Coupling Verification and Optimization Method for Cold Start Focusing Strategy of High-Temperature Molten Salt Absorber
By measuring the incident heat flux density and using a three-dimensional thermo-mechanical coupling model to screen target focusing strategies, the problems of temperature difference and thermal stress during the cold start-up phase of high-temperature chloride salt receivers were solved, achieving an efficient and safe cold start-up process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-02
AI Technical Summary
During the cold start phase, high-temperature chloride salt receivers suffer from excessive circumferential temperature difference and transient thermal stress concentration due to non-uniform irradiation, which is difficult to measure directly. Traditional strategies lack systematic experimental-simulation coupling verification methods, making it difficult to guarantee safety and efficiency.
By measuring the incident heat flux density, a set of candidate operating conditions is constructed, and the temperature is monitored in real time. Combined with a three-dimensional unsteady thermo-mechanical coupling numerical model, target focusing strategies that meet the requirements of safety constraints and heating efficiency are selected, including turning on the light source in stages and adjusting the position of the light spot.
It enables quantitative evaluation and screening of the cold start process, reduces the risk of thermal stress, improves heating efficiency and safety, and provides a scientific basis for strategy formulation.
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Figure CN122133504A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of solar thermal power generation and high-temperature heat transfer testing technology, specifically involving a coupled verification and optimization method for a cold start focusing strategy of a high-temperature molten salt receiver. Background Technology
[0002] Concentrating Solar Power (CSP) is considered a key technological path for building new power systems due to its high efficiency in concentrating solar energy and large-scale thermal storage capabilities, enabling stable power supply and flexible peak shaving. CSP systems include tower, trough, dish, and linear Fresnel types, among which the tower system (SolarPower Tower, SPT) is considered a key development direction for achieving higher efficiency power cycles due to its high concentration ratio and ability to achieve higher absorber temperatures. To further reduce the levelized cost of electricity (LCOE) and improve conversion efficiency, the industry trend is to raise the system operating temperature to approximately 700 °C and couple it with a supercritical carbon dioxide Brayton cycle.
[0003] However, one direct consequence of higher temperatures is the higher energy flux density and more non-uniform spatial distribution on the absorber surface. This significantly intensifies the temperature gradients in the circumferential and axial directions of the absorber tubes, inducing greater thermal stress risks. Simultaneously, chloride salts typically have high melting points and a high risk of solidification. Improper temperature control during startup can easily lead to solidification, adhesion, or even blockage, thus placing higher demands on startup control strategies.
[0004] The start-up process of a receiver can be divided into a cold start phase before molten salt circulation and an operational phase after circulation is established. The cold start process typically refers to preheating the receiver in the morning before introducing the molten salt working medium to reduce the risk of solidification or blockage during the initial molten salt flow. Studies indicate that compared to the molten salt circulation phase, the heat load during the cold start phase is more uneven, making it more prone to inducing thermal stress concentration. In the initial stage of cold start, the receiver tubes are often in an air environment with weak internal convection heat transfer, resulting in a more significant circumferential temperature difference between the sun-facing and shaded sides. This further exacerbates transient thermal stress and presents greater structural safety challenges.
[0005] To address the safety and efficiency of cold start processes, existing research has explored various approaches, including preheating strategies, dynamic temperature control methods, and mirror / light source regulation and focusing strategies. These include introducing heating rate constraints and using temperature feedback to dynamically control the preheating process. Meanwhile, the non-uniformity of light concentration and the position of the light spot directly affect the temperature distribution of the receiver, making focusing strategy optimization an important research direction. However, most existing research focuses on nitrate systems. High-temperature chloride receivers differ significantly in their operating temperature range, thermal properties, and solidification risks, resulting in higher circumferential temperature differences and greater thermal stress during cold start processes. Therefore, related system research remains relatively limited.
[0006] From the perspective of experimental and evaluation methods, the screening and optimization of cold-start focusing strategies requires the establishment of a closed-loop evaluation system encompassing "irradiation boundary—temperature response—thermal stress risk." Different light source combinations, focusing positions, and timing sequences correspond to different incident heat flux density distributions, necessitating reproducible methods for measuring and constructing heat flux distributions. Simultaneously, thermal stress is difficult to measure directly and completely in experiments; strategy evaluation often relies on thermo-mechanical coupled numerical models and unified criteria that are cross-checked with experimental data. Furthermore, cold starts must simultaneously meet both anti-condensation temperature requirements and overheating limits, further increasing the difficulty of comprehensive strategy evaluation and engineering feasibility verification.
[0007] In summary, to address the problem of thermal stress concentration caused by uneven temperature during the cold start-up phase of high-temperature chloride receivers, there is an urgent need for a systematic method that can obtain the incident heat flux boundary under controlled irradiation conditions, conduct cold start temperature response tests, and combine three-dimensional transient thermo-mechanical coupling analysis to evaluate and screen focusing strategies for transient peak constraints. This would provide reliable technical support for the formulation and optimization of cold start-up operation strategies for high-temperature chloride receivers. Summary of the Invention
[0008] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a coupled verification and optimization method for a cold start focusing strategy of a high-temperature molten salt receiver. This method screens target focusing strategies that meet safety constraints and heating efficiency requirements, and solves the technical problems of existing high-temperature chloride salt receivers in the cold start stage, such as excessive circumferential temperature difference due to non-uniform irradiation, concentrated transient thermal stress that is difficult to measure directly, and the lack of systematic experimental-simulation coupled verification methods, which only focus on steady-state temperature and ignore the risk of transient peaks. This provides a technical basis for the formulation of cold start operation strategies and the setting of safety thresholds for high-temperature molten salt receivers.
