Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation o...Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation on a linear Fresnel reflector was investigated.The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer,scanning electron microscope,and X-ray diffractometer.The results showed that the dust density on the mirror increased,and the relative reflectivity decreased with an increase in the dust accumulation time.During 48 days of dust accumulation,the average relative reflectivity decreased 9.4%for a 1 g/m^(2)increase in the dust density.Additionally,the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle.The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation.The main component of the dust particles in the test area was SiO_(2),and the particle size range of the dust was 0.9 um to 87µm.According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror,a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed.The predicted results deviated about 1%from the test results.展开更多
In the present review,parabolic trough collector(PTC)and linear Fresnel reflector(LFR)are comprehensively and comparatively reviewed in terms of historical background,technological features,recent advancement,economic...In the present review,parabolic trough collector(PTC)and linear Fresnel reflector(LFR)are comprehensively and comparatively reviewed in terms of historical background,technological features,recent advancement,economic analysis and application areas.It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal(CST)technologies,they are now standing at different stages of development and facing their individual opportunities and challenges.For PTC,the development is commercially mature with steady and reliable performance;therefore,extension of application is the main future demand.For LFR,the development is still in rapid progress to commercial maturity,yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs.The question,which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies,becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.展开更多
Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keep...Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keeping in view the objective to enhance its functionality and performance.For achieving the same objective,this study presents a novel concept where a conventional LFR is enclosed in a greenhouse called greenhouse-LFR.It was expected that such an enclosure can:(1)increase the incoming solar radiation,(2)further improve the overall efficiency due to simplified cleaning process and(3)reduce the capital cost for the construction of LFR support system.A complete thermal and optical analysis was presented for modeling and performance evaluation of the solar field of both conventional-LFR and novel greenhouse-LFR.Sets of non-linear equations for each system were solved using Newton-Raphson method.More detailed optical analysis was further performed for conventional-LFR considering the seasonal variations.The results concluded that the greenhouse-LFR is better than the conventional-LFR as it had higher efficiency and useful heat with lesser heat losses.For greenhouse-LFR,the maximum thermal efficiency was 73.2%whereas for conventional-LFR it was 37.2%.Also,there was an average increase of useful heat by 3 times in the month of February and 4.7 times in the month of September.SolTrace^(TM) analysis indicated significant spillage loss when a conventional-LFR was used without a secondary reflector or slight curvature of the mirrors.展开更多
Linear Fresnel collector system as main solar energy collecting technology is widely studied.The secondary reflector has significant influence on the heat flux distribution on the linear Fresnel collector.In this work...Linear Fresnel collector system as main solar energy collecting technology is widely studied.The secondary reflector has significant influence on the heat flux distribution on the linear Fresnel collector.In this work,the heat flux and temperature distribution on linear Fresnel collector is compared with different secondary reflectors of simple trapezoidal concentrator,segmented parabolic concentrator and compound parabolic concentrator under varied incident ray angle.The uniformity index is applied to evaluate the Linear Fresnel reflector system heat flux distribution performance.The results show that the value of uniformity index increases with the increasing of incident ray angle.The compound parabolic concentrator has the highest value of uniformity index compared with simple trapezoidal concentrator and segmented parabolic concentrator in this work.The highest value of uniformity index is 0.8137 with compound parabolic concentrator.This work provides effective and practical guide to design and evaluate the secondary reflector in linear Fresnel reflector system.展开更多
The linear Fresnel reflector concentrator(LFRC)is widely used in the field of solar energy utilization due to its simple structure,low cost,and excellent wind resistance.Nevertheless,the LFRC operates outdoors all yea...The linear Fresnel reflector concentrator(LFRC)is widely used in the field of solar energy utilization due to its simple structure,low cost,and excellent wind resistance.Nevertheless,the LFRC operates outdoors all year round,and the dust accumulation on the mirror will reduce the optical efficiency of the system,so it needs to be perfected and improved.In this paper,a focal plane energy flux experimental device was designed to test the energy flux of the system under different dust accumulation times.The results indicate that,the dust density on the mirror increased and the energy flux on the focal plane decreased with increase of dust accumulation time.After undergoing dust accumulation for 35 days,the dust density on the mirror reached 4.33 g/m^(2)and the average energy flux on the focal plane decreased to 1.78 kW/m^(2).Additionally,the variation of reflectivity caused by dust accumulation on mirror was taken as the quantitative index,and a prediction model for the impact of dust on the optical efficiency of the system was proposed.The results will provide guidance for improving the optical efficiency of the LFRC.展开更多
