Multi-working fluid micro heat pipe heat collecting device

Abstract

The present application relates to the technical field of solar heat collection, in particular to a multi-working medium micro heat pipe heat collection device, which comprises heat collection pipes and a heat collection assembly arranged in a heat collection box; the heat collection assembly comprises glass cover plates, a selective absorption coating, a strip-shaped micro heat pipe module and a heat preservation layer arranged in layers; the strip-shaped micro heat pipe module comprises first and second micro heat pipes arranged at intervals, and is filled with a first working medium with a boiling point of -30-50 DEG C and a second working medium with a boiling point of 50-130 DEG C; the area ratio of the two strips is 30:70 to 70:30, and the first micro heat pipe has a larger micro channel aperture than the second micro heat pipe; the second micro heat pipe is provided with a capillary structure in the evaporation section; the condensation sections of the first and second micro heat pipes are thermally coupled with the heat collection pipes, and the selective absorption coating is arranged between the glass cover plates and the module. The device realizes high-efficiency heat collection in a wide temperature range and overcomes the poor adaptability of the existing single-working medium heat collection device.

Description

Technical Field

[0001] This invention relates to the field of solar thermal collector technology, specifically to a multi-working-medium micro heat pipe thermal collector device. Background Technology

[0002] With the development of new energy technologies, solar thermal utilization is gradually evolving from traditional flat-plate collectors to high-efficiency, wide-temperature-range composite collectors. Among existing technologies, flat-plate micro heat pipe collectors are widely used in domestic hot water, building heating, and some industrial heating applications due to their fast start-up and high heat transfer efficiency. However, existing single-working-fluid micro heat pipe collectors suffer from insufficient adaptability in different seasons and environments: in low-temperature environments, the working fluid does not evaporate easily, resulting in a higher start-up temperature and less than ideal heat collection performance in winter or under low light conditions; in high-temperature conditions, low-boiling-point working fluids can lead to excessively high steam pressure, affecting system stability and service life.

[0003] Chinese Patent CN108981191A discloses a flat-plate micro heat pipe type vacuum tube solar collector, including a shell, which is an insulated shell; a heat transfer copper tube, in which a heat-collecting working medium is disposed; multiple flat-plate micro heat pipes, in which a heat transfer working medium is disposed, and the multiple flat-plate micro heat pipes are linearly and uniformly distributed on the heat transfer copper tube; multiple vacuum tubes, each corresponding to a flat-plate micro heat pipe, and the vacuum tubes are sleeved on the flat-plate micro heat pipes; and sealing plugs through which the flat-plate micro heat pipes pass. The advantages of this invention are: high heat collection efficiency, good heat preservation performance, and significantly improved photothermal conversion efficiency; and the device is easy to assemble and disassemble, facilitating maintenance. However, this device uses only a single working medium, which cannot simultaneously achieve rapid low-temperature start-up and stable high-temperature operation, resulting in significant efficiency fluctuations under different climatic conditions.

[0004] Chinese patent CN105042908A discloses a hybrid flow channel dual-effect solar collector core and collector, including end faces at both ends, an absorber plate between the two end faces, a base plate below the absorber plate, and a ventilation layer in the cavity between the absorber plate, the base plate, and the end faces. A grid-shaped fluid channel is provided on the back of the absorber plate. An air guide plate is provided along the length of the collector core within the ventilation layer, and an air inlet pipe and an air outlet pipe are connected to the ventilation layer. This hybrid flow channel dual-effect solar collector core has high heat collection efficiency and can employ hot air heating, hot water supply, or simultaneous hot air and hot water supply according to different seasonal temperature changes and actual needs. However, this scheme requires complex loop switching and control, resulting in high system cost and poor reliability, making it unsuitable for the widespread application of integrated plate collectors.

[0005] To address the aforementioned issues, designing a heat collection device that can be stably applied to different climatic conditions, while simultaneously meeting the requirements of rapid start-up at low temperatures and stable output at high temperatures, has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the insufficient adaptability of existing flat-plate micro heat pipe collectors to different ambient temperature ranges, this application provides a multi-working-medium micro heat pipe collector device, comprising: a collector pipe and a collector assembly disposed within a collector box. The collector assembly includes a glass cover plate, a selective absorption coating, a strip-shaped micro heat pipe module, and an insulation layer arranged in layers. The strip-shaped micro heat pipe module includes at least two types of micro heat pipes arranged at intervals, with different types of micro heat pipes filled with working fluids of different boiling points, forming a sequentially activated evaporation structure. The different types of micro heat pipes are arranged side-by-side in strip form, forming a preset strip area ratio. The strip-shaped micro heat pipe module is inclined, and each type of micro heat pipe includes an evaporation section and a condensation section. The evaporation section is located at a lower position, and the condensation section is located at a higher position and thermally coupled to the collector pipe. This structure utilizes gravity-assisted liquid reflux to form a unidirectional heat transfer thermal diode effect, thereby blocking reverse heat dissipation from the collector pipe to the micro heat pipes.

