The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.H...The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.However,further exploration is required to suppress the outward thermal losses from the nanofluid at high temperatures.Herein,this paper proposes a novel NDASC in which the outer surface of the collector tube is covered with functional coatings and a three-dimensional computational fluid dynamics model is established to study the energy flow distributions on the collector within the temperature range of 400-600 K.When the nanofluid’s absorption coefficient reaches 80 m^(-1),the NDASC shows the optimal thermal performance,and the NDASC with local Sn-In_(2)O_(3) coating achieves a 7.8% improvement in thermal efficiency at 400 K compared to the original NDASC.Furthermore,hybrid coatings with Sn In_(2)O_(3)/WTi-Al_(2)O_(3) are explored,and the optimal coverage angles are determined.The NDASC with such coatings shows a 10.22%-17.9% increase in thermal efficiency compared to the original NDASC and a 7.6%-19.5% increase compared to the traditional surface-type solar collectors,demonstrating the effectiveness of the proposed energy flow control strategy for DASCs.展开更多
Direct absorption solar collectors use nanofluids to absorb and convert solar radiation. Despite the limitations of the photothermal properties of these nanofluids within the absorption spectra range, modifying the su...Direct absorption solar collectors use nanofluids to absorb and convert solar radiation. Despite the limitations of the photothermal properties of these nanofluids within the absorption spectra range, modifying the surface structure of the nanoparticles can broaden their absorption spectrum, thereby significantly improving the solar thermal conversion efficiency. This paper utilizes the finite element method to investigate the influence of surface pits on the photothermal properties of plasmonic nanoparticles, considering both material composition and surface micro-nano structures. Based on the findings, a novel Ti N nanoparticle is proposed to enhance photothermal performance. This nanoparticle exhibits the lowest average reflectance(0.0145) in the 300–1100 nm wavelength range and the highest light absorption intensity across the solar spectrum, enabling highly efficient solar energy conversion. It not only reduces material costs but also effectively broadens the light absorption spectrum of spherical plasmonic nanoparticles. The distributions of the electric field, magnetic field, and energy field of the nanoparticles indicate that the combination of the “lightning rod” effect and surface plasmon resonance(SPR) significantly enhances both the electric and magnetic fields, thereby increasing the localized heating effect and improving the photothermal performance. Additionally, the number and size of the pits have a significant impact on the absorption efficiency(η_(abs)) of TiN nanoparticles. When the surface of the nanoparticles has 38 pits, η_(abs) can reach90%, with the minimum optical penetration depth(h) of the nanofluid being 7 mm and the minimum volume fraction(f_(v))being 6.95×10^(-6). This study demonstrates that nanoparticles with micro-nano structures have immense potential in solar thermal applications, particularly in the field of direct absorption solar collectors.展开更多
An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar ...An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.展开更多
Nanofluids based direct absorption solar collectors(DASCs) are considered as the important alternative for further improve the utilization of solar energy. However the low-quality energy and aggregation of nanoparticl...Nanofluids based direct absorption solar collectors(DASCs) are considered as the important alternative for further improve the utilization of solar energy. However the low-quality energy and aggregation of nanoparticles obstructs their large-scale application. In this work, a new method of using magnetic nanofluids in DASCs is proposed. By this method, not only high-quality energy is got as well as the problems of blockage and corrosion in heat exchanger are well avoided. The result shows that the maximum temperature can reach 98℃ under 3 solar irradiations and the photothermal conversion efficiency can be further increased by 12.8% when the concentration is 500 ppm after adding an external rotating magnetic field. The highest viscosity of working fluid reduced by 21% when the concentration is 500 ppm at 95℃ after separating the Fe_(3)O_(4)@C nanoparticles from the nanofluids via magnetic separation technology. Meanwhile, the obtained pure base liquids with high temperature flow to heat exchanger, which also reduces the flow resistance in pipeline and avoids the problems such as blockage and corrosion in heat exchanger. This research promotes a new way for the efficient utilization of solar energy.展开更多
In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and tradition...In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and traditional solar collectors were compared. The sensitivity of the parameters to the radiative heat loss was investigated. Finally, the radiative heat transfer characteristics were discussed using the radiative exchange factor. The results of this study validated the advantages of the novel solar collector at both the surface and fluid temperatures. Under the conditions used in this study, the maximum temperature difference of the novel solar collector was 30 K, compared with 193 K for the traditional solar collector. Furthermore, the collector was divided into several units along the flow direction. The radiative exchange factor indicated that with an increase in the attenuation coefficient, the percentage of radiation intensity in the total solar radiation absorbed by the corresponding unit increased.Simultaneously, it decreased with an increase in the incident angle and scattering albedo. These results provide a reference for addressing the low efficiency and thermal damage caused by traditional solar collectors at high temperatures.展开更多
