Liquid hydrogen storage tank thermal stratification suppression system and method

Abstract

The present application relates to the technical field of low-temperature hydrogen storage, and particularly relates to a liquid hydrogen storage tank thermal stratification suppression system and method, at least comprising: a liquid hydrogen storage tank main body; a bionic fractal flow channel network arranged in the liquid hydrogen storage tank main body, which is in a tree root-like fractal structure and comprises a main stem flow channel and at least two levels of branch flow channels; a plurality of root tip heating units respectively arranged at the end of each terminal branch flow channel and used for locally heating liquid hydrogen; a temperature sensor array distributedly arranged along the height direction of the liquid hydrogen storage tank main body and used for collecting liquid hydrogen temperature data in real time; and a control unit connected with the temperature sensor array and the root tip heating units respectively and used for controlling heating parameters according to temperature differences. The present application can suppress the thermal stratification phenomenon of the liquid hydrogen storage tank in a motionless component-free and self-adaptive adjustment manner.

Description

TECHNICAL FIELD

[0001] The application relates to the field of low-temperature hydrogen storage, and in particular to a liquid hydrogen storage tank thermal stratification suppression system and method. BACKGROUND

[0002] Liquid hydrogen (LH2) is a high-efficiency and clean cryogenic energy carrier with important applications in aerospace propulsion systems, hydrogen fuel cell vehicles, energy storage power stations, and deep space exploration due to its extremely high mass energy density (about 142 MJ / kg) and zero carbon emission characteristics. However, the extremely low temperature characteristics (boiling point 20.27 K, density about 70.8 kg / m³) of liquid hydrogen also pose complex thermal physical and storage problems, with the most prominent being the thermal stratification phenomenon.

[0003] During long-term static storage of liquid hydrogen, due to heat leakage between the storage tank wall and the environment, radiation heat transfer, and latent heat exchange at the gas-liquid interface, a temperature gradient is formed in the liquid hydrogen in the storage tank from top to bottom. The upper layer of liquid hydrogen has a higher temperature and lower density due to heat absorption, while the lower layer of liquid hydrogen remains at a lower temperature, forming a stable density stratification structure. Thermal stratification can cause the following serious problems:

[0004] First, evaporation loss is intensified: the increase in temperature of the upper layer of liquid hydrogen causes the saturation vapor pressure to rise, accelerating vaporization and causing a decrease in effective storage capacity. Second, pressure fluctuation and control difficulty: local vaporization causes non-steady changes in tank pressure, increasing the risk of frequent opening and closing of safety valves. Third, thermal stress and structural fatigue: temperature non-uniformity causes local temperature difference stress in the inner wall of the storage tank, affecting the service life of the structure. Fourth, output quality degradation: for aerospace engine applications, temperature non-uniformity of the propellant can affect combustion stability and specific impulse. Studies have shown that, without intervention, a liquid hydrogen storage tank can form a thermal stratification structure with a temperature difference of more than 2 K and a thickness of 0.3 m within 72 hours, with an evaporation loss rate of more than 30%.

[0005] Based on the above problems, liquid hydrogen storage tank thermal stratification suppression mainly relies on the following technologies:

[0006] (1) Mechanical stirring method - liquid hydrogen is disturbed by built-in rotating blades or stirrers to force mixing. Although this method is direct and effective, it has the following problems in the extremely low temperature (20 K) environment: mechanical seals are prone to failure, leading to hydrogen leakage; bearings and transmission mechanisms have difficulty in lubrication at low temperatures, and wear is aggravated; external driving power is introduced, and the system has high energy consumption; it is not suitable for long-term unattended or aerospace microgravity environments.

[0007] (2) Top jet mixing method - inject low-temperature hydrogen jet from the top of the tank to impact the liquid surface and induce convection. This method does not require internal moving parts, but has the following disadvantages: the injected gas may carry impurities, contaminating the liquid hydrogen; the jet may exacerbate liquid surface evaporation, causing secondary loss; the convection organization is uneven, easy to form local mixing blind area; it relies on external gas source and booster system, the structure is complex.

[0008] (3) Circulating pump heating method - extract liquid hydrogen from the bottom of the tank through an external pump, heat it through an external heater, and then inject it into the upper part of the tank to form a forced circulation. The limitations of this method include: large heat loss in the pipeline and pump body, low energy efficiency; the heater is easy to cause local overheating, causing flash evaporation or gas jam; the system is large in size, not conducive to the compact design of the tank; the circulation efficiency decreases significantly under microgravity or inclined conditions.