[0007] Preferably, the strip-shaped micro heat pipe module includes a first micro heat pipe and a second micro heat pipe spaced apart. The first micro heat pipe is filled with a first working fluid, and the second micro heat pipe is filled with a second working fluid. Under standard atmospheric pressure, the boiling point of the second working fluid is higher than that of the first working fluid. The first and second micro heat pipes are arranged side by side in a strip-like form, forming a preset strip area ratio, wherein the strip area ratio refers to the ratio of the total coverage area of ​​the first micro heat pipe to the total coverage area of ​​the second micro heat pipe. The first micro heat pipe includes a first evaporation section and a first condensation section, and the second micro heat pipe includes a second evaporation section and a second condensation section. Both the first and second condensation sections are thermally coupled to the heat collection pipe. With this structural design, the first micro heat pipe is preferentially activated at a lower temperature, and the second micro heat pipe operates at a higher temperature, thereby achieving staged evaporation. The first and second condensation sections are both thermally coupled to the heat collection pipe, achieving efficient heat transfer.

[0008] To adapt to varying solar radiation levels and seasonal differences in different regions, this application further limits the strip area ratio of the first and second micro heat pipes to a range of 30:70 to 70:30. By changing the width or number of strips, the light exposure ratio of different working fluids can be adjusted. For example, in high-latitude, low-temperature regions, the coverage area of ​​the first micro heat pipe can be appropriately increased to ensure rapid evaporation of the low-temperature working fluid; in low-latitude, high-temperature regions, the coverage ratio of the second micro heat pipe can be increased to obtain higher heat output.

[0009] Preferably, the boiling point of the first working fluid is -30℃ to 50℃, and the boiling point of the second working fluid is 50℃ to 130℃. In this way, the first working fluid can evaporate rapidly in a low-temperature environment, ensuring the heat collection efficiency in winter and early morning; the second working fluid can operate stably in a high-temperature environment, suitable for summer and midday strong sunlight conditions, avoiding structural damage caused by excessive pressure.

[0010] Preferably, the first working fluid includes R134a, R152a, R1234yf, R1234ze, R1233zd(E), R1336mzz(Z), and cyclopentane; the second working fluid includes water, a 10%~60% volume concentration ethylene glycol aqueous solution, a 10%~60% volume concentration propylene glycol aqueous solution, isopropanol, acetone, methanol, and ethanol. Different applicable temperature ranges can be obtained through reasonable combinations. For example, the combination of R1233zd(E) and water is suitable for medium- and low-temperature hot water applications; the combination of R1234yf and a 50% volume concentration ethylene glycol aqueous solution is suitable for scenarios requiring both rapid low-temperature start-up and stable high-temperature heating.

[0011] Preferably, the liquid volume fraction of the first micro heat pipe is 25%~45%, and the liquid volume fraction of the second micro heat pipe is 20%~40%. A higher filling rate can improve heat exchange capacity, but may increase the start-up temperature; a lower filling rate is beneficial for rapid start-up, but may cause the evaporation section to dry out. By optimizing the filling amount, a balance between start-up performance and stability can be achieved.

[0012] Considering the differences in physical properties and gas-liquid two-phase flow resistance between different working fluids, the first microchannel aperture of the first micro heat pipe is designed to be larger than the second microchannel aperture of the second micro heat pipe. The first working fluid has extremely low surface tension and a large saturated vapor specific volume, making it prone to reaching the gas-liquid carrying limit and generating huge frictional vapor resistance within narrow channels. Therefore, a larger aperture must be used to reduce flow resistance. On the other hand, the second working fluid not only has extremely high surface tension, providing very high capillary suction force, but also has a relatively high viscosity in its high-boiling-point liquid phase. By reducing the aperture and combining it with an internal capillary structure, it can effectively overcome viscous frictional resistance by relying on a large Laplace capillary pressure difference, preventing the occurrence of high-temperature dry burning limit.

