CN111737925B - Heliostat structure based on phase-change material and design optimization method thereof - Google Patents

Heliostat structure based on phase-change material and design optimization method thereof Download PDF

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CN111737925B
CN111737925B CN202010853636.6A CN202010853636A CN111737925B CN 111737925 B CN111737925 B CN 111737925B CN 202010853636 A CN202010853636 A CN 202010853636A CN 111737925 B CN111737925 B CN 111737925B
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heliostat
phase change
heat exchange
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parameters
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CN111737925A (en
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童哲铭
杨琦
陈伟
童水光
唐宁
李昂铮
陆成
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Xizi clean energy equipment manufacturing Co.,Ltd.
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Hangzhou Boiler Group Co Ltd
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    • F24—HEATING; RANGES; VENTILATING
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Abstract

The invention relates to a heliostat structure based on a phase-change material and an optimization method of the design thereof, which comprises the following steps: s1: calculating the heliostat field efficiency of the heliostat according to the heliostat parameters, the heat absorber parameters and the working medium parameters; s2: calculating the heat efficiency of the working medium of the phase change layer according to the mirror field efficiency; s3: calculating the thickness of the phase change layer by utilizing a thermodynamic iteration mode; s4: based on the mirror field efficiency, the phase change layer working medium thermal efficiency and the phase change layer thickness calculated in the steps S1-S3, input different heat exchange tube parameters are subjected to optimization screening based on a database-neural network algorithm; the calculation, the iteration process and the optimization screening process of the steps S1-S4 are all realized in three-dimensional modeling software. The optimization method provided by the invention can perform the optimization process of the thermal efficiency on the parameters of the heat exchanger before the heliostat structure is actually produced, so as to screen out the optimal design scheme and provide data support for the design and production of the subsequent actual structure.

Description

Heliostat structure based on phase-change material and design optimization method thereof
Technical Field
The invention belongs to the technical field of solar energy application, and particularly relates to a heliostat structure based on a phase-change material and a design optimization method thereof.
Background
A heliostat is a flat mirror device that projects sunlight in a directional manner, and is widely used in the technical field of solar energy application. Sunlight is reflected by the heliostat to gather heat energy into the heat absorber, working media in the heat absorber are heated at high temperature to push the generator to rotate, and photoelectric conversion is realized to generate electric energy. Because the heliostat is exposed to strong solar radiation for a long time, and needs to adjust the steering or focus to follow the sun according to the position of the sun in order to better realize the reflection effect of sunlight, the surface temperature of the heliostat is higher, and the heliostat is in a state of large and uneven thermal stress for a long time, thereby not only causing the waste of heat energy, but also reducing the service life of the heliostat.
The shape-stabilized phase change material is a special phase change material which can keep the macroscopic shape and the self temperature unchanged when the phase change occurs and store absorbed energy. The phase-change material is widely applied to engineering, such as widely used in hot blast stoves, heat exchangers and boilers in industry, and plays a role in heat storage and heat preservation in domestic electric heaters.
At present, a lot of researches are carried out on the combination of a phase change material and a solar thermal power generation system, but most of the phase change materials are applied to a system heat storage part such as a heat collector, and no research is carried out on the combination of a heliostat and the phase change material. The detection of the prior art finds that the design of the heliostat has the following defects: the change of the structural parameters of the heat exchanger can affect the thermal efficiency of the heliostat, and an optimal product cannot be accurately manufactured in the actual structural design and production; the heliostat is exposed in a severe high-temperature environment for a long time, and the mirror surface of the heliostat is unevenly heated due to local high temperature, so that the thermal stress is large, the service life is shortened, and the economical efficiency and the safety of a power generation system are reduced; the solar radiation obtained by the heliostat is removed from the reflected part, and the rest energy is not well utilized, so that certain energy loss is caused.
Disclosure of Invention
In order to solve the problems, the invention provides a heliostat structure based on a phase-change material and a design optimization method thereof, which can perform an optimization process on the thermal efficiency of parameters of a heat exchanger before actually producing the heliostat structure so as to screen out an optimal design scheme and provide data support for the design and production of a subsequent actual structure.
