A nanofluid direct absorption solar collector

Abstract

This invention belongs to the field of energy-saving and environmental protection technology, specifically relating to a nanofluid direct absorption solar collector. It comprises a closed space enclosed by a metal outer wall panel and a transparent glass cover, including a heat collection and storage zone, an insulation and pressurization zone, and a heat exchange zone. The heat collection and storage zone uses nanofluid as the direct heat collection medium, utilizing low-temperature and high-temperature heat storage bodies. The low-temperature heat storage body is composed of fins and a low-melting-point phase change material, while the high-temperature heat storage body is composed of transparent glass and a high-melting-point phase change material. The insulation and pressurization zone pressurizes the nanofluid via a circulating pump and sends it to the heat collection channel. The heat exchange zone consists of a heat exchange box and heat exchange coils, with the coils connected to the inlet and outlet. The nanofluid and phase change materials with different melting points form a multi-layered radiation absorption structure, offering advantages over traditional collectors such as high heat collection efficiency, low heat loss, and large heat storage capacity. It eliminates the need for a separate hot water storage tank, has a compact structure, and is more adaptable to different weather conditions.

Description

Technical fields:

[0002] This invention belongs to the field of energy conservation and environmental protection technology, and specifically relates to a nanofluid direct absorption solar collector. Background technology:

[0004] Traditional solar collectors have a selective absorption coating on their sun-facing surface. This coating absorbs solar radiation, heats up, and then transfers the heat to the working medium. However, the high temperature of the coating results in significant heat loss, and the indirect heat collection process also reduces collection efficiency. Therefore, direct absorption solar collectors have emerged. These collectors contain heat-absorbing particles that efficiently absorb solar radiation while also functioning as a heat exchanger, avoiding the heat losses caused by the high-temperature coating and indirect heat collection of traditional solar collectors.

[0005] Solar collectors and hot water storage tanks are typically installed separately. The hot water storage tanks use sensible heat storage, which has several drawbacks: firstly, the tank's heat storage capacity is limited, making it difficult to meet demand at night or during prolonged periods of cloudy or rainy weather; secondly, the tanks are bulky, unsightly, and occupy building space. In recent years, phase change thermal storage technology has received widespread attention due to its advantages such as high energy density and constant-temperature heat release. Using phase change thermal storage devices can improve energy storage efficiency, reduce building space requirements, and enhance heating stability. Research indicates that integrating the collector and phase change material into a single integrated collector-storage device will further improve solar energy utilization and save building space.

[0006] Conventional phase change energy storage devices use only one type of phase change material with a specific melting point, resulting in a narrow operating temperature range and poor weather adaptability. In contrast, devices employing multiple phase change materials with different melting points allow the heat absorption and release processes to proceed sequentially between these materials, driven by temperature differences. This results in a wider operating temperature range, stronger climate adaptability, and the ability to achieve graded storage and utilization of solar energy.

[0007] Multilayer semi-transparent medium full-spectrum absorption is the latest hot research direction in the field of photothermal conversion and transmission. Applying it to the design of solar collectors and optimizing the selection of glass plates, heat-absorbing working fluids and transparent phase change materials with different absorption radiation characteristics is conducive to achieving efficient absorption of the full spectrum of solar energy. Summary of the Invention:

[0009] The purpose of this invention is to provide a nanofluid direct absorption solar collector. Addressing the shortcomings of existing technologies, this invention uses nanofluid as the heat collection medium to improve heat collection efficiency, while embedding phase change materials to design an integrated heat collection and storage device, saving costs and space. It also employs high and low temperature melting point phase change materials to overcome the problem of limited applicable temperature range for single-melting-point phase change materials. Furthermore, it designs a multi-layered semi-transparent radiation absorption structure to promote full-spectrum absorption of solar energy.

[0010] The technical solution adopted in this invention is: a nanofluid direct absorption solar collector, characterized in that: the solar collector is a closed cavity surrounded by a metal outer wall plate and a first light-transmitting glass, and the closed cavity is divided into three zones by the metal plate: a heat collection and storage zone, a heat preservation and pressurization zone, and a heat exchange zone.