[0009] The present invention adopts the following technical solution: A coupled verification and optimization method for cold start focusing strategies of high-temperature molten salt receivers includes the following steps: S1. Measure the incident heat flux density of the solar simulator acting on the sun-facing surface of the absorber under different light source configurations, obtain the incident heat flux density data at each measuring point, and establish an incident heat flux density database at each measuring point as the boundary condition for subsequent numerical calculations. S2. Generate a candidate operating condition set according to the preset cold start focusing strategy. Each operating condition in the candidate operating condition set is determined by one or more of the following: xenon lamp turning-on combination, spot position parameters, and timing control parameters executed in stages. S3. Based on the current operating condition in the candidate operating condition set, control the solar simulator to irradiate the receiver, drive the receiver to enter the cold start heating process, and simultaneously collect the temperature time series data of each measuring point on the outer wall of the receiver at a preset sampling frequency. S4. During the execution of step S3, the highest temperature of the outer wall of the absorber is monitored in real time. If the monitored temperature exceeds the preset safety threshold, the solar simulator is immediately shut down and the current working condition experiment is terminated. If it does not exceed the threshold, the execution continues until the thermal balance judgment condition is met. S5. When the temperature time series data collected in step S3 shows that the temperature change rate of each measuring point is lower than the preset threshold and remains at the preset duration, it is determined that the experimental platform has reached thermal equilibrium, the steady-state temperature data under this condition is recorded and the experiment is ended. S6. Construct a three-dimensional unsteady thermo-mechanical coupling numerical model consistent with the geometric structure and material properties of the receiver. Verify the numerical model using benchmark experimental data under single xenon lamp irradiation conditions. If the deviation between the numerical simulation results and the benchmark experimental data is within the allowable range, the model is deemed valid; otherwise, the model parameters are corrected until the verification is passed. S7. The incident heat flux density distribution measured in step S1 is used as the outer wall heat flux boundary. The temperature time series data collected in step S3 is used as the initial or boundary constraint input into the verified three-dimensional unsteady thermo-mechanical coupling numerical model to solve for the transient temperature field of the entire cold start process. Based on the transient temperature field, the transient thermal stress field is further calculated. S8. Extract key evaluation indicators from the transient temperature field and transient thermal stress field obtained in step S7. The key evaluation indicators include the maximum temperature rise rate, the peak value of the circumferential temperature difference of the cross section, and the peak value of the maximum equivalent thermal stress during the entire cold start process. S9. Compare the key evaluation indicators extracted in step S8 with the preset safety constraints and performance targets, and select and optimize them to obtain a target-focusing strategy that simultaneously meets the requirements of thermal stress safety threshold, circumferential temperature difference limit and temperature rise efficiency.
[0010] Preferably, in step S1, the specific process of determining the incident heat flux density distribution includes: An energy flux meter was placed at the center of the Lambertian target and aligned near the focal point of the solar simulator. Single xenon lamps were turned on one by one to obtain the incident heat flux distribution at each measuring point when a single lamp was used. An incident heat flux density database under different light source configurations was established by linear superposition or experimental combination.
[0011] Preferably, in step S2, the timing control parameters for phased execution include multiple time nodes for each phase and the xenon lamp on / off status corresponding to each phase. In step S9, the selected target focusing strategy is a phased lighting strategy that sequentially turns on xenon lamps No. 7, No. 2 and No. 6, and the condition for phase switching is that the temperature rise rate, circumferential temperature difference or the highest temperature of the outer wall reaches a preset switching threshold.
[0012] Preferably, in step S4, if the current working condition experiment is terminated because the monitored temperature exceeds the preset safety threshold, the current working condition is marked as an invalid strategy, and a new candidate working condition is generated after removing or adjusting the timing control parameters from the candidate working condition set, and the process returns to step S3.
[0013] Preferably, in step S5, the preset duration is 5 to 10 minutes, and the preset threshold is when the temperature change is less than a set value.
[0014] Preferably, in step S6, the reference experimental data comes from temperature data collected by three thermocouple measuring points set at different heights at the center of the sun-facing side and the center of the shadow side of each heat-absorbing tube. The thermal model in the three-dimensional unsteady thermo-mechanical coupling numerical model is an unsteady heat conduction model that simultaneously considers radial, circumferential, and axial heat conduction in cylindrical coordinates.
[0015] Preferably, when constructing the numerical model, the inner cavity of the heat absorber is set to be filled with air. Since the natural convection effect on the inner wall surface is very small, the natural convection heat transfer can be ignored within the allowable error range, and only the radiation heat transfer between the inner wall surfaces is considered as the inner wall boundary condition. The outer wall boundary of the heat absorber tube is defined to include the incident irradiated heat flow and the convective-radiative combined heat transfer boundary with the environment. The circumferential direction is set to use periodic boundary conditions, the upper and lower end faces are set to use adiabatic boundary conditions, and the initial temperature is set to room temperature.
[0016] Preferably, in step S7, the transient temperature field is solved using an explicit second-order difference discretization method; the time step and grid interval of the explicit second-order difference discretization method are determined based on Fourier number stability constraints; the calculation of the transient thermal stress field based on the transient temperature field specifically includes: obtaining the equivalent thermal stress by synthesizing the calculated radial, circumferential and axial thermal stress components according to the Von Mises equivalent stress intensity theory.