Recently, a solar thermal collector often employs nanoparticle suspension to absorb the solar radiation directly by a working fluid as well as to enhance its thermal performance. The collector efficiency of a direct a...Recently, a solar thermal collector often employs nanoparticle suspension to absorb the solar radiation directly by a working fluid as well as to enhance its thermal performance. The collector efficiency of a direct absorption solar collector （DASC） is very sensitive to optical properties of the working fluid, such as absorption and scattering coefficients. Most of the existing studies have neglected particle scattering by assuming that the size of nanoparticle suspension is much smaller than the wavelength of solar radiation （i.e., Rayleigh scattering is applicable）. If the nanoparticle suspension is made of metal, however, the scattering cross-section of metallic nanoparticles could be comparable to their absorption cross-section depending on the particle size, especially when the localized surface plasmon （LSP） is excited. Therefore, for the DASC utilizing a plasmonic nanofluid supporting the LSP, light scattering from metallic particle suspension must be taken into account in the thermal analysis. The present study investigates the scattering effect on the thermal performance of the DASC employing plasmonic nanofluid as a working fluid. In the analysis, the Monte Carlo method is employed to numerically solve the radiative transfer equation considering the volume scatter- ing inside the nanofluid. It is found that the light scattering can improve the collector performance if the scattering coefficient of nanofluid is carefully engineered depending on its value of the absorption coefficient.展开更多
An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prio...An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.展开更多
The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of ...The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of 1.5μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated,calibrated by a commercial optical frequency comb.The locking performances have been analyzed by in-loop and out-loop noises,indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h.Then,the application of this stabilized laser to the direct absorption spectroscopy has been performed.With the help of balanced detection,the detection sensitivity,in terms of optical density,can reach to 9.4×10^(-6).展开更多
At present, the use of furnaces in the northern rural areas of China is very common, due to the insufficient burning of fuel (coal, wood, etc.), carbon monoxide (CO) and other toxic gases are produced, CO colorless an...At present, the use of furnaces in the northern rural areas of China is very common, due to the insufficient burning of fuel (coal, wood, etc.), carbon monoxide (CO) and other toxic gases are produced, CO colorless and odorless, difficult to find in time, and bring huge safety risks to the life and health of residents. Based on the above problems, we developed a gas monitoring and removal device which could reduce the effect of extinction coefficient. The device was composed of ash settling area, gas disturbance area, spectral absorption identification area and gas removal area. After the air entered the device, the large-size particles were first settled to purify the solid particles in the gas, the gas was disturbed through the multi-layer separator to achieve the turbulent production of the gas, and then the gas was identified through the optical element of the direct absorption spectrum technology. When the toxic gas component reached the threshold, the spray device would automatically start for chemical removal to achieve the role of purifying the gas. At the same time, the device’s alarm could be alerted by buzzer and flash to remind users to evacuate in time. By improving the optical device, the effect of extinction coefficient on measurement was reduced and the monitoring accuracy was improved.展开更多
Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superre...Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge2Sb2Te5 thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.展开更多
基金Project(52476095)supported by the National Natural Science Foundation of ChinaProject(kq2506013)supported by Changsha Outstanding Innovative Youth Training Program,China。
文摘The nanofluid-based direct absorption solar collector(NDASC)ensures that solar radiation passing through the tube wall is directly absorbed by the nanofluid,reducing thermal resistance in the energy transfer process.However,further exploration is required to suppress the outward thermal losses from the nanofluid at high temperatures.Herein,this paper proposes a novel NDASC in which the outer surface of the collector tube is covered with functional coatings and a three-dimensional computational fluid dynamics model is established to study the energy flow distributions on the collector within the temperature range of 400-600 K.When the nanofluid’s absorption coefficient reaches 80 m^(-1),the NDASC shows the optimal thermal performance,and the NDASC with local Sn-In_(2)O_(3) coating achieves a 7.8% improvement in thermal efficiency at 400 K compared to the original NDASC.Furthermore,hybrid coatings with Sn In_(2)O_(3)/WTi-Al_(2)O_(3) are explored,and the optimal coverage angles are determined.The NDASC with such coatings shows a 10.22%-17.9% increase in thermal efficiency compared to the original NDASC and a 7.6%-19.5% increase compared to the traditional surface-type solar collectors,demonstrating the effectiveness of the proposed energy flow control strategy for DASCs.