The organic Rankine cycle(ORC)coupled with a linear Fresnel reflector(LFR)utilizes a low-grade heat source.This article presents the study of a small-scale LFR-ORC power-generation plant under the climatic conditions ...The organic Rankine cycle(ORC)coupled with a linear Fresnel reflector(LFR)utilizes a low-grade heat source.This article presents the study of a small-scale LFR-ORC power-generation plant under the climatic conditions of Almatret,Spain.The mathematical modelling is performed using thermodynamic equations and simulations are conducted to evaluate the optical performance of the LFR system and thermal performance of the ORC plant.Therminol-62 is used as a heat-transfer fluid(HTF)in the solar field,whereas NOVEC^(TM) 649 is used as the working fluid in the ORC power system.The LFR is integrated with a thermal-storage unit based on a two-tank system and stores the solar thermal energy via a heat exchanger.The thermal-energy output of the receiver tube of the LFR system is 108 kW and thermal losses are 7.872 kW during the peak time operation of a day at 1:00 p.m.The mechanical power output of the ORC turbine is 7.296 kW using the specific design conditions and the two-tank thermal-storage system adds 4 operation hours to the power plant after sunset.展开更多
To address the stochasticity and nonlinearity of solar collector power systems,a soft sensor prediction model with a hybrid convolutional neural network(CNN)and long short-term memory network(LSTM)was constructed,and ...To address the stochasticity and nonlinearity of solar collector power systems,a soft sensor prediction model with a hybrid convolutional neural network(CNN)and long short-term memory network(LSTM)was constructed,and the hyperparameter optimization of the hybrid neural network(CNN-LSTM)was carried out by using the sparrow search algorithm(SSA).The model utilized the powerful feature extraction and non-linear mapping capabilities of deep learning to effectively handle the complex relationship between input and target variables.The batch normalization technique was used to speed up the training and improve the stability of the soft-sensing model,and the random discard technique was used to prevent the soft-sensing model from overfitting.Finally,the mean absolute error(MAE)was used to assess the accuracy of the soft sensor model predictions.This study compared the proposed model with soft sensor prediction models like Bp,Elman,CNN,LSTM,and CNN-LSTM,using dynamic thermal performance data from the solar collector field of the molten salt linear Fresnel photovoltaic demonstration power plant.The deep learning-based soft sensor model outperformed the other models according to the experimental data.Its coefficients of determination(namely R^(2))are higher by 6.35%,8.42%,5.69%,6.90%,and 3.67%,respectively.The accuracy and robustness have been significantly improved.展开更多
Phase imaging coupled to micro-tomography acquisition has emerged as a powerful tool to investigate specimens in a non-destructive manner. While the intensity data can be acquired and recorded, the phase information o...Phase imaging coupled to micro-tomography acquisition has emerged as a powerful tool to investigate specimens in a non-destructive manner. While the intensity data can be acquired and recorded, the phase information of the signal has to be “retrieved” from the data modulus only. Phase retrieval is an ill-posed non-linear problem and regularization techniques including a priori knowledge are necessary to obtain stable solutions. Several linear phase recovery methods have been proposed and it is expected that some limitations resulting from the linearization of the direct problem will be overcome by taking into account the non-linearity of the phase problem. To achieve this goal, we propose and evaluate a non-linear algorithm for in-line phase micro-tomography based on an iterative Landweber method with an analytic calculation of the Fréchet derivative of the phase-intensity relationship and of its adjoint. The algorithm was applied in the projection space using as initialization the linear mixed solution. The efficacy of the regularization scheme was evaluated on simulated objects with a slowly and a strongly varying phase. Experimental data were also acquired at ESRF using a propagation-based X-ray imaging technique for the given pixel size 0.68 μm. Two regularization scheme were considered: first the initialization was obtained without any prior on the ratio of the real and imaginary parts of the complex refractive index and secondly a constant a priori value was assumed on ?. The tomographic central slices of the refractive index decrement were compared and numerical evaluation was performed. The non-linear method globally decreases the reconstruction errors compared to the linear algorithm and is achieving better reconstruction results if no prior is introduced in the initialization solution. For in-line phase micro-tomography, this non-linear approach is a new and interesting method in biomedical studies where the exact value of the a priori ratio is not known.展开更多
基金This research was supported by the National Natural Science Foundation of China(NO.51766012)the Inner Mongolia Graduate Research and Innovation Project in 2019(NO.B20191126Z)+1 种基金the Inner Mongolia Science and Technology Major Project in 2019,the Inner Mongolia Financial Innovation Funding Project in 2017,the Inner Mongolia Natural Science Foundation of china(No.2019MS05025)the Fundamental Research Funds for the Central Universities(WUT Grant No.2019IVB082).
