Preparation method of TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material

Abstract

The present invention discloses a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material, specifically relating to the technical field of thermal storage. The method comprises the following steps: uniformly stirring a phase-change material powder and modified expanded graphite in a mass ratio of 6.5-7.2:1, followed by heating, mixing, vacuum drying, and directional pressing to obtain a high-density composite phase-change thermal storage material block. Beneficial Effects: The present invention provides a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material. The modified expanded graphite not only significantly improves thermal conductivity but also strengthens the material interface stability through bonding, fundamentally suppressing leakage of the phase-change medium during recycling. The preparation method has the characteristics of strong controllability of process parameters and high equipment compatibility, providing a reliable technical path for the large-scale production of high-performance phase-change energy storage materials.

Description

Technical Field

[0001] The patent of this invention relates to the field of heat storage technology, and specifically to a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change heat storage material. Background Art

[0002] Solar phase change thermal storage technology uses phase change materials (PCMs) to store heat in a thermal storage device, effectively alleviating the intermittent and unstable nature of solar energy. Currently, commonly used phase change thermal storage materials include two major categories: inorganic and organic. Among them, the existing patent application number CN202411393184.2, entitled "A Method for Preparing a Composite Phase Change Thermal Storage Material," discloses that phase change material powder and modified expanded graphite are stirred and uniformly mixed in a mass ratio of 7-7.5:1, followed by heating, mixing, vacuum drying, and briquetting to obtain a composite phase change thermal storage material block. The preparation method of the modified expanded graphite includes the following steps: (1) pretreatment; (2) mixing; (3) crushing and cooling; and (4) filtration and drying. It has good dispersion stability and strong lipophilicity, effectively improving the thermal conductivity of the modified expanded graphite, and has excellent heat transfer, thermal stability, and anti-leakage properties. However, the aforementioned phase-change thermal storage materials suffer from bottleneck issues such as discontinuous thermal conduction networks (i.e., thermal conductivity of only 8.93 W / (m·K)), weak interfacial bonding (i.e., leakage rate >1.5% after 1000 thermal cycles), and insufficient material density (i.e., leakage occurs when density ≥821 kg / m³) due to their single physical adsorption modification. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material, which significantly improves the heat conduction efficiency, enhances the material interface stability, and inhibits the leakage of the phase change medium during recycling.

[0004] The purpose of the present invention is implemented by the following technical solution: a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material, comprising the following steps: stirring and uniformly mixing phase change material powder and modified expanded graphite in a mass ratio of 6.5-7.2:1, then heating and mixing, vacuum drying and directional pressing to obtain a high-density composite phase change thermal storage material block;

[0005] The preparation method of the phase change material powder comprises the following steps: mixing 72-75 parts by weight of glyceryl behenate (BG), 14-15 parts of stearyl alcohol (SA), and 1.2-1.5 parts of nano-titanium dioxide in a water bath, stirring and mixing, then naturally cooling to room temperature to solidify, and finally grinding into a powder with a particle size of 120-160 μm, and sealing and storing;

[0006] The preparation method of the modified expanded graphite comprises the following steps:

[0007] (1) Pretreatment process: The graphite expansion powder is dried to completely remove the trace moisture adsorbed by the raw material, and then transferred to a muffle furnace at 820-880℃ and calcined for 53-58s in an oxygen-rich environment with an oxygen concentration of 95-98%. This allows the graphite intercalation compound to rapidly decompose and expand by up to 200-300 times, forming expanded graphite with a three-dimensional interconnected pore structure. Its porosity is ≥92% and its specific surface area is 200-250m² / g, providing an ideal carrier structure for subsequent nano-intercalation.

[0008] (2) Nano-intercalation mixing: The expanded graphite, titanium dioxide concentration of 0.02-0.05 mol / L oleic acid ethanol (OAE) solution and boron nitride nanosheets (BNNS) in step (1) are mixed, and the long-chain alkyl of the OAE molecule interacts with the π-π of the graphite surface to achieve directional intercalation of the nanosheets; then, magnetic-ultrasonic alternating stirring is performed at a temperature of 50-52°C for 25-28 minutes to allow the BNNS to intercalate along the graphite sheets at the nanoscale, forming a graphite / boron nitride heterostructure. In this process, the OAE solution acts as a dispersion medium, and its carboxylic acid groups can form hydrogen bonds with the edges of the graphite to ensure the stable anchoring of the BNNS, thereby obtaining a graphite / boron nitride material;

[0009] (3) Grafting: The graphite / boron nitride material of step (2), a titanium dioxide ethanol solution with a concentration of 0.15-0.2 mol / L, and a silane coupling agent (KH550) are mixed, and then the grafting reaction is carried out at a temperature of 55-58 ° C for 65-70 min. The aminosiloxane group of KH550 undergoes a condensation reaction with the hydroxyl group on the graphite surface, and Si-OB bonds are formed at the edge of BNNS to construct a three-dimensional cross-linked network. Subsequently, an ultrasonic treatment is carried out for 6-6.5 h to eliminate nanoaggregates and promote the extension and arrangement of the grafted molecular chains through the cavitation effect, and finally a dense organic-inorganic composite interface layer is formed on the graphite surface to obtain a mixed solution;

[0010] (4) Filtration and drying: The mixed solution in step (3) is filtered and then dried at 78-80° C. for 11-11.5 hours to obtain the modified expanded graphite with a particle size of 50-75 μm.

