- 标题
- 摘要
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- 实验方案
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Effects of receiver parameters on the optical performance of a fixed-focus Fresnel lens solar concentrator/cavity receiver system in solar cooker
摘要： To facilitate building integration with solar cooker for household, a solar cooker based on a fixed-focus Fresnel lens solar concentrator/cavity receiver system was proposed. To increase the system optical efficiency, the cavity receiver with bottom reflective cone was used as a fixed receiver. Expecting to optimize the system and receiver of better optical performance, the effects of receiver parameters on it were studied. To evaluate the effects, a significance test of key factors was conducted. Comparative analysis of fixed-focus food cooking system was undertaken. The analysis shows that average optical efficiencies using cavity receiver with bottom reflective cone of spherical, cylindrical, conical are 72.23%, 68.37% and 76.40%, respectively, while that of their corresponding conventional cavity receivers are 68.49%, 31.91% and 74.61%. The former significantly increased 3.74%, 36.46% and 1.79%, respectively. Moreover, cavity receiver with bottom reflective cone angle 90° is able to hold a higher amount of incoming energy from concentrator, compared to other three angles. Increasing the bottom reflective cone reflectivity and cavity receiver surface absorptivity can improve optical efficiency. In addition, the cavity receiver surface absorptivity and concentrated sunlight incidence angle have the most significant influence on the optical efficiency and flux uniformity, respectively. The conical cavity receiver with bottom reflective cone is the most suitable one for system. This work is expected to be useful for further optimization of solar concentrator/cavity receiver system.
关键词： Cavity receiver,Solar cooker,Fixed-focus,Fresnel lens,Optical performance
更新于2025-09-23 15:23:52
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Thermal performance analysis of a novel linear cavity receiver for parabolic trough solar collectors
摘要： The trough solar thermal power generation system is one of the most mature solar thermal power generation systems. A novel major arc-shaped linear cavity receiver with a lunate channel based on the black cavity effect principle for parabolic trough solar collectors is proposed in this work. The effects of the inclination angle, collecting temperature, surface emissivity and aperture width on the heat loss are thoroughly analyzed with a two-dimensional numerical model coupling natural convection with surface radiation. In addition, the thermal performance of the proposed linear cavity receiver is compared with that of the Solel’s UVAC series evacuated collector tube. The results show that: (1) The natural convection heat loss is significantly affected by the inclination angle, while the radiation heat loss is mainly affected by the surface emissivity and the collecting temperature. (2) The aperture width of the receiver has a great impact on the thermal performance. The larger the aperture width is, the greater the heat losses. However, the aperture width can also affect the optical performance and the manufacturing cost. The reasonable aperture width for this kind of linear cavity receiver is about 50–70 mm with consideration of all these factors. (3) The proposed linear cavity receiver demonstrates comparative or even better thermal performance as traditional evacuated collector tubes, especially in high temperature range. In general, the proposed linear cavity receiver has the comparative shape and size as the traditional evacuated collector tubes. More importantly, it has the advantages of raising the collecting temperature and reducing the production and maintenance costs. Therefore, it can be used to replace the evacuated collector tube which has poor performance due to long-term operation.
关键词： Cavity receiver,Parabolic trough solar collector,Surface radiation,Natural convection,Thermal performance,Linear receiver
更新于2025-09-23 15:23:52
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Review of Infrared signature suppression systems using optical blocking method
摘要： With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line-Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.
关键词： IR signature level,Performance penalty,Engine back-pressure,IR signature suppression,Optical blocking
更新于2025-09-23 15:23:52
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Passive cooling of building-integrated photovolatics in desert conditions: Experiment and modeling
摘要： The ef?ciency of photovoltaic modules depends mainly on the cell operating temperatures. Performance enhancement of building-integrated photovoltaic (BIPV) panels by passive cooling has been investigated both experimentally and with computational modeling. It has been shown that mounting the BIPV with a narrow channel can reduce the operating temperature of the photovoltaic panel. This enhancement in the heat transfer from the PV panel results in decreasing the average temperature of the PV panel from 5 to 10 (cid:1)C. Results show that having a 30 cm channel beneath the panel can increase the electrical output by 3e4%. This increase in PV output can translate into a signi?cant amount over the life cycle of a given PV module. Various channel aspect ratios have been tested in order to correlate the enhancement in performance to the cooling channel geometry. There is signi?cant consistency between the experimentally measured PV panel surface temperatures and those obtained from the computational model.
