Heat absorber enhanced heat transfer design method based on effective absorptivity of solar flow

Abstract

The invention discloses a heat absorber enhanced heat transfer design method based on the effective absorptivity of solar flow, and belongs to the technical field of tower type photo-thermal power stations. Aiming at the problems of large surface temperature gradient, large heat loss and relatively low light-heat conversion efficiency of a chloride heat absorber, the method comprises the following steps of: constructing an optical model by adopting a Monte Carlo ray tracing method through a grid discrete heat absorber to obtain annual average solar flow distribution, and establishing a flow and heat transfer model to calculate annual average values of efficiency, temperature and heat loss; and solving the annual average solar energy flow effective absorptivity alpha (i, j) of each grid, taking a truncation index beta = alphamax-5% as a criterion, only arranging a spiral twisted strip in a high-absorption area in which alpha (i, j) is greater than beta, and determining the arrangement length of the twisted strip through performance calculation and iterative optimization. Fine design of the spiral twisted belt in the chlorate heat absorber is achieved, heat loss is reduced while balance among efficiency, flow heat transfer performance and flow resistance is achieved, light-heat conversion efficiency is effectively improved, and the spiral twisted belt is suitable for optimization of the chlorate heat absorber of the tower type photo-thermal power station.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal power generation technology, and particularly relates to a heat transfer enhancement design method for a receiver based on the effective absorption rate of solar energy flow. Background Technology

[0002] Tower solar thermal power generation technology can achieve high energy flux density and operating temperature while being combined with thermal storage systems. This allows for efficient and stable operation while effectively overcoming the intermittency and volatility of solar energy, demonstrating the potential for large-scale, low-cost power generation. Among various heat transfer media, molten salts have been used in operational tower solar thermal power plants due to their high specific heat capacity, good chemical stability, and dual functions of heat transfer and thermal storage. However, the operating temperature of tower solar thermal power plants is typically below 600℃ due to the limitations of nitrate thermophysical properties, restricting further improvements in light-heat-electricity conversion efficiency. To overcome this bottleneck, the development goal for next-generation tower solar thermal power plants is to raise the operating temperature to above 700℃ and combine them with supercritical carbon dioxide Brayton cycle power generation systems to improve power generation efficiency and reduce power generation costs. Therefore, chloride salts, with their superior thermal stability, have become an ideal choice for heat transfer media under high-temperature operating conditions.

[0003] It is important to note that high-temperature operation also leads to a significant increase in radiative heat loss, which in turn causes a critical problem of reduced light-to-thermal conversion efficiency. To ensure the efficient operation of high-temperature chloride salt receivers, researchers have conducted studies from multiple perspectives. Regarding heliostat field layout, Wang et al. proposed three gradually sparser biomimetic field layouts based on the original biomimetic field, which can improve the uniformity of solar energy flow on the receiver surface while increasing the energy cutoff, thus improving receiver efficiency. Regarding focusing strategies, Wang et al. combined equatorial aiming and multi-point aiming strategies, utilizing the advantages of both in light-to-thermal conversion efficiency and stress safety to propose a novel hybrid multi-point aiming strategy. Regarding receiver structural design, Yang et al., by utilizing the inconsistent energy flow distribution and temperature distribution on the receiver surface, designed a high-low temperature dual-fluid receiver using a defined cutoff index. Regarding enhanced heat transfer within the tube, Liu et al. compared and analyzed the influence of several different structural insert forms on the temperature distribution of a single receiver tube. Compared to the other three methods, the in-tube enhanced heat transfer technology only involves the local modular design of the absorber tubes, resulting in a relatively small scope of modification. It does not affect the optical design and layout of the entire tower solar thermal power plant, making it easy to integrate and retrofit. Furthermore, the form of the in-tube enhanced heat transfer structure can be flexibly selected to suit different solar energy flow, temperature, and molten salt conditions, resulting in lower implementation costs.