[0011] Furthermore, the stirring and mixing under water bath heating is specifically carried out under water bath heating conditions at a temperature of 82-84° C., stirring for 8.2-8.8 hours to achieve uniform mixing, wherein the stirring speed is 890-920 r / min.

[0012] Furthermore, the graphite expansion powder in step (1) has a particle size of 150-200 mesh and a purity of 97-98%; the graphite expansion powder is dried in a drying oven with a vacuum degree of ≤100 Pa at a constant temperature of 85-88°C for 13-14 hours.

[0013] Furthermore, in step (2), the mass ratio of expanded graphite, oleic acid ethanol solution and boron nitride nanosheets is 32-34:60-62:4-8, wherein the thickness of the boron nitride nanosheets is 5-8 nm and the aspect ratio is >200.

[0014] Furthermore, in step (2), the magnetic-ultrasonic alternating stirring is specifically as follows: magnetic stirring and ultrasonic stirring are performed alternately every 5-8 minutes, wherein the speed of magnetic stirring is 880-910 r / min, and the working condition parameters of ultrasonic stirring include: ultrasonic power is 223-354 W, and stirring speed is 880-910 r / min.

[0015] Furthermore, in step (3), the mass ratio of graphite / boron nitride material, titanium dioxide ethanol solution and silane coupling agent is 28-30:58-61:9-14; the conditions of ultrasonic treatment are: frequency of 220-256kHz, pulse duty cycle of 12-23%.

[0016] Furthermore, the specific conditions of the heating and mixing are: placing the uniformly mixed materials in an environment of 83-85° C., stirring once every 50 minutes, and continuing for 10-10.5 hours to obtain a mixed material.

[0017] Furthermore, each stirring time is 6-7 minutes, and the stirring speed is 850-880 r / min.

[0018] Furthermore, the vacuum drying is specifically as follows: placing the mixed material in a vacuum drying oven, heating and drying at a temperature of 82-84° C. and a vacuum degree of 9500-11500 Pa for 15.2-15.8 hours, and then naturally cooling to room temperature to obtain a composite phase change thermal storage material.

[0019] Furthermore, the directional briquetting is specifically as follows: the composite phase change thermal storage material is briquetted by a tabletting machine to obtain 800-860 kg / m 3 The composite phase change thermal storage material block is pressurized in three stages using a tablet press: the first stage: pre-pressing at 5.5-6.0 MPa for 20-25 seconds, the second stage: main pressing at 9.0-9.5 MPa for 38-43 seconds, and the third stage: stabilizing pressure at 7.0-7.5 MPa for 12-14 seconds.

[0020] Advantages of the present invention:

[0021] 1. The present invention provides a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material, wherein a three-dimensional composite reinforced structure is constructed through the synergistic effect of nano-intercalation and grafting; and a continuous heat-conducting network and a cross-linked interface are formed in the graphite skeleton by utilizing the directional intercalation of two-dimensional nanomaterials and the interfacial grafting of organic molecules, thereby effectively solving the problems of discontinuous heat-conducting paths of traditional materials and poor wettability of phase-change materials; the modified expanded graphite with the above-mentioned multi-level structural design not only significantly improves the heat conduction efficiency, but also strengthens the material interface stability through bonding, fundamentally suppressing the leakage of the phase-change medium during recycling.

[0022] 2. The present invention provides a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material. This breakthrough is achieved through the synergistic modification technology of BNNS directional intercalation and KH550 grafting: BNNS with an aspect ratio of >200 are interspersed in the gaps between EG layers to construct a three-dimensional continuous thermally conductive heterojunction. The Si-OB / graphite bond bridging effect of KH550 is combined to strengthen the interfacial bonding, thereby increasing the thermal conductivity to 9.58 W / (m·K), a 7.3% increase compared to the existing patent. Simultaneously, a three-stage pressurization process is used to optimize the material's compactness, increasing the density to 860 kg / m³ (porosity ≤5%). Chemical bonding is used to suppress leakage of the phase-change medium under thermal cycling, reducing the leakage rate to 0.5% after 1000 cycles of heat storage and release (a 74.7% reduction compared to the existing patent). This technology uses a synergistic strategy of nano-enhancement and interface bonding to overcome the technical barriers of thermal path breakage, nano-agglomeration and unstable physical adsorption in traditional EG modification, and realizes a composite phase change thermal storage material with high thermal conductivity (9.58 W / (m·K)), ultra-low leakage (≤0.5%) and long-term stability.

[0023] 3. The present invention provides a method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material. It adopts a new process system that combines heating mixing with three-stage pressurization molding, accurately controls the phase transition process of the material, and realizes the uniform distribution and directional arrangement of the nano-reinforced phase in the matrix; adopts an alternating stirring mode and a multi-stage pressurization process to overcome the technical difficulties in the densification molding of high-porosity materials, ensuring the integrity of the composite material structure and the consistency of performance; the preparation method has the characteristics of strong controllability of process parameters and high equipment compatibility, providing a reliable technical path for the large-scale production of high-performance phase-change energy storage materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a flow chart of TiO2-BG-SA prepared in Example 1 of the present invention.