[0017] Preferably, in step S8, when extracting the key evaluation indicators, the transient extreme points of the temperature field and thermal stress field during the cold start process are identified; It was confirmed that the peak value of the circumferential temperature difference and the peak value of the maximum equivalent thermal stress of the cross section occurred at the transient moment of the cold start process rather than at the final steady state moment, and the maximum value of the key evaluation index was used as the final value of the key evaluation index throughout the cold start process.
[0018] Preferably, in step S9, the preset safety constraints include the minimum temperature safety threshold of the receiver's outer wall, the maximum temperature safety threshold of the outer wall, the upper limit of the circumferential temperature difference of the cross section, the upper limit of the equivalent thermal stress, and the upper limit of the temperature rise rate. The performance target is that the temperature rise efficiency of the receiver during cold start meets the preset molten salt anti-condensation temperature requirement, and the heating time of the entire cold start process is controlled within a preset range. When screening target focusing strategies, if there are multiple focusing strategies that simultaneously meet the conditions, the optimal target focusing strategy is determined by prioritizing the minimum peak value of the maximum equivalent thermal stress and the minimum peak value of the circumferential temperature difference of the cross section.
[0019] Compared with the prior art, the present invention has at least the following beneficial effects: A coupled verification and optimization method for cold start focusing strategies of high-temperature molten salt receivers deeply couples experimental measured data with numerical simulations, overcoming the limitations of existing technologies that rely solely on experiments or simulations. This method enables quantitative evaluation and selection of cold start focusing strategies. It not only accurately reproduces the transient temperature field during the cold start process but also solves for the transient thermal stress field, which is difficult to measure directly. In particular, the safety monitoring and thermal balance determination mechanisms ensure equipment safety and data validity under extreme operating conditions; while the model verification step guarantees high confidence in the numerical calculations. Ultimately, this method can select the optimal strategy based on the peak indicators throughout the cold start process, effectively addressing the structural failure risk caused by thermal stress concentration due to large circumferential temperature differences in high-temperature molten salt receivers. This provides scientific and quantitative technical support for developing cold start strategies that balance heating efficiency and structural safety.
[0020] Furthermore, the 2.5-second high-frequency sampling can accurately capture the transient characteristics of rapid temperature changes during the initial cold start, avoiding missing key temperature jump points and providing high temporal resolution data support for subsequent model verification; the 950-degree Celsius safety threshold is a protective temperature upper limit set by combining the temperature resistance and safety margin of the corrosion-resistant Inconel 625 alloy material used in the heat absorber tube, to prevent material performance degradation or damage to the heat absorber tube due to local overheating during the cold start process; and the 5 to 10-minute thermal equilibrium waiting period eliminates environmental fluctuation interference, ensuring that the recorded steady-state data is true and reliable.
[0021] Furthermore, by transforming failure cases into optimization inputs, we can quickly converge to a safe and feasible strategy space, significantly shortening the R&D cycle.
[0022] Furthermore, ignoring natural convection within the cavity and considering only radiative heat transfer through the inner wall reflects the real physical scenario of no working fluid flow within the tube during the initial cold start phase, where heat transfer relies primarily on radiation. The outer wall employs a combined convection-radiation heat transfer boundary to fully describe the energy exchange between the receiver and the environment. The setting of periodic boundaries and adiabatic end faces simplifies the computational scale while maintaining the representativeness of the physical field, eliminating computational errors caused by oversimplification of the model, and making the obtained transient temperature field closer to actual operating conditions.
[0023] Furthermore, by arranging three thermocouples at different heights at the center of the light-facing and shadow-facing sides of each absorber tube, a three-dimensional temperature monitoring network was constructed. This network comprehensively reflects the temperature gradients of the absorber tubes in the radial, axial, and circumferential directions, providing comprehensive data support for verifying the three-dimensional model. Employing an unsteady heat conduction model in cylindrical coordinates that considers radial, circumferential, and axial heat transfer, the complex heat transfer behavior of the absorber tubes under non-uniform irradiation can be accurately described, particularly capturing the circumferential temperature difference that leads to thermal stress concentration.
[0024] Furthermore, based on the Von Mises equivalent stress strength theory, the radial, circumferential, and axial stress components are synthesized into equivalent thermal stress, which conforms to the yield and failure criteria of metallic materials under multiaxial stress. On the one hand, the explicit difference method is suitable for handling transient heat conduction problems with strong nonlinearity and complex boundaries, and has high computational efficiency. On the other hand, the Von Mises criterion can accurately predict the plastic deformation risk of the heat absorber tube under complex thermal loads.
[0025] Furthermore, it can capture dangerous operating conditions that appear safe under steady-state conditions but experience a huge thermal shock at startup due to a mismatch in the rate of temperature rise.
[0026] Furthermore, by first activating part of the light source for preheating to establish a basic temperature field, and then gradually increasing the heat load, the circumferential temperature difference and temperature rise rate in the initial stage were significantly reduced. At the same time, the strategy was dynamically adjusted based on the switching conditions of real-time temperature indicators, enhancing the system's adaptability to uncertainties.
[0027] Furthermore, while ensuring the accuracy of the measured basic data, the combined approach significantly reduces the workload of full-condition measurements, improving the efficiency of strategy selection. Establishing a standardized heat flux density database allows for the quantification and reuse of boundary conditions under different focusing strategies, providing precise input boundaries for the numerical model.