关键词： Building-integrated,Thermal performance,Passive cooling,Photovoltaic array
更新于2025-09-23 15:23:52
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Sub-ppm level NO2 sensing properties of polyethyleneimine-mediated WO3 nanoparticles synthesized by a one-pot hydrothermal method
摘要： A novel sensing material of polyethyleneimine-mediated WO3 nanoparticles was prepared by a simple and efficient one-pot hydrothermal method. The structure and morphology characteristics of the as-prepared WO3 nanoparticles were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that the as-prepared WO3 nanomaterials were composed of highly dispersible WO3 nanoparticles, and these nanoparticles with the particle size in the range of 10e50 nm showed a monoclinic structure. NO2 sensing measurements demonstrated that WO3 nanoparticles-based gas sensor exhibited superior response, outstanding selectivity, excellent reversibility, and good long-term stability. The sensor response increased as NO2 concentration increased. The highest response value of 251.7 was achieved to 5 ppm NO2 at the optimal operating temperature of 100 (cid:1)C. Especially, the sensor response could reach 3.2e50 ppb NO2. It also exhibited fast response and recovery times with a high sensor response even in a high-humidity environment. The excellent gas sensing properties of WO3 nanoparticles could be ascribed to their high effective surface areas as well as numerous oxygen vacancies, which foresee the great potential application for fast and effective detection of sub-ppm level NO2 under different humidity environments.
关键词： Nanoparticles,NO2,Gas sensing performance,WO3,Hydrothermal
更新于2025-09-23 15:23:52
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Novel design of photocatalyst coaxial ferromagnetic core and semiconducting shell microwire architecture
摘要： We report a novel design of coaxial core-shell magnetic-semiconductor microwire, as a catalyst under sunlight irradiation. The nano/micro hierarchical architecture-like device is comprised of a coaxial core-shell microwire where the core is the ferromagnetic Fe metal and the shell is formed by a semiconducting hematite layer. The fabrication process of our substrate-free device is simply based on controlled thermal oxidation process revealing a simple and low-cost method. The hematite outer microlayer has a mesoporous structure decorated with nanowires. The ferromagnetic and metallic core assume fundamental importance as to mechanical stability, collect the generated photoelectrons, and to be removed back from the dye solution by a magnetic field gradient or simply a magnet. This nano/micro device has exhibited photocatalytic activity to degrade the methylene blue dye under simulated sunlight irradiation. Additionally, the coaxial magnetic/semiconducting can also be designed as a photoanode to drive water oxidation reaction. The coaxial magnetic/semiconducting photoanode response has shown good chemical stability and long activity under simulated sunlight radiation. In fact, this designed architecture gives novel perspective in the development of substrate free photocatalyst.
关键词： Photoelectrochemical performance,Hematite photoanodes,Photodegradation,Micro/nano architecture,Core-shell microstructures,Thermal oxidation
更新于2025-09-23 15:23:52
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Treatment of sanitary landfill leachate by the combination of photo-Fenton and biological processes
摘要： In this work, the pollutant reduction performance in landfill leachate by combining both photo-Fenton and biological processes was investigated. First, conventional biological treatment was performed, consisting of a decantation process, with centrifugation at 5000 rpm for 15 min, followed by the biological process conducted at 2.36 ± 0.1 mg mg?1 (BOD5/MLSS) and 0.571 ± 0.04 vvm (L L?1 min?1) for 40 h. At the same time, in the application of the photo-Fenton process, a central composite rotatable design (CCRD) was applied to evaluate the effect of main process variables. The quadratic models of chemical oxygen demand (COD) and 5 days biological oxygen demand (BOD5) removal were proposed and validated, being separately used as objective functions during the search for optimal operating conditions. After the application of the conventional biological process, removals of 87 ± 2% and 84 ± 2% were obtained for COD and BOD5, respectively. For the photo-Fenton process under optimum conditions (3400 mg H2O2 L?1, 80 mg Fe2? L?1, pH = 2.40 and 120 min), removals of 89 ± 3% COD and 75 ± 1% BOD5 were obtained. However, both processes did not meet effluent discharge standards. So, the optimized photo-Fenton process was then combined with the biological process, performed for 150 h with 1.571 ± 0.06 vvm and 4.41 ± 0.3 mg mg?1 (BOD5/MLSS). With the combined process, it was possible to treat an effluent with high organic load, achieving a removal of 98% COD and BOD5 and meeting the restrictive standards of release in recipient water bodies.