[0026] Figure 2 This is a flow chart of preparing CEG-BNNS according to Example 1 of the present invention.

[0027] Figure 3 This is a flow chart of preparing TiO2-BG-SA / CEG-BNNS in Example 1 of the present invention.

[0028] Figure 4 Actual photos of EG and CEG-BNNS after preprocessing.

[0029] Figure 5 Contact diagrams of EG and CEG-BNNS sheets with water and oil, respectively.

[0030] Figure 6 Fourier transform infrared spectra of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG.

[0031] Figure 7 XRD diffraction patterns of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG.

[0032] Figure 8 These are photos of the appearance of composite phase change thermal storage material blocks with different densities after 120 cycles of heat storage and release.

[0033] Figure 9 These are SEM images of TiO2-BG-SA / EG in Comparative Example 1, CEG-BNNS in Example 1, and TiO2-BG-SA / CEG-BNNS in Example 1.

[0034] Figure 10 It is a heat storage / release flow chart; (a) is the heat storage flow chart, and (b) is the heat release flow chart.

[0035] Figure 11 (a) is the heat storage temperature change curve, and (b) is the heat release temperature change curve. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below by way of examples.

[0037] Example 1: A method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material, comprising the following steps:

[0038] like Figure 1 As shown, the preparation method of phase change material powder (TiO2-BG-SA) includes the following steps: stirring and mixing 720g of BG, 140g of SA and 12g of TiO2 in a water bath at a temperature of 82-84°C, stirring for 8.2-8.8h to mix them evenly, wherein the stirring speed is 890-920r / min, then naturally cooling to room temperature to solidify, and finally grinding into powder with a particle size of 120-160μm and sealing for storage.

[0039] like Figure 2 As shown, the preparation method of modified expanded graphite (CEG-BNNS) includes the following steps:

[0040] (1) Pretreatment process: The graphite expansion powder is dried and then transferred to a muffle furnace at 820-880℃ and calcined for 53-58s in an oxygen-rich environment with an oxygen concentration of 95-98% to form expanded graphite (EG) with a three-dimensional interconnected pore structure, a porosity of ≥92%, and a specific surface area of 200-250m² / g; the particle size of the graphite expansion powder is 150-200 mesh and the purity is 97-98%; the drying conditions of the graphite expansion powder are constant temperature drying at 85-88℃ for 13-14h in a drying oven with a vacuum degree of ≤100Pa.

[0041] (2) Nano-intercalation mixing: 100 g of expanded graphite, 190 g of oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02-0.05 mol / L, and 18.75 g of boron nitride nanosheets (BNNS) in step (1) were mixed, and then magnetic-ultrasonic alternating stirring was performed for 25-28 min at a temperature of 50-52 ° C to obtain a graphite / boron nitride material; wherein the thickness of the boron nitride nanosheets was 5-8 nm and the aspect ratio was >200; the magnetic-ultrasonic alternating stirring was specifically as follows: magnetic stirring and ultrasonic stirring were alternately performed every 5-8 min, wherein the speed of magnetic stirring was 880-910 r / min, and the working condition parameters of ultrasonic stirring included: ultrasonic power of 223-354 W and stirring speed of 880-910 r / min.

[0042] (3) Grafting: 121 g of the graphite / boron nitride material of step (2), 256 g of a titanium dioxide ethanol solution with a concentration of 0.15-0.2 mol / L, and 47.5 g of a silane coupling agent (KH550) were mixed, and then a grafting reaction was carried out at a temperature of 55-58°C for 65-70 min, followed by ultrasonic treatment for 6-6.5 h to obtain a mixed solution; wherein the ultrasonic treatment conditions are: a frequency of 220-256 kHz and a pulse duty cycle of 12-23%.

[0043] (4) Filtration and drying: The mixed solution in step (3) is filtered and then dried at 78-80°C for 11-11.5 hours to obtain modified expanded graphite with a particle size of 50-75 μm.

[0044] like Figure 3 As shown, 52.5g of phase change material powder and 7.5g of modified expanded graphite were stirred and mixed evenly, and then the mixed materials were placed in an environment of 83-85°C, stirred once every 50min, each stirring time was 6-7min, and the stirring speed was 850-880r / min, and continued for 10-10.5h to obtain a mixed material; then the mixed material was placed in a vacuum drying oven, heated and dried at a temperature of 82-84°C and a vacuum degree of 9500-11500Pa for 15.2-15.8h, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material was briquetteed using a tablet press to obtain 800-860kg / m 3 The composite phase change thermal storage material block (TiO2-BG-SA / CEG-BNNS) is pressurized in three stages using a tablet press: the first stage: pre-pressing at 5.5-6.0 MPa for 20-25 seconds, the second stage: main pressing at 9.0-9.5 MPa for 38-43 seconds, and the third stage: stabilizing pressure at 7.0-7.5 MPa for 12-14 seconds.

