Cavity Aperture Research Articles

Design optimization of a new cavity receiver for a parabolic trough solar collector

The most important parameter affecting the optical efficiency, the upper limit for an overall efficiency of parabolic trough solar collector (PTC), is the net absorbed heat rate by receiver on which solar beam radiation is concentrated. The objective of this study is to propose and optimize a new cavity receiver used in PTC for increasing optical efficiency. Three different geometries (triangle, rectangle and polygon), aperture widths, heights and positions of cavity receiver are taken as optimization parameters. A design of experiments (DoE) approach is used to evaluate the effects of these parameters on the absorbed radiation heat rate by receiver at the same time. SolTrace is used to investigate the effects of these parameters by optical analysis. The results indicate that the optimum cavity geometry is polygonal, and the cavity depth and aperture both are equal to 0.05 m. Moreover, it is found that the most effective parameter is the position of the cavity receiver, and the optimum position is at the focal line of the parabolic concentrator. The highest absorbed radiation rate by the cavity receiver and the optical efficiency of the PTC are equal to 3241.99 W and 81.05 % respectively for the optimum cavity receiver design.

A Planar-Cavity Receiver Configuration for High-Temperature Solar Thermal Processes

Next-generation concentrating solar thermal power (CSP) technologies target a wide spectrum of applications including electricity generation, thermochemical processes, and industrial process heat for broad decarbonization potential. Many of these applications require higher temperatures than those of current commercial nitrate salt systems. Particulate materials are promising candidates for next-generation high-temperature heat transfer and low-cost storage media and can facilitate operation over a wide temperature range. However these materials necessitate novel receiver configurations to accept the high incident flux concentrations that enable high solar-to-thermal receiver efficiency. One option is a novel light-trapping planar cavity receiver configuration in which small cavity-like structures are formed from opaque planar surfaces such that a high incident flux concentration at the cavity aperture is reduced to a wall-absorbed solar flux concentration that is manageable within limited wall-to-particle heat transfer rates. The paper introduces the receiver configuration and provides calculated optical performance for a preliminary 50 MWt receiver design.

Power generation for off‐grid building with a small segments parabolic dish concentrator and ORC unit: Numerical investigation

AbstractIn this research, the small segments parabolic dish concentrator (SSPDC) with a modified cavity was optically and thermally investigated. The SSPDC consisted of small mirrors that were tracking the sun individually. The SSPDC allows using different concentration ratios and aperture areas. Oil, pure water, and water + perypolen glycol (PG) were evaluated as working fluids. Different structural characteristics of the solar system were investigated, including dish focal distance, cavity outer diameter, and cavity aperture area. Then the investigated solar system was explored as a heat source of an organic Rankine cycle (ORC) unit for providing the power for a house. Finally, some environmental parameters of the investigated ORC units, such as carbon dioxide emission and carbon dioxide credits, were evaluated. The results reveal that the investigated solar unit had a dish depth of 0.14 m, a focal distance of 1 m, a cavity aperture outer diameter of 0.1 m, and a cavity aperture inner diameter of 0.08 m for a 10‐mrad optical error and a 1° tracking error. Usage of pure water is recommended for low‐temperature application, water + PG for medium‐temperature application, and oil for high‐temperature application. It was concluded that two units of the proposed ORC could provide energy to the house with solar radiation of more than 800 W/m2 and the number of units should be increased for achieving the required power with decreasing solar radiation.