[0004] It is important to note that in next-generation tower solar thermal power plants, the height of the non-uniform energy flow received by each tube bank in the chloride receiver may differ, and the flow heat transfer state within the tubes may also vary. Current research combining in-tube enhanced heat transfer technology with concentrated solar thermal power generation technology mostly focuses on individual receiver tubes, failing to fully reflect the impact of enhanced heat transfer technology on the overall flow heat transfer performance of the receiver. Furthermore, in application, enhanced heat transfer inserts are mostly placed within the entire receiver tube, and no effective guidance strategy has been developed for their installation position. Therefore, further research is needed to improve the efficient operation of complete chloride receivers under actual non-uniform energy flow and high-temperature conditions. In application, the length and position of the spiral twisted ribbon within the chloride receiver should be meticulously designed to achieve a balance between light-to-thermal conversion efficiency, flow heat transfer performance, and flow resistance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a heat transfer enhancement design method for receivers based on the effective absorptivity of solar flow. The method allows for the placement of enhanced heat transfer inserts according to the effective absorptivity of solar flow in a complete chloride receiver tube bank. This approach can balance the receiver's flow heat transfer performance and flow resistance while reducing the temperature gradient on the receiver's outer wall and radiative heat loss, thereby improving the receiver's light-to-heat conversion efficiency.

[0006] A method for enhancing heat transfer in a receiver based on the effective absorption rate of solar energy flow, specifically including the following steps: S1, Discretize the chloride salt absorber into i×j There are 1 grid (each grid has an area of ​​1). A physical model of the concentrating solar collector subsystem, including the heliostat field and the receiver, was constructed and used as a standard chloride receiver to provide a spatial unit basis for subsequent refined analysis.

[0007] S2. An optical model of the heliostat field to the standard chloride receiver is constructed using the Monte Carlo ray tracing method. The incident solar flux density of each grid on the outer wall of the receiver is calculated at all times throughout the year. qin(i,j) In order to obtain the annual average solar energy flow distribution qin,ave(i,j) It accurately captures the spatial distribution characteristics of non-uniform energy flow fields, providing a basis for the targeted arrangement of helical twisted belts.

[0008] S3. Establish a flow and heat transfer model for a standard chloride salt receiver based on the finite volume method, using the incident solar flux density. qin(i,j) As boundary conditions, calculate the heat absorption efficiency and the outer wall mesh temperature at each time step. T(i,j) and heat loss qloss (i,j) The annual average parameters were obtained by averaging the values ​​under typical operating conditions (noon at the spring equinox, summer solstice, autumn equinox, and winter solstice). (ηR, ave、Tave(i,j)、qloss,ave(i,j)) The quantitative analysis of temperature gradient and heat loss distribution provides a benchmark for determining the necessity of the helical twisted belt arrangement.

[0009] S31. The formula for calculating the absorber efficiency of a standard chloride absorber at each time point is: (1) in, or R The absorber efficiency of a standard chloride salt absorber at each time point. Q HTF The energy absorbed by the chloride salt in the standard chloride salt receiver at each time point. Q R The energy received by the outer wall of the standard chloride salt receiver at each moment.

[0010] S32. The formula for calculating the heat absorbed by the chloride in the standard chloride absorber at each moment is: (3) in, q m This represents the mass flow rate of chloride. T in and T out These represent the temperatures of the chloride salt at the inlet and outlet of the standard chloride salt absorber, respectively.

[0011] S33. The formula for calculating the energy received by the outer wall of the standard chloride salt absorber at each moment is: (4) in, a This refers to the number of tube banks in a standard chloride salt absorber. b This refers to the number of grids per tube bank in a standard chloride salt absorber.

[0012] The average receiver efficiency of a standard chloride receiver at noon during the representative spring equinox, summer solstice, autumn equinox, and winter solstice was used as the annual average receiver efficiency of the standard chloride receiver. or R,ave And at each moment, the outer wall surface of the standard chloride receiver has each grid... T ( i , j ), q loss ( i , j The annual average temperature can be obtained directly using the finite volume method. Further calculations of all times throughout the year and averaging of the results yield the annual average temperature for each grid cell. T ave ( i ,j and the average annual heat loss per grid q loss,ave ( i , j ).

[0013] S4. Solve for the annual average effective absorption rate of solar flow for each grid on the outer wall of the standard chloride salt receiver. The calculation formula is as follows: (5) in, α ( i , j The effective absorption rate of solar flow per grid on the outer wall of a standard chloride salt absorber is the annual average value.