The technical scheme of the invention is as follows:
a method for optimizing structural design of a heliostat based on a phase-change material comprises the following steps:
s1: calculating the heliostat field efficiency of the heliostat according to the heliostat parameters, the heat absorber parameters and the working medium parameters;
s2: calculating the heat efficiency of the working medium of the phase change layer according to the mirror field efficiency;
s3: calculating the thickness of the phase change layer by utilizing a thermodynamic iteration mode;
s4: based on the mirror field efficiency, the phase change layer working medium thermal efficiency and the phase change layer thickness calculated in the steps S1-S3, input different heat exchange tube parameters are subjected to optimization screening based on a database-neural network algorithm;
the calculation, the iteration process and the optimization screening process of the steps S1-S4 are all realized in three-dimensional modeling software.
Preferably, the heliostat field efficiency
Figure 825368DEST_PATH_IMAGE001
Calculated by the following formula:
Figure 323346DEST_PATH_IMAGE002
；
Figure 94993DEST_PATH_IMAGE003
；
wherein the content of the first and second substances,
Figure 107948DEST_PATH_IMAGE004
to output thermal power for the heliostat field,
Figure 990453DEST_PATH_IMAGE005
for the input of power to the heat sink,
Figure 342937DEST_PATH_IMAGE006
is the area of the heliostat, and is,
Figure 347802DEST_PATH_IMAGE007
the number of the heliostats is,
Figure 848054DEST_PATH_IMAGE008
is the irradiance of the sun,
Figure 268671DEST_PATH_IMAGE009
is the flow rate of the working medium,
Figure 741240DEST_PATH_IMAGE010
is the specific heat capacity of the water,
Figure 917007DEST_PATH_IMAGE011
is the temperature of the working medium outlet,
Figure 842238DEST_PATH_IMAGE012
is the working medium inlet temperature.
Preferably, the phase-change working medium has thermal efficiency
Figure 66545DEST_PATH_IMAGE013
The calculation formula is as follows:
Figure 190359DEST_PATH_IMAGE014
；
wherein the content of the first and second substances,
Figure 474710DEST_PATH_IMAGE015
in order to determine the shadow loss rate,
Figure 887237DEST_PATH_IMAGE016
in order to obtain the cosine loss rate,
Figure 915236DEST_PATH_IMAGE017
in order to obtain the rate of loss of atmospheric attenuation,
Figure 159135DEST_PATH_IMAGE018
in order to achieve the rate of overflow loss,
Figure 348808DEST_PATH_IMAGE019
in order to obtain the reflection efficiency of the heliostat,
Figure 248631DEST_PATH_IMAGE020
is the heliostat cleaning rate.
Preferably, the process of optimizing screening specifically includes:
s4.1: establishing a heat exchange tube structure-heliostat heat efficiency database, establishing a heat exchange tube structure-heliostat model in FLUENT software, and changing input parameters of the model to obtain a simulation result of the heat efficiency of the corresponding heliostat;
s4.2: training a heat exchange tube structure-heliostat structure thermal efficiency model by using MATLAB software and a neural network algorithm, changing input heat exchanger parameters, and outputting corresponding heliostat thermal efficiency;
s4.3: comparing the error of the model training result with the database, constraining the error, and repeating the training of the heat exchange tube structure-heliostat structure thermal efficiency model until the error is within the range of a preset value if the error is larger than the preset value;
s4.4: and when the error is within the range of the preset value, outputting a training result of the neural network algorithm in a chart form through software, and confirming the optimization parameters required by the design of the heliostat according to the result.
Preferably, the input parameters in the step S4.1 include a heat exchange tube diameter, a heat exchange tube length, and a heat exchange tube structure, and the input heat exchanger parameters in the step S4.2 include a heat exchange tube diameter, a heat exchange tube length, and a heat exchange tube arrangement; the heat exchange tubes are arranged in a mode of forward flow, reverse flow, forward flow and reverse flow.
The invention also provides a heliostat structure based on the phase-change material, and an optimization method of the heliostat structure design based on the phase-change material, wherein the heliostat structure comprises a heliostat, a phase-change layer is fixed at the back of the mirror surface of the heliostat, a heat-insulating layer is coated outside the phase-change layer, a heat exchange tube is embedded inside the phase-change layer, and the mirror surface of the heliostat is also connected with a heliostat support; and a working medium inlet and a working medium outlet for circulating the heat exchange working medium are also arranged outside the phase change layer.