Large-area Fe–C eutectic fixed-points for radiation and contact thermometry

Abstract High-quality metal (carbide)–carbon eutectic materials based on high-temperature fixed points (HTFPs) are widely used in radiometry and thermometry as reference standards. HTFPs on the base of iron–carbon (Fe–C) binary eutectic alloys, with a nominal melting temperature of about 1154 °C (just above the copper freezing point of 1084.62 °C), are one of the promising candidates among the eutectic materials. To establish new HTFPs as reference metrological tools for high-temperature thermometry, their performance should be thoroughly investigated regarding reproducibility and stability. In this work, two large-area (8 mm aperture, 107 mm cavity/thermowell length) Fe–C fixed-point cells were constructed and studied in detail using a radiation thermometer and two different thermocouples (TCs). Three different furnaces were used to explore the thermal behaviors of the cells at various furnace gradients and furnace offsets. The melting temperature at the inflections point of the melting curves of the cells studied across extensive measurement campaigns demonstrated good performance with repeatability of less than 9 mK (assessed from four successive runs) and reproducibility—less than 100 mK (at different furnaces and furnace offsets). The melting temperature agreement between both cells in the same experimental conditions was better than 30 mK. In addition, the equivalence of the developed large-area cells and a small-area radiometric cell (3 mm cavity aperture, and 35 mm cavity length) were comparatively examined in the same experimental conditions. The coherence of the obtained results for the melting temperature of large-area Fe–C cells indicates the feasibility of using large-volume cells for precise calibration of both radiation thermometers and TCs.

Aeroacoustics and shear layer characteristics of confined cavities subject to low Mach number flow

Numerous engineering applications involve low Mach number flow in cavity aperture geometries, which can generate flow-excited acoustic oscillations and hence high amplitudes of noise and vibration. This is caused by the instability of the shear layer interacting with the acoustic modes of the system. In this study, we experimentally investigate ducted cylindrical cavities with aspect ratios (Depth/Diameter) of 0.5, 1, and 1.5 up to flow velocities of Mach 0.4. We examine the influence of the cavity confinement (Cavity Width/Duct Width) on the aeroacoustics response, as well as the downstream impingement behaviour of the shear layer. Rectangular and square cavities bearing similar geometric parameters are also investigated to compare the effect of the cavity shape on the shear layer dynamics and the aeroacoustics response. The results confirm resonance behaviour at frequencies well predicted by the theory, as well as Strouhal periodicities that agree with reported literature. However, cylindrical and square cavities with aspect ratio of 0.5 exhibit stronger dependence on the aspect ratio due to the interference of the recirculation region by the cavity floor, ultimately modifying the symmetry of the shear layer. This asymmetric flow pattern affects the velocity-dependent tones, generating much lower Strouhal numbers than the estimated values, and must be accounted for in equipment design. Moreover, Particle Image Velocimetry (PIV) measurements further illustrate the spatial characteristics of the shear layer dynamics for the various shaped cavities. The visualizations demonstrate enhanced flow modulation at higher acoustic pressure amplitudes, as well as reveal the flow asymmetry and the three-dimensional shear layer topology in cylindrical and square cavities.

Sawtooth V-Trough Cavity for Low-Concentration Photovoltaic Systems Based on Small-Scale Linear Fresnel Reflectors: Optimal Design, Verification, and Construction

Ensuring the uniformity of solar irradiance distribution on photovoltaic cells is a major challenge in low-concentrating photovoltaic systems based on a small-scale linear Fresnel reflector. A novel sawtooth V-cavity design method based on an optimization algorithm to achieve uniform irradiance distribution on photovoltaic cells is presented. The reliability of the design was verified using the Monte Carlo ray-tracing method and a laser experiment. A prototype was built using 3D printing technology with a biodegradable green polymer material known as polylactic acid. The new cavity was compared to the standard V-trough cavity, keeping the cavity aperture, reflective surface area, and photovoltaic cell width constant. In addition, the focal height, number of mirrors, mirror width, and mirror spacing were also kept constant; so, the cost of the two configurations was the same from the point of view of the primary reflector system. The new design ensured the uniform distribution of solar irradiation and significantly reduced the height of the cavity. The significant decrease in the height of the proposed cavity has the following advantages: (i) a decrease in the dimensions of the fixed structure of the small-scale linear Fresnel reflector, thus reducing its cost, (ii) a significant decrease in the surface area exposed to wind loads, thus reducing the cost of the fixed structure and secondary system structures, (iii) a reduction in the difficulty of the manufacture, maintenance, and transportation of the cavity’s reflecting walls, and (iv) an increase in the cooling surface area, which increases the electrical efficiency of the photovoltaic cells.