[0028] Furthermore, safety constraints are quantified into indicators such as the outer wall temperature limit and the upper limit of the circumferential temperature difference. Performance targets are anchored to the control of molten salt anti-solidification temperature and heating time, taking into account both cold start safety and engineering heating efficiency. At the same time, for multiple compliance strategies, the maximum equivalent thermal stress peak value and the minimum cross-sectional circumferential temperature difference peak value are established as the priority screening criteria, which solves the problem of ambiguity in the judgment of multiple strategies.
[0029] In summary, the method of this invention constructs a two-way coupled closed loop of experiment and simulation, ensures data quality through high-frequency sampling and safety monitoring, and accurately captures the peak value of transient stress during cold start using a three-dimensional transient thermo-mechanical model. This overcomes the shortcomings of traditional methods that ignore transient risks, realizes quantitative optimization of the focusing strategy, and significantly improves the safety and efficiency of cold start of high-temperature receivers.
[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0031] Figure 1 This is a schematic diagram of the experimental platform for the high-temperature chloride salt absorber used in this invention; Figure 2 This is a schematic diagram of the structure and distribution of temperature measuring points on the tube wall of the high-temperature chloride salt absorber prototype used in this invention. Figure 3 This is a schematic diagram of the solar simulator concentration characteristic testing system used in this invention; Figure 4 A schematic diagram of the heat transfer process and mesh generation of the heat absorber prototype; Figure 5 The experimental and numerical results of temperature changes of different heat absorbers under single xenon lamp conditions are shown in the figure. (a) shows the temperature change of tube 1 and tube 2 over time, and (b) shows the temperature change of tube 3 and tube 4 over time. Figure 6 The diagram shows the temperature change trend of the receiver's light-facing surface and the steady-state temperature distribution of the outer wall surface under the original dual-lamp working condition. (a) is the transient response curve of the temperature at each measuring point on the receiver's light-facing surface as a function of time, and (b) is the steady-state temperature cloud map of the receiver's outer wall surface after reaching thermal equilibrium. Figure 7 The diagram shows the temperature change trend of the receiver's light-facing surface and the steady-state temperature distribution of the outer wall surface under the original four-lamp working condition. Among them, (a) is the transient response curve of the temperature change of each measuring point on the light-facing surface of the receiver with time, and (b) is the steady-state temperature cloud map of the outer wall surface of the receiver after reaching thermal equilibrium. Figure 8 The diagram shows the temperature change trend of the receiver's light-facing surface and the steady-state temperature distribution of the outer wall surface under the original three-lamp working condition. Among them, (a) is the transient response curve of the temperature change of each measuring point on the light-facing surface of the receiver with time, and (b) is the steady-state temperature cloud map of the outer wall surface of the receiver after reaching thermal equilibrium. Figure 9 This is a graph showing the trend of equivalent thermal stress and circumferential temperature difference of the heat absorber under the original three-lamp working condition. Figure 10The diagram shows the cross-sectional temperature distribution at the peak thermal stress point of the receiver under the original three-lamp operating condition. (a) is the cross-sectional temperature distribution at the peak thermal stress point of the receiver at the moment of peak thermal stress; (b) is the cross-sectional temperature distribution at the peak thermal stress point of the receiver at the moment of steady state during the cold start process. Figure 11 The comparison diagrams of steady-state heat flux distribution on the outer wall of the receiver before and after the improvement of the focusing strategy are shown. (a) is the cloud map of steady-state heat flux density distribution on the outer wall when the original focusing strategy is used, and (b) is the cloud map of steady-state heat flux density distribution on the outer wall when the staged focusing strategy optimized by the present invention is used. Figure 12 A comparison chart of temperature change trends during the cold start process of the receiver before and after the improvement of the focusing strategy; Figure 13 A comparison chart showing the trend of peak thermal stress variation during the cold start process of the receiver before and after the improvement of the focusing strategy; Figure 14 This is a schematic diagram of the invention method. Detailed Implementation
[0032] 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, not all, of the embodiments of the present invention. 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.
[0033] This invention provides a coupled verification and optimization method for cold-start focusing strategies of high-temperature molten salt receivers. First, the incident heat flux density acting on the sun-facing surface of the receiver at various measuring points on a solar simulator is measured to form heat flux boundary conditions corresponding to each operating condition. Operating conditions are set according to different cold-start focusing strategies, and cold-start experiments are conducted according to candidate operating conditions. Temperature time series at multiple points on the outer wall of the receiver are collected, and over-temperature protection and thermal balance determination are performed simultaneously. Then, a three-dimensional transient thermo-mechanical coupling model is constructed and verified to solve for the temperature field and thermal stress field during the cold-start process. Finally, indicators such as the temperature rise rate, circumferential temperature difference of the cross-section, and maximum equivalent thermal stress are calculated. The target focusing strategy is screened based on the peak values throughout the cold-start process and preset constraints. This invention enables quantitative evaluation and screening of cold-start focusing strategies, reduces the risks of temperature difference and thermal stress, and improves cold-start safety and heating efficiency.
[0034] Please see Figure 14 The present invention discloses a coupled verification and optimization method for a cold start focusing strategy of a high-temperature molten salt receiver, comprising the following steps: S1. Measure the incident heat flux density acting on the sun-facing surface of the absorber at each measuring point of the solar simulator, obtain the incident heat flux density data at each measuring point, and obtain the incident heat flux density database at each measuring point. S2. Set the operating conditions according to different cold start focusing strategies. The operating conditions include: xenon lamp on / off combination, spot position, and timing parameters for phased execution. S3. Under the operating conditions, conduct a cold start test of the receiver to allow the receiver to be irradiated and enter the cold start heating process, and simultaneously collect the temperature data of the outer wall of the receiver and record the time series. The temperature data was sampled at an interval of 2.5 seconds.