基金supported by the National Natural Science Foundation of China (Grant No. 52106099)the Taishan Scholars Program。
文摘Direct absorption solar collectors use nanofluids to absorb and convert solar radiation. Despite the limitations of the photothermal properties of these nanofluids within the absorption spectra range, modifying the surface structure of the nanoparticles can broaden their absorption spectrum, thereby significantly improving the solar thermal conversion efficiency. This paper utilizes the finite element method to investigate the influence of surface pits on the photothermal properties of plasmonic nanoparticles, considering both material composition and surface micro-nano structures. Based on the findings, a novel Ti N nanoparticle is proposed to enhance photothermal performance. This nanoparticle exhibits the lowest average reflectance(0.0145) in the 300–1100 nm wavelength range and the highest light absorption intensity across the solar spectrum, enabling highly efficient solar energy conversion. It not only reduces material costs but also effectively broadens the light absorption spectrum of spherical plasmonic nanoparticles. The distributions of the electric field, magnetic field, and energy field of the nanoparticles indicate that the combination of the “lightning rod” effect and surface plasmon resonance(SPR) significantly enhances both the electric and magnetic fields, thereby increasing the localized heating effect and improving the photothermal performance. Additionally, the number and size of the pits have a significant impact on the absorption efficiency(η_(abs)) of TiN nanoparticles. When the surface of the nanoparticles has 38 pits, η_(abs) can reach90%, with the minimum optical penetration depth(h) of the nanofluid being 7 mm and the minimum volume fraction(f_(v))being 6.95×10^(-6). This study demonstrates that nanoparticles with micro-nano structures have immense potential in solar thermal applications, particularly in the field of direct absorption solar collectors.
基金supported by the National Natural Science Foundation of China(Grant No.11272338)the Science and Technology on Scramjet Key Laboratory Funding,China(Grant No.STSKFKT 2013004)the China Scholarship Council
文摘An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.
基金supported by National Natural Science Foundation of China(51590901&51876112&51906132&51906123)Shanghai Municipal Natural Science Foundation(Grant No.17ZR1411000)+1 种基金the Key Subject of Shanghai Polytechnic University(Material Science and engineeringGrant Nos.XXKZD1601 and EGD18YJ0042)。
文摘Nanofluids based direct absorption solar collectors(DASCs) are considered as the important alternative for further improve the utilization of solar energy. However the low-quality energy and aggregation of nanoparticles obstructs their large-scale application. In this work, a new method of using magnetic nanofluids in DASCs is proposed. By this method, not only high-quality energy is got as well as the problems of blockage and corrosion in heat exchanger are well avoided. The result shows that the maximum temperature can reach 98℃ under 3 solar irradiations and the photothermal conversion efficiency can be further increased by 12.8% when the concentration is 500 ppm after adding an external rotating magnetic field. The highest viscosity of working fluid reduced by 21% when the concentration is 500 ppm at 95℃ after separating the Fe_(3)O_(4)@C nanoparticles from the nanofluids via magnetic separation technology. Meanwhile, the obtained pure base liquids with high temperature flow to heat exchanger, which also reduces the flow resistance in pipeline and avoids the problems such as blockage and corrosion in heat exchanger. This research promotes a new way for the efficient utilization of solar energy.