[0011] The heat collection and storage area includes a second transparent glass, a third transparent glass, a metal inner wall panel, a metal baffle, and ribs; a vacuum insulation layer is located between the second and first transparent glass. The heat collection channel between the second and third transparent glass is connected to the heat exchange box on both sides through nanofluidic tubes. A metal baffle is installed inside the heat collection channel. The metal baffle is staggered and welded to the inner wall of the metal outer wall panel. Several inclined ribs are welded on the metal baffles, and the ribs are filled with phase change material B; phase change material A is filled between the third transparent glass and the metal plate.

[0012] The heat-insulating and pressurizing zone includes nanofluid tubes, circulation pumps, and valves on both sides. The circulation pumps and valves are installed on one side of the nanofluid tubes, and the heat-insulating and pressurizing zone is filled with heat-insulating material.

[0013] The heat exchange zone includes a heat exchange coil and a heat exchange box. The heat exchange coil is located inside the heat exchange box and has an inlet and an outlet at both ends. The heat exchange box contains nanofluid, which is circulated by a circulating pump and flows through the nanofluid tube to the heat collection channel.

[0014] Furthermore, the angle between the ribs and the metal baffle is 45°, and several ribs are arranged in an alternating pattern on the staggered metal baffle, and are distributed in an alternating pattern along the flow direction of the nanofluid.

[0015] Furthermore, both phase change material A and phase change material B are paraffin wax, wherein phase change material A has a melting point of 60-65℃ and a filling thickness of 100-200mm; and phase change material B has a melting point of 40-45℃ and a filling thickness of 10-30mm.

[0016] Furthermore, the thickness of the vacuum insulation layer is 6-20mm, and its perimeter is sealed with epoxy resin sealant.

[0017] Furthermore, the insulation material is disposed in the insulation and pressurization zone and in the interlayer between the outer metal wall panel and the inner metal wall panel, and the insulation material is polyurethane (PU) or extruded polystyrene foam (XPS).

[0018] Furthermore, the nanofluid is an ATO (antimony-doped tin oxide) / water nanofluid with a particle size of 30 mm and a concentration of 1% vol to 2% vol.

[0019] 7. Furthermore, the rib is made of aluminum alloy, stainless steel or copper.

[0020] The beneficial effects of this invention are as follows: It provides a nanofluid-based direct absorption solar collector, addressing the shortcomings of existing technologies. By using nanofluid as the heat collection medium to improve heat collection efficiency, it integrates heat collection and storage into a phase change material design, saving cost and space. The use of high and low temperature melting point phase change materials overcomes the limitation of single-melting-point phase change materials having a limited applicable temperature range. A multi-layered semi-transparent radiation absorption structure promotes full-spectrum solar energy absorption. The nanofluid and phase change materials with different melting points form a multi-layered radiation absorption structure, which, compared to traditional collectors, offers advantages such as high heat collection efficiency, low heat loss, and large heat storage capacity. It eliminates the need for a separate hot water storage tank, resulting in a compact structure and better weather adaptability. Specific advantages are as follows:

[0021] (1) Using nanofluid as the heat collection medium in the direct absorption process can avoid the large amount of heat loss caused by the heating of the coating heat collection and improve the heat collection efficiency.

[0022] (2) Embedding phase change materials into solar collectors and utilizing their latent heat storage capacity increases solar energy storage capacity. The integrated heat storage design does not occupy building space.

[0023] (3) By using two phase change materials with different melting points, the temperature range of solar heat collection and storage is expanded. Through energy graded storage and release, temperature self-control and heat cascade utilization can be realized. At the same time, it is conducive to constant temperature heat release and improving the stability of heating.

[0024] (4) The device designs materials such as glass, nanofluid and paraffin into a multi-layer radiation absorption structure to form a spectral filtering effect, realize the full spectrum dynamic absorption of solar energy, and improve the heat collection efficiency. Attached image description:

[0026] Figure 1 This is a cross-sectional view of the solar collector in Example 1;

[0027] Figure 2 This is a schematic diagram of the cross-sectional structure of the solar collector channel in Embodiment 1;

[0028] Figure 3 This is a top view of the heat exchange zone of the solar collector in Example 1. Detailed implementation method:

[0030] Example 1

[0031] Referring to the figures, a nanofluid direct absorption solar collector is described. The solar collector comprises a closed cavity enclosed by a metal outer wall plate 7 and a first transparent glass plate 1. The dimensions of the metal outer wall plate are: length 2-2.2m, preferably 2.1m; width 1.5-1.8m, preferably 1.65m; and height 0.6-0.8m, preferably 0.7m. This closed cavity is divided into three zones by a metal plate 13: a heat collection and storage zone, a heat insulation and pressurization zone, and a heat exchange zone.