[0045] The actual photos of pre-treated expanded graphite (EG) and modified expanded graphite (CEG-BNNS) are shown in Figure 4 The dispersibility of CEG-BNNS is better than that of pretreated EG; and the wettability of pretreated EG and CEG-BNNS is studied by compressing EG and CEG-BNNS into thin slices with a diameter of 10 mm and a height of 1 mm under a pressure of 7.0 MPa, and then testing the contact angles of EG and CEG-BNNS slices with water and oil (OA), as shown in Figure 2. Figure 5 As shown, from Figure 5 (a) and Figure 5 As can be seen from (b), the contact angle between EG and water is 61°, while the contact angle between CEG-BNNS and water is 128°, indicating that the hydrophobicity of CEG-BNNS is improved. Figure 5 (c) and Figure 5 As can be seen in (d), the contact angle between EG and OA is 55°, while the contact angle between CEG-BNNS and OA is about 2°, which indicates that the lipophilicity of CEG-BNNS has been significantly improved. Obviously, the hydrophobicity and lipophilicity of CEG-BNNS have been significantly improved, reducing the phase separation phenomenon of PCM after synthesis; in this embodiment, after the nano-intercalation and grafting process of EG, the original worm-like microstructure is destroyed, the lamellar structure is broken, the particles tend to be micronized, and their dispersibility is improved, making it easier to disperse in organic solvents.

[0046] Example 2: A method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material, comprising the following steps:

[0047] The preparation method of phase change material powder (TiO2-BG-SA) includes the following steps: 552g BG, 105g SA and 10.4g TiO2 are stirred and mixed in a water bath at a temperature of 82-84°C, and stirred for 8.2-8.8h to mix them evenly, wherein the stirring speed is 890-920r / min, and then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 120-160μm and sealed for storage.

[0048] The preparation method of modified expanded graphite (CEG-BNNS) includes the following steps:

[0049] (1) Pretreatment process: The graphite expansion powder is dried and then transferred to a muffle furnace at 820-880℃ and calcined for 53-58s in an oxygen-rich environment with an oxygen concentration of 95-98% to form expanded graphite (EG) with a three-dimensional interconnected pore structure, a porosity of ≥92%, and a specific surface area of 200-250m² / g; the particle size of the graphite expansion powder is 150-200 mesh and the purity is 97-98%; the drying conditions of the graphite expansion powder are constant temperature drying at 85-88℃ for 13-14h in a drying oven with a vacuum degree of ≤100Pa.

[0050] (2) Nano-intercalation mixing: 33 g of expanded graphite, 62 g of oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02-0.05 mol / L, and 4.2 g of boron nitride nanosheets (BNNS) in step (1) were mixed, and then magnetic-ultrasonic alternating stirring was performed for 25-28 min at a temperature of 50-52 ° C to obtain a graphite / boron nitride material; wherein the thickness of the boron nitride nanosheets was 5-8 nm and the aspect ratio was >200; the magnetic-ultrasonic alternating stirring was specifically as follows: magnetic stirring and ultrasonic stirring were alternately performed every 5-88 min, wherein the speed of magnetic stirring was 880-910 r / min, and the working condition parameters of ultrasonic stirring included: ultrasonic power of 223-354 W and stirring speed of 880-910 r / min.

[0051] (3) Grafting: 28 g of the graphite / boron nitride material from step (2), 60 g of a titanium dioxide ethanol solution with a concentration of 0.15-0.2 mol / L, and 10 g of a silane coupling agent (KH550) were mixed, followed by a grafting reaction at a temperature of 55-58°C for 65-70 min, followed by an ultrasonic treatment for 6-6.5 h to obtain a mixed solution; wherein the ultrasonic treatment conditions are: a frequency of 220-256 kHz and a pulse duty cycle of 12-23%.

[0052] (4) Filtration and drying: The mixed solution in step (3) is filtered and then dried at 78-80°C for 11-11.5 hours to obtain modified expanded graphite with a particle size of 50-75 μm.

[0053] 325g phase change material powder and 50g modified expanded graphite were stirred and mixed evenly, and then the mixed materials were placed in an environment of 83-85°C, stirred once every 50min, each stirring time was 6-7min, and the stirring speed was 850-880r / min, and continued for 10-10.5h to obtain a mixed material; then the mixed material was placed in a vacuum drying oven, heated and dried at a temperature of 82-84°C and a vacuum degree of 9500-11500Pa for 15.2-15.8h, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material was briquetteed using a tablet press to obtain 800-860kg / m 3 The composite phase change thermal storage material block (TiO2-BG-SA / CEG-BNNS) is pressurized in three stages using a tablet press: the first stage: pre-pressing at 5.5-6.0 MPa for 20-25 seconds, the second stage: main pressing at 9.0-9.5 MPa for 38-43 seconds, and the third stage: stabilizing pressure at 7.0-7.5 MPa for 12-14 seconds.

[0054] Example 3: A method for preparing a TiO2-BG-SA / CEG-BNNS composite phase-change thermal storage material, comprising the following steps:

[0055] The preparation method of phase change material powder (TiO2-BG-SA) includes the following steps: stirring and mixing 547g of BG, 113g of SA and 11g of TiO2 in a water bath at a temperature of 82-84°C, stirring for 8.2-8.8h to mix them evenly, wherein the stirring speed is 890-920r / min, and then naturally cooling to room temperature to solidify, and finally grinding into powder with a particle size of 120-160μm and sealing for storage.