[0035] S4. Monitor the highest temperature of the outer wall of the absorber during the cold start experiment. When the monitored temperature exceeds the preset safety threshold, shut down the solar simulator. The safety threshold is 950 degrees Celsius for the outer wall temperature of the absorber.
[0036] S5. After the experiment has been running for a period of time, when the temperature readings at each measuring point show a stable trend, continue to wait for the preset time. If the temperature no longer changes or the change is less than the preset threshold within the preset time, it is determined that the experimental platform has reached thermal equilibrium and the cold start process is over. The preset duration is 5-10 minutes.
[0037] S6. Construct a three-dimensional unsteady thermo-mechanical coupling model that matches the geometry and material parameters of the heat absorber. Conduct a benchmark experiment under single xenon lamp irradiation conditions. Compare the temperature values of different heat absorbers with the experimental results to verify the rationality and effectiveness of the model. The temperature acquisition points are three thermocouple points set at different heights at the center of the sun-facing side and the center of the shaded side of each heat-absorbing tube.
[0038] The three-dimensional transient thermal model is an unsteady thermal conduction model that simultaneously considers radial, circumferential, and axial thermal conduction in cylindrical coordinates.
[0039] S7. Using the heat flux density distribution obtained in step S1 and the experimental temperature data obtained in step S3 as model inputs, solve for the temperature field and thermal stress field during the cold start process. The inner cavity of the heat absorber tube is filled with air. Since the natural convection effect on the inner wall surface is very small, the natural convection heat transfer can be ignored within the allowable error range, and only the radiation heat transfer between the inner wall surfaces is considered as the inner wall boundary condition.
[0040] The outer wall boundary of the absorber tube includes the incident irradiated heat flow and the convective-radiative combined heat transfer boundary with the environment.
[0041] Periodic boundary conditions are used in the circumferential direction, and adiabatic boundary conditions are used on the upper and lower end faces. The initial temperature is taken as room temperature.
[0042] The numerical solution of the temperature field was obtained using the explicit second-order difference discretization method implemented in MATLAB.
[0043] Explicit difference solution satisfies Fourier number stability constraint Based on this, the time step and grid interval are determined.
[0044] The equivalent thermal stress is calculated from the radial, circumferential and axial thermal stress components based on Von Mises' equivalent stress strength theory.
[0045] S8. Calculate evaluation indicators based on the temperature field and thermal stress field. The evaluation indicators include the temperature rise rate, the circumferential temperature distribution of the cross section, and the maximum equivalent thermal stress. The extracted peak value of equivalent thermal stress and peak value of circumferential temperature difference appear at the transient moment of the cold start process rather than at the final steady state moment, and the maximum value of the entire cold start process is used as the basis for strategy determination.
[0046] S9. Compare the evaluation indicators with preset constraints, and select and optimize to obtain target-focusing strategies that meet the conditions.
[0047] The target focusing strategy includes a combination of phased activation of the xenon lamps and adjustment of the focusing position. The phased activation strategy involves sequentially activating xenon lamps 7, 2, and 6, with switching conditions based on the rate of temperature rise, circumferential temperature difference, or the highest temperature on the outer wall reaching a threshold between phases.
[0048] Please see Figure 1 The system used in this embodiment consists of a control section, an experimental section, and a data acquisition section. The control section is used to set and execute the cold start focusing strategy, including the combination of light source activation, the setting of the focusing position or the center offset of the light spot, and the stage switching; the experimental section includes a solar simulator and a high-temperature molten salt receiver prototype, which are used to reproduce the non-uniform irradiation heating of the cold start process under controlled indoor conditions; the data acquisition section is used to perform multi-channel real-time acquisition, storage, and visualization of the receiver's outer wall temperature, environmental parameters, etc.
[0049] Please see Figure 2 The high-temperature chloride salt absorber prototype consists of four absorber tubes arranged side by side. The tubes are made of corrosion-resistant Inconel 625 alloy, capable of withstanding temperatures up to approximately 1050°C, making them suitable for high-temperature chloride salt environments. The outer surface of the absorber tubes is coated with an absorbent coating to improve absorption efficiency. Temperature measuring points are arranged at different heights at the center of the sun-facing and shadow-facing sides of each absorber tube. The temperature signals are input into a data acquisition system and recorded as a temperature-time series at fixed sampling intervals.
[0050] Please see Figure 3 To obtain the incident heat flux density distribution corresponding to different focusing strategies, this embodiment constructs a solar simulator concentrating characteristic testing system: a Lambertian target and a heat flux meter are arranged near the focal point, and the target surface is scanned point by point by a moving measuring mechanism to obtain the spatial distribution of heat flux density.
[0051] Please see Figure 4 To obtain quantities such as thermal stress during the cold start phase that are difficult to measure directly experimentally, this implementation establishes a three-dimensional transient thermo-mechanical coupled numerical model consistent with the geometry and materials of the receiver. The model includes three-dimensional unsteady-state heat conduction solution and thermal stress solution: first, the temperature field is obtained from the incident heat flow boundary and the heat transfer boundary, and then the thermal stress field is calculated from the temperature field to obtain the equivalent thermal stress distribution.
