a winding device. After winding two layers, reinforcement layer I1-2 and reinforcement layer II1-3 are formed respectively. During the winding process, the tension is controlled to ensure tight adhesion; finally, HDPE or PERT granules are melted and extruded again at 200℃ using an extruder, so that they are coated on the outer wall of reinforcement layer II1-3 to form the outer protective layer 1-4, completing the preparation of the base tube layer 1; the inner diameter of the base tube layer 1 is 1800mm and the wall thickness is 20mm; 2) Coating of adhesive transition layer 2: The mixture of ethylene-vinyl acetate copolymer and silane coupling agent at a ratio of 98.8:1.2 is coated on the outer wall of outer protective layer 1-4 at a temperature of 140°C and allowed to cool naturally to room temperature to form adhesive transition layer 2 with a thickness of 2 mm. 3) Composite of phase change insulation layer 3: Modified melamine foam is used as the supporting skeleton, erythritol phase change material is used and nano-silica is added as an auxiliary modifier, and a phase change insulation preform is formed by vacuum impregnation. The purity of the erythritol is ≥99%, the particle size of the nano-silica is 70nm, the mass ratio of erythritol to nano-silica is 98:2, and the thickness of the phase change insulation layer 3 is 15mm. Then, the phase change insulation preform is wound around the outer surface of the bonding transition layer 2 and hot-pressed at a temperature of 100℃ and a pressure of 0.5MPa to make it tightly bonded to the bonding transition layer 2, forming a phase change insulation layer 3 with a thickness of 15mm. The vacuum impregnation method is as follows: melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.6 kPa and maintained for 15 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 45 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation prefabricated body. 4) Coating of photothermal conversion layer 4: Polydopamine and waterborne polyurethane composite emulsion are uniformly sprayed onto the outer surface of phase change insulation layer 3 under a pressure of 0.4 MPa and a spray distance of 25 cm. After curing, a photothermal conversion layer is formed. The mass ratio of polydopamine is 30% to 40%. Then, it is dried at 80°C for 4 hours to form a photothermal conversion layer 4 with a thickness of 3 mm. 5) Forming of protective layer 5: Polyvinyl fluoride particles are melted and extruded at 220°C to uniformly coat the outer surface of the photothermal conversion layer 4. After cooling and shaping, a protective layer 5 with a thickness of 2mm is formed, resulting in a flexible composite tube for solar photothermal conversion.

[0023] This invention achieves efficient insulation and solar energy utilization of heating pipelines through a multi-layer coaxial integrated design, combined with photothermal conversion and phase change energy storage technologies. Specific advantages are as follows: Stable structure and convenient construction: The multi-layer integrated design avoids delamination, the interlayer bonding strength is ≥1.2MPa, and no additional insulation layer is required during construction, improving installation efficiency by more than 40%. Photothermal-phase change synergistic energy saving: The average photothermal efficiency of the photothermal conversion layer 4 is ≥62%, which can efficiently utilize solar energy; the phase change insulation layer 3 has a high heat storage enthalpy (350-365J / g) and a low thermal conductivity (0.044-0.047W / m·K), which reduces heat loss by more than 50% compared with traditional insulated pipes; Long-lasting and durable: The phase change insulation layer 3 enhances thermal cycling stability through auxiliary modifiers and modified skeletons, with latent heat loss ≤5% after 200 thermal cycles; the protective layer 5 is weather-resistant and corrosion-resistant, adaptable to environments from 30℃ to 150℃, and has a service life of more than 15 years. High flexibility and adaptability: The phase change insulation layer 3 is supported by flexible modified melamine foam, and the pipe can be bent to a curvature radius of ≤10cm, adapting to complex terrain and pipe fittings; it is compatible with different pipe diameters of 50-2000mm and is suitable for various scenarios such as centralized heating and industrial steam transportation.

[0024] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0025] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A photothermal conversion phase change insulating flexible composite tube, characterized in that: The system includes a base tube layer (1) and, from the inside out, an adhesive transition layer (2), a phase change insulation layer (3), a photothermal conversion layer (4), and a protective layer (5) arranged sequentially outside the base tube layer (1). The adhesive transition layer (2) is a mixed layer composed of ethylene-vinyl acetate copolymer and silane coupling agent. The phase change insulation layer (3), which is used for energy storage and heat conduction insulation, is bonded and fixed to the outer wall of the base tube layer (1) through the adhesive transition layer (2). The photothermal conversion layer (4) is a composite layer formed by polydopamine and waterborne polyurethane to absorb solar radiation and convert it into heat energy. The photothermal conversion layer (4) is fixed to the outer wall of the phase change insulation layer (3). The protective layer (5) is made of polyvinyl fluoride material with weather resistance, wear resistance, and corrosion resistance.