关键词： Toxic effluent,Processes combination,Biodegradability,Processes performance assessment
更新于2025-09-23 15:23:52
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Electrochemical properties of PEDOT: PSS /V2O5 hybrid fiber based supercapacitors
摘要： Binary conducting polymer (CP)/transition metal oxides (TMOs) fiber-based supercapacitors (FSCs) are considered to possess good electrochemical performance and cyclic stability compared with unitary ones since TMOs within FSCs can prevent the structure damage of CP during charge/discharge cycles to some extent. In this study, the CP/TMOs hybrid fibers are made by directly injecting the solution into capillary. Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate /30 wt% vanadium pentoxide (PEDOT: PSS/30 wt% V2O5) fiber-based electrode has good electrochemical performance and cyclic stability (cycle retention: 94.02% after 4000 cycles at 0.1 mA/cm2). The energy density of the PEDOT: PSS/30 wt% V2O5 fiber in gel electrolyte is 1.37 μWh/cm2 at power density of 20 μW/cm2, which is much lower than the one in organic electrolyte (21.46 μWh/cm2 at power densities of 162.5 μW/cm2). Therefore, the method developed in this work induces good electrochemical performance for hybrid FSCs and promotes scalable fabrication of FSCs.
关键词： transition metal oxides,supercapacitor,Conducting polymers,electrochemical performance,hybrid fiber
更新于2025-09-23 15:23:52
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Spacecraft Formation Design for Bistatic SAR with GEO Illuminator and LEO Receiver
摘要： The bistatic synthetic aperture radar (BiSAR) system consists of a geosynchronous Earth orbit (GEO) illuminator and a low Earth orbit (LEO) receiver. Compared with GEO SAR, it offers great advantages of higher signal-to-noise ratio (SNR) and finer spatial resolution with lower system complexity. The concept also raises significant technical challenges. The spacecraft formation has great effect on radar performance, such as spatial resolution, the angle of two-dimensional (2-D) resolution direction and noise-equivalent sigma zero (NESZ). This paper establishes the relationship between the imaging performance and the formation parameters. Then, a novel design method of spacecraft formation is presented, identifying the principal formation design choices and constraints. Finally, simulation results are provided for typical observational tasks, to verify the effectiveness of the proposed method.
关键词： imaging performance,spacecraft formation,bistatic SAR,geosynchronous
更新于2025-09-23 15:23:52
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Development of a sub-miniature gamma camera for multimodal imaging system
摘要： In the recent past, gamma-ray imaging detectors have achieved an intrinsic spatial resolution of less than 1 mm within a few centimeters of a useful field of view (UFOV). Unlike to conventional gamma cameras, which are large and heavy, the compact gamma-ray imaging detectors can improve the performances of the gamma cameras used in the various fields. In this study, we developed a sub-miniature gamma camera for a multimodal imaging system. The camera has a gamma-ray detector, miniature electronics modules, and a diverging hole collimator. The detector consisted of the sub-millimeter pixelated Ce:GAGG array and the silicon photomultiplier (SiPM) array module. We organized the miniature electronics modules according to the functions; an MPPC base board, analog signal processing board, integrated power supply board, and compact data acquisition (DAQ) base board. The diverging hole collimator widened an imaging area of the gamma camera from the UFOV of the detector. On the detector side, dimensions of each hole and septa were identical to the pixel and inter-pixel thickness of the reflector of scintillator array. For the intrinsic performance test, we acquired a flood map image of 729 (27 × 27) scintillator pixels, and the energy resolution was 18.9 % for an integrated energy histogram of 99mTc (140 keV). For the extrinsic performance test, we used the 57Co sheet source, and made a 99mTc line source using a capillary tube. The sources located at 10 cm apart from the collimator surface. The imaging area was three times wider than the UFOV of the detector. The system sensitivity was 19 CPM/μCi and the spatial resolution was 3.5 mm. The usability of the proposed gamma camera will not be confined to existing applications due to its compactness and novelty.
关键词： Sub-miniature gamma camera,Gamma camera performance evaluation,Front-end electronics,Multimodal imaging system,Diverging hole collimator
更新于2025-09-23 15:23:52