Photo-thermal conversion phase change heat storage structure with reverse temperature gradient and preparation method of photo-thermal conversion phase change heat storage structure

Abstract

The invention discloses a photo-thermal conversion phase change heat storage structure with a reverse temperature gradient and a preparation method, belongs to the technical field of photo-thermal conversion phase change heat storage, and solves the problems that the heat storage direction of an existing photo-thermal conversion phase change material is not matched with the demand of a user side, the heat transfer efficiency is low, and the radiation heat dissipation loss is high. Comprising an optical fiber film, and a collecting lens is arranged above the optical fiber film; shape-stabilized phase-change material layers are arranged on the two sides of the optical fiber film in a mirroring mode to form a sandwich structure, second expanded graphite plates are arranged on the lower portions of the shape-stabilized phase-change material layers, and gap spaces exist between the bottom end of the optical fiber film and the tops of the second expanded graphite plates. The purpose is that the photo-thermal conversion element with the optical fiber film as the core is located in the center, and the collecting lens and the optical fiber film are matched to guide light to the bottom to ensure that high-energy-density light is directionally conveyed to the deep layer of the structure, so that heat is preferentially transmitted to the shape-stabilized phase change material layer close to the user side, and the heat is transmitted to the light source end after the heat requirement of the user side is preferentially met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photothermal conversion phase change heat storage, and particularly relates to a photothermal conversion phase change heat storage structure with a reverse temperature gradient and a preparation method. BACKGROUND

[0002] With the rapid development of renewable energy technology, the combination of solar photothermal conversion and phase change energy storage has become an important research direction to improve energy utilization efficiency. In the process of photothermal conversion, the surface (the surface receiving solar radiation) of the traditional phase change energy storage material is usually high in temperature, and the bottom (the surface transferring heat to the user end) is low in temperature. Heat is transferred from the high-temperature light source end to the low-temperature user end. The inherent low thermal conductivity of the phase change material and the limitation of the temperature gradient direction result in low heat transfer efficiency at the user end. The long surface-bottom-user end heat transfer process seriously affects the effective utilization of solar energy. In addition, the surface of the traditional photothermal conversion phase change material can reach a temperature of more than 120 DEG C under the sun. In the process of continuous energy storage, the surface with the highest temperature continuously radiates heat to the surrounding environment, causing an irreparable infrared radiation loss and reducing the energy storage efficiency of the photothermal conversion phase change material. The existing technology solves the low heat transfer efficiency at the user end by adding high-thermal-conductivity fillers to improve the thermal conductivity of the material. However, this method often sacrifices the phase change enthalpy of the material and cannot solve the contradiction between the temperature gradient direction and the heat transfer demand, and the defect of high surface radiation heat loss still exists. Therefore, the existing technology has the problems of mismatch between the heat storage direction of the photothermal conversion phase change material and the demand of the user end, low heat transfer efficiency, and high radiation heat loss. SUMMARY

[0003] To solve the above technical problems, the application provides a photothermal conversion phase change heat storage structure with a reverse temperature gradient and a preparation method. The optical fiber film as the core photothermal conversion element is located at the center. The condenser and the optical fiber film cooperate to guide light to the bottom, ensuring that high-energy-density light is directed to the deep layer of the structure, realizing the downward movement of the photothermal conversion position, breaking the traditional surface heating mode. After the energy density light is converted into heat energy, the first expanded graphite plate on both sides close to the user end is heated first. The first expanded graphite plate serves as a high-efficiency heat conduction layer, so that heat is preferentially transferred to the shaped phase change material layer close to the user side. The shaped phase change material layer serves as the main heat storage body, preferentially meets the heat demand of the user end, and then transfers to the light source end, reducing the loss on the heat transfer path, improving the system response speed and efficiency, and realizing the bidirectional transfer and storage of heat.

[0004] The technical scheme adopted by the application is as follows:

[0005] A light-heat conversion phase change heat storage structure of reverse temperature gradient, comprising a fiber film, a condenser is arranged above the fiber film; mirror image of the fiber film is arranged with a shaped phase change material layer on both sides to form a sandwich structure, the lower part of the shaped phase change material layer is provided with a second expanded graphite plate, and the bottom end of the fiber film has a gap space with the top of the second expanded graphite plate.