Research on electromagnetic coupling characteristics of UAV circuits in the Complex electromagnetic environment

The overall circuit model and Complex electromagnetic environment model of a typical UAV are built to explore the survivability of multirotor in the complex electromagnetic environment. The composite theoretical calculation model of the metal cavity aperture coupling and internal circuit coupling is constructed using the established UAV circuit model, which is based on the equivalent magnetic dipole algorithm and the FDTD algorithm. The terminal coupling voltage in the UAV circuit and the electromagnetic field distribution inside the metal cavity are estimated. CST software is used to simulate the response of UAV circuits in the same condition, and the correctness of the theoretical calculation model is confirmed. Then, the terminal coupling voltage of the PCB is used to create an electromagnetic coupling efficiency model. The findings reveal that the constructed composite theoretical model can accurately characterize the electromagnetic coupling characteristics of UAV circuits in the complex electromagnetic environment, with an error range of 1%~8%. When comparing the terminal coupling voltage of PCB in various complicated electromagnetic environments, the High-power microwave (HPM) has the maximum coupling efficiency. HPM initially causes the UAV circuits to attain the damage threshold under identical event conditions and target specifications. The findings could be used as a guide for multirotor circuit board protection in the complex electromagnetic environment, as well as for the development of high-power electromagnetic pulse weaponry.

Polarization-pinning in substrate emission multi-mode vertical-cavity surface-emitting lasers using deep trenches

We investigated the stable polarization-pinning properties of substrate emission InGaAs-based 980 nm multi-mode vertical-cavity surface-emitting lasers (VCSELs). For the multi-mode 40 um diameter aperture VCSELs, we introduced 30 μm wide, 9 μm depth deep trenches that are 15 μm away from the cavity aperture. The VCSELs with trench structure produced higher transverse-electric (TE) polarized light output power, as compared with transverse-magnetic (TM) polarized light output power, namely, the effective TM polarization suppression was realized. These trench-etched VCSELs exhibited a 7.5 dB orthogonal polarization suppression ratio with 16.8 mW of light output power at 60 mA of current injection. The dominant TE polarization distribution was observed in polarization-resolved near-field images of spontaneous and stimulated emission due to the induced strain by the etched trenches.

Real-time full-field imaging through scattering media by all-optical feedback

Full-field imaging through scattering media is fraught with many challenges. Despite many achievements in recent years, current imaging methods are too slow to deal with fast dynamics that occur for example in biomedical imaging. Here we present an ultra-fast all-optical method, where the object to be imaged and the scattering medium (diffuser) are inserted into a highly multimode self-imaging laser cavity. We show that the intra-cavity laser light from the object is mainly focused onto specific regions of the scattering medium where the phase variations are low. Thus, round trip loss within the laser cavity is minimized, thereby overcoming most of the scattering effects. The method is exploited to image objects through scattering media whose diffusion angle is lower than the numerical aperture of the laser cavity. As our method is based on optical feedback inside a laser cavity, it can deal with temporal variations that occur on timescales as short as several cavity round trips, with an upper bound of 200 ns.

Structure, substrate binding, and symmetry of the mitochondrial ADP/ATP carrier in its matrix-open state

The mitochondrial ADP/ATP carrier (AAC) performs the first and last step in oxidative phosphorylation by exchanging ADP and ATP across the mitochondrial inner membrane. Its optimal function has been shown to be dependent on cardiolipins (CLs), unique phospholipids located almost exclusively in the mitochondrial membrane. In addition, AAC exhibits an enthralling threefold pseudosymmetry, a unique feature of members of the SLC25 family. Recently, its conformation poised for binding of ATP was solved by x-ray crystallography referred to as the matrix state. Binding of the substrate leads to conformational changes that export of ATP to the mitochondrial intermembrane space. In this contribution, we investigate the influence of CLs on the structure, substrate-binding properties, and structural symmetry of the matrix state, employing microsecond-scale molecular dynamics simulations. Our findings demonstrate that CLs play a minor stabilizing role on the AAC structure. The interdomain salt bridges and hydrogen bonds forming the cytoplasmic network and tyrosine braces, which ensure the integrity of the global AAC scaffold, highly benefit from the presence of CLs. Under these conditions, the carrier is found to be organized in a more compact structure in its interior, as revealed by analyses of the electrostatic potential, measure of the AAC cavity aperture, and the substrate-binding assays. Introducing a convenient structure-based symmetry metric, we quantified the structural threefold pseudosymmetry of AAC, not only for the crystallographic structure, but also for conformational states of the carrier explored in the molecular dynamics simulations. Our results suggest that CLs moderately contribute to preserve the pseudosymmetric structure of AAC.