[0056] The preparation method of modified expanded graphite (CEG-BNNS) includes the following steps:

[0057] (1) Pretreatment process: The graphite expansion powder is dried and then transferred to a muffle furnace at 820-880℃ and calcined for 53-58s in an oxygen-rich environment with an oxygen concentration of 95-98% to form expanded graphite (EG) with a three-dimensional interconnected pore structure, a porosity of ≥92%, and a specific surface area of 200-250m² / g; the particle size of the graphite expansion powder is 150-200 mesh and the purity is 97-98%; the drying conditions of the graphite expansion powder are constant temperature drying at 85-88℃ for 13-14h in a drying oven with a vacuum degree of ≤100Pa.

[0058] (2) Nano-intercalation mixing: 29 g of expanded graphite, 56 g of oleic acid ethanol (OAE) solution with a titanium dioxide concentration of 0.02-0.05 mol / L, and 6 g of boron nitride nanosheets (BNNS) in step (1) were mixed, and then magnetic-ultrasonic alternating stirring was performed for 25-28 min at a temperature of 50-52 ° C to obtain a graphite / boron nitride material; wherein the thickness of the boron nitride nanosheets was 5-8 nm and the aspect ratio was >200; the magnetic-ultrasonic alternating stirring was specifically as follows: magnetic stirring and ultrasonic stirring were alternately performed every 5-8 min, wherein the speed of magnetic stirring was 880-910 r / min, and the working condition parameters of ultrasonic stirring included: ultrasonic power of 223-354 W and stirring speed of 880-910 r / min.

[0059] (3) Grafting: 29 g of the graphite / boron nitride material from step (2), 63 g of a titanium dioxide ethanol solution with a concentration of 0.15-0.2 mol / L, and 11 g of a silane coupling agent (KH550) were mixed, followed by a grafting reaction at a temperature of 55-58°C for 65-70 min, followed by an ultrasonic treatment for 6-6.5 h to obtain a mixed solution; wherein the ultrasonic treatment conditions are: a frequency of 220-256 kHz and a pulse duty cycle of 12-23%.

[0060] (4) Filtration and drying: The mixed solution in step (3) is filtered and then dried at 78-80°C for 11-11.5 hours to obtain modified expanded graphite with a particle size of 50-75 μm.

[0061] 358g of phase change material powder and 53g of modified expanded graphite were stirred and mixed evenly, and then the mixed materials were placed in an environment of 83-85°C, stirred once every 50min, each stirring time was 6-7min, and the stirring speed was 850-880r / min, and continued for 10-10.5h to obtain a mixed material; then the mixed material was placed in a vacuum drying oven, heated and dried at a temperature of 82-84°C and a vacuum degree of 9500-11500Pa for 15.2-15.8h, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material was briquetteed using a tablet press to obtain 800-860kg / m 3 The composite phase change thermal storage material block (TiO2-BG-SA / CEG-BNNS) is pressurized in three stages using a tablet press: the first stage: pre-pressing at 5.5-6.0 MPa for 20-25 seconds, the second stage: main pressing at 9.0-9.5 MPa for 38-43 seconds, and the third stage: stabilizing pressure at 7.0-7.5 MPa for 12-14 seconds.

[0062] Comparative Example 1: The overall method is the same as that of Example 1, except that only the pretreatment in step (1) is performed, and the pretreated expanded graphite obtained in step (1) is directly mixed with the phase change material powder.

[0063] Comparative Example 2: A composite phase change thermal storage material block prepared by using a preparation method of a composite phase change thermal storage material disclosed in an existing patent (application number CN202411393184.2).

[0064] Experiment 1:

[0065] Fourier transform infrared spectroscopy was performed on TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG. The results are shown in Figure 2. Figure 6 As shown. Located at 2915cm -1 and 2846cm -1 The peak at 3000 cm represents the stretching vibration of -CH3 and -CH2 functional groups. -1 and 2750cm -1 The absorption band of OH stretching vibration is in the range of 1696 cm, which usually overlaps with the absorption band of fatty acid CH stretching vibration. -1 The peak at 1472 cm is the characteristic absorption peak of C=O stretching vibration. -1The peak at 1295 cm is the -CH2 bending peak. -1 The bending peaks of CH and CC are located at 934 cm -1 and 723cm -1 The peaks at 2915 cm-1 correspond to rocking vibration and bending, which are the characteristics of aliphatic chains. -1 、2846cm -1 、1696cm -1 、1472cm -1 、1295cm -1 、934cm -1 and 723cm -1 There are absorption peaks with the same characteristics at the same place, and no new absorption peaks appear, indicating that the TiO2-BG-SA / EG in Comparative Example 1 is only physically combined and no chemical reaction occurs.