[0009] (4) Passive heat conduction enhancement structure - add fins or heat-conducting ribs to the inner wall of the tank to enhance radial heat transfer. This method has no moving parts, but the uniform temperature speed is slow, and the effect of suppressing the axial temperature gradient is limited, making it difficult to cope with severe heat load changes.

[0010] With the expansion of the application of liquid hydrogen in large-scale energy storage, space propulsion and other fields, the demand for mechanical movement-free, low-power, self-adaptive and high-reliability thermal management technology is increasingly urgent. Therefore, how to achieve liquid hydrogen thermal stratification suppression and temperature regulation in a mechanical movement-free, low-power, controllable and uniform manner has become a technical problem that needs to be overcome in the field of low-temperature energy storage technology. SUMMARY

[0011] The first object of the present application is to provide a liquid hydrogen tank thermal stratification suppression system to solve the technical problem of suppressing the thermal stratification of the liquid hydrogen tank in a movement-free and self-adaptive manner.

[0012] The second object of the present application is to provide a liquid hydrogen tank thermal stratification suppression method to achieve the technical problem of rapid and self-adaptive homogenization of the temperature field inside the liquid hydrogen tank.

[0013] The liquid hydrogen tank thermal stratification suppression system of the present application is implemented as follows:

[0014] A liquid hydrogen tank thermal stratification suppression system, at least comprising:

[0015] a liquid hydrogen tank body;

[0016] a bionic fractal flow channel network arranged in the liquid hydrogen tank body, which has a tree root-like fractal structure and includes a main flow channel and at least two levels of branch flow channels;

[0017] a plurality of root tip heating units respectively arranged at the end of each terminal branch flow channel for locally heating the liquid hydrogen;

[0018] A temperature sensing array is distributed along the height direction of the liquid hydrogen storage tank body for real-time collection of liquid hydrogen temperature data.

[0019] A control unit is connected with the temperature sensing array and the root tip heating unit respectively, and is used for controlling the heating parameter according to the temperature difference.

[0020] In the optional embodiment of the present application, the branch length L and the diameter D of the bionic fractal flow channel network satisfy the fractal proportion relationship:

[0021]

[0022] r L = 0.6-0.7, r D = 0.65-0.75.

[0023] In the optional embodiment of the present application, the at least two levels of branch flow channels include the second level of branch flow channels which are shaped by being outwardly bifurcated from the main stem flow channel at an included angle of 35°-45°, and the third level of branch flow channels which are shaped by being bifurcated again from the second level of branch flow channels at an included angle of 30°-40°; and

[0024] The fractal dimension of the bionic fractal flow channel network Df = 1.55-1.70.

[0025] In the optional embodiment of the present application, the bottom area of the liquid hydrogen storage tank body covered by the last level of branch of the fractal flow channel network is not less than 90%, and the inner wall surface roughness Ra of each main stem flow channel and branch flow channel is ≤0.8 μm.

[0026] In the optional embodiment of the present application, the control unit uses the phased array technology to control the operation state of the multiple root tip heating units in time and in different zones.

[0027] The liquid hydrogen storage tank thermal stratification suppression method of the present application is realized as follows:

[0028] A liquid hydrogen storage tank thermal stratification suppression method, which uses the liquid hydrogen storage tank thermal stratification suppression system; comprising:

[0029] Step S1: obtaining temperature difference, collecting the temperature difference ΔT and the temperature difference direction of the liquid hydrogen at different heights in the liquid hydrogen storage tank body in real time through the temperature sensing array;

[0030] Step S2: heating control, judging whether to start the root tip heating unit according to the temperature difference ΔT obtained in step S1 and the preset temperature difference at the same height and the same temperature difference direction; if yes, then controlling to start the root tip heating unit;

[0031] ​​Step S3: temperature difference feedback, adjusting the operation parameters of the root tip heating unit according to the real-time temperature difference change rate during the operation of the root tip heating unit, so that the temperatures of the liquid hydrogen at different heights in the liquid hydrogen storage tank body reach a balanced state.