[0052] In its specific implementation, this invention includes the following steps: S1. Place the energy flow meter at the center of the Lambert target and align it near the focal point of the solar simulator. Turn on one xenon lamp at a time to obtain the incident heat flow distribution at each measuring point when one lamp is used.
[0053] S2. Set candidate strategies according to the research objectives, such as strategies for simultaneously turning on multiple lights in different combinations, and a combination strategy of turning on lights in stages and adjusting the position of the light spot. Specific operating conditions are shown in Table 1. Table 1. Operating Condition Settings for Candidate Cold Start Focusing Strategy
[0054] S3. Start the solar simulator according to the strategy in S2, and activate the corresponding lamp groups to initiate the cold start process for the receiver. During the entire cold start process, record the temperature time series at the measuring points on the outer wall of the receiver at 2.5-second sampling intervals. S4. To avoid localized overheating during cold start, this implementation method monitors the highest temperature of the outer wall of the absorber in real time. When the highest temperature of the outer wall exceeds the preset safety threshold of 950°C, the solar simulator is shut down.
[0055] S5. If the temperature of the inner and outer walls no longer changes or the change is less than the preset threshold within the preset time (5-10 minutes), the experimental platform is determined to have reached thermal equilibrium and the cold start process is determined to be over. The solar simulator is then turned off and the experimental site is ventilated and cooled. S6. Construct a three-dimensional transient thermo-mechanical coupling model with the heat absorber, conduct a benchmark experiment under single xenon lamp irradiation conditions, compare the temperature values of different heat absorbers with the experimental results, and verify the rationality and effectiveness of the model. S7. Using the heat flux density distribution obtained in step S1 and the experimental temperature data obtained in step S3 as model inputs, solve for the temperature field and thermal stress field during the cold start process. When setting boundary conditions, apply the incident irradiation heat flow boundary to the outer wall and superimpose the convection-radiation composite heat transfer boundary with the environment; during the cold start process, natural convection of the inner wall can be ignored, and only the radiative heat transfer between the inner wall surfaces is considered as the inner wall boundary; end-face insulation and circumferential periodic boundary settings can be adopted at the end of the absorber and in the circumferential direction; the initial temperature is taken as room temperature.
[0056] The temperature field is solved using an explicit second-order finite difference method, and the Fourier number stability constraint is satisfied to determine the time step and grid spacing. At the same time, the independence of the grid and the time step is verified to ensure the accuracy and stability of transient calculation.
[0057] After obtaining the temperature field, the radial stress, circumferential stress and axial stress components are calculated, and the equivalent thermal stress is obtained based on the Von Mises equivalent stress strength theory.
[0058] S8. Compare the evaluation indicators under each working condition with the preset constraints, and select the target-focusing strategy that meets the conditions. The preset constraints include the safety thresholds for the minimum and maximum temperatures of the outer wall, the upper limit of the circumferential temperature difference, the upper limit of the equivalent thermal stress, and the upper limit of the temperature rise rate.
[0059] Example 1: Verification of the baseline working condition model A cold start-up temperature rise experiment was conducted under the condition of single lamp on, with a fixed spot position, to obtain experimental results on the temperature changes of different absorber tubes under different xenon lamp irradiation. A three-dimensional transient thermo-mechanical model was established according to S6, and the single-lamp heat flux boundary generated in S1 was input into the model to obtain numerical results on temperature changes. The experimental and numerical results were verified, and the average relative temperature deviations for each typical condition (tube 1 lamp 1, tube 1 lamp 2, tube 2 3, tube 2 lamp 4, tube 3 lamp 5, tube 3 lamp 6, tube 4 lamp 7, and tube 4 lamp 1) were 8.93%, 5.00%, 6.76%, 6.65%, 9.39%, 9.82%, 1.16%, and 6.99%, respectively. Figure 5 As shown, due to experimental measurement errors and model simplification assumptions, the model has biases, but it can still accurately reflect the temperature change trend, verifying the model's rationality.
[0060] Example 2: Original Multi-Lamp Heating and Focusing Strategy Cold start-up temperature rise experiments were conducted using the original two-lamp combination, the original three-lamp combination, and the original four-lamp combination. The temperature change trends and steady-state temperature distribution of the receiver's outer wall surface under operating conditions 2, 4, and 3 were obtained. Figure 6 , 7 As shown in Figure 8.
[0061] Under the original dual-lamp combination, the steady-state peak temperatures of the four heat-absorbing tubes were 554.62°C, 657.39°C, 543.40°C and 388.76°C, respectively, all occurring at the geometric center of their respective light-facing surfaces; the average temperature of the light-facing surface of the heat absorber under steady-state conditions.
[0062] The temperatures were 331.59°C, 420.48°C, 369.81°C, and 270.46°C, respectively, which were insufficient to reach the melting point of molten salt. Meanwhile, tube 2 experienced a higher temperature rise rate, was subjected to localized concentrated heat loads, and exhibited significant differences in temperature distribution between the light-facing surfaces of tubes 2 and 4, resulting in uneven heat flux density distribution. Therefore, an improved focusing strategy is needed.