[0006] The gap space between the bottom end of the fiber film and the top of the second expanded graphite plate is 50-100% of the diameter of the fiber.

[0007] The fiber film as the core light-heat conversion element is located in the center, the condenser and the fiber film cooperate to guide light to the bottom to ensure that high-energy-density light is directed to the deep layer of the structure, the light-heat conversion position is lowered, and the traditional surface heating mode is broken; after the energy density light is converted into heat, the second expanded graphite plate as a high-efficiency heat conduction layer preferentially transmits heat to the shaped phase change material layer close to the user side, the shaped phase change material layer as the main heat accumulator preferentially meets the heat demand of the user side and then transmits heat to the light source end, thereby reducing the loss on the heat transmission path, improving the system response speed and efficiency, and realizing bidirectional heat transmission and storage; the shaped phase change material layer ensures the shape stability during the phase change and prevents leakage, and balances the heat storage amount and the heat conduction efficiency.

[0008] Preferably, a first expanded graphite plate is further arranged between the shaped phase change material layer on each side and the adjacent fiber film, and the bottom end of each first expanded graphite plate is connected with the upper part of the second expanded graphite plate.

[0009] The first expanded graphite plate strengthens the heat conduction capacity on both sides, which is helpful to the rapid diffusion and storage of heat in the user end area to the shaped phase change material layer; the first expanded graphite plate directly performs bidirectional heat transfer, thereby shortening the heat transmission path and constituting a dynamic cycle of efficient horizontal heat storage and vertical reverse heat transfer.

[0010] Preferably, the fiber film adopts epoxy resin, a plurality of fiber tube segments with the same length are encapsulated in the epoxy resin, and the plurality of fiber tube segments are closely arranged in the epoxy resin.

[0011] The epoxy resin encapsulates and fixes the position of the fiber tube segments, prevents displacement of the fiber tube segments from causing a decrease in light guiding efficiency, and the closely arranged fiber tube segments ensure efficient introduction of condensed light to the deep layer of the structure, and the fiber film is both a light guiding medium and a light-heat conversion surface, thereby providing an efficient and concentrated light-heat input mode.

[0012] Further, the fiber tube segments adopt PMMA optical fibers.

[0013] Preferably, the first and second expanded graphite plates are both prepared by pressing expanded graphite and phase change material at a pressure of 10-30 MPa.

[0014] By using the above technical solution, the graphite plate pressed at a high pressure of 10-30 MPa can ensure high thermal conductivity and structural strength. The first and second expanded graphite plates pressed at a high pressure not only have high thermal conductivity, but also are more conducive to lateral heat transfer. Moreover, the first and second expanded graphite plates pressed at a high pressure also have certain heat storage capacity, and can store heat when the user end is heated. In addition, the high thermal conductivity of the first and second expanded graphite plates plays an important role in achieving reverse temperature gradient and rapid heating of the phase change material layers on both sides.

[0015] Preferably, the optical fiber film, the first and second expanded graphite plates, and the phase change material layer are all bonded by using heat-conducting silicone grease.

[0016] By using the above technical solution, the use of heat-conducting silicone grease for bonding ensures that the contact thermal resistance between the layers is reduced, and the heat-conducting silicone grease bonding ensures low thermal resistance between the layers.

[0017] Preferably, the diameter of the optical fiber tube segment is 50-300% of the thickness of the phase change material.

[0018] A preparation method of a reverse temperature gradient light-heat conversion phase change heat storage structure is used to prepare the reverse temperature gradient light-heat conversion phase change heat storage structure described above, and includes the following steps:

[0019] Step 1: preparing an optical fiber film, a first expanded graphite plate, a second expanded graphite plate, and a phase change material layer, respectively;

[0020] Step 2: preparing a combined stack composed of the optical fiber film, the first expanded graphite plate, the second expanded graphite plate, and the phase change material layer in sequence;

[0021] Step 3: setting a light collector above the combined stack prepared in step 2.