[0014] S5, Utilization α ( i , j The distribution characteristic decreasing from the center to the edge enables differentiated design, avoiding ineffective investment in low-absorption areas, thus balancing enhanced heat transfer performance, flow resistance, and material costs. The annual average solar flow effective absorption rate is used as the cutoff indicator. β The effective annual solar energy absorption rate of each grid on the outer wall of the standard chloride salt receiver was used as the criterion for classification, along with the corresponding tube bank length. Considering that the effective annual solar energy absorption rate of the outer wall of the standard chloride salt receiver exhibits a decreasing trend from the center of the tube bank towards the outer edges, the following criteria were first used: β = α max -5% is used as the criterion. That is, in α ( i , j (greater than) β The corresponding standard chloride absorber has a spiral twisted arrangement of tube bank length and position, while... α ( i , j Less than β The corresponding standard chloride absorber does not have a spiral twisted band in the tube length and position. The chloride absorber with a spiral twisted band inside the absorber tube is named the spiral twisted chloride absorber.

[0015] For the spiral twisted ribbon chloride receiver, the receiver efficiency was calculated at noon on the spring equinox, summer solstice, autumn equinox and winter solstice respectively, and the annual average receiver efficiency of the spiral twisted ribbon chloride receiver was further calculated.

[0016] S51. The formula for calculating the absorber efficiency of a spiral twisted ribbon chloride absorber at a single moment is: (6) in, orR,TT The absorber efficiency of the spiral twisted ribbon chloride absorber at each moment. Q HTF,TT The energy absorbed by the chloride in the spiral twisted chloride absorber at each moment.

[0017] Furthermore, the average receiver efficiency of the spiral twisted ribbon chloride receiver at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice is the annual average receiver efficiency of the spiral twisted ribbon chloride receiver. or R,TT,ave .

[0018] Further, calculate the relative rate of change of the annual average receiver efficiency of the spiral twisted chloride receiver relative to the annual average receiver efficiency of the standard chloride receiver. If the relative rate of change is greater than 0, proceed to the next step and record the data; if the relative rate of change is less than 0, record the data at 5% intervals. β Subtract 5% again and judge. β Is it less than or equal to 0? If yes, proceed directly to step eight; otherwise, return to step five and redesign.

[0019] S52. The formula for calculating the relative change rate of the annual average receiver efficiency of the spiral twisted ribbon chloride receiver compared to the annual average receiver efficiency of the standard chloride receiver is as follows: (7) S6. Considering that while adding a spiral twisted ribbon inside the absorber tube improves flow heat transfer performance, it also increases flow resistance within the tube. Both factors must be considered comprehensively to obtain the optimal overall heat transfer performance. Therefore, the overall heat transfer performance index of the spiral twisted ribbon chloride absorber needs to be calculated at four design operating points. Further calculations are then performed to obtain the annual average overall heat transfer performance index of the spiral twisted ribbon chloride absorber. When the overall heat transfer performance index is greater than 1, it indicates that the benefit of the improved flow heat transfer capacity of the spiral twisted ribbon chloride absorber compared to the standard chloride absorber can offset the adverse effects caused by the increased flow resistance.

[0020] S61. The formula for calculating the comprehensive heat transfer performance index of the spiral twisted ribbon chloride absorber at a single moment is: (8) in, No TT The Nusselt number in the spiral twisted ribbon chloride absorber. No P This refers to the Nusselt number in a standard chloride salt absorber. f TT The flow resistance coefficient in the spiral twisted ribbon chloride absorber. f P This is the flow resistance coefficient in a standard chloride salt absorber.

[0021] S62. The formula for calculating the Nusselt number is: (9) in, h The heat transfer coefficient, d The hydraulic diameter of the heat absorber tube. l is the thermal conductivity of the chloride salt.

[0022] S63. Formula for calculating the flow resistance coefficient: (10) in, The pressure difference between the inlet and outlet of the absorber is the pressure difference of the chloride salt. L The length of the heat absorption tube in the heat absorber. r The density of the chloride salt, u The flow rate of the chloride salt is [value missing].