[0013] Furthermore, the first microchannel has an aperture of 2mm to 6mm, and the second microchannel has an aperture of 0.5mm to 3.0mm. This size ratio ensures that the first microheat pipe has a rapid response, while the second microheat pipe has good liquid reflux performance. For example, when the first working fluid is acetone, a 3mm aperture is sufficient for rapid evaporation; when the second working fluid is ethylene glycol, a 1mm aperture capillary structure can provide sufficient reflux driving force.

[0014] Furthermore, it also includes a regulating valve disposed at the water inlet end of the heat collection tube, and a temperature sensor for monitoring the temperature of the strip-shaped micro heat pipe module; the regulating valve adjusts the flow rate of the heat transfer medium in the heat collection tube according to the feedback signal of the temperature sensor.

[0015] Furthermore, the angle of inclination of the strip-shaped micro heat pipe module (2) to the horizontal plane is not less than 15°.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. By arranging a first micro heat pipe and a second micro heat pipe filled with different working fluids side by side in a strip-shaped micro heat pipe module, wherein the first working fluid is a low-boiling-point fluid and the second working fluid is a high-boiling-point fluid, the device can start up quickly under low-temperature conditions and maintain stable output under high-temperature conditions, thus achieving efficient heat collection over a wide temperature range and overcoming the shortcomings of poor adaptability of existing single-working-fluid micro heat pipes.

[0017] 2. By setting the strip area ratio of the first and second micro heat pipes (30:70 to 70:30) and combining it with different liquid charge volume fractions, passive adjustment of the device's start-up temperature and operating characteristics is achieved. Without the need for a complex control system, it can be adapted to different regional sunlight conditions or usage requirements, improving the system's reliability and economy.

[0018] 3. By differentiating the microchannel apertures of the first and second micro heat pipes, which are 2mm to 6mm and 0.5mm to 3.0mm respectively, the rapid evaporation of low-boiling-point working fluids is ensured, while the capillary reflux capacity of high-viscosity working fluids is enhanced, thereby improving the overall heat transfer stability.

[0019] 4. By setting a sintered layer, mesh material or microfins and other capillary structures in the evaporation section of the second micro heat pipe, the liquid reflux rate of the high boiling point working fluid is significantly improved, the drying phenomenon is prevented, and the continuous operation of the device under high temperature conditions is guaranteed.

[0020] 5. The device adopts an integrated plate design, and the strip-shaped micro heat pipe modules can be modularly packaged in parallel, which is not only convenient for production and processing, but also conducive to large-scale application, and has high promotion value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the framework structure of the present invention; Figure 2 This is a schematic diagram of the layered structure of the present invention; Figure 3 This is a schematic diagram of the strip-shaped micro heat pipe module of the present invention with a strip area ratio of 40:60; Figure 4 This is a schematic diagram of the strip-shaped micro heat pipe module of the present invention with a strip area ratio of 50:50; Figure 5 This is a schematic diagram of the strip-shaped micro heat pipe module of the present invention with a strip area ratio of 60:40; Figure 6 This is a simulated temperature distribution cloud map of the total temperature of the device of the present invention when it is filled with acetone working fluid at four ambient temperatures: -10℃, 0℃, 10℃, and 20℃. Figure 7 This is a simulated temperature distribution cloud map of the total temperature of the device of the present invention when it is filled with R134a working fluid under four ambient temperatures: -10℃, 0℃, 10℃, and 20℃. Figure 8 This is a simulated temperature distribution cloud map of the total temperature under four ambient temperatures: -10℃, 0℃, 10℃, and 20℃, when the device of the present invention adopts an acetone-R134a cross-arrangement structure.

[0022] In the figure: 1. Glass cover plate; 2. Strip-shaped micro heat pipe module; 21. First micro heat pipe; 211. First evaporation section; 212. First condensation section; 22. Second micro heat pipe; 221. Second evaporation section; 222. Second condensation section; 3. Insulation layer; 4. Heat collection pipe; 5. Heat collection box; 6. Selective absorption coating. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Existing flat-plate micro heat pipe collectors mostly employ a single working fluid design: when using a low-boiling-point working fluid, although it can start up quickly in low-temperature environments, it is prone to excessively high steam pressure in strong light or high-temperature environments, affecting system safety and lifespan; when using a high-boiling-point working fluid, although it can meet the stable heating requirements under high-temperature conditions, it is difficult to start up in cold regions or under low-light conditions, resulting in low efficiency in winter or early morning. Therefore, the main problem with existing technologies is that they are difficult to balance rapid start-up at low temperatures and stable operation at high temperatures, resulting in insufficient adaptability.