Preferably, the mirror surface of the heliostat is of a rectangular design.
Preferably, the heat exchange tube is an aluminum tube.
Preferably, the phase change layer is made of a shaped composite phase change material.
Preferably, the heliostat support is a spinning elevation support or a single-arm support.
The invention has the beneficial effects that:
1. the optimization method provided by the invention can perform the optimization process of the thermal efficiency on the parameters of the heat exchanger before the heliostat structure is actually produced so as to screen out the optimal design scheme and provide data support for the design and production of the subsequent actual structure;
2. the heliostat structure provided by the invention can alleviate the surface temperature change of the heliostat, reduce the phenomenon of thermal stress increase caused by local high temperature caused by sun tracking process, cloud cover, fault and other factors, ensure that the temperature distribution of the heliostat is more uniform, prolong the service life and further improve the economical efficiency and safety of the operation of a solar thermal power generation system; meanwhile, the surface temperature of the heliostat is reduced, and energy which is not reflected is transmitted to a water using end, so that the energy is fully and efficiently utilized, and the energy utilization rate and the economical efficiency of a power station are improved.
Drawings
FIG. 1 is a flow chart of an optimization screening process.
Fig. 2 is a side cross-sectional view of a heliostat structure.
Fig. 3 is a heat exchange tube layout diagram of a heliostat structure.
Description of reference numerals: 1. a heliostat mirror face; 2. a phase change layer; 3. a heat-insulating layer; 4. a heat exchange pipe; 5. a heliostat support.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The embodiment of the invention provides an optimization method for heliostat structure design based on a phase-change material, which comprises the following steps:
1. and calculating the heliostat field efficiency of the heliostat.
The heliostat field efficiency of the heliostat is calculated according to heliostat parameters, heat absorber parameters and working medium parameters through a calculation formula, wherein the specific formula is as follows:
Figure 877059DEST_PATH_IMAGE021
；
Figure 178727DEST_PATH_IMAGE003
(ii) a Wherein the content of the first and second substances,
Figure 539301DEST_PATH_IMAGE004
to output thermal power for the heliostat field,
Figure 988737DEST_PATH_IMAGE005
for the input of power to the heat sink,
Figure 358538DEST_PATH_IMAGE006
is the area of the heliostat, and is,
Figure 311451DEST_PATH_IMAGE007
the number of the heliostats is,
Figure 233139DEST_PATH_IMAGE008
is the irradiance of the sun,
Figure 841975DEST_PATH_IMAGE009
is the flow rate of the working medium,
Figure 15468DEST_PATH_IMAGE010
is the specific heat capacity of the water,
Figure 88466DEST_PATH_IMAGE011
is the temperature of the working medium outlet,
Figure 56422DEST_PATH_IMAGE012
is the working medium inlet temperature. The data are from a database of the solar thermal power generation system, wherein the flow of the working medium is obtained by measuring through a flowmeter, the outlet temperature and the inlet temperature of the working medium are obtained by measuring through a thermometer, the specific heat capacity of water is obtained by looking up a table through the inlet temperature of the working medium, and the irradiance can be obtained by measuring through an irradiator configured in the power generation system.
2. And calculating the thermal efficiency of the working medium of the phase change layer.
Calculating according to the heliostat field efficiency of the heliostat and a calculation formula, wherein the specific formula is as follows:
Figure 152554DEST_PATH_IMAGE014
(ii) a Wherein the content of the first and second substances,
Figure 926475DEST_PATH_IMAGE015
in order to determine the shadow loss rate,
Figure 853980DEST_PATH_IMAGE016
in order to obtain the cosine loss rate,
Figure 55154DEST_PATH_IMAGE017
in order to obtain the rate of loss of atmospheric attenuation,
Figure 700899DEST_PATH_IMAGE018
in order to achieve the rate of overflow loss,
Figure 950614DEST_PATH_IMAGE019
in order to obtain the reflection efficiency of the heliostat,
Figure 998205DEST_PATH_IMAGE020
is the heliostat cleaning rate. Wherein the shadow loss rate is calculated according to the arrangement of the heliostats; the cosine loss rate is a cosine value of the solar incident angle, and the solar incident angle can be obtained by inquiring at different moments; the atmospheric attenuation loss rate can be obtained by calculation according to the distance between the heliostat and the heat absorber; the overflow loss rate can be obtained according to the tracking precision of the heliostat; the heliostat reflection efficiency is obtained according to the heliostat reflectivity; heliostat cleaning rate according toThe system for automatically measuring the surface cleanliness of the heliostat is obtained.