基金supported by the National Natural Science Foundation of China (Grant No. 52041601)Hebei Natural Science Foundation (Grant No. E202203156)+1 种基金Chinese Scholarship Council (Grant No. 202106120167)partly funded the research activities—Enabling cooperation of the Harbin Institute of Technology with the Technical University of Denmark。
文摘In this study, a novel model of photothermal conversion in a direct absorption solar collector based on the Monte Carlo and finite volume methods was built and validated and the temperatures of the novel and traditional solar collectors were compared. The sensitivity of the parameters to the radiative heat loss was investigated. Finally, the radiative heat transfer characteristics were discussed using the radiative exchange factor. The results of this study validated the advantages of the novel solar collector at both the surface and fluid temperatures. Under the conditions used in this study, the maximum temperature difference of the novel solar collector was 30 K, compared with 193 K for the traditional solar collector. Furthermore, the collector was divided into several units along the flow direction. The radiative exchange factor indicated that with an increase in the attenuation coefficient, the percentage of radiation intensity in the total solar radiation absorbed by the corresponding unit increased.Simultaneously, it decreased with an increase in the incident angle and scattering albedo. These results provide a reference for addressing the low efficiency and thermal damage caused by traditional solar collectors at high temperatures.
文摘Recently, a solar thermal collector often employs nanoparticle suspension to absorb the solar radiation directly by a working fluid as well as to enhance its thermal performance. The collector efficiency of a direct absorption solar collector （DASC） is very sensitive to optical properties of the working fluid, such as absorption and scattering coefficients. Most of the existing studies have neglected particle scattering by assuming that the size of nanoparticle suspension is much smaller than the wavelength of solar radiation （i.e., Rayleigh scattering is applicable）. If the nanoparticle suspension is made of metal, however, the scattering cross-section of metallic nanoparticles could be comparable to their absorption cross-section depending on the particle size, especially when the localized surface plasmon （LSP） is excited. Therefore, for the DASC utilizing a plasmonic nanofluid supporting the LSP, light scattering from metallic particle suspension must be taken into account in the thermal analysis. The present study investigates the scattering effect on the thermal performance of the DASC employing plasmonic nanofluid as a working fluid. In the analysis, the Monte Carlo method is employed to numerically solve the radiative transfer equation considering the volume scatter- ing inside the nanofluid. It is found that the light scattering can improve the collector performance if the scattering coefficient of nanofluid is carefully engineered depending on its value of the absorption coefficient.
基金supported by the National Key Scientific Instrument and Equipment Development Project under Grant No.2012YQ22011902
文摘An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.
基金supported by the National Key R&D Program of China(Grant No.2017YFA0304203)the National Natural Science Foundation of China(Grant Nos.61875107,61905136,61905134,62175139)+1 种基金Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi,China(Grant No.2019L0062)Opening Foundation of Key Laboratory of Laser&Infrared System(Shandong University)。
文摘The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques.A stable and tunable optical frequency at wavelength of 1.5μm obtained by a cavity with high finesse of 96000 and a fiber laser has been demonstrated,calibrated by a commercial optical frequency comb.The locking performances have been analyzed by in-loop and out-loop noises,indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h.Then,the application of this stabilized laser to the direct absorption spectroscopy has been performed.With the help of balanced detection,the detection sensitivity,in terms of optical density,can reach to 9.4×10^(-6).
文摘At present, the use of furnaces in the northern rural areas of China is very common, due to the insufficient burning of fuel (coal, wood, etc.), carbon monoxide (CO) and other toxic gases are produced, CO colorless and odorless, difficult to find in time, and bring huge safety risks to the life and health of residents. Based on the above problems, we developed a gas monitoring and removal device which could reduce the effect of extinction coefficient. The device was composed of ash settling area, gas disturbance area, spectral absorption identification area and gas removal area. After the air entered the device, the large-size particles were first settled to purify the solid particles in the gas, the gas was disturbed through the multi-layer separator to achieve the turbulent production of the gas, and then the gas was identified through the optical element of the direct absorption spectrum technology. When the toxic gas component reached the threshold, the spray device would automatically start for chemical removal to achieve the role of purifying the gas. At the same time, the device’s alarm could be alerted by buzzer and flash to remind users to evacuate in time. By improving the optical device, the effect of extinction coefficient on measurement was reduced and the monitoring accuracy was improved.
基金partially supported by National Natural Science Foundation of China (Nos. 51172253 and 61137002)
文摘Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge2Sb2Te5 thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.