文摘Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation on a linear Fresnel reflector was investigated.The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer,scanning electron microscope,and X-ray diffractometer.The results showed that the dust density on the mirror increased,and the relative reflectivity decreased with an increase in the dust accumulation time.During 48 days of dust accumulation,the average relative reflectivity decreased 9.4%for a 1 g/m^(2)increase in the dust density.Additionally,the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle.The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation.The main component of the dust particles in the test area was SiO_(2),and the particle size range of the dust was 0.9 um to 87µm.According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror,a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed.The predicted results deviated about 1%from the test results.
基金The present work is financially supported by National Natural Science Foundation of China(51776196)the Natural Science Foundation of Shaanxi Province(2020JM-048)+2 种基金the Shaanxi Creative Talents Promotion Plan-Technological Innovation Team(2019TD-039)the Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratory(XHD2020-001)Fundamental Research Funds for the Central Universities.
文摘In the present review,parabolic trough collector(PTC)and linear Fresnel reflector(LFR)are comprehensively and comparatively reviewed in terms of historical background,technological features,recent advancement,economic analysis and application areas.It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal(CST)technologies,they are now standing at different stages of development and facing their individual opportunities and challenges.For PTC,the development is commercially mature with steady and reliable performance;therefore,extension of application is the main future demand.For LFR,the development is still in rapid progress to commercial maturity,yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs.The question,which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies,becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.
基金The authors extend their appreciation to the Deputyship for Research&Innovation,“Ministry of Education”in Saudi Arabia for funding this research work through the project number IFKSURG-2020-200.
文摘Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keeping in view the objective to enhance its functionality and performance.For achieving the same objective,this study presents a novel concept where a conventional LFR is enclosed in a greenhouse called greenhouse-LFR.It was expected that such an enclosure can:(1)increase the incoming solar radiation,(2)further improve the overall efficiency due to simplified cleaning process and(3)reduce the capital cost for the construction of LFR support system.A complete thermal and optical analysis was presented for modeling and performance evaluation of the solar field of both conventional-LFR and novel greenhouse-LFR.Sets of non-linear equations for each system were solved using Newton-Raphson method.More detailed optical analysis was further performed for conventional-LFR considering the seasonal variations.The results concluded that the greenhouse-LFR is better than the conventional-LFR as it had higher efficiency and useful heat with lesser heat losses.For greenhouse-LFR,the maximum thermal efficiency was 73.2%whereas for conventional-LFR it was 37.2%.Also,there was an average increase of useful heat by 3 times in the month of February and 4.7 times in the month of September.SolTrace^(TM) analysis indicated significant spillage loss when a conventional-LFR was used without a secondary reflector or slight curvature of the mirrors.
基金financially supported by National Natural Science Foundation of China(NSFC)(51906003)Hebei province key research and development program(19214303D)Inner Mongolia Science and Technology Major Project(2021SZD0036)。
文摘Linear Fresnel collector system as main solar energy collecting technology is widely studied.The secondary reflector has significant influence on the heat flux distribution on the linear Fresnel collector.In this work,the heat flux and temperature distribution on linear Fresnel collector is compared with different secondary reflectors of simple trapezoidal concentrator,segmented parabolic concentrator and compound parabolic concentrator under varied incident ray angle.The uniformity index is applied to evaluate the Linear Fresnel reflector system heat flux distribution performance.The results show that the value of uniformity index increases with the increasing of incident ray angle.The compound parabolic concentrator has the highest value of uniformity index compared with simple trapezoidal concentrator and segmented parabolic concentrator in this work.The highest value of uniformity index is 0.8137 with compound parabolic concentrator.This work provides effective and practical guide to design and evaluate the secondary reflector in linear Fresnel reflector system.
基金financial support provided by the National Natural Science Foundation of China(No.51766012)the Scientific Research Project of Colleges and Universities in Inner Mongolia Autonomous Region(No.NJZY21322)+2 种基金Major science and Technology Project of Inner Mongolia(No.2019ZD014 and No.2021ZD0030)the Natural Science Foundation of Inner Mongolia(No.2019MS05025)the Scientific Research Project of Inner Mongolia University of Technology(No.ZZ202019)。
文摘The linear Fresnel reflector concentrator(LFRC)is widely used in the field of solar energy utilization due to its simple structure,low cost,and excellent wind resistance.Nevertheless,the LFRC operates outdoors all year round,and the dust accumulation on the mirror will reduce the optical efficiency of the system,so it needs to be perfected and improved.In this paper,a focal plane energy flux experimental device was designed to test the energy flux of the system under different dust accumulation times.The results indicate that,the dust density on the mirror increased and the energy flux on the focal plane decreased with increase of dust accumulation time.After undergoing dust accumulation for 35 days,the dust density on the mirror reached 4.33 g/m^(2)and the average energy flux on the focal plane decreased to 1.78 kW/m^(2).Additionally,the variation of reflectivity caused by dust accumulation on mirror was taken as the quantitative index,and a prediction model for the impact of dust on the optical efficiency of the system was proposed.The results will provide guidance for improving the optical efficiency of the LFRC.