[0066] The XRD diffraction patterns of TiO2-BG-SA, CEG-BNNS, TiO2-BG-SA / CEG-BNNS, EG and TiO2-BG-SA / EG are shown in Figure 2. Figure 7 As shown. It can be seen that the strong diffraction peak of TiO2-BG-SA corresponds one to one with the strong diffraction peak of TiO2-BG-SA / CEG-BNNS in Example 1. Since the amount of CEG-BNNS added to TiO2-BG-SA / CEG-BNNS is small, the diffraction peak of CEG-BNNS in TiO2-BG-SA / CEG-BNNS is not obvious. The strong diffraction peak of TiO2-BG-SA / EG in Comparative Example 1 corresponds one to one with the strong diffraction peaks of TiO2-BG-SA / CEG-BNNS and EG in Example 1, and no new diffraction peaks are found, indicating that the TiO2-BG-SA / CEG-BNNS in Example 1 is only physically combined, and further verification shows that no chemical reaction occurs.

[0067] Experiment 2:

[0068] The thermal stability test was conducted on 9 composite phase change thermal storage material blocks prepared in Example 1 with different densities (see Table 1 for specific densities). The 9 composite phase change thermal storage material blocks prepared in Example 1 with different densities were placed in a water bath and heated from 25 to 90°C. When the temperature reached 90°C, the water bath was controlled to cool down. The water bath was programmed to automatically cycle heat storage and release for 120 times. After that, photos were taken to obtain appearance photos of the 9 composite phase change thermal storage material blocks with different densities, as shown in FIG. Figure 8 shown.

[0069] Table 1 Density values of composite phase change thermal storage material blocks

[0070]

[0071] from Figure 8 It can be seen that the density is 875kg / m 3 Up to 920kg / m 3 Cracks appeared in the composite phase change thermal storage material blocks within the range, and the degree of cracks increased with the increase of block density. This is because when the block density is low, the bonding force between the materials is weak, and the thermal expansion and contraction during the solid-liquid conversion of the PCM leave micro-gap hysteresis space, so it is not easy to leak. When the block density exceeds 860kg / m 3 When the density of the briquette is too high, the pore structure of CEG-BNNS is seriously damaged, the hysteresis space is reduced, and TiO2-BG-SA is squeezed out. At the same time, overload causes cracking. When the density of the briquette is 800g / m 3 Up to 860kg / m 3 When the composite phase change thermal storage material block is basically unchanged, the density of the block formed by pressing is 800-860kg / m 3 The composite phase change thermal storage material block has excellent thermal stability and anti-leakage performance.

[0072] Experiment 3:

[0073] The composite phase-change thermal storage material blocks prepared in Example 1 and Comparative Example 1 were subjected to differential scanning calorimetry (DSC) testing, with the DSC equipment temperature parameter range set at 25-90°C. The results are shown in Table 2. As can be seen from Table 2, the thermal conductivity of the TiO2-BG-SA / CEG-BNNS prepared in Example 1 reached 9.58 W / (m∙K), which is 35.5 times that of the TiO2-BG-SA / EG prepared in Comparative Example 1. Clearly, the composite phase-change thermal storage material block prepared in Example 1 of the present invention has better heat transfer performance. The thermal diffusivity of the TiO2-BG-SA / CEG-BNNS prepared in Example 1 is 36.8 times that of the TiO2-BG-SA / EG prepared in Comparative Example 1, and the thermal storage coefficient of the TiO2-BG-SA / CEG-BNNS prepared in Example 1 is 6.4 times that of the TiO2-BG-SA / EG prepared in Comparative Example 1, indicating that the thermal stability of the composite phase change thermal storage material block prepared in Example 1 of the present invention has been significantly improved.

[0074] Table 2 Comprehensive thermal coefficients of TiO2-BG-SA / EG and TiO2-BG-SA / CEG-BNNS

[0075]

[0076] Experiment 4:

[0077] The microstructures of TiO2-BG-SA / EG in Comparative Example 1, CEG-BNNS in Example 1, and TiO2-BG-SA / CEG-BNNS in Example 1 were observed by scanning electron microscopy (SEM). Figure 9 ,in Figure 9 (a) is the SEM image of TiO2-BG-SA / EG. Figure 9 (b) is the SEM image of CEG-BNNS. Figure 9 (c) is the SEM image of TiO2-BG-SA / CEG-BNNS. Figure 9 As can be seen in (a), the SEM of the TiO2-BG-SA / EG composite material shows that the unmodified expanded graphite (EG) presents a typical worm-like porous structure (pore size 50-200 μm), the phase change material (TiO2-BG-SA) is locally aggregated at the entrance of the EG pores, the TiO2 particles are agglomerated at the micron level, and there are obvious gaps at the interface, which confirms the weak bonding between EG and the phase change matrix; Figure 9 (b) shows that the modified CEG-BNNS exhibits a micronized structure with broken layers (50-75 μm), BNNS is directionally intercalated along the graphite crystal plane (interlayer spacing 1.5-2.2 nm), and the surface is covered with a nano-island organic coating layer formed by KH550 (thickness 10-15 nm). Its rough surface is directly related to its superlipophilic properties. Figure 9 (c) The TiO2-BG-SA / CEG-BNNS composite shows CEG-BNNS uniformly dispersed in the phase change matrix. BG-SA fills the nanoscale pores (20-50 nm) via capillary action, while TiO2 particles embed themselves in the pore walls to form a confined structure with no cracks or voids at the interface. This multiscale structural evolution reveals the synergistic mechanism of modified graphite intercalation through BNNS to form a heterogeneous thermal conductive network, KH550 grafting to strengthen interfacial bonding, and TiO2-induced nanocrystallization of the phase change material, ultimately achieving a thermal conductivity of 9.58 W / (m·K), a contact angle of <5°, and a leakage rate of ≤0.5%.