[0023] Furthermore, the average comprehensive heat transfer performance index of the spiral twisted ribbon chloride receiver at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice is the annual average comprehensive heat transfer performance index of the spiral twisted ribbon receiver. TEF ave .

[0024] Furthermore, if TEF ave If the value is greater than 1, record the data and proceed to the next step; if the value is less than 1, then... β Subtract 5% to determine β If the value is less than or equal to 0, proceed directly to step eight; otherwise, return to step five and redesign.

[0025] S7. Due to significant heat loss under high-temperature operating conditions, the effective absorption rate of the annual average solar flow in each grid on the outer wall of the standard chloride salt receiver will inevitably be less than 0 at some points. Furthermore, the enhanced heat transfer effect of the spiral twisted belt is limited to locations where the effective absorption rate of the annual average solar flow is greater than 0. Therefore, it is determined that… β Is it less than or equal to 0? If yes, proceed to the next step; otherwise, proceed to the next step. β Subtract 5% and judge again. β If the value is less than or equal to 0, proceed directly to step eight; otherwise, return to step five.

[0026] S8. Based on the recorded results, comprehensively select... TEF ave × i The parameter combination at maximum, according to the corresponding α ( i , jThe design results, including the length of each tube bank in the spiral twisted ribbon chloride absorber, the annual average absorber efficiency, and the annual average comprehensive heat exchange performance index of the spiral twisted ribbon chloride absorber, are output, and the design process is completed.

[0027] Compared with the prior art, the present invention has at least the following beneficial technical effects: 1) This invention solves for the effective absorption rate of the annual average solar flow. a(i,j) To cut off the indicator β=α max -5% is the criterion, only when... α(i,j)>β The high-absorption performance area is arranged with spiral twisted ribbons, enabling precise design of the arrangement length. Based on grid discretization analysis and annual energy flow characteristic data, this design enhances heat transfer in key areas while avoiding ineffective investment in low-absorption areas, thus reducing material waste and significantly improving overall heat absorption efficiency.

[0028] 2) This invention dynamically adjusts the cutoff index β, combined with the relative rate of change of the receiver efficiency and the comprehensive heat transfer performance index. TEF ave Through multi-parameter verification, a closed-loop process of "layout-calculation-adjustment-re-optimization" is formed. This design method can improve design accuracy and efficiency by iteratively selecting the optimal parameter combination, and achieve a dynamic balance between flow heat transfer performance and flow resistance.

[0029] 3) This invention uses the "annual average value of comprehensive heat exchange performance index" as the basis. TEF ave The core optimization objective is "annual average heat absorption efficiency θ", which balances heat transfer enhancement and energy loss. This design avoids performance imbalances caused by optimizing a single indicator. It can reduce the wall temperature gradient of the high-temperature chloride salt absorber in a relatively low-cost way, reduce radiative heat loss, and improve light-to-light conversion efficiency, thus achieving comprehensive and reasonable control of efficiency, energy consumption, and cost. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a conventional chloride salt absorber; Figure 2 This is a schematic diagram of the connection between the heat absorber tube and the spiral twisted band in the existing technology; Figure 3 This is a schematic diagram of the implementation process of this embodiment; Figure 4 This is a schematic diagram of the annual average solar energy flow of the chloride salt absorber in this embodiment; Figure 5 This is a schematic diagram of the annual average temperature of the chloride salt absorber in this embodiment; Figure 6 This is a schematic diagram of the annual average heat loss of the chloride salt absorber in this embodiment; Figure 7 This is a schematic diagram of the annual average effective absorption rate of solar energy flow for the chloride salt absorber in this embodiment.

[0031] In the diagram: 1. Back plate; 2. Connecting pipe; 3. Heat absorption pipe; 4. Spiral twisted ribbon. 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 embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This embodiment uses the SolarTwo tower-type molten salt solar thermal power plant as an application scenario to provide a detailed description of the chloride salt receiver heat transfer optimization design method of the present invention. This embodiment is only for explaining the invention and does not constitute a limitation on the scope of protection of the present invention.