[0032] In the optional embodiment of the present application, in step S2:

[0033] When ΔT≥ΔT0, start all or specified area root tip heating units and maintain the active heating mode of high power output;

[0034] When ΔT1<ΔT<ΔT0, the root tip heating unit maintains the steady-state maintenance mode of low power output;

[0035] When ΔT≤ΔT1, then turn off the root tip heating unit to enter the energy-saving shutdown mode; wherein

[0036] ΔT0 is a preset upper threshold, and ΔT1 is a preset lower threshold.

[0037] In the optional embodiment of the present application, each of the root tip heating units adopts a microwave heating coil structure.

[0038] In the optional embodiment of the present application, the outer wall of each of the main flow channel and the branch flow channel is wrapped with an electromagnetic shielding sleeve.

[0039] In the optional embodiment of the present application, the microwave control parameters of the microwave heating coil structure satisfy the following formula: fMW(t)

[0040]

[0041] Wherein f 0 is a basic frequency, k f is a temperature difference response coefficient.

[0042] ​The liquid hydrogen storage tank thermal stratification suppression system and method have the following beneficial effects: (1) the sealing, wear and reliability problems caused by mechanical stirring are completely eliminated, and the system is particularly suitable for long-term on-orbit, deep-sea and other harsh or unattended environments; (2) the microwave energy directly acts on the bottom region with the lowest temperature and the most heating required, and the convection is efficiently organized through the bionic flow channel, so that the average operating power consumption can be reduced and the energy utilization rate can be improved; (3) the distributed multi-point heating is combined with closed-loop feedback control, so that the temperature difference of the liquid hydrogen in the main body of the liquid hydrogen storage tank is not more than 0.1 K, and the thermal stratification thickness is controlled to be less than 0.05 m; (4) the system has strong adaptability: the control unit can dynamically adjust the heating strategy according to the real-time temperature difference, and adapt to the working condition changes under different filling rates and different heat leakage conditions; (5) the system has compact structure and is easy to integrate: the bionic fractal flow channel network can be directly integrated in the main body of the liquid hydrogen storage tank, and does not occupy too much internal space, so that the system is suitable for new tank manufacturing and old tank modification. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 FIG. 1 is a structural schematic diagram of the liquid hydrogen storage tank thermal stratification suppression system of the present application;

[0044] Figure 2 FIG. 2 is a structural schematic diagram of the bionic fractal flow channel network of the liquid hydrogen storage tank thermal stratification suppression system of the present application.

[0045] In the figure: liquid hydrogen storage tank main body 1, inner container 11, main flow channel 21, secondary branch flow channel 22, tertiary branch flow channel 23, liquid hydrogen 4, high-frequency coil 5, temperature sensor 6, root tip heating unit 7. DETAILED DESCRIPTION

[0046] In order to make the content of the present application easier to be clearly understood, the present application will be further described in detail below according to specific embodiments and in combination with the drawings.

[0047] Embodiment 1:

[0048] Please refer to Figure 1 and Figure 2 , the present embodiment provides a liquid hydrogen storage tank thermal stratification suppression system, which at least comprises: a liquid hydrogen storage tank main body 1, a bionic fractal flow channel network, a plurality of root tip heating units 7 and a temperature sensor array, and a control unit.

[0049] Specifically, first of all, the liquid hydrogen storage tank main body 1 adopts a double-layer vacuum insulation structure, and the inner container 11 can be selected as austenitic stainless steel.

[0050] Secondly, the bionic fractal flow channel network arranged in the liquid hydrogen storage tank body 1 is in a tree root-like fractal structure, including a main stem flow channel 21 and at least two levels of branch flow channels. In detail, in combination with a specific optional case shown in the drawings, the at least two levels of branch flow channels include second-level branch flow channels 22 formed by being bifurcated outward from the main stem flow channel 21 at an angle of 35°-45°, and third-level branch flow channels 23 formed by being bifurcated again from the second-level branch flow channels 22 at an angle of 30°-40°; and a fractal dimension of the bionic fractal flow channel network Df =1.55-1.70. The bionic fractal flow channel network can be made of, for example but not limited to, 316L stainless steel after precision casting and electrolytic polishing, and has good low-temperature toughness and low magnetic permeability.