[0078] Experiment 5:

[0079] The composite phase change thermal storage material blocks prepared in Example 1, Comparative Example 1 and Comparative Example 2 were respectively placed in a water bath and heated from 20 to 80°C. When the temperature reached 80°C, the water bath was controlled to cool down. After setting the water bath program, 0, 200, 400, 600, 800 and 1000 cycles of heat storage and release were performed. Then, DSC tests were performed on the material blocks after the heat storage and release. The specific test results are shown in Table 3-5. It can be seen from Table 3-5 that the melting temperature of TiO2-BG-SA / EG after 1000 cycles of heat storage and release decreased by 2.86°C, and the melting temperature of TiO2-BG-SA / CEG-BNNS after 1000 cycles decreased by only 0.41°C. , the latent heat of melting only decreased by 1.57 J / g, the solidification temperature only decreased by 0.11°C, and the latent heat of solidification only decreased by 1.9 J / g; compared with TiO2-BG-SA / EG, the phase change temperature and phase change latent heat of TiO2-BG-SA / CEG-BNNS remained almost unchanged after 1000 cycles of heat storage and release, and it has good thermal stability; and after 1000 cycles of heat storage and release, the cyclic leakage rate of TiO2-BG-SA / CEG-BNNS dropped to 0.5%, compared with the cyclic leakage rate of 1.9% of MgO-PGSA-SFA / CEG, the cyclic leakage rate of TiO2-BG-SA / CEG-BNNS of the present invention was reduced by 74.7%.

[0080] Table 3 Thermal performance of TiO2-BG-SA / CEG-BNNS prepared in Example 1 at different cycle times

[0081]

[0082] Table 4 Thermal performance of TiO2-BG-SA / EG prepared in Comparative Example 1 at different cycle times

[0083]

[0084] Table 5 Thermal performance of MgO-PGSA-SFA / CEG prepared in Comparative Example 2 at different cycle times

[0085]

[0086] Experiment 6:

[0087] In order to verify the heat storage / release performance of TiO2-BG-SA / CEG-BNNS prepared in Experimental Example 1 and TiO2-BG-SA / EG prepared in Comparative Example 1 in actual application, Guangzhou Jiaxin Material Co., Ltd. was commissioned to conduct heat storage / release tests according to the two PCM production process requirements. The specific heat storage / release process is as follows: Figure 10As shown. It mainly includes a plate-type phase change energy storage device, a water supply system and a temperature acquisition system. Among them, the water supply system mainly includes a normal pressure hot water boiler, a variable frequency circulation pump and a PPR pipe. During the experiment, high-temperature water and low-temperature water flow into the energy storage device for heat storage experiment and heat release experiment respectively. The temperature change process of the fluid and the plate-type phase change unit is observed by collecting signals through the thermal resistor and the temperature acquisition instrument. Test instruments used in the experiment: (1) Normal pressure hot water boiler. Provides cold source and heat source for the energy storage device in the experimental test system. (2) Ultrasonic heat meter. Set at the inlet of the energy storage device, it can measure a small flow range. (3) Temperature acquisition instrument. It is controlled by a microprocessor and can be used with a variety of thermal resistors and thermocouples. (4) Circulation pump. It can be used with a manual regulating valve to adjust the inlet flow according to the experimental requirements. Experimental preparation: Turn on the boiler, maintain the water temperature in the hot water storage tank to the initial temperature, and adjust the flow meter to the flow required for the experiment. The experiment begins by heating the water in the boiler to the desired inlet temperature. The variable frequency pump is turned on, and the HTF flows from the inlet into the hot water storage tank through a pipe. The HTF then flows out of the outlet and back into the boiler through a pipe. A 50mm x 50mm opening is left in the top cap of the hot water storage tank to facilitate access to the RTD wiring. A temperature probe is connected to the wiring from the water tank, and the experimental data is recorded on a computer. The experiment ends by shutting off the variable frequency pump and boiler power, and saving the experimental data. The experimental process follows the same boundary conditions as the simulation. During the thermal storage process, the initial temperature of the water inside the thermal storage device is maintained at 30°C, the inlet temperature at 65°C, and the inlet velocity at 0.16 m / s. The phase change unit (PCU) is placed in the thermal storage device before the experiment begins. The experiment begins when the internal PCU temperatures reach the initial set temperature. The thermal storage experiment ends when the temperature of each PCU layer reaches 65°C. When conducting the heat release experiment, each thermal storage unit is first heated to an internal temperature of 65°C, and heat is released at 0.16m / s and 30°C inlet boundary conditions. The experiment ends when the internal temperature of the thermal storage unit reaches 30°C. In order to avoid experimental errors during the heat storage / release process, the internal temperature changes of the four phase change units are averaged, and the thermal performance changes of TiO2-BG-SA / CEG-BNNS and TiO2-BG-SA / EG during actual application are analyzed. The temperature change curves are shown as follows: Figure 11 As shown in the figure, during the heat storage process, the heat storage completion time of TiO2-BG-SA / CEG-BNNS is 5600s, and the heat storage completion time of TiO2-BG-SA / EG is 7400s. During the heat release process, the time for TiO2-BG-SA / CEG-BNNS to reach the inlet temperature is 5200s, and the heat release completion time of TiO2-BG-SA / EG is 11800s. The experiment verified that TiO2-BG-SA / CEG-BNNS has a faster thermal response rate and excellent heat transfer performance in practical applications.