[0034] like Figure 1-7 As shown, a heat transfer enhancement design method for a receiver based on the effective absorption rate of solar energy flow is presented. The specific implementation process of the method is as follows: The cylindrical receiver in the SolarTwo tower solar thermal power plant is used as the chloride receiver in this embodiment. The structure of the chloride receiver is as follows (e.g. Figure 1~2 As shown in the diagram, the chloride absorber consists of 24 absorber tube rows 3, each of which comprises 32 absorber tubes 1 and a back plate 2. Each absorber tube row has a tube header 4 connected to its upper and lower ends, and every two absorber tube rows are connected by a tube header connecting pipe 5. The chloride absorber is divided into two flow paths, each including 12 absorber tube rows. The 12 absorber tube rows in the two flow paths are connected by flow path connecting pipes a and b, respectively. The inlet and outlet temperatures of the chloride at flow path connecting pipes a and b are 520°C and 720°C, respectively.

[0035] like Figure 3-7 As shown, the specific steps are as follows: S1. Divide the chloride salt absorber into 24×46080 (i×j) grids. Each tube bank is divided into 46080 grids along its length. The grid size is determined based on the tube length (e.g., approximately 10m for a single tube) and the required calculation accuracy. The area of ​​each grid is 9.04×10⁻⁶. -5 m 2 ( ).

[0036] S2. Using the Monte Carlo ray tracing method, establish an optical model from the heliostat field to the chloride receiver at any given time, and calculate the incident solar flux density of each grid on the outer wall of the chloride receiver at every time of the year. q in ( i , j This allows us to obtain the annual average solar flow distribution of each grid on the outer wall of the chloride receiver. q in,ave ( i , j ).

[0037] S3. Establish a flow heat transfer model for the chloride salt absorber using the finite volume method, with the solar energy flow... q in ( i , j Using these as boundary conditions, the receiver efficiency of the chloride salt receiver at each time step is calculated, and the temperature distribution of each grid on the outer wall is obtained. T ( i (j) and heat loss q loss ( i , j Furthermore, the annual average receiver efficiency of the standard chloride salt receiver and the annual average temperature of each grid on the outer wall were calculated separately. T ave ( i (j) and the annual average heat loss for each grid q loss,ave ( i , j ).

[0038] S31. The formula for calculating the absorber efficiency of the chloride salt absorber at each moment is: (1) in, or R The absorber efficiency of the chloride salt absorber at each time point. Q HTF The energy absorbed by the chloride salt in the chloride salt absorber at each moment. Q R The energy received by the outer wall of the chloride salt absorber at each moment.

[0039] S32. The formula for calculating the heat absorbed by the chloride salt in the chloride salt absorber at each moment is: (3) in, q m This represents the mass flow rate of chloride. Tin and T out The temperatures of the chloride salt at the inlet and outlet of the chloride salt absorber are 520℃ and 720℃, respectively.

[0040] S33. The formula for calculating the energy received by the outer wall of the chloride salt absorber at each moment is: (4) in, a The number of tube banks in a standard chloride salt absorber is 24 in this embodiment; b The number of grids for each standard chloride absorber absorber tube row 3 is 46080 in this embodiment.

[0041] Furthermore, the average receiver efficiency of the chloride salt receiver at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice is used as the annual average receiver efficiency of the chloride salt receiver. or R,ave Calculated or R,ave It is 84.02%.

[0042] S4. Solve for the annual average effective absorption rate of solar flow for each grid on the outer wall of the chloride salt receiver. The calculation formula is as follows: (5) in, α ( i , j The effective absorption rate of solar flow per grid on the outer wall of the standard chloride salt absorber 4 is the annual average value.

[0043] Furthermore, a schematic diagram of the annual average solar energy flow effective absorption rate of a standard chloride salt absorber was obtained.

[0044] S5. Cutoff index based on annual average solar flow effective absorption rate β To determine the criteria, the annual average solar flow effective absorption rate and corresponding tube bank length were used to divide each grid on the outer wall of the chloride salt receiver. Considering that the annual average solar flow effective absorption rate of the standard chloride salt receiver's outer wall gradually decreases from the center of the tube bank towards the two edges, based on multiple simulation results, the following criteria were first used: β = α max -5% was used as the criterion. Calculations showed that the outer wall surface of the chloride salt absorber... α max The initial value is 84.77%. To facilitate design, it is rounded to 85%. β =80%, the rounding error has less than 1% impact on the results of subsequent iterations, which is acceptable in engineering.