3. And calculating the thickness of the phase change layer.
The thickness of the phase change layer is calculated according to thermodynamic equilibrium iteration, and a specific thermodynamic equilibrium equation set is as follows:
a heliostat:
Figure 307963DEST_PATH_IMAGE022
；
phase change layer:
Figure 378688DEST_PATH_IMAGE023
；
Figure 494411DEST_PATH_IMAGE024
；
Figure 334191DEST_PATH_IMAGE025
；
Figure 877168DEST_PATH_IMAGE026
；
Figure 169609DEST_PATH_IMAGE027
；
a heat exchange tube:
Figure 26707DEST_PATH_IMAGE028
；
insulating layer:
Figure 720993DEST_PATH_IMAGE029
。
in the above-mentioned formulas, the first and second substrates,
Figure 434871DEST_PATH_IMAGE008
the solar irradiation amount is the amount of solar irradiation,
Figure 480188DEST_PATH_IMAGE030
is the surface area of the heliostat,
Figure 875397DEST_PATH_IMAGE031
in order to be the absorption rate of the heliostat,
Figure 486507DEST_PATH_IMAGE032
the heat conduction between the heliostat and the phase change layer,
Figure 574549DEST_PATH_IMAGE033
the amount of convective heat transfer between the heliostat and the environment,
Figure 903899DEST_PATH_IMAGE034
is the amount of heat exchange between the heliostat and the ambient radiation,
Figure 102799DEST_PATH_IMAGE035
is the radiation heat exchange quantity between the heliostat and the ground,
Figure 568415DEST_PATH_IMAGE036
in order to accumulate the heat absorption of the phase change layer,
Figure 827358DEST_PATH_IMAGE037
the phase change layer and the heat exchange tube conduct heat,
Figure 644005DEST_PATH_IMAGE038
the heat conduction quantity of the phase change layer and the heat insulation layer,
Figure 381016DEST_PATH_IMAGE039
is the heat absorption of the PCM layer per unit time,
Figure 904402DEST_PATH_IMAGE040
the heat absorption capacity is accumulated for the solid phase of the phase change layer,
Figure 396563DEST_PATH_IMAGE041
the heat absorption is accumulated in the liquid phase of the phase change layer,
Figure 372609DEST_PATH_IMAGE042
is the specific heat capacity of the solid phase of the phase change layer,
Figure 913312DEST_PATH_IMAGE043
is the liquid phase specific heat capacity of the phase change layer,the solid-phase density of the phase-change layer,
Figure 954266DEST_PATH_IMAGE045
is the density of the liquid phase of the phase change layer,
Figure 683188DEST_PATH_IMAGE046
in order to the thickness of the phase change layer,
Figure 824319DEST_PATH_IMAGE047
in order to have a width of the phase change layer,
Figure 322297DEST_PATH_IMAGE048
as to the length of the phase change layer,
Figure 828364DEST_PATH_IMAGE049
is the phase transition temperature of the phase change layer,
Figure 106899DEST_PATH_IMAGE050
is the latent heat of phase change of the phase change layer,
Figure 989404DEST_PATH_IMAGE051
is the temperature of the phase-change layer,
Figure 404205DEST_PATH_IMAGE052
in order to be the quality of the phase change layer,
Figure 346753DEST_PATH_IMAGE053
is the convective heat transfer coefficient of the working medium and the heat exchange tube,
Figure 784688DEST_PATH_IMAGE054
is the surface area of the heat exchange tube,
Figure 205305DEST_PATH_IMAGE055
as the outlet of working mediumThe temperature of the mixture is controlled by the temperature,
Figure 740191DEST_PATH_IMAGE056
is the temperature of the working medium inlet, and is,
Figure DEST_PATH_IMAGE057
the heat exchange quantity of the heat preservation layer and the environment is convection. The parameters are partially fixed, and the other part is generated in an iterative process.