[0022] Preferably, the preparation method of the optical fiber film in step 1 is as follows:

[0023] Step a1: cutting PMMA optical fibers;

[0024] Step a2: tightly arranging the optical fibers in a mold, and pouring epoxy resin to completely cover them;

[0025] Step a3: placing the mold in a 45℃ oven for curing, and obtaining the optical fiber film after demolding.

[0026] Preferably, the preparation method of the first and second expanded graphite plates in step 1 is as follows:

[0027] Step b1: weighing expanded graphite and phase change material powder according to a mass ratio of 1:2-9;

[0028] Step b2: after mixing evenly, placing in a mold, and compression molding under a pressure of 10-30 MPa;

[0029] Step b3: demolding for standby.

[0030] Therefore, by adopting the technical scheme, the present application has the following beneficial effects:

[0031] The optical fiber film as the core light-heat conversion element is located at the center, and the light collector and the optical fiber film cooperate to guide light to the bottom to ensure that high-energy-density light is directed to the deep layer of the structure, realizing the downward movement of the light-heat conversion position, breaking the traditional surface heating mode, and after the energy density light is converted into heat energy, the second expanded graphite plate close to the user end is heated first, the second expanded graphite plate as the high-efficiency heat conduction layer makes the heat preferentially transmitted to the shaped phase change material layer close to the user side, the shaped phase change material layer as the main heat accumulator preferentially meets the heat demand of the user end and then transmits to the light source end, reduces the loss on the heat transmission path, improves the system response speed and efficiency, and realizes the bidirectional transmission and storage of heat; the shaped phase change material layer ensures the shape stability in the phase change process, prevents leakage, and balances the heat storage amount and the heat conduction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0032] The present application will be described by way of example and with reference to the accompanying drawings, in which:

[0033] Figure 1 is a schematic diagram of the light-heat conversion phase change heat storage structure of the present application in a reverse temperature gradient;

[0034] Figure 2 is a schematic diagram of the structure of the optical fiber film in the present application;

[0035] Figure 3 is a schematic diagram of the temperature measurement points in the experiment of the present application;

[0036] Figure 4 is a schematic diagram of the temperature change detection of each measurement point at different times in Example 2-Example 4 and Comparative Example 1-Comparative Example 3 of the present application;

[0037] Figure 5 is a temperature rise curve of a conventional light conversion phase change material;

[0038] Figure 6 is an infrared thermal imaging image under a xenon lamp with time change;

[0039] Figure 7 is a schematic diagram of the temperature change detection of each measurement point at different times in Comparative Example 4 of the present application.

[0040] Among the accompanying drawings Figures 4-5In 7, 1 represents the test result of measuring point 1, 2 represents the test result of measuring point 2, 3 represents the test result of measuring point 3, and Ambient represents the ambient temperature.

[0041] Figure Labels

[0042] 1-Fiber optic film, 2-First expanded graphite plate, 3-Second expanded graphite plate, 4-Condenser lens, 5-Shaping phase change material layer, 6-Fiber optic segment, 7-Epoxy resin, 8-Gap space. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] The following is combined Figures 1-7 The present invention will be described in detail below.

[0045] Example 1

[0046] A photothermal conversion phase change heat storage structure with reverse temperature gradient, comprising an optical fiber film 1, as shown in the attached figure. Figures 1-2 A condenser lens 4 is disposed above the optical fiber film 1; a shaped phase change material layer 5 is mirror-displayed on both sides of the optical fiber film 1 to form a sandwich structure; a second expanded graphite plate 3 is disposed below the shaped phase change material layer 5; a gap space 8 exists between the bottom end of the optical fiber film 1 and the top end of the second expanded graphite plate 3; the optical fiber film 1, as the core photothermal conversion element, is located at the center; the condenser lens 4 and the optical fiber film 1 cooperate to guide light to the bottom, ensuring that high energy density light is directionally delivered to the deep layers of the structure, realizing the downward shift of the photothermal conversion position, breaking the traditional surface heating mode, and increasing energy density. After light is converted into heat energy, it first heats the second expanded graphite plate 3 near the user end. The second expanded graphite plate 3, as a highly efficient heat-conducting layer, allows heat to be preferentially transferred to the shape-stabilized phase change material layer 5 near the user side. The shape-stabilized phase change material layer 5, as the main heat storage body, prioritizes meeting the heat demand of the user end before transferring it to the light source end, reducing heat loss along the heat transfer path, improving system response speed and efficiency, and realizing bidirectional heat transfer and storage. The shape-stabilized phase change material layer 5 ensures the shape stability during the phase change process and prevents leakage, balancing the heat storage capacity and heat conduction efficiency.