[0051] The bionic fractal flow channel network can be fixed on the tank cover of the liquid hydrogen storage tank body 1, or be fixed on the tank bottom of the liquid hydrogen storage tank body 1 by, for example but not limited to, electron beam welding embedding. In this regard, for example, the bionic fractal flow channel network is bifurcated by two levels to form 36 final-level root tip flow channels, which can uniformly cover the tank bottom of the liquid hydrogen storage tank body 1. The final-level branches of the fractal flow channel network cover no less than 90% of the bottom area of the liquid hydrogen storage tank body 1, and the inner walls of each main stem flow channel 21 and branch flow channel are polished to have a surface roughness Ra≤0.8 μm, so as to reduce flow resistance and formation of an attachment layer.

[0052] Based on the above, it is necessary to note that the branch length L and the diameter D of the bionic fractal flow channel network of the embodiment satisfy a fractal proportion relationship: , wherein r L =0.6-0.7, r D =0.65-0.75.

[0053] In this regard, the embodiment also studies the influence of the fractal proportion coefficient r L、 r D and the fractal dimension Df on the system performance by numerical simulation. Taking the liquid hydrogen storage tank body 1 of the embodiment as a model and keeping the total microwave input power unchanged, the simulation results show that:

[0054] When r L =0.65, r D =0.70, Df ≈1.62, the flow resistance of the flow channel network is the smallest, the circulating flow rate of the liquid hydrogen 4 reaches a peak value (about 0.045 m / s), and the time required from start to destruction of the stratification is the shortest (about 12 minutes).

[0055] If r L or r D too small (e.g. less than 0.55), the branches are too dense, the flow resistance increases, and the flow is not smooth; if r L or r D too large (e.g. greater than 0.80), the coverage area is insufficient, and there is a heating blind area. When the fractal dimension Df is near 1.6, the system has the best overall performance. When Df <1.4, the structure is too simple, and is similar to a single path, with poor uniform heating; when Df >1.8, the flow channel is too complex, and the flow resistance increases sharply, which is also not conducive to convection circulation. Therefore, the preferred parameter range of the bionic fractal flow channel network of the present embodiment is: r L =0.62-0.68, r D =0.68-0.72, Df =1.58-1.65.

[0056] Furthermore, a plurality of root tip heating units 7 are arranged at the ends of the final-stage branch flow channels (in the present embodiment, the ends of the third-stage branch flow channels 23 away from the second-stage branch flow channels 22 and the ends of the second-stage branch flow channels 22 away from the main stem flow channel 21), for locally heating the liquid hydrogen 4. In the present embodiment, as an example of a specific optional case, each root tip heating unit 7 adopts a microwave heating coil structure. The microwave heating coil structure herein can adopt any mature technology in the prior art, and generally includes a high-frequency coil 5 and a ceramic insulating shell covering the outside of the coil, and a waveguide cavity formed in the ceramic insulating shell for enhancing the local microwave energy density; the ceramic insulating shell can be made of high-purity alumina ceramic to ensure the insulation performance and mechanical strength at extremely low temperatures, the working frequency of the high-frequency coil 5 is 1.8-3.0 GHz, the output power of a single coil is 1-50 W, and a temperature rise of 0.1-0.3 K can be generated in the local liquid hydrogen 4. It should be noted that the ends of the final-stage branch flow channels are designed to be insulated, so as to limit the microwave heating area to the inside of the flow channel, and avoid electromagnetic leakage from the external wall.

[0057] More specifically, the microwave control parameters of the microwave heating coil structure satisfy the following formula: f MW (t)

[0058] ; wherein f 0 is the basic frequency (generally 2.45 GHz),​k f is the temperature difference response coefficient, based on the microwave control parameter f MW (t) Power adaptive adjustment is used to realize the microwave heating coil structure.

[0059] Based on the above, in the optional implementation, the outer walls of each main flow channel 21 and branch flow channel are wrapped with an electromagnetic shielding sleeve. The electromagnetic shielding sleeve here can optionally adopt a multi-layer metal shielding film and wave-absorbing material composite structure to ensure that the microwave energy generated by the microwave heating coil structure is limited inside the main flow channel 21 and branch flow channel, and the shielding effectiveness is not less than 30 dB.

[0060] Next is the temperature sensing array, which is distributed along the height direction of the liquid hydrogen storage tank body 1 for real-time collection of liquid hydrogen 4 temperature data. In this regard, optionally, 8 Pt100 temperature sensors 6, for example but not limited to, are arranged along the height direction of the liquid hydrogen storage tank body 1 to form a sensing array. The Pt100 temperature sensor 6 has a temperature measurement range of 15-25 K and an accuracy of ±0.01 K.