[0063] Under the original four-lamp configuration, the steady-state peak temperatures of the four absorber tubes are 775.44℃, 959.90℃, 917.27℃, and 702.40℃, respectively, all occurring at the geometric center of their respective light-facing surfaces. The steady-state average temperatures of the absorber's light-facing surfaces are 522.79℃, 697.32℃, 685.59℃, and 568.50℃, respectively. At this point, the peak temperature of tube 2's light-facing surface is too high, posing a risk of overheating. Meanwhile, the average temperatures of tubes 1 and 4's light-facing surfaces are too low, posing a risk of molten salt solidification and pipe blockage. Furthermore, tubes 2 and 3 experience a high rate of temperature rise during the initial startup phase, posing a risk of rapid temperature increases due to concentrated heat load and potential localized thermal stress.
[0064] Under the original four-lamp configuration, the steady-state peak temperatures of the four absorber tubes were 800.38°C, 923.25°C, 935.08°C, and 787.59°C, respectively; the steady-state average temperatures of the absorber's light-facing surface were 613.26°C, 721.28°C, 737.93°C, and 647.30°C, respectively. During cold start-up, the temperature rise rate of tube 3 remained relatively high, necessitating adjustments to the light spot position and a staged heating strategy to mitigate the risk of localized thermal stress caused by rapid temperature increases.
[0065] Based on the thermo-mechanical coupling model of the receiver and MATLAB software, this example numerically simulates the change of thermal stress at the peak temperature point during the cold start experiment of the receiver. It obtains the trends of equivalent thermal stress and circumferential temperature difference in the receiver tube under the original three-lamp condition, as well as the cross-sectional temperature distribution at the peak thermal stress point of the receiver. Figure 9 , 10As shown in the figure, the results indicate that the equivalent thermal stress of the absorber tube follows the same trend as the circumferential temperature difference, meaning that the circumferential temperature difference is the main factor affecting the equivalent thermal stress during the cold start-up of the absorber tube. It is noteworthy that the peak values of both the equivalent thermal stress and the circumferential temperature difference occur at a transient state during the cold start-up of the absorber, rather than at the final steady state. Comparing the temperature distribution at the peak thermal stress cross-section of tube 3 at the steady state and at the peak thermal stress point, the results show that the temperature at this cross-section is generally higher at the steady state than at the peak thermal stress point, but its circumferential temperature difference is smaller. This indicates that during the cold start-up of the absorber, uneven heating of the absorber tube leads to differences in the rate of temperature rise, resulting in a circumferential temperature difference and generating significant thermal stress.
[0066] Example 3: Improved Focusing Strategy This embodiment employs an improved focusing strategy by adjusting the xenon lamp's focusing position and implementing staged lamp activation for heating. By comparing the focusing strategies before and after the improvement, the steady-state heat flux distribution, temperature change trend, and peak thermal stress change trend during the receiver's cold start process were analyzed. The results are as follows: Figure 11 , 12 As shown in Figure 13.
[0067] The improved focusing strategy adjusted the xenon lamp focusing position and adopted a phased activation method for xenon lamps 7, 2, and 6, effectively improving the uniformity of heat flux distribution and reducing the peak heat flux from 292550.77. Reduced to 246815.14 Meanwhile, the improved focusing strategy ensured that the steady-state temperature met the requirements for cold start, and the rate of temperature rise was reduced through staged heating. Comparative analysis showed that, due to the reduced rate of temperature rise, the improved focusing strategy resulted in a more gradual change in thermal stress after each xenon lamp activation. Throughout the cold start process, the peak circumferential temperature difference and thermal stress of the receiver occurred in tube 4, decreasing by 162.85℃ and 286.22MPa, respectively, compared to before the improved focusing strategy.
[0068] In summary, this invention provides a coupled verification and optimization method for a cold-start focusing strategy for high-temperature molten salt receivers. Through deep coupling of experimental measurements and numerical simulations, it successfully solves the technical challenges of large circumferential temperature differences and concentrated transient thermal stress during the cold start process of high-temperature molten salt receivers due to uneven heat flow distribution, which are difficult to measure directly. It can accurately identify transient temperature and stress peaks throughout the cold start process, rather than focusing solely on the steady state, thus effectively avoiding the risk of structural failure at the start-up moment. Through the optimized screening of a staged focusing strategy, the temperature rise rate and maximum equivalent thermal stress of the receiver tube are significantly reduced (peak stress reduced by approximately 286 MPa), improving heating efficiency while ensuring no overheating or solidification. This provides a quantitative strategic basis and threshold setting standard for the safe start-up of high-temperature chloride salt receivers, and has significant engineering application value.