4. And (5) parameter optimization process of the heat exchanger.
The optimization process is completed based on a database-neural network algorithm, and is specifically divided into database establishment and neural network training based on FLUENT.
As shown in fig. 1, the optimization process includes changing a heat exchange tube structure in FLUENT software, including a heat exchange tube diameter, a heat exchange tube length and a heat exchange tube structure, performing numerical simulation on heliostat thermal efficiency, researching an influence manner of the heat exchange tube structure on the heliostat efficiency, and establishing a heat exchange tube structure-heliostat thermal efficiency database with a simulation result. Establishing a heat exchange tube structure-heliostat structure thermal efficiency model in MATLAB, taking the diameter of a heat exchange tube, the length of the heat exchange tube and the arrangement of the heat exchange tube as input in neural network training, taking the thermal efficiency of a heliostat as output, and taking the error of a calculation result and a simulation result in a database as a constraint condition, wherein the arrangement mode of the heat exchange tube comprises downstream flow, upstream flow, downstream flow and upstream flow. If the error is smaller than the precision condition, outputting an optimization design result, otherwise, repeating the neural network training until the precision requirement is met. The error value is set to 2% in the present embodiment.
5. And when the error is within the range of the preset value, outputting a training result of the neural network algorithm in a chart form through software, and confirming the optimization parameters required by the design of the heliostat according to the result.
The method is utilized to screen the parameters of the heat exchange tube to obtain the optimal or most needed structural design parameters, and the optimal or most needed structural design parameters are applied to the structural design of a specific product. Phase change layer 2 is fixed in 1 back of heliostat mirror surface, and the cladding of heat preservation 3 is outside 2 in phase change layer, and heat exchange tube 4 inlays in phase change layer 2 inside, and the heat transfer working medium flows in heat exchange tube 4, and heliostat support 5 is connected with heliostat mirror surface 1.
As a specific embodiment of the present invention, the heliostat mirror takes a rectangular form.
As a specific embodiment of the invention, the phase change layer is made of a shape-stabilized composite phase change material, the raw materials of the phase change layer are selected from paraffin, high-density polyethylene and expanded graphite, the ratio of the paraffin to the high-density polyethylene is 4:1, and the amount of the expanded graphite is selected according to actual conditions.
As a specific embodiment of the invention, the heat exchange working medium selects water, enters the phase change layer through a working medium inlet connected to the outer part of the phase change layer, leaves the phase change layer through a working medium outlet, and the water after heat exchange is connected with a water end and can be used as hot water in a nearby building, as shown in figure 3.
In the embodiment, the circular light pipe is arranged in a countercurrent mode, and the corrugated pipe or the flat box-shaped heat exchange pipe can be selected according to actual conditions.
As a specific embodiment of the present invention, the heliostat support is of a spin-elevation rotation type or a single-arm support type.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the present invention in its spirit and scope. Are intended to be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (9)

1. A method for optimizing structural design of a heliostat based on a phase-change material is characterized by comprising the following steps:
s1: calculating the heliostat field efficiency of the heliostat according to the heliostat parameters, the heat absorber parameters and the working medium parameters;
s2: calculating the heat efficiency of the working medium of the phase change layer according to the mirror field efficiency;
s3: calculating the thickness of the phase change layer by utilizing a thermodynamic iteration mode;
s4: based on the mirror field efficiency, the phase change layer working medium thermal efficiency and the phase change layer thickness calculated in the steps S1-S3, input different heat exchange tube parameters are subjected to optimization screening based on a database and a neural network algorithm;
the calculation, the iteration process and the optimization screening process of the steps S1-S4 are all realized in three-dimensional modeling software;
the optimization screening process specifically comprises the following steps:
s4.1: establishing a heat exchange tube structure-heliostat heat efficiency database, establishing a heat exchange tube structure-heliostat model in FLUENT software, and changing input parameters of the model to obtain a simulation result of the heat efficiency of the corresponding heliostat;
s4.2: training a heat exchange tube structure-heliostat structure thermal efficiency model by using MATLAB software and a neural network algorithm, changing input heat exchanger parameters, and outputting corresponding heliostat thermal efficiency;
s4.3: comparing the error of the model training result with the database, constraining the error, and repeating the training of the heat exchange tube structure-heliostat structure thermal efficiency model until the error is within the range of a preset value if the error is larger than the preset value;
s4.4: and when the error is within the range of the preset value, outputting a training result of the neural network algorithm in a chart form through software, and confirming the optimization parameters required by the design of the heliostat according to the result.