[0045] Furthermore, in α ( i , j Spiral twisted ribbons are arranged for more than 80% of the pipe bank length and location, while... α ( i , j For tube bank lengths and positions less than 80%, spiral twisted ribbons are not arranged to form a spiral twisted ribbon chloride receiver. In existing technologies, spiral twisted ribbons are mostly arranged along the entire tube length, failing to consider the non-uniformity of energy flow distribution on the receiver surface. This results in ineffective ribbon deployment in low absorption regions and increased resistance. This invention addresses this issue by… α ( i , j Screening for high absorption regions, only... α ( i , j > β The area arrangement of twisted belts achieves 'on-demand enhancement', balancing heat transfer performance and flow resistance.

[0046] Using the noon times of the spring equinox, summer solstice, autumn equinox, and winter solstice as design operating points, the absorber efficiency of the spiral twisted ribbon chloride absorber was calculated respectively, and the annual average absorber efficiency of the spiral twisted ribbon chloride absorber was further calculated.

[0047] S51. The formula for calculating the absorber efficiency of a spiral twisted ribbon chloride absorber at a single moment is: (6) in, or R,TT The absorber efficiency of the spiral twisted ribbon chloride absorber at each moment. Q HTF,TT The energy absorbed by the chloride in the spiral twisted chloride absorber at each moment.

[0048] Furthermore, the average receiver efficiency of the spiral twisted ribbon chloride receiver at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice is the annual average receiver efficiency of the spiral twisted ribbon chloride receiver. or R,TT,ave .

[0049] Further, calculate the relative rate of change of the annual average receiver efficiency of the spiral twisted chloride receiver relative to the annual average receiver efficiency of the standard chloride receiver. If the relative rate of change is greater than 0, proceed to the next step and record the data; if the relative rate of change is less than 0, record the data at 5% intervals. β Subtract 5% again and judge. β Is it less than or equal to 0? If yes, proceed directly to step eight; otherwise, return to step five and redesign.

[0050] S52, the formula for calculating the relative change rate of the annual average receiver efficiency of the spiral twisted ribbon chloride receiver relative to the annual average receiver efficiency of the standard chloride receiver is as follows: (7) S6. Considering that adding a spiral twisted ribbon to the absorber tube of a chloride salt receiver improves flow heat transfer performance but also increases flow resistance within the tube, both factors need to be considered to obtain the optimal overall heat exchange performance. Therefore, the overall heat exchange performance index of the spiral twisted ribbon chloride salt receiver at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice needs to be calculated separately. The annual average overall heat exchange performance index of the spiral twisted ribbon chloride salt receiver is then calculated. When the overall heat exchange performance index is greater than 1, it indicates that the benefit of the improved flow heat transfer capacity of the spiral twisted ribbon chloride receiver compared to the standard chloride salt receiver can offset the adverse effects caused by the increased flow resistance.

[0051] S61. The formula for calculating the comprehensive heat transfer performance index of the spiral twisted ribbon chloride absorber at a single moment is: (8) in, No TT The Nusselt number in the spiral twisted ribbon chloride absorber. No P This refers to the Nusselt number in a standard chloride salt absorber. f TT The flow resistance coefficient in the spiral twisted ribbon chloride absorber is [missing information]. f P This is the flow resistance coefficient in a standard chloride salt absorber.

[0052] S62. The formula for calculating the Nusselt number is: (9) in, h The heat transfer coefficient, d The hydraulic diameter of the heat absorber tube. l is the thermal conductivity of the chloride salt.

[0053] S63. Formula for calculating the flow resistance coefficient: (10) in, The pressure difference between the inlet and outlet of the absorber is the pressure difference of the chloride salt. L The length of the heat absorber tube. r The density of the chloride salt, u The flow rate of the chloride salt is [value missing].

[0054] Furthermore, the average comprehensive heat transfer performance index of the spiral twisted ribbon chloride absorber at noon on the spring equinox, summer solstice, autumn equinox, and winter solstice is the annual average comprehensive heat transfer performance index of the spiral twisted ribbon absorber. TEF ave .