[0069] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
Claims
1. A coupled verification and optimization method for cold start focusing strategy of high-temperature molten salt receiver, characterized in that, Includes the following steps: S1. Measure the incident heat flux density of the solar simulator acting on the sun-facing surface of the absorber under different light source configurations, and establish a database of incident heat flux density at each measuring point as the boundary condition for subsequent numerical calculations. S2. Generate candidate operating conditions according to the preset cold start focusing strategy. Each operating condition in the candidate operating condition set is determined by one or more of the following: xenon lamp turning-on combination, spot position parameters, and timing control parameters executed in stages. S3. Based on the current operating condition in the candidate operating condition set, control the solar simulator to irradiate the receiver, drive the receiver to enter the cold start heating process, and simultaneously collect the temperature time series data of each measuring point on the outer wall of the receiver at a preset sampling frequency. S4. During the execution of step S3, the highest temperature of the outer wall of the absorber is monitored in real time. If the monitored temperature exceeds the preset safety threshold, the solar simulator is immediately shut down and the current working condition experiment is terminated. If it does not exceed the threshold, the execution continues until the thermal balance judgment condition is met. S5. When the temperature time series data collected in step S3 shows that the temperature change rate of each measuring point is lower than the preset threshold and remains at the preset duration, it is determined that the experimental platform has reached thermal equilibrium, the steady-state temperature data under this condition is recorded and the experiment is ended. S6. Construct a three-dimensional unsteady thermo-mechanical coupling numerical model consistent with the geometric structure and material properties of the receiver. Verify the numerical model using benchmark experimental data under single xenon lamp irradiation conditions. If the deviation between the numerical simulation results and the benchmark experimental data is within the allowable range, the model is deemed valid; otherwise, the model parameters are corrected until the verification is passed. S7. The incident heat flux density distribution measured in step S1 is used as the outer wall heat flux boundary. The temperature time series data collected in step S3 is used as the initial or boundary constraint input into the verified three-dimensional unsteady thermo-mechanical coupling numerical model to solve for the transient temperature field of the entire cold start process. Based on the transient temperature field, the transient thermal stress field is further calculated. S8. Extract key evaluation indicators from the transient temperature field and transient thermal stress field obtained in step S7. The key evaluation indicators include the maximum temperature rise rate, the peak value of the circumferential temperature difference of the cross section, and the peak value of the maximum equivalent thermal stress during the entire cold start process. S9. Compare the key evaluation indicators extracted in step S8 with the preset safety constraints and performance targets, and select and optimize them to obtain a target-focusing strategy that simultaneously meets the requirements of thermal stress safety threshold, circumferential temperature difference limit and temperature rise efficiency.
2. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S1, the specific process of determining the incident heat flux density distribution includes: An energy flux meter was placed at the center of the Lambertian target and aligned near the focal point of the solar simulator. Single xenon lamps were turned on one by one to obtain the incident heat flux distribution at each measuring point when a single lamp was used. An incident heat flux density database under different light source configurations was established by linear superposition or experimental combination.
3. The coupled verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S2, the timing control parameters for phased execution include time nodes for multiple phases and the xenon lamp on-state for each phase. In step S9, the selected target focusing strategy is a phased lighting strategy that sequentially turns on xenon lamps No. 7, No. 2 and No. 6, and the condition for phase switching is that the temperature rise rate, circumferential temperature difference or the highest temperature of the outer wall reaches a preset switching threshold.
4. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S4, if the current working condition experiment is terminated because the monitored temperature exceeds the preset safety threshold, the current working condition is marked as an invalid strategy, and a new candidate working condition is generated after removing or adjusting the timing control parameters from the candidate working condition set, and the process returns to step S3.
5. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S5, the preset duration is 5 to 10 minutes, and the preset threshold is when the temperature change is less than a set value.
6. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S6, the reference experimental data comes from the temperature data collected by three thermocouple measuring points set at different heights at the center of the sun-facing side and the center of the shadow side of each heat-absorbing tube. The thermal model in the three-dimensional unsteady thermo-mechanical coupling numerical model is an unsteady heat conduction model that simultaneously considers radial, circumferential, and axial heat conduction in cylindrical coordinates.
7. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 6, characterized in that, When constructing the numerical model, the inner cavity of the heat absorber tube is set to be filled with air. Since the natural convection effect on the inner wall surface is very small, the natural convection heat transfer can be ignored within the allowable error range, and only the radiation heat transfer between the inner wall surfaces is considered as the inner wall boundary condition. The outer wall boundary of the heat absorber tube is defined to include the incident irradiated heat flow and the convective-radiative combined heat transfer boundary with the environment. The circumferential direction is set to use periodic boundary conditions, the upper and lower end faces are set to use adiabatic boundary conditions, and the initial temperature is set to room temperature.
8. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S7, the transient temperature field is solved using an explicit second-order difference discretization method; the time step and grid spacing of the explicit second-order difference discretization method are determined based on Fourier number stability constraints; the calculation of the transient thermal stress field based on the transient temperature field specifically includes: based on the Von Mises equivalent stress intensity theory, the equivalent thermal stress is obtained by synthesizing the calculated radial, circumferential and axial thermal stress components.
9. The coupling verification and optimization method for the cold start focusing strategy of a high-temperature molten salt receiver according to claim 1, characterized in that, In step S8, when extracting the key evaluation indicators, the transient extreme points of the temperature field and thermal stress field during the cold start process are identified. It was confirmed that the peak value of the circumferential temperature difference and the peak value of the maximum equivalent thermal stress of the cross section occurred at the transient moment of the cold start process rather than at the final steady state moment, and the maximum value of the key evaluation index was used as the final value of the key evaluation index throughout the cold start process.
10. The coupling verification and optimization method for the cold start focusing strategy of the high-temperature molten salt receiver according to claim 1, characterized in that, In step S9, the preset safety constraints include the minimum temperature safety threshold of the receiver's outer wall, the maximum temperature safety threshold of the outer wall, the upper limit of the circumferential temperature difference of the cross section, the upper limit of the equivalent thermal stress, and the upper limit of the temperature rise rate. The performance target is that the temperature rise efficiency of the receiver during cold start meets the preset molten salt anti-condensation temperature requirement, and the heating time of the entire cold start process is controlled within the preset range. When screening target focusing strategies, if there are multiple focusing strategies that simultaneously meet the conditions, the optimal target focusing strategy is determined by prioritizing the minimum peak value of the maximum equivalent thermal stress and the minimum peak value of the circumferential temperature difference of the cross section.