[0061] Finally, the control unit is connected with the temperature sensing array and the root tip heating unit 7 respectively, and is used to control the heating parameters according to the temperature difference. The control unit here uses phased array technology to control the operating state of multiple root tip heating units 7 (the operating state here includes the switching of the start and stop modes of the heating unit and the specific operating parameters in the start state of the heating unit).

[0062] The control unit activates all 36 microwave heating coil structures in the final stage root tip flow channel through the phased array controller. Since the dielectric constant of liquid hydrogen is about 1.26, it can absorb part of the microwave energy and generate dielectric loss heat. Each microwave heating coil structure works at a power of 10 W, and the microwave energy is absorbed by the surrounding liquid hydrogen 4, causing the temperature of the liquid hydrogen 4 at the root tip to rise by about 0.15 K, and the density to decrease. Driven by buoyancy, the heated liquid hydrogen 4 flows upward along the fractal flow channel branches and gradually flows into the main stem to form an upward flow. The upper layer of colder and denser liquid hydrogen 4 sinks along the tank wall area of the liquid hydrogen storage tank body 1 and is supplemented to the bottom, thereby forming a natural convection circulation covering the entire cross section of the liquid hydrogen storage tank body 1.

[0063] In summary, in this embodiment, through the cooperation of the liquid hydrogen storage tank body 1, the bionic fractal flow channel network, the multiple root tip heating units 7, the temperature sensing array, and the control unit, when the root tip heating unit 7 heats the liquid hydrogen 4, the temperature of the lower layer of local liquid hydrogen 4 rises and the density decreases. Since the density of liquid hydrogen 4 is extremely sensitive to temperature (about -0.02 kg / m³·K -1), the bottom liquid generates buoyancy, rises along the branches of the bionic fractal flow channel network, converges into the main channel and moves up to the middle and upper layers. At the same time, the upper layer of cold liquid hydrogen 4 sinks along the tank wall to supplement the bottom area, forming a closed natural circulation flow loop. After the cooperative action of multiple root tip heating units 7, the bottom flow field presents a honeycomb-like convection mode, and the overall flow rate is about 0.02-0.05 m / s, which can significantly destroy the thermal stratification phenomenon of the liquid hydrogen storage tank body 1 within 10-20 minutes, and make the temperature gradient tend to balance. It should be noted that the principle of the liquid hydrogen storage tank thermal stratification suppression system of the embodiment is not limited to liquid hydrogen 4 storage tanks. By adjusting the microwave frequency to adapt to the dielectric loss characteristics of different media and re-optimizing the size of the fractal flow channel, it can be widely used in the storage thermal management field of other low-temperature media such as liquid helium (4.2K), liquid nitrogen (77K), liquid oxygen (90K), etc., and has significant generalization potential.

[0064] Embodiment 2:

[0065] Please refer to Figure 1 and Figure 2 The liquid hydrogen storage tank thermal stratification suppression system of embodiment 1 is provided with a liquid hydrogen storage tank thermal stratification suppression method, which specifically comprises:

[0066] Step S1: Obtain temperature difference, real-time collect the temperature difference ΔT and temperature difference direction of liquid hydrogen 4 at different heights in the liquid hydrogen storage tank body 1 through the temperature sensing array.

[0067] Step S2: Heating control, judge whether to start the root tip heating unit 7 according to the temperature difference ΔT obtained in step S1 and the preset temperature difference at the same height and in the same temperature difference direction; if yes, control to start the root tip heating unit 7.

[0068] Step S3: Temperature difference feedback, adjust the operating parameters of the root tip heating unit 7 according to the real-time temperature difference change rate during the operation of the root tip heating unit 7, so that the temperature of the liquid hydrogen 4 at different heights in the liquid hydrogen storage tank body 1 reaches a balanced state.

[0069] Based on the above, further, the following three cases are included in step S2:

[0070] The first case is when ΔT≥ΔT0, start all or specified area of root tip heating unit 7 and keep the active heating mode of high power output; it should be noted that based on the temperature difference of liquid hydrogen 4 at different heights of the overall liquid hydrogen storage tank body 1, it may only be necessary to start the root tip heating unit 7 closest to the bottom of the bionic fractal flow channel network in the form of a tree root-like fractal structure, or it may be necessary to start the root tip heating unit 7 at different height layers of the liquid hydrogen storage tank body 1. The specific case is adaptively selected in combination with the temperature difference ΔT obtained in step S1, which is not absolutely limited by the embodiment.