[0088] The above is a preferred embodiment of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material, characterized in that: The method comprises the following steps: mixing the phase change material powder and the modified expanded graphite in a mass ratio of 6.5-7.2:1, and then heating and mixing, vacuum drying and directional briquetting. The directional briquetting is specifically: using a tablet press to briquette the composite phase change thermal storage material to obtain 800-860kg / m 3 The composite phase change thermal storage material block is subjected to three-stage pressurization and compaction using a tablet press: the first stage is pre-pressing at 5.5-6.0 MPa for 20-25 seconds, the second stage is main pressing at 9.0-9.5 MPa for 38-43 seconds, and the third stage is steady pressure at 7.0-7.5 MPa for 12-14 seconds. The preparation method of the phase change material powder comprises the following steps: mixing 72-75 parts by weight of glyceryl behenate, 14-15 parts of stearyl alcohol, and 1.2-1.5 parts of nano-titanium dioxide in a water bath, stirring and mixing, then naturally cooling to room temperature to solidify, and finally grinding into a powder with a particle size of 120-160 μm, and sealing and storing; The preparation method of the modified expanded graphite comprises the following steps: (1) Pretreatment process: The graphite expansion powder is dried and then transferred to a muffle furnace at 820-880°C and calcined for 53-58 seconds in an oxygen-rich environment with an oxygen concentration of 95-98% to form expanded graphite; (2) Nano-intercalation mixing: the expanded graphite in step (1), an oleic acid ethanol solution with a titanium dioxide concentration of 0.02-0.05 mol / L, and boron nitride nanosheets are mixed; then, magnetic-ultrasonic alternating stirring is performed at a temperature of 50-52°C for 25-28 minutes to obtain a graphite / boron nitride material; (3) Grafting: The graphite / boron nitride material of step (2), a titanium dioxide ethanol solution with a concentration of 0.15-0.2 mol / L, and a silane coupling agent are mixed, followed by a grafting reaction at a temperature of 55-58°C for 65-70 minutes, followed by ultrasonic treatment for 6-6.5 hours to obtain a mixed solution; (4) Filtration and drying: The mixed solution in step (3) is filtered and then dried at 78-80° C. for 11-11.5 hours to obtain the modified expanded graphite with a particle size of 50-75 μm.

2. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: The stirring and mixing under water bath heating is specifically carried out under water bath heating conditions at a temperature of 82-84° C., stirring for 8.2-8.8 hours to achieve uniform mixing, wherein the stirring speed is 890-920 r / min.

3. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: The graphite expansion powder in step (1) has a particle size of 150-200 mesh and a purity of 97-98%. The drying conditions of the graphite expansion powder are to dry it at a constant temperature of 85-88° C. for 13-14 hours in a drying oven with a vacuum degree of ≤100 Pa.

4. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: In step (2), the mass ratio of expanded graphite, oleic acid ethanol solution and boron nitride nanosheets is 32-34:60-62:4-8, wherein the thickness of the boron nitride nanosheets is 5-8 nm and the aspect ratio is >200.

5. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: In step (2), the magnetic-ultrasonic alternating stirring is specifically as follows: magnetic stirring and ultrasonic stirring are performed alternately every 5-8 minutes, wherein the speed of magnetic stirring is 880-910 r / min, and the working condition parameters of ultrasonic stirring include: ultrasonic power is 223-354 W, and stirring speed is 880-910 r / min.

6. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: In step (3), the mass ratio of graphite / boron nitride material, titanium dioxide ethanol solution and silane coupling agent is 28-30:58-61:9-14; the conditions of ultrasonic treatment are: frequency of 220-256kHz, pulse duty cycle of 12-23%.

7. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 1, characterized in that: The specific conditions of the heating and mixing are: placing the uniformly mixed materials in an environment of 83-85° C., stirring once every 50 minutes, and continuing for 10-10.5 hours to obtain a mixed material.

8. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 7, characterized in that: Each stirring time is 6-7 minutes, and the stirring speed is 850-880r / min.

9. The method for preparing a TiO2-BG-SA / CEG-BNNS composite phase change thermal storage material according to claim 7, characterized in that: The vacuum drying is specifically as follows: placing the mixed material in a vacuum drying oven, heating and drying at a temperature of 82-84° C. and a vacuum degree of 9500-11500 Pa for 15.2-15.8 hours, and then naturally cooling to room temperature to obtain a composite phase change thermal storage material.

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