[0055] Furthermore, if TEF ave If the value is greater than 1, record the data and proceed to the next step; if the value is less than 1, then... β Subtract 5% to determine β If the value is less than or equal to 0, proceed directly to step eight; otherwise, return to step five and redesign.

[0056] S7. Due to significant heat loss under high-temperature operating conditions, the effective absorption rate of the annual average solar flow in each grid on the outer wall of the chloride salt receiver must be less than 0 at some points. Furthermore, the enhanced heat transfer effect of the spiral twisted belt is limited to locations where the effective absorption rate of the annual average solar flow is greater than 0. Therefore, it is determined that… β Is it less than or equal to 0? If yes, proceed to the next step; otherwise, proceed to the next step. β Subtract 5% and judge again. β Check if it is less than or equal to 0. If yes, proceed directly to step eight; otherwise, return to step five.

[0057] S8. Based on the recorded results, determine the appropriate... β= At 70%, TEF ave × i The maximum value can be obtained, which is 0.04. At this time, the lengths of each tube bank in the spiral twisted ribbon receiver are shown in Table 1 below. The annual average receiver efficiency of the spiral twisted ribbon chloride receiver is... or R,TT =86.27%, the annual average comprehensive heat exchange performance index of the spiral twisted ribbon chloride absorber TEF ave =1.47.

[0058] Table 1. Length of the spiral twist in each tube bank of the spiral twisted chloride absorber.

[0059] In summary, this embodiment solves for the effective absorption rate of the annual average solar flow. α ( i , j ), to cut off indicators β To determine the differentiated arrangement of the spiral twisted belts, multi-condition verification and iterative optimization were combined to ultimately achieve a synergistic improvement in heat absorption efficiency and overall heat exchange performance, thus verifying the effectiveness of the method of this invention.

[0060] This embodiment verifies that the design method can effectively balance the issues of photo-thermal conversion efficiency, flow heat transfer performance and flow resistance of chloride salt receivers. At the same time, it can also save material costs by arranging spiral twisted belts in a regionalized manner, and is suitable for the heat transfer optimization design of chloride salt receivers in tower solar thermal power plants.

[0061] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for heat transfer enhancement design of a solar energy based heat absorber based on effective solar flow absorptivity, characterized in that, Includes the following steps: S1. Discretize the chloride salt absorber into i×j A grid of equal area, area =0.01-0.1m 2 ,in i This represents the total number of tube banks in the chloride salt absorber. j The number of grids for a single tube array; construct a physical model of the concentrating solar collector subsystem containing the heliostat field and the chloride receiver, defined as a standard chloride receiver; S2. An optical model of the heliostat field to the standard chloride receiver is constructed using the Monte Carlo ray tracing method. The incident solar flux density of each grid on the outer wall is calculated at all times throughout the year to obtain the annual average solar flux distribution. S3. The flow and heat transfer model of a standard chloride salt receiver is established using the finite volume method. The incident solar flux density is used as the boundary condition. The heat absorption efficiency, outer wall grid temperature and heat loss at each time are calculated, and the annual average values ​​of these parameters are obtained. S4. Solve for the annual average effective absorptivity of solar flow for each grid on the outer wall of a standard chloride receiver to truncate the index. β The criterion is to subtract 5% from the maximum annual average effective solar energy absorption rate. If the annual average effective solar energy absorption rate is greater than... β The tube bank is arranged with spiral twisted ribbons to form a chloride salt absorber with spiral twisted ribbons; S5. Calculate the heat absorption efficiency, annual average heat absorption efficiency, and comprehensive heat exchange performance index and its annual average value of the chloride salt heat absorber with spiral twisted band at key operating points at noon in all four seasons. S6. Adjust through iterative optimization β Select the parameter that maximizes "annual average value of comprehensive heat exchange performance index × annual average heat absorption efficiency" to determine and output the arrangement length of the spiral twisted band in each pipe bank.

2. The method according to claim 1, characterized in that, The specific steps for obtaining the annual average value in step S3 are as follows: The average heat absorption efficiency at noon in all four seasons is used as the annual average heat absorption efficiency of the standard chloride salt absorber. The annual average temperature of the outer wall mesh and the annual average heat loss at each time point are obtained by directly solving the finite volume method.