[0025] Existing single-working-fluid solar collectors struggle to simultaneously handle both low-temperature and high-temperature conditions. This invention provides a multi-working-fluid micro heat pipe solar collector, as described in the reference. Figures 1-2It includes: a heat collection tube 4 and a heat collection assembly installed inside the heat collection box 5. The heat collection assembly includes a glass cover plate 1, a selective absorption coating 6, a strip-shaped micro heat pipe module 2 and an insulation layer 3 arranged in layers. The strip-shaped micro heat pipe module 2 includes at least two types of micro heat pipes arranged at intervals. The different types of micro heat pipes are filled with working fluids with different boiling points to form staged evaporation and condensation. The various types of micro heat pipes are arranged side by side in strip form to form a preset strip area ratio. Each type of micro heat pipe includes an evaporation section and a condensation section. The evaporation section is located at a low position and the condensation section is located at a high position and is thermally coupled to the heat collection tube 4.

[0026] In a preferred embodiment, reference Figure 3 The strip-shaped micro heat pipe module 2 includes a first micro heat pipe 21 and a second micro heat pipe 22 spaced apart. The first micro heat pipe 21 is filled with a first working fluid, and the second micro heat pipe 22 is filled with a second working fluid. Under standard atmospheric pressure, the boiling point of the second working fluid is higher than that of the first working fluid. The first micro heat pipe 21 and the second micro heat pipe 22 are arranged side by side in a strip form, forming a preset strip area ratio, where the strip area ratio refers to the ratio of the total coverage area of ​​the first micro heat pipe 21 to the total coverage area of ​​the second micro heat pipe 22. The first micro heat pipe 21 includes a first evaporation section 211 and a first condensation section 212, and the second micro heat pipe 22 includes a second evaporation section 221 and a second condensation section 222. Both the first condensation section 212 and the second condensation section 222 are thermally coupled to the heat collection pipe 4. This invention utilizes gravity to achieve the thermal diode effect. In actual installation, the strip-shaped micro heat pipe module 2 must maintain a certain tilt angle (usually ≥15°). When the first micro heat pipe 21 is activated at a low temperature and heats up the collector pipe 4, although the second micro heat pipe 22 has not yet reached the phase change triggering condition and the temperature of the evaporation section is lower than that of the collector pipe 4, due to gravity, all the liquid working fluid in the second micro heat pipe 22 is deposited in the bottom evaporation section, and the condensation section is in a dry and liquid-free state. Therefore, the reverse phase change cycle of condensation in the evaporation section and evaporation in the condensation section cannot occur, fundamentally blocking the physical path of the collected heat flowing back to the environment.

[0027] This invention employs two types of working fluids, and their boiling point ranges are set based on the following relationship: , in, The start-up temperature of the solar collector depends on the saturation temperature of the working fluid at the operating pressure. The boiling point referred to in this invention is a conventional classification standard for different working fluids with varying physical properties. Under actual closed vacuum operation, the first working fluid, operating in the low-temperature range of -30°C to 50°C, possesses a relatively high and moderate saturated vapor pressure and vapor density, enabling rapid initiation of continuous phase change cycles and ensuring a fast response in winter. The second working fluid, operating in this low-temperature range, has extremely low saturated vapor pressure and is non-conductive, but its latent heat of phase change is large in the high-temperature range of 50°C to 130°C, exhibiting excellent heat-carrying potential and superior thermal stability, thus preventing system overpressure. Through this structural design, the first working fluid preferentially initiates rapid evaporation at lower temperatures, ensuring heat collection efficiency in winter and early morning; the second working fluid operates stably in high-temperature environments, suitable for summer and midday sunlight conditions, avoiding structural damage due to excessive pressure, thereby achieving staged evaporation. It should be noted that in this application, the "boiling point" of the working fluid is not fixed at standard atmospheric pressure. The standard boiling point only represents the temperature at which a substance vaporizes at 1 atmosphere. However, within a sealed or vacuum-sealed micro heat pipe, the internal pressure is typically lower or higher than standard atmospheric pressure, causing a deviation in the actual vaporization temperature. When the interior is partially vacuumed, the actual boiling point of the working fluid will be significantly lower; for example, water begins to boil at approximately 90°C at 70 kPa, thus facilitating rapid low-temperature start-up. Conversely, under high-pressure operation or with a large filling volume, the boiling point of the working fluid will increase accordingly, preventing premature vaporization. Furthermore, the curvature pressure generated by the capillary structure within the microchannel will further alter the local phase transition conditions, causing a difference between the actual vaporization temperature and the standard value. Therefore, this invention, by controlling the sealing pressure, capillary size, and filling rate, allows the first and second working fluids to sequentially enter the evaporation state in different temperature zones, achieving staged heat absorption and efficient heat transfer.