2. The photothermal conversion phase change insulating flexible composite tube according to claim 1, characterized in that: The base tube layer (1) includes, from the inside out, an inner liner layer (1-1), a reinforcing layer I (1-2), a reinforcing layer II (1-3), and an outer protective layer (1-4). The inner liner layer (1-1) is formed by extruding molten polymer particles. The reinforcing layers I (1-2) and II (1-3) are both made by cross-winding one or more of polyester fibers, aramid fibers, glass fibers, and carbon fibers. The outer protective layer (1-4) is made of HDPE or PERT that is extruded in a molten state and encapsulates the reinforcing layer II (1-3) inside it.

3. The photothermal conversion phase change insulating flexible composite tube according to claim 2, characterized in that: The polymer is one or more of PE, PERT, PVDF, and PA.

4. The photothermal conversion phase change insulating flexible composite tube according to claim 1, characterized in that: The mass ratio of polydopamine in the photothermal conversion layer (4) is 30% to 40%.

5. The method for preparing the photothermal conversion phase change insulating flexible composite tube according to claim 1, 2, 3, or 4, characterized in that: The preparation steps of the photothermal conversion phase change heat-insulating flexible composite tube are as follows: 1) Preparation of the base pipe layer (1): First, one or more high molecular polymer granules of PE, PERT, PVDF and PA are melted and extruded at 200°C to form an inner liner layer (1-1); then, one of polyester fiber, glass fiber and carbon fiber is cross-wound to the outside of the inner liner layer (1-1) using a winding device. After winding two layers, reinforcement layer I (1-2) and reinforcement layer II (1-3) are formed respectively; finally, HDPE or PERT granules are melted and extruded again at 200°C through an extruder to coat the outer wall of reinforcement layer II (1-3) to form an outer protective layer (1-4), thus completing the preparation of the base pipe layer (1); 2) Coating of the adhesive transition layer (2): The mixture of ethylene-vinyl acetate copolymer and silane coupling agent in a certain proportion is coated on the outer wall of the outer protective layer (1-4) at a temperature of 120℃~140℃ to form the adhesive transition layer (2). 3) Composite of phase change insulation layer (3): Modified melamine foam is used as the supporting skeleton. Erythritol phase change material is used and nano-silica auxiliary modifier is added. The phase change insulation preform is formed by vacuum impregnation. Then the phase change insulation preform is wrapped around the outer surface of the bonding transition layer (2) and hot-pressed at a temperature of 80℃~100℃ and a pressure of 0.3~0.5MPa to make it tightly bonded to the bonding transition layer (2) to form phase change insulation layer (3). 4) Coating of photothermal conversion layer (4): Polydopamine and waterborne polyurethane composite emulsion are uniformly sprayed onto the outer surface of phase change insulation layer (3) under a pressure of 0.2-0.4 MPa and a spray distance of 15-25 cm. After curing, a photothermal conversion layer is formed, wherein the mass ratio of polydopamine is 30%-40%. Then, it is dried at a temperature of 60-80℃ for 3-4 hours to form a photothermal conversion layer (4) with a thickness of 1-3 mm. 5) Forming of the protective layer (5): Polyvinyl fluoride particles are melted and extruded at 200-220°C, so that they are uniformly wrapped on the outer surface of the photothermal conversion layer (4). After cooling and shaping, a protective layer (5) with a thickness of 0.8-2 mm is formed, and a flexible composite tube for solar photothermal conversion is obtained.

6. The method for preparing the photothermal conversion phase change insulating flexible composite tube according to claim 5, characterized in that: In step 2) above, the thickness of the adhesive transition layer (2) is 0.5mm to 2mm.

7. The method for preparing the photothermal conversion phase change insulating flexible composite tube according to claim 6, characterized in that: In step 3) above, the purity of the erythritol is ≥99%, the particle size of the nano silica is 30-80nm, the mass ratio of the erythritol to the nano silica is 98:2, and the thickness of the phase change insulation layer (3) is 10-15mm.

8. The method for preparing the photothermal conversion phase change insulating flexible composite tube according to claim 5, characterized in that: In step 3) above, the vacuum impregnation method is as follows: melamine foam is placed in a vacuum chamber, then the vacuum degree is evacuated to 0.4-0.6 kPa and maintained for 10-15 minutes to fully degas. Then, without breaking the vacuum, a pre-melted and uniformly mixed erythritol and nano-silica melt is introduced to completely immerse the melamine foam. The vacuum environment is maintained and impregnated for 20-45 minutes. Finally, the vacuum is slowly broken, and atmospheric pressure is used to further press the melt into the tiny pores of the foam to form a phase change insulation preform.

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