[0047] The gap 8 between the bottom of the fiber optic film 1 and the top of the second expanded graphite plate 3 has a height of 3 mm.

[0048] In the embodiment, the shaped phase change material layer 5 on both sides is further provided with a first expanded graphite plate 2, and the bottom end of each first expanded graphite plate 2 is connected with the upper part of the second expanded graphite plate 3; the first expanded graphite plate 2 strengthens the heat conduction capacity on both sides, and helps the rapid diffusion and storage of heat in the user end area to the shaped phase change material layer 5; the first expanded graphite plate 2 directly performs bidirectional heat transfer, shortens the heat transfer path, and constitutes a dynamic cycle of efficient horizontal heat storage and longitudinal reverse heat transfer.

[0049] In the embodiment, the optical fiber film 1 adopts epoxy resin 7, a plurality of optical fiber tube segments 6 with the same length are encapsulated in the epoxy resin 7, and the plurality of optical fiber tube segments 6 are closely arranged in the epoxy resin 7 and closely close to or contact each other; the epoxy resin 7 encapsulates and fixes the position of the optical fiber tube segments 6, prevents the displacement of the optical fiber tube segments 6 from causing the light guide efficiency to decrease, and ensures that the concentrated light is efficiently introduced into the deep layer through the closely arranged optical fiber tube segments 6; and the optical fiber film 1 is not only a light guide medium but also a light-heat conversion surface, and provides an efficient and concentrated light-heat input mode.

[0050] In the embodiment, the optical fiber tube segment 6 adopts PMMA optical fiber.

[0051] In the embodiment, the first expanded graphite plate 2 and the second expanded graphite plate 3 are both made of expanded graphite and phase change material under a pressure of 20 MPa; the graphite plate pressed under a high pressure of 20 MPa can ensure high heat conductivity and structural strength; the first expanded graphite plate 2 and the second expanded graphite plate 3 pressed under a high pressure not only have high heat conductivity, but also are more conducive to horizontal heat transfer, and also have a certain heat storage capacity; when the user end is heated, the first expanded graphite plate 2 and the second expanded graphite plate 3 can store heat, and the high heat conductivity of the first expanded graphite plate 2 and the second expanded graphite plate 3 also plays an important role in realizing the reverse temperature gradient and rapidly heating the shaped phase change material layer 5 on both sides.

[0052] In the embodiment, the optical fiber film 1, the first expanded graphite plate 2, the second expanded graphite plate 3 and the shaped phase change material layer 5 are all bonded by using heat-conducting silicone grease; the use of heat-conducting silicone grease bonding ensures that the contact thermal resistance between the layers is reduced.

[0053] In the embodiment, the heat-conducting silicone grease bonding ensures low thermal resistance between the layers, the length of the optical fiber tube segment 6 is 35 mm, and the diameter of the optical fiber tube segment 6 is 3.3 mm.

[0054] In the embodiment, the thickness of the optical fiber film 1 in the X direction is 3.5 mm, the thickness of the first expanded graphite plate 2 in the X direction is 3 mm, and the thickness of the shaped phase change material layer 5 in the X direction is 5 mm; the length of the optical fiber film 1, the first expanded graphite plate 2 and the shaped phase change material layer 5 in the Y and Z directions is 40 mm respectively; the thickness controls the thermal resistance distribution, the thin graphite plate accelerates heat transfer, and the thick phase change material increases heat storage.