[0028] The surface area of ​​the working fluid exposed to light is directly proportional to its latent heat of vaporization: , in Let i be the absorbed power corresponding to the i-th type of working fluid. Solar irradiance (W / m²) For the areas of the first and second micro heat pipe strips, To improve absorption efficiency, and to adapt to varying solar radiation levels and seasonal differences in different regions, this application further defines the strip area ratio of the first micro heat pipe 21 and the second micro heat pipe 22. : =30:70∼70:30. Figures 3-5 Strip-shaped micro heat pipe modules with strip area ratios of 40:60, 50:50, and 60:40 are shown respectively. By changing the width or number of strips, the light exposure ratio of different working fluids can be adjusted. For example, in high-latitude, low-temperature regions, the coverage area of ​​the first micro heat pipe 21 can be appropriately increased to ensure rapid evaporation of the low-temperature working fluid; in low-latitude, high-temperature regions, the coverage ratio of the second micro heat pipe 22 can be increased to obtain higher heat output.

[0029] For example, the first working fluid includes R134a, R152a, R1234yf, R1234ze, R1233zd(E), R1336mzz(Z), cyclopentane, etc., and the second working fluid includes water, 10%~60% volume concentration of ethylene glycol aqueous solution, 10%~60% volume concentration of propylene glycol aqueous solution, isopropanol, acetone, methanol, ethanol, etc. Different applicable temperature ranges can be obtained through reasonable combinations. For example, the combination of R1233zd(E) and water is suitable for medium and low temperature hot water applications; the combination of R1234yf and 50% volume concentration of ethylene glycol aqueous solution is suitable for scenarios requiring both rapid low-temperature start-up and stable high-temperature heating. Considering safety and explosion prevention, some common working fluids that meet boiling point requirements are excluded, such as isobutane, dimethyl ether, toluene, etc. It should be noted that applications containing flammable solvents, such as acetone and ethanol, are only suitable for sealed vacuum chambers. Under certain operating conditions, acetone, methanol, ethanol, cyclopentane, etc. can also be used as the primary working fluid.

[0030] In a preferred embodiment of the present invention, the thermal response behavior of the solar collector is highly correlated with the thermophysical properties of the working fluid inside the flat micro heat pipe. To verify the technical advantages of the present invention, a solar radiation intensity of 700 W / m² was used. 2 Under the condition of a constant inlet water temperature of 20℃, CFD simulation analysis was conducted on the acetone-R134a cross-arrangement structure device system at four ambient temperatures (-10℃, 0℃, 10℃, and 20℃). The results are as follows: Figures 6-8 As shown in the diagram, by comparing simulated heat pipe diagrams at different ambient temperatures, it can be observed that the collector filled with R134a exhibits a significant start-up advantage at low temperatures of -10℃ and 0℃. Because R134a, as a low-boiling-point working fluid, has an extremely low phase change point within the vacuum chamber, even at sub-zero ambient temperatures, the heat pipe can rapidly activate the internal evaporation-condensation cycle, quickly transferring heat from the absorber plate. The temperature rise reflected in the heat pipe diagram shows a very uniform temperature rise on the absorber surface, and the heat flow channel towards the collector pipe is established extremely quickly, effectively solving the thermal hysteresis phenomenon commonly seen in extremely cold regions.

[0031] In contrast, when using pure acetone as the working fluid, its performance at low temperatures is slightly less sluggish. Simulation results are as follows... Figure 6As shown, even under vacuum, the temperature difference required for acetone to start up is still greater than R134a. In the cloud map at -10℃, a large blue-green area exists in the center of the absorber plate, indicating that the micro heat pipe has not yet fully entered the working state, and heat transfer is limited by the slow evaporation rate of the working fluid. However, the heat transfer potential of acetone is released in the high-temperature range. When the ambient temperature rises to 20℃, the high-temperature consistency of its cloud map significantly improves. This is mainly due to the high latent heat of vaporization of acetone, which gives it better thermal stability when facing high radiative loads and can effectively avoid the drying limit caused by local heat accumulation.