[0032] The heat collection and storage area includes a second transparent glass 3, a third transparent glass 6, a metal inner wall plate 9, a metal baffle 16, and ribs 17. A vacuum insulation layer 2 is located between the second transparent glass 3 and the first transparent glass 1. The heat collection channel 4 between the second transparent glass 3 and the third transparent glass 6 is connected to the heat exchange box 15 on both sides via nanofluidic tubes 10. A metal baffle 16 is installed inside the heat collection channel 4, and the metal baffle 16 is staggered and welded to the inner wall of the metal outer wall plate 7. Several inclined ribs 17 are welded onto the metal baffle 16, and the ribs 17 are filled with phase change material B 18. Phase change material A 5 is filled between the third transparent glass 6 and the metal plate 13. The heat collection and storage area consists of a heat collection channel, a low-temperature heat storage body, a high-temperature heat storage body, a vacuum insulation layer, and metal baffles. The low-temperature heat storage body is composed of ribs and the phase change material B filled inside them, while the high-temperature heat storage body is composed of the third transparent glass, the metal plate, and the phase change material A filled between them.

[0033] The heat preservation and pressurization zone includes nanofluid tubes 10 on both sides, a circulation pump 11 and a valve 12. The circulation pump 11 and the valve 12 are installed on the nanofluid tube 10 on one side, and the heat preservation and pressurization zone is filled with heat preservation material 8.

[0034] The heat exchange zone includes a heat exchange coil 14 and a heat exchange box 15. The heat exchange coil 14 is located inside the heat exchange box 15, and its two ends are respectively provided with a water inlet 19 and a water outlet 20. The heat exchange box 15 is provided with nanofluid. The nanofluid is circulated by a circulation pump 14 and flows through the nanofluid tube 10 to be sent to the heat collection channel 4.

[0035] The included angle between the rib 17 and the metal baffle 16 is 45°. Several ribs (17) are arranged in an alternating manner on the staggered metal baffle 16 and are staggered along the flow direction of the nanofluid.

[0036] Both phase change material A5 and phase change material B18 are paraffin wax, wherein phase change material A5 has a melting point of 60-65℃ and a filling thickness of 100-200mm, preferably 150mm; phase change material B18 has a melting point of 40-45℃ and a filling thickness of 10-30mm, preferably 20mm.

[0037] The thickness of the vacuum insulation layer 2 is 6-20mm, preferably 15mm, and its perimeter is sealed with epoxy resin sealant.

[0038] The thermal insulation material 8 is disposed in the interlayer between the thermal insulation and pressurization zone and the metal outer wall panel 7 and the metal inner wall panel 9. The thermal insulation material 8 is polyurethane (PU) or extruded polystyrene foam material (XPS).

[0039] The nanofluid is an ATO (antimony-doped tin oxide) / water nanofluid with a particle size of 30 mm and a concentration of 1% vol-2% vol.

[0040] The rib 17 is made of aluminum alloy, stainless steel or copper.

[0041] The working principle of the nanofluid direct absorption solar collector is as follows:

[0042] (1) During the heat collection process, the nanofluid flowing out of the heat exchange box is pressurized by the circulation pump and flows into the heat collection channel. During the day, solar radiation enters the heat collection channel after passing through the first transparent glass, the vacuum layer and the second transparent glass. The infrared sunlight is absorbed by the selective absorption working medium (ATO / water nanofluid), while the remaining visible light is transmitted through the third transparent glass to the phase change material A and absorbed.

[0043] (2) Heat storage process: The heat storage body is divided into two parts: a high-temperature heat storage body and a low-temperature heat storage body. The low-temperature heat storage body consists of fins and phase change material B filled inside them. The nanofluid in the heat collection channel transfers heat to the phase change material B for storage through convection and thermal conduction. The high-temperature heat storage body consists of a third transparent glass and a metal plate, with phase change material A filling the gap between the two. The phase change material A absorbs the visible light energy directly transmitted through the third transparent glass by solar energy and the heat transferred by the nanofluid in the heat collection channel through the third transparent glass, thus achieving heat storage.