[0055] Embodiment 2

[0056] A preparation method of a light-heat conversion phase change heat storage structure with reverse temperature gradient, for preparing the light-heat conversion phase change heat storage structure with reverse temperature gradient, comprising the following steps:

[0057] Step 1: respectively preparing the optical fiber film 1, the first expanded graphite plate 2, the second expanded graphite plate 3 and the shaped phase change material layer 5;

[0058] Step 2: preparing the combined stack of the optical fiber film 1, the first expanded graphite plate 2, the second expanded graphite plate 3 and the shaped phase change material layer 5 in order, the layers of the optical fiber film 1, the expanded graphite plate and the shaped phase change material are bonded with each other by using heat-conducting silicone grease to reduce the interfacial thermal resistance, and the light-heat conversion phase change heat storage structure is obtained after the heat-conducting silicone grease is shaped;

[0059] Step 3: setting the condenser 4 directly above the combined stack in step 2.

[0060] In this embodiment, the preparation method of the optical fiber film 1 in step 1 is: cutting the PMMA optical fiber with a diameter of 3.3 mm to a length of 35 mm; arranging the PMMA optical fiber in the mold, pouring into the epoxy resin 7 and placing in a 45 ℃ oven, taking out from the mold after curing, and obtaining the optical fiber film 1 with a volume of 40×40×3.5 mm after demolding;

[0061] In this embodiment, the preparation method of the first expanded graphite plate 2 and the second expanded graphite plate 3 in step 1 is as follows:

[0062] Step b1: weighing the expanded graphite and paraffin powder according to the mass ratio of 1:3;

[0063] Step b2: after mixing uniformly, placing in a mold and pressing into shape under the conditions of 42 ℃ and 25 MPa pressure;

[0064] Step b3: the thermal conductivity is 13.6 W / m-1K-1, the light absorption reaches 97.6%, and it is ready for use after demolding.

[0065] In this embodiment, the shape-stabilized phase change material in step 1 is composed of melamine foam skeleton, hydrogenated styrene-butadiene block copolymer (SEBS) and cetyl alcohol. The open-cell melamine foam (density ≈ 9.5 kg / m³) is cut to the target size of 40 × 40 × 5 mm, and is placed in a 60 °C oven for 2 hours to dry to remove moisture and volatile impurities. SEBS particles are weighed according to the mass ratio (SEBS: cetyl alcohol = 92:8), and are added to molten cetyl alcohol heated to 100 °C. Mechanical stirring (300 rpm) is performed for 1 hour until SEBS is completely swollen and dispersed, forming a uniform viscous cetyl alcohol / SEBS mixed solution. The dried foam is vertically immersed in the mixed solution, transferred to a vacuum tank, vacuumed and pressure maintained for 3 hours, and the solution is driven to penetrate into the foam pores by negative pressure. After the cetyl alcohol is completely crystallized and solidified, a three-dimensional shape-stabilized structure of the SEBS / cetyl alcohol composite phase change material uniformly coated on the foam skeleton is obtained, with a thermal conductivity of 0.37 W·m-1K-1 and a latent heat of 212 J / g.

[0066] Example 3

[0067] Different from example 2, in this embodiment, the preparation method of the first expanded graphite plate 2 and the second expanded graphite plate 3 in step 1 is as follows:

[0068] Step b1: expanded graphite and polyethylene glycol powder are weighed according to the mass ratio of 1:3;

[0069] Step b2: after mixing, it is placed in a mold and molded under the conditions of 42 °C and 25 MPa pressure;

[0070] Step b3: the thermal conductivity is 12.3 W / m-1K-1, the light absorption reaches 96.2%, and the mold is ready for use.

[0071] Example 4

[0072] Different from example 2, in this embodiment, the preparation method of the qualitative phase change material is as follows: first, hydroxyethyl cellulose is dissolved in deionized water, stirred in a 30 °C water bath, and a 2wt% hydroxyethyl cellulose hydrogel is prepared. Pour the hydrogel into a mold and dry it in a freeze dryer to obtain a hydroxyethyl cellulose aerogel. SEBS particles are weighed according to the mass ratio (SEBS: paraffin = 9:1), and are added to molten paraffin heated to 100 °C. Mechanical stirring (300 rpm) is performed for 1 hour until SEBS is completely swollen and dispersed, forming a uniform viscous paraffin / SEBS mixed solution. The dried foam is vertically immersed in the mixed solution, transferred to a vacuum tank, vacuumed and pressure maintained for 3 hours, and the solution is driven to penetrate into the foam pores by negative pressure. After the paraffin is completely crystallized and solidified, a three-dimensional shape-stabilized structure of the SEBS / paraffin composite phase change material uniformly coated on the hydroxyethyl cellulose aerogel is obtained, with a thermal conductivity of 0.29 W·m-1K-1 and a latent heat of 196 J / g.