[0032] This embodiment utilizes a spatial heterogeneous layout with acetone and R134a heat pipes arranged in a cross configuration, leveraging the complementary properties of the two working fluids to achieve performance self-adaptation across the entire temperature range. During initial startup or in extremely cold conditions, the R134a heat pipe acts as a thermal trigger, activating heat transfer. The resulting localized temperature rise helps the adjacent acetone heat pipes quickly overcome the startup threshold. At higher temperatures, acetone, with its superior heat-carrying capacity, assumes the main load, effectively mitigating the potential internal high-pressure risk that R134a might face under extreme radiation. Simulation results show that this hybrid configuration maintains high heat collection efficiency within an environment ranging from -10℃ to 20℃, and significantly smooths the temperature gradient on the absorber surface. This synergistic working mechanism, where low-temperature startup is aided by the first working fluid and high-temperature operation is guaranteed by the second working fluid, not only reduces localized overheating caused by performance bottlenecks in a single working fluid but also provides more reliable technical support for the widespread application of solar collectors in different climate zones.

[0033] The optimal charge amount for a micro heat pipe is related to its internal volume and evaporation length. The formula for the charge volume fraction is: , in To fill the volume fraction, For liquid volume, The total volume is considered. An appropriate liquid volume fraction is crucial for ensuring the high efficiency of the heat pipe. If the liquid volume fraction is too high, it can easily cause intermittent boiling, disrupting heat transfer stability; a lower liquid volume fraction is beneficial for rapid start-up response, but it can easily lead to the drying out of the evaporation section under localized high heat flux density. In a preferred embodiment, the liquid volume fraction of the first micro heat pipe 21 is 25%~45%, for example, 25%, 27%, 30%, 35%, 40%, 45%; the liquid volume fraction of the second micro heat pipe 22 is 20%~40%, for example, 20%, 22%, 25%, 30%, 33%, 35%, 40%. By optimizing the liquid volume, a balance between start-up performance and stability can be achieved.

[0034] Considering the differences in the physical properties of different working fluids, the microchannel pore size should be matched with the capillary pressure difference. Specifically, the capillary reflux capacity is determined by the Laplace formula: , in For capillary pressure difference, For surface tension, Contact angle, This is the equivalent pore radius. High-boiling-point working fluids have high viscosity and require a large capillary pressure differential; therefore, the pore size should be reduced. Low-boiling-point working fluids have low viscosity and require less capillary reflux, allowing for the use of large pore sizes to increase flow rate and evaporation area. Therefore, the first microchannel pore size of the first micro heat pipe 21 is designed to be larger than the second microchannel pore size of the second micro heat pipe 22. This differentiated pore size design enhances the overall heat transfer stability of the system.

[0035] In a preferred embodiment, the first microchannel pore size is 2mm to 6mm, and the second microchannel pore size is 0.5mm to 3.0mm. This size ratio ensures that the first microheat pipe 21 has a rapid response, and the second microheat pipe 22 has good liquid reflux performance. For example, when the first working fluid is acetone, a 3mm pore size is sufficient for rapid evaporation; when the second working fluid is ethylene glycol, a 1mm pore size capillary structure can provide sufficient reflux driving force.

[0036] For the second micro heat pipe 22, due to its high operating temperature and high working fluid viscosity, a capillary structure, such as a sintered layer, mesh material, or microfins, is incorporated into its evaporation section to improve liquid reflux rate and prevent drying. This capillary structure is particularly necessary when using high-viscosity working fluids. The sintered layer is formed by sintering metal powder to create a porous capillary core with pore sizes between 10μm and 100μm, providing strong capillary pressure suitable for high-viscosity working fluid reflux, such as a 50% volume concentration ethylene glycol aqueous solution. The mesh material can be made of copper, stainless steel, or nickel mesh, arranged closely to the channel wall, utilizing capillary adsorption to enhance liquid reflux rate. The microfin structure involves machining fine fins or grooves on the inner wall of the channel to increase liquid film flow channels and improve liquid replenishment efficiency, suitable for low-viscosity working fluids such as water and isopropanol.