3. The method according to claim 1, characterized in that, Step S3 further includes: S31. Calculate the heat absorption efficiency at each moment: the ratio of the energy absorbed by the chloride salt to the energy received by the outer wall of the absorber at that moment; S32. Calculate the energy absorbed by chloride salt: determined by the mass flow rate of chloride salt, specific heat capacity at constant pressure, and the temperature difference between inlet and outlet; S33. Calculate the energy received by the outer wall surface: the sum of the products of the incident solar flux density of all grids and the area of ​​a single grid.

4. The method according to claim 1, characterized in that, In step S4: The annual average solar flux effective absorption rate of a single grid is defined as the ratio of the annual average heat absorbed by the standard chloride receiver in that grid to the annual average incident solar flux density of that grid. The specific method for arranging the spiral twisted band is as follows: β The value is taken as 5% of the maximum annual average effective solar energy absorption rate, while a preset lower threshold is set; the preset lower threshold can be dynamically adjusted according to the power plant type, operating conditions, and actual application scenarios. SolarTwo In this embodiment, the preset lower threshold is 80%; when β When the effective absorption rate of the annual average solar flow is greater than or equal to the preset lower threshold, it will only be applied when the effective absorption rate is greater than or equal to the preset lower threshold. β The spiral twisted belt is positioned in a specific location; when β When the annual average solar flow effective absorption rate is less than the preset lower threshold, the spiral twisted belt is not arranged at the position where the preset lower threshold is used as the criterion.

5. The method according to claim 1, characterized in that, Step S4 further includes: Using the noon of each season as the design operating point, the heat absorption efficiency of the chloride salt absorber with spiral twisted band at each operating point is calculated; the average value is taken as the annual average heat absorption efficiency. Calculate the relative change rate of the annual average heat absorption efficiency relative to the standard absorber: if >0, proceed to step S5 and record; if <0, then... β Decrease by 5% to determine the adjustment. β If the value is ≤0: if yes, proceed to step S5; otherwise, return to step S3 to redesign.

6. The method according to claim 1, characterized in that, The calculation of the comprehensive heat transfer performance index in step S5 includes: S51. Comprehensive heat transfer performance index at key operating points: This is the ratio of the Nusselt number of the coiled torsion band heat exchanger to that of the standard receiver, and the ratio of their flow resistance coefficients. 1 / 3 The ratio of powers; S52. Nusselt number: determined by the heat transfer coefficient, the hydraulic diameter of the absorber tube, and the thermal conductivity of the chloride salt; S53. Flow resistance coefficient: determined by the pressure difference between the inlet and outlet of the chloride salt, the hydraulic diameter and length of the heat absorber tube, the density of the chloride salt, and the flow velocity; The critical operating point is noon in all four seasons, and the average value of its comprehensive heat exchange performance index is taken as the annual average value.

7. The method according to claim 1, characterized in that, Step S5 further includes: If the annual average comprehensive heat transfer performance index is >1, then record and execute step S6; if it is <1, then... β Decrease by 5% to determine the adjustment. β If the value is ≤0: if yes, proceed to step S6; otherwise, return to step S3 to redesign.

8. The method according to claim 1, characterized in that, Iterative optimization in step S6 β Also includes: If, during the adjustment, there are grids with an annual average solar flow effective absorptivity < 0, determine if β ≤ 0: if yes, continue iteration; otherwise, [the process will be changed]. β After decreasing by 5%, the judgment is re-evaluated until... β ≤0 or meet the condition of maximizing the annual average value of the comprehensive heat exchange performance index × the annual average heat absorption efficiency.

9. The method according to claim 1, characterized in that, The specific steps for determining and outputting the arrangement length in step S6 are as follows: The output parameters that maximize the annual average solar flow effective absorption rate distribution, the arrangement length of the spiral twisted belt in each tube bank, the annual average heat absorption efficiency of the chloride absorber with the spiral twisted belt, and the annual average comprehensive heat exchange performance index are: the annual average value of the comprehensive heat exchange performance index × the annual average heat absorption efficiency.

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