[0071] The second case is when ΔT1<ΔT<ΔT0, the root tip heating unit 7 remains in the steady-state maintenance mode with low power output. In this case, an intermittent and low-power strategy is adopted, only part of the root tip heating unit 7 is started to maintain the balance of the liquid hydrogen 4 temperature at different heights of the liquid hydrogen storage tank body 1.

[0072] The third case is when ΔT≤ΔT1, the root tip heating unit 7 is turned off and enters the energy-saving shutdown mode. In this case, the temperature difference ΔT and the temperature difference direction of the liquid hydrogen 4 at different heights in the liquid hydrogen storage tank body 1 are always collected in real time through the temperature sensor array; wherein ΔT0 is the preset upper threshold (which can also be understood as the starting threshold, for example, 0.3K), and ΔT1 is the preset lower threshold (which can also be understood as the shutdown threshold, for example, 0.1K).

[0073] For example, at the initial moment, the liquid hydrogen storage tank body 1 forms thermal stratification due to heat leakage, and the temperature of the upper layer of liquid hydrogen 4 is 0.32K higher than that of the lower layer. The temperature sensor array transmits the data to the control unit. The control unit calculates the temperature difference ΔT=0.32K>ΔT0(0.3K), and then starts all or specified area of the root tip heating unit 7 and maintains the active heating mode with high power output. The microwave heating coil structure works at a power of 10W, and the microwave energy is absorbed by the surrounding liquid hydrogen 4, which makes the temperature of the liquid hydrogen 4 at the root tip rise by about 0.15K, and the density decreases. Driven by buoyancy, the heated liquid hydrogen 4 flows upward along the fractal flow channel branches and gradually flows into the main stem to form an upward flow. The upper layer of cold and dense liquid hydrogen 4 sinks along the tank wall area of the liquid hydrogen storage tank body 1 and supplements to the bottom, thereby forming a natural convection large circulation covering the entire cross section of the liquid hydrogen storage tank body 1. With the continuous convection, the temperature difference ΔT between the upper and lower layers of liquid hydrogen 4 in the liquid hydrogen storage tank body 1 gradually decreases. When the ΔT detected by the temperature sensor array decreases to 0.2K (between ΔT1 and ΔT0), it is switched to the steady-state maintenance mode, and the microwave heating coil structure intermittently operates at a power of 5W (for example, works for 30 seconds and stops for 30 seconds). About 30 minutes later, when the ΔT detected by the temperature sensor array decreases to 0.05K, which is less than or equal to ΔT1, it enters the energy-saving shutdown mode. During the whole process, the thermal stratification of the liquid hydrogen storage tank body 1 is effectively destroyed, and the liquid hydrogen 4 in the liquid hydrogen storage tank body 1 enters a thermal equilibrium state.

[0074] In summary, the working process of the liquid hydrogen storage tank thermal stratification suppression method of the embodiment can be summarized as: real-time monitoring→temperature difference judgment→microwave start→convection formation→feedback adjustment→steady-state maintenance. It is a complete closed-loop intelligent control process.

[0075] Example 3:

[0076] Please refer to Figure 1 and Figure 2Based on the liquid hydrogen storage tank thermal stratification inhibition method of embodiment 2, the control unit of the liquid hydrogen storage tank thermal stratification inhibition method provided in the embodiment can not only provide the longitudinal temperature difference in the liquid hydrogen storage tank body 1, but also fit the two-dimensional distribution cloud map of the liquid hydrogen 4 temperature in the liquid hydrogen storage tank body 1 through multi-point data, assuming that the temperature of the right side area of the liquid hydrogen storage tank body 1 is generally high and the temperature of the left side area is low due to uneven external sunlight irradiation. After the control unit identifies the transverse temperature difference, the partition control strategy is started: for the right side area with high temperature, the root tip heating unit 7 in the corresponding area is given a lower reference power or a longer shutdown time. For the left side area with low temperature, the root tip heating unit 7 in the corresponding area is increased in power (such as 20%) or is preferentially started. The fine spatial energy distribution based on the phased array makes the temperature equalization speed increase by about 35% compared with the global uniform heating mode of embodiment 2, and realizes true three-dimensional adaptive temperature equalization.