[0037] Through systematic analysis of the thermophysical properties, physical properties, and operational characteristics of the working fluid, this invention establishes a synergistic design relationship in terms of material selection, microchannel structure, charge volume control, and area ratio optimization. This enables the solar collector to achieve full-cycle operation capabilities, from rapid response at low temperatures to continuous heating at medium temperatures, and then to stable output at high temperatures, significantly improving the overall efficiency and environmental adaptability of the solar thermal utilization system.

[0038] In an optional embodiment, a selective absorption coating 6 is disposed between the glass cover plate 1 and the strip-shaped micro heat pipe module 2. The selective absorption coating 6 can be made of black chromium, TiNOx, black nickel, or carbon nanotubes, with an absorption rate of sunlight α ≥ 0.9 and an infrared emissivity ε ≤ 0.2, which can significantly improve the photothermal conversion efficiency, enabling the micro heat pipe evaporation section to achieve a higher heat flux density and enhancing the evaporation driving force. Furthermore, the insulation layer 3 can be made of polyurethane foam, aerogel, vacuum insulation panels, etc., which improves the overall thermal efficiency of the heat collection device by reducing heat conduction and convection losses to the back side. These two elements create a closed-loop optimization at the input and output ends of the heat collector; this coordinated design significantly improves the heat collection efficiency.

[0039] Based on this, multiple sets of heat collection tubes 4 and heat collection components can be encapsulated within a heat collection box 5.

[0040] Examples of different scenarios are listed below.

[0041] Example 1

[0042] In low-latitude regions, the average annual solar radiation intensity is high, and the required temperature for household hot water is generally 40℃~60℃. R1233zd(E) is selected as the primary working fluid, and water as the secondary working fluid. R1233zd(E) can still evaporate rapidly in the early morning or on cloudy days, while water provides high-temperature output during periods of strong sunlight. The strip area ratio is designed to be 50:50 to balance low-temperature start-up and high-temperature stability. R1233zd(E) has a low viscosity, so a 3mm pore size is selected; water has a slightly higher viscosity, so a 1mm pore size is selected, and a sintered capillary structure is added to the evaporation section. For R1233zd(E), a 30% volume fraction is selected to ensure rapid evaporation; for water, a 25% volume fraction is selected to balance reflux and the evaporation interface. In winter mornings at 10℃, the R1233zd(E) evaporation temperature is about 10℃~20℃ to start, ensuring the water tank is initially heated; in summer midday at 35℃, the water pipe temperature can stably output 60℃ hot water to meet the hot water needs of the household.

[0043] Example 2

[0044] In northern regions where winter temperatures can drop to -10°C, the heating system requires temperatures between 50°C and 80°C. The primary working fluid is R1234yf, ensuring evaporation even at extremely low temperatures. The secondary working fluid is a 30% (v / v) propylene glycol aqueous solution, guaranteeing good antifreeze properties and heating stability under strong sunlight. The strip area ratio is designed to be 70:30 to improve low-temperature start-up capability and ensure heating on winter mornings. R1234yf has extremely low viscosity and is designed with a 4mm pore size; the 30% (v / v) propylene glycol aqueous solution has slightly higher viscosity and is designed with a 1.2mm pore size, employing a microfin capillary structure to enhance reflux. For R1234yf, a 40% (v / v) volume fraction is used to improve low-temperature evaporation capacity; for the 30% (v / v) propylene glycol aqueous solution, a 25% (v / v) volume fraction is used to avoid reflux obstruction due to excessive liquid.

[0045] Example 3

[0046] Based on the aforementioned dual-working-fluid micro heat pipe heat collection device scheme, under high radiation and high ambient temperature conditions in summer, micro heat pipes that are continuously filled with low-boiling-point working fluid are prone to bursting due to excessive internal steam pressure. To address this issue, this embodiment optimizes the operating conditions by adding a valve control mechanism, specifically as follows: An adjustable valve is installed at the water inlet of the heat collection pipe 4. By controlling the valve opening, the flow rate of the heat transfer medium inside the heat collection pipe 4 is changed, thereby achieving temperature and pressure regulation under different radiation conditions.