2. The phase change material based stator of claim 1The optimization method of the heliostat structural design is characterized in that the heliostat field efficiency of the heliostat
Figure 694668DEST_PATH_IMAGE001
Calculated by the following formula:
Figure 674125DEST_PATH_IMAGE002
；
Figure 453862DEST_PATH_IMAGE003
；
wherein the content of the first and second substances,
Figure 849072DEST_PATH_IMAGE004
to output thermal power for the heliostat field,
Figure 473564DEST_PATH_IMAGE005
for the input of power to the heat sink,
Figure 296026DEST_PATH_IMAGE006
is the area of the heliostat, and is,
Figure 563059DEST_PATH_IMAGE007
the number of the heliostats is,
Figure 824276DEST_PATH_IMAGE008
is the irradiance of the sun,
Figure 493155DEST_PATH_IMAGE009
is the flow rate of the working medium,
Figure 299568DEST_PATH_IMAGE010
is the specific heat capacity of the water,
Figure 53898DEST_PATH_IMAGE011
is the temperature of the working medium outlet,
Figure 790910DEST_PATH_IMAGE012
is the working medium inlet temperature.
3. The method of claim 1, wherein the phase change layer working medium thermal efficiency is optimized for heliostat structural design based on phase change material
Figure 376612DEST_PATH_IMAGE013
The calculation formula is as follows:
Figure 806456DEST_PATH_IMAGE014
；
wherein the content of the first and second substances,
Figure 48081DEST_PATH_IMAGE001
in order to be the mirror field efficiency of the heliostat,
Figure 136254DEST_PATH_IMAGE015
in order to determine the shadow loss rate,
Figure 779725DEST_PATH_IMAGE016
in order to obtain the cosine loss rate,
Figure 114892DEST_PATH_IMAGE017
in order to obtain the rate of loss of atmospheric attenuation,
Figure 906130DEST_PATH_IMAGE018
in order to achieve the rate of overflow loss,
Figure 984945DEST_PATH_IMAGE019
in order to obtain the reflection efficiency of the heliostat,
Figure 482922DEST_PATH_IMAGE020
is the heliostat cleaning rate.
4. The optimization method for heliostat structure design based on phase-change material according to claim 1, wherein the input parameters in step S4.1 comprise heat exchange tube diameter, heat exchange tube length, and heat exchange tube structure, and the input heat exchanger parameters in step S4.2 comprise heat exchange tube diameter, heat exchange tube length, and heat exchange tube arrangement; the heat exchange tubes are arranged in a mode of forward flow, reverse flow, forward flow and reverse flow.
5. A phase-change-material-based heliostat structure, based on the optimization method of the design of the phase-change-material-based heliostat structure of any one of claims 1 to 4, characterized in that the heliostat structure comprises a heliostat, a phase-change layer is fixed on the back of the mirror surface of the heliostat, the phase-change layer is externally wrapped with a heat-insulating layer, a heat exchange tube is embedded in the phase-change layer, and the mirror surface of the heliostat is also connected with a heliostat support; and a working medium inlet and a working medium outlet for circulating the heat exchange working medium are also arranged outside the phase change layer.
6. The phase change material based heliostat structure of claim 5, wherein the mirror face of the heliostat is of rectangular design.
7. The phase change material based heliostat structure of claim 5, wherein the heat exchange tubes are aluminum tubes.
8. The phase change material based heliostat structure of claim 5, wherein the phase change layer is comprised of a shaped composite phase change material.
9. The phase change material based heliostat structure of claim 5, wherein the heliostat support is a spinning elevation or single-arm support.
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