[0073] Comparative Example 1

[0074] Different from Example 2, the first expanded graphite plate 2 between the shaped phase change material layer 5 and the adjacent optical fiber film 1 is cancelled, and only the second expanded graphite plate 3 is arranged at the lower part of the phase change material and the optical fiber film 1.

[0075] Comparative Example 2

[0076] Different from Example 2, the optical fiber tube segment 6 adopts mainstream quartz optical fiber, and high-purity silicon dioxide is used as the material.

[0077] Comparative Example 3

[0078] Different from Example 2, in this embodiment, the first expanded graphite plate 2 and the second expanded graphite plate 3 are prepared without adding phase change material.

[0079] Comparative Example 4

[0080] Referring to the accompanying drawings Figure 7 Different from Example 2, the first expanded graphite plate 2 between the shaped phase change material layer 5 and the adjacent optical fiber film 1 is retained, and the second expanded graphite plate 3 arranged at the lower part of the phase change material and the optical fiber film 1 is cancelled.

[0081] Referring to the accompanying drawings Figure 3 1-3 are temperature measuring points, and 4 is a reference Figure 4 The temperature change detection of the measuring points 1-3 under the time change can show that the trends of Examples 2-4 are basically consistent.

[0082] Comparative Example 1 has no first expanded graphite plate 2, which leads to slow heat transfer in the Z direction, uneven temperature distribution, local high temperature at the bottom, and low temperature of the measuring points 1 and 2. If the heat is localized at a certain position, the temperature exceeds the phase change temperature, the system starts to use sensible heat energy storage instead of latent heat energy storage, the density of sensible heat energy storage is very low, and obviously it is not cost-effective. The specific heat capacity of the material is about 2.5 J / (g.K), but the latent heat is as high as 212 J / g. For a phase change latent heat energy storage system, it is optimal to use the high-density energy storage in the phase change temperature interval.

[0083] Comparative Example 2 has low overall light absorption due to poor light absorption of quartz. Although the light transmission loss rate of quartz optical fiber is lower, compared with the quartz glass multimode optical fiber with a large core diameter of 50 / 125 μm and 62.5 / 125 μm, the core diameter of PMMA optical fiber is as high as 1000-5000 μm, and the cost is low, the light absorption rate is high, the light transmission efficiency is higher, and it is suitable for short-distance high-power transmission working conditions in this structure. Therefore, it can be seen from Figure 4 The temperature of each measuring point in Example 2 is higher than that in Comparative Example 2.

[0084] Comparative Example 3: If paraffin wax is not added as a binder during the pressing of the phase change plate, the thermal conductivity is reduced, and the temperature is not uniform due to the low thermal conductivity of the graphite plate, but is more uniform than Comparative Example 1.

[0085] In Comparative Example 4, since the straight-line transmission of radiation inside the optical fiber is dominant, when the second expanded graphite plate is removed, the optical fiber penetrates the phase change module and is not absorbed, resulting in low overall temperature and energy storage efficiency.

[0086] Referring to the accompanying drawings Figure 5 It can be seen that the ordinary homogeneous light-heat conversion phase change material has a local high temperature on the surface (measurement point 1) and a low temperature at the bottom, so the surface heat radiation and convection loss are high.

[0087] Referring to the accompanying drawings Figure 6 It can be seen that the thermal imaging temperature distribution (side) of Example 2 is high at the bottom and low at the top, but the temperature of each measurement point is uniformly distributed, effectively improving the light-heat conversion efficiency.