[0047] A proportional regulating valve and a temperature sensor are installed at the water inlet of collector tube 4. When under high radiation conditions and the collector temperature approaches the safe pressure threshold of the first working fluid, the regulating valve increases its opening, increasing the flow rate of cold water inside collector tube 4. At this time, the second working fluid, with its huge latent heat of vaporization and excellent phase change heat transfer capacity, bears the main heat load, rapidly removing the heat from the entire collector assembly through extremely high heat transfer flux. Due to the uniform temperature effect of heat conduction within the same plate, the efficient heat dissipation of the second working fluid forcibly suppresses the local temperature of the first micro heat pipe within a safe range, effectively curbing its internal saturated vapor pressure. This control mechanism, without wasting solar energy, utilizes the large latent heat dissipation channel of the second working fluid to perfectly ensure the structural safety and operational life of the first micro heat pipe under extreme conditions.

[0048] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A multi-working-medium micro heat pipe heat collection device, comprising: The heat collection tube (4) and heat collection assembly are installed inside the heat collection box (5). The heat collection assembly includes a glass cover plate (1), a selective absorption coating (6), a strip-shaped micro heat pipe module (2), and a heat insulation layer (3) arranged in sequence. The heat collection assembly is characterized by... The strip-shaped micro heat pipe module (2) includes at least two types of micro heat pipes spaced apart. Different types of micro heat pipes are filled with working fluids with different boiling points to form an evaporation structure that starts sequentially. The different types of micro heat pipes are arranged side by side in strip form to form a preset strip area ratio; The strip-shaped micro heat pipe module (2) is inclined. The different types of micro heat pipes all include an evaporation section and a condensation section. The evaporation section is in a low position, and the condensation section is in a high position and is thermally coupled to the heat collection pipe (4).

2. The multi-working-medium micro heat pipe heat collection device according to claim 1, characterized in that, The strip-shaped micro heat pipe module (2) includes a first micro heat pipe (21) and a second micro heat pipe (22) arranged at intervals. The first micro heat pipe (21) is filled with a first working fluid, and the second micro heat pipe (22) is filled with a second working fluid. Under standard atmospheric pressure, the boiling point of the second working fluid is higher than that of the first working fluid. The first micro heat pipe (21) and the second micro heat pipe (22) are arranged side by side in the form of strips to form a preset strip area ratio, wherein the strip area ratio refers to the ratio of the total coverage area of ​​the first micro heat pipe (21) to the total coverage area of ​​the second micro heat pipe (22); The first micro heat pipe (21) includes a first evaporation section (211) and a first condensation section (212), and the second micro heat pipe (22) includes a second evaporation section (221) and a second condensation section (222). The first condensation section (212) and the second condensation section (222) are both thermally coupled to the heat collection pipe (4).

3. The multi-working-medium micro heat pipe heat collection device according to claim 2, characterized in that, The area ratio of the strips is 30:70 to 70:

30.

4. The multi-working-medium micro heat pipe heat collection device according to claim 2, characterized in that, The boiling point of the first working substance is -30℃ to 50℃, and the boiling point of the second working substance is 50℃ to 130℃.

5. The multi-working-medium micro heat pipe heat collection device according to claim 4, characterized in that, The first working medium includes R134a, R152a, R1234yf, R1234ze, R1233zd(E), R1336mzz(Z), and cyclopentane. The second working medium includes water, an aqueous solution of ethylene glycol with a volume concentration of 10% to 60%, an aqueous solution of propylene glycol with a volume concentration of 10% to 60%, isopropanol, acetone, methanol, and ethanol.

6. The multi-working-medium micro heat pipe heat collection device according to claim 2, characterized in that, The liquid volume fraction of the first micro heat pipe (21) is 25%~45%, and the liquid volume fraction of the second micro heat pipe (22) is 20%~40%.

7. The multi-working-medium micro heat pipe heat collection device according to claim 2, characterized in that, The first microchannel aperture of the first micro heat pipe (21) is larger than the second microchannel aperture of the second micro heat pipe (22).

8. The multi-working-medium micro heat pipe heat collection device according to claim 7, characterized in that, The first microchannel has a diameter of 2mm to 6mm, and the second microchannel has a diameter of 0.5mm to 3.0mm.

9. The multi-working-medium micro heat pipe heat collection device according to claim 1, characterized in that, It also includes a regulating valve installed at the water inlet of the heat collection tube (4) and a temperature sensor for monitoring the temperature of the strip-shaped micro heat pipe module (2); the regulating valve adjusts the flow rate of the heat transfer medium in the heat collection tube (4) according to the feedback signal of the temperature sensor.

10. The multi-working-medium micro heat pipe heat collection device according to claim 1, characterized in that, The angle of inclination of the strip-shaped micro heat pipe module (2) to the horizontal plane is not less than 15°.

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