文摘The organic Rankine cycle(ORC)coupled with a linear Fresnel reflector(LFR)utilizes a low-grade heat source.This article presents the study of a small-scale LFR-ORC power-generation plant under the climatic conditions of Almatret,Spain.The mathematical modelling is performed using thermodynamic equations and simulations are conducted to evaluate the optical performance of the LFR system and thermal performance of the ORC plant.Therminol-62 is used as a heat-transfer fluid(HTF)in the solar field,whereas NOVEC^(TM) 649 is used as the working fluid in the ORC power system.The LFR is integrated with a thermal-storage unit based on a two-tank system and stores the solar thermal energy via a heat exchanger.The thermal-energy output of the receiver tube of the LFR system is 108 kW and thermal losses are 7.872 kW during the peak time operation of a day at 1:00 p.m.The mechanical power output of the ORC turbine is 7.296 kW using the specific design conditions and the two-tank thermal-storage system adds 4 operation hours to the power plant after sunset.
基金supported by National Natural Science Foundation of China(No.52266012)Gansu Province College Industry Support Plan Project(No.2022CYZC-34)+1 种基金Gansu Province Major Science and Technology Special Project(Nos.20ZD7GF011,22ZD6GA063)Jiuquan City Science and Technology Programme Project(No.2023CA3058).
文摘To address the stochasticity and nonlinearity of solar collector power systems,a soft sensor prediction model with a hybrid convolutional neural network(CNN)and long short-term memory network(LSTM)was constructed,and the hyperparameter optimization of the hybrid neural network(CNN-LSTM)was carried out by using the sparrow search algorithm(SSA).The model utilized the powerful feature extraction and non-linear mapping capabilities of deep learning to effectively handle the complex relationship between input and target variables.The batch normalization technique was used to speed up the training and improve the stability of the soft-sensing model,and the random discard technique was used to prevent the soft-sensing model from overfitting.Finally,the mean absolute error(MAE)was used to assess the accuracy of the soft sensor model predictions.This study compared the proposed model with soft sensor prediction models like Bp,Elman,CNN,LSTM,and CNN-LSTM,using dynamic thermal performance data from the solar collector field of the molten salt linear Fresnel photovoltaic demonstration power plant.The deep learning-based soft sensor model outperformed the other models according to the experimental data.Its coefficients of determination(namely R^(2))are higher by 6.35%,8.42%,5.69%,6.90%,and 3.67%,respectively.The accuracy and robustness have been significantly improved.
文摘Phase imaging coupled to micro-tomography acquisition has emerged as a powerful tool to investigate specimens in a non-destructive manner. While the intensity data can be acquired and recorded, the phase information of the signal has to be “retrieved” from the data modulus only. Phase retrieval is an ill-posed non-linear problem and regularization techniques including a priori knowledge are necessary to obtain stable solutions. Several linear phase recovery methods have been proposed and it is expected that some limitations resulting from the linearization of the direct problem will be overcome by taking into account the non-linearity of the phase problem. To achieve this goal, we propose and evaluate a non-linear algorithm for in-line phase micro-tomography based on an iterative Landweber method with an analytic calculation of the Fréchet derivative of the phase-intensity relationship and of its adjoint. The algorithm was applied in the projection space using as initialization the linear mixed solution. The efficacy of the regularization scheme was evaluated on simulated objects with a slowly and a strongly varying phase. Experimental data were also acquired at ESRF using a propagation-based X-ray imaging technique for the given pixel size 0.68 μm. Two regularization scheme were considered: first the initialization was obtained without any prior on the ratio of the real and imaginary parts of the complex refractive index and secondly a constant a priori value was assumed on ?. The tomographic central slices of the refractive index decrement were compared and numerical evaluation was performed. The non-linear method globally decreases the reconstruction errors compared to the linear algorithm and is achieving better reconstruction results if no prior is introduced in the initialization solution. For in-line phase micro-tomography, this non-linear approach is a new and interesting method in biomedical studies where the exact value of the a priori ratio is not known.