[0044] (3) During the heat release process, at night or in rainy weather, the temperature of the nanofluid slowly decreases. When the temperature approaches the melting point of phase change material A, phase change material A in the high-temperature heat storage body begins to solidify and release latent heat, which is transferred to the nanofluid in the heat collection channel and heat exchange box through the third transparent glass and metal plate. After phase change material A is completely solidified, it releases heat further. At this time, the temperature of the nanofluid decreases as the temperature of phase change material A decreases. When the temperature drops to the melting point of phase change material B, phase change material B in the low-temperature heat storage body begins to enter the latent heat release stage, and heat continues to be released to the nanofluid. The entire process achieves the cascade utilization of thermal energy through stable heat release at high and low temperatures.

[0045] (4) Heat exchange process: the nanofluid exchanges heat indirectly with the water in the heat exchange coil in the heat exchange box. The heat exchange coil is connected to the water outlet and the water inlet, and provides heat to the corresponding terminal heating device according to the different hot water temperatures.

[0046] The fins located at the inlet and outlet of the heat collection channel gradually decrease in length along the flow direction of the nanofluid, forming a gradient in the length of the fin protrusions. The purpose is to allow the nanofluid and the fins to fully contact and exchange heat.

[0047] While the specific embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention, and modifications or variations that do not constitute creative effort, are still within the protection scope of the present invention.

Claims

1. A nanofluid direct absorption solar collector, characterized in that: The solar collector is a closed cavity formed by a metal outer wall plate (7) and a first transparent glass (1). The closed cavity is divided into three zones by a metal plate (13): a heat collection and storage zone, a heat preservation and pressurization zone, and a heat exchange zone. The heat collection and storage area includes a second transparent glass (3), a third transparent glass (6), a metal inner wall plate (9), a metal baffle (16), and ribs (17); a vacuum insulation layer (2) is between the second transparent glass (3) and the first transparent glass (1); the heat collection channel (4) between the second transparent glass (3) and the third transparent glass (6) is connected to the heat exchange box (15) on both sides through nanofluid tubes (10); a metal baffle (16) is provided in the heat collection channel (4); the metal baffle (16) is staggered and welded to the inner wall of the metal outer wall plate (7); a number of inclined ribs (17) are welded on the metal baffle (16); phase change material B (18) is filled in the ribs (17); phase change material A (5) is filled between the third transparent glass (6) and the metal plate (13). The heat preservation and pressurization zone includes nanofluid tubes (10) on both sides, a circulation pump (11) and a valve (12). The circulation pump (11) and the valve (12) are installed on the nanofluid tube (10) on one side. The heat preservation and pressurization zone is filled with heat preservation material (8). The heat exchange zone includes a heat exchange coil (14) and a heat exchange box (15). The heat exchange coil (14) is located inside the heat exchange box (15), and its two ends are respectively provided with a water inlet (19) and a water outlet (20). The heat exchange box (15) is provided with nanofluid. The nanofluid is driven by a circulating pump (11) and flows through the nanofluid tube (10) to be sent to the heat collection channel (4).

2. The nanofluid direct absorption solar collector according to claim 1, characterized in that: The angle between the ribs (17) and the metal baffle (16) is 45°. Several ribs (17) are arranged in an alternating pattern on the staggered metal baffles (16) and are staggered along the flow direction of the nanofluid.

3. The nanofluid direct absorption solar collector according to claim 1, characterized in that: Both phase change material A (5) and phase change material B (18) are paraffin wax. The melting point of phase change material A (5) is 60-65℃ and the filling thickness is 100-200mm. The melting point of phase change material B (18) is 40-45℃ and the filling thickness is 10-30mm.

4. The nanofluid direct absorption solar collector according to claim 1, characterized in that: The thickness of the vacuum insulation layer (2) is 6-20mm, and its perimeter is sealed with epoxy resin sealant.

5. The nanofluid direct absorption solar collector according to claim 1, characterized in that: The insulation material (8) is placed in the interlayer between the insulation and pressurization zone and the metal outer wall panel (7) and the metal inner wall panel (9). The insulation material (8) is polyurethane (PU) or extruded polystyrene foam material (XPS).

6. The nanofluid direct absorption solar collector according to claim 1, characterized in that: The nanofluid is an ATO / water nanofluid with a particle size of 30 mm and a concentration of 1% vol to 2% vol.

7. The nanofluid direct absorption solar collector according to claim 1, characterized in that: The rib (17) is made of aluminum alloy, stainless steel or copper.

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