[0077] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above are only specific embodiments of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

[0078] In the description of the present application, it should be understood that the terms indicating the position or positional relationship are based on the position or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular position, be constructed and operated in a particular position, and therefore cannot be understood as a limitation on the present application.

[0079] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0080] In the description of the application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the product of the application is used, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second", "third" and the like are only used to distinguish descriptions and cannot be understood as indicating or implying relative importance.

[0081] In addition, the terms "horizontal", "vertical", "overhang" and the like do not mean that the component must be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0082] In the present application, unless otherwise explicitly specified and limited, the first feature above or below the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature therebetween. Moreover, the first feature above, above and above the second feature includes that the first feature is directly above and obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature below, below and below the second feature includes that the first feature is directly below and obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

Claims

1. A liquid hydrogen storage tank thermal stratification suppression system, characterized in that, At least including: Main body of liquid hydrogen storage tank; A biomimetic fractal flow channel network is arranged in the main body of the liquid hydrogen storage tank. It has a root-like fractal structure, including a main flow channel and at least two levels of branch flow channels. Multiple root tip heating units are respectively set at the end of each final-stage branch flow channel for local heating of liquid hydrogen; A temperature sensor array is distributed along the height of the liquid hydrogen storage tank body to collect liquid hydrogen temperature data in real time. The control unit is connected to both the temperature sensor array and the root tip heating unit, and is used to control the heating parameters based on the temperature difference; wherein The branch length L and diameter D of the biomimetic fractal flow channel network satisfy a fractal proportional relationship: , in r L =0.6~0.7, r D =0.65~0.75; The at least two-level branch channels include secondary branch channels that branch outward from the main channel at an angle of 35° to 45°, and tertiary branch channels that branch again from the secondary branch channels at an angle of 30° to 40°; and The fractal dimension of the biomimetic fractal flow channel network Df =1.55~1.

70.

2. The liquid hydrogen storage tank thermal stratification suppression system according to claim 1, characterized in that, The final branch of the fractal flow channel network covers at least 90% of the bottom area of ​​the liquid hydrogen storage tank body, and the inner wall surface roughness Ra of each of the main flow channels and branch flow channels is ≤0.8μm.

3. The liquid hydrogen storage tank thermal stratification suppression system according to claim 1, characterized in that, The control unit uses phased array technology to control the operating status of multiple root tip heating units in a time-division and zone-division manner.

4. A method for suppressing thermal stratification in a liquid hydrogen storage tank, characterized in that, The liquid hydrogen storage tank thermal stratification suppression system as described in any one of claims 1 to 3 is employed, comprising: Step S1: Obtain the temperature difference by collecting the temperature difference ΔT and direction of the liquid hydrogen at different heights in the main body of the liquid hydrogen storage tank in real time through a temperature sensor array; Step S2: Heating control. Based on the temperature difference ΔT obtained in step S1 and the preset temperature difference at the same height and in the same temperature difference direction, determine whether to start the root tip heating unit; if so, control the start of the root tip heating unit. Step S3: Temperature difference feedback. During the operation of the root tip heating unit, the operating parameters of the root tip heating unit are adjusted according to the real-time temperature difference change rate to make the temperature of liquid hydrogen at different heights in the main body of the liquid hydrogen storage tank reach a balanced state.

5. The method for suppressing thermal stratification in a liquid hydrogen storage tank according to claim 4, characterized in that, In step S2: When ΔT≥ΔT0, the root tip heating unit of all or a specified area is activated and the active heating mode with high power output is maintained. When ΔT1 < ΔT < ΔT0, the root tip heating unit maintains a steady-state mode with low power output; When ΔT≤ΔT1, the root tip heating unit is turned off and enters the energy-saving shutdown mode; in ΔT0 is the upper limit of the preset threshold, and ΔT1 is the lower limit of the preset threshold.

6. The method for suppressing thermal stratification in a liquid hydrogen storage tank according to claim 4 or 5, characterized in that, Each of the root tip heating units employs a microwave heating coil structure.

7. The method for suppressing thermal stratification in a liquid hydrogen storage tank according to claim 6, characterized in that, The outer wall of each of the main and branch channels is covered with an electromagnetic shielding sleeve.

8. The method for suppressing thermal stratification in a liquid hydrogen storage tank according to claim 6, characterized in that, Microwave control parameters of the microwave heating coil structure f MW (t) Satisfy the following formula: ； in f 0 Based on the base frequency, k f This is the temperature difference response coefficient.

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