[0088] Table 1 is a light-heat conversion efficiency table of Examples 2-4 and Comparative Examples 1-3

[0089] Efficiency of light-to-heat conversion Example 2 93.7% Example 3 92.8% Example 4 93.5% Comparative Example 1 76.4% Comparative Example 2 85.2% Comparative Example 3 81.3% Comparative Example 4 50.4%

[0090] Table 1 is the ratio of the heat storage amount of the phase change module to the input radiation amount within a period of time, which is the light-heat conversion efficiency, and the heat storage amount is the sum of latent heat and sensible heat, which is directly related to temperature.

[0091]

[0092] In the formula, m is the mass of the sample; Cp is the specific heat capacity of the sample; T0 and T1 are the temperatures at the beginning and end of the phase change, respectively; I is the irradiation intensity, S is the surface area receiving the light intensity; t0 and t1 are the beginning and end times of the phase change, respectively.

[0093] It should be noted that:

[0094] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A light-to-heat conversion phase change heat storage structure of inverse temperature gradient, characterized in that, Including optical fiber film (1), the upper of optical fiber film (1) is provided with condenser (4);The both sides of optical fiber film (1) are mirror image and are provided with the layer of shaped phase change material (5) and form sandwich structure, the lower part of shaped phase change material (5) is provided with the second expanded graphite plate (3), and the bottom end of optical fiber film (1) has gap space (8) with the top of second expanded graphite plate (3).

2. The light-to-heat conversion phase change heat storage structure of reverse temperature gradient according to claim 1, characterized in that, The both sides of the layer of shaped phase change material (5) are further provided with the first expanded graphite plate (2) between adjacent optical fiber film (1), and the bottom end of each first expanded graphite plate (2) is connected with the upper part of second expanded graphite plate (3).

3. The light-to-heat conversion phase change heat storage structure of reverse temperature gradient according to claim 1, characterized in that, The optical fiber film (1) adopts epoxy resin (7), a plurality of optical fiber tube segments (6) with same length are encapsulated in the inside of epoxy resin (7), and the plurality of optical fiber tube segments (6) are closely arranged in the inside of epoxy resin (7). 4.The inverse temperature gradient photothermal conversion phase change heat storage structure according to claim 1 or 2, characterized in that, The first expanded graphite plate (2) and the second expanded graphite plate (3) are both made of expanded graphite and phase change material under 10-30 MPa pressure. 5.The inverse temperature gradient photothermal conversion phase change heat storage structure according to claim 1 or 2, characterized in that, The contact surfaces between the optical fiber film (1), the first expanded graphite plate (2), the second expanded graphite plate (3) and the layer of shaped phase change material (5) are all bonded by heat-conducting silicone grease.

6. The light-to-heat conversion phase change heat storage structure of reverse temperature gradient according to claim 3, characterized in that, The diameter of the optical fiber tube segment (6) is 50-300% of the thickness of the phase change material.

7. A method for preparing a light-to-heat conversion phase change heat storage structure of inverse temperature gradient, characterized in that, A light-heat conversion phase change heat storage structure with reverse temperature gradient is prepared by the following steps: Step 1: preparing optical fiber film (1), first expanded graphite plate (2), second expanded graphite plate (3) and layer of shaped phase change material (5) respectively; Step 2: preparing the combination stack of optical fiber film (1), first expanded graphite plate (2), second expanded graphite plate (3) and layer of shaped phase change material (5) in sequence; Step 3: erecting condenser (4) directly above the combination stack of step 2.

8. The preparation method of the light-to-heat conversion phase change heat storage structure of inverse temperature gradient according to claim 7, characterized in that, The preparation method of optical fiber film (1) in step 1 is as follows: Step a1: cutting PMMA optical fiber; Step a2: closely arranging optical fiber in mold, pouring epoxy resin (7) to completely cover; Step a3: placing in 45 ℃ oven for curing, and obtaining optical fiber film (1) after demolding.

9. The preparation method of the light-to-heat conversion phase change heat storage structure of inverse temperature gradient according to claim 7, characterized in that, The preparation method of first expanded graphite plate (2) and second expanded graphite plate (3) in step 1 is as follows: Step b1: weighing expanded graphite and phase change material powder according to mass ratio 1:2-9; Step b2: mixing uniformly and placing in mold, and pressing molding under 10-30 MPa pressure; Step b3: demolding for standby.

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