Optimization design and analysis of honeycomb micro-perforated plate broadband sound absorber

The sound absorption performance of micro-perforated plate (MPP) is mainly restricted by four parameters: cavity depth, aperture, plate thickness and perforation rate. The concept of change rate of sound absorption coefficient is introduced, which is taken as the measuring standard to judge the influence of changing these parameters on the sound absorption performance of MPP. Generally, the parameter sensitivity of MPP sound absorber from large to small is as follows: cavity depth, aperture, perforation rate, plate thickness. According to the characteristic that the resonant frequency of MPP will shift when the cavity depth changes, combined with the acoustoelectric analogy principle, two kinds of single-layer honeycomb micro-perforated plate (HMPP) structures with different cavity depth are designed by using particle swarm optimization algorithm. Simulation and experimental results show that the structures can use their own different depth of honeycomb cores to achieve the purpose of broadband sound absorption. The feasibility of using particle swarm optimization algorithm to design broadband sound absorber is verified. In addition, through the contrastive analysis of the two structures, compared to the four regions HMPP, the experimental results of the seven regions HMPP are closer to the theoretical and simulation results, which is consistent with the characteristics of particle swarm optimization (PSO): the more optimization parameters are, the better the performance is.

Ontogenetic variation in human nasal morphology.

Internal nasal cavity morphology has long been thought to reflect respiratory pressures related to heating and humidifying inspired air. Yet, despite the widely recognized importance of ontogeny in understanding climatic and thermoregulatory adaptations, most research on nasal variation in modern and fossil humans focuses on static adult morphology. This study utilizes cross-sectional CT data of three morphologically distinct samples (African, European, Arctic) spanning from infancy to adulthood (total n=321). Eighteen landmarks capturing external and internal regions of the face and nose were subjected to generalized Procrustes and form-space principal component analyses (separately conducted on global and individual samples) to ascertain when adult-specific nasal morphology emerges during ontogeny. Across the global sample, PC1 (67.18% of the variation) tracks age-related size changes regardless of ancestry, while PC2 (6.86%) differentiates between the ancestral groups irrespective of age. Growth curves tracking morphological changes by age-in-years indicate comparable growth trajectories across all three samples, with the majority of nasal size and shape established early in ontogeny (<5 years of age). Sex-based trends are also evident, with females exhibiting a more truncated growth period than males, particularly for nasal height dimensions. Differences are also evident between the anterior and posterior nose, with the height and breadth dimensions of the anterior nasal aperture and nasal cavity showing differential ontogenetic patterns compared to the choanae. Cumulatively, these results suggest that multiple selective pressures influence human nasal morphology through ontogenetic processes, including metabolic demands for sufficient oxygen intake and climatic demands for adequate intranasal air conditioning.

X-band TE101 rectangular aperture cavity for in vivo EPR tooth dosimetry after radiation emergency

The TE101 mode rectangle EPR cavity was newly developed to achieve X-band in vivo EPR tooth dosimetry for the rescue of nuclear emergency. An aperture for sample detection was opened on the cavity's surface. Its characteristics were evaluated by measuring DPPH and intact human incisor samples. Remarkable radiation induced signal from EPR spectrum of 1Gy–8Gy irradiated teeth was observed. In vivo measurements of rat was performed to verify its application for in vivo tooth dosimetry.

Artificial Neural network and experimental work of a solar cavity collector

A collector is a device that can convert the available sun’s radiations into some useful heat energy with better entrapment of sunlight and is economical too. To heat the water and aqueous fluids, flat plate collector (FPC) is widely used. The main objective of this study is to find out the alternate for FPC with improved performance. Solar cavity collector (SCC) is one such type of an enhanced model of FPC. It consists of five cavities that have an arrangement for inlet and also outlet tubes to flow over. The same has been constructed with copper pipes as a receiver material to carry out the trails in order to find the suitable parametric study. The performance of any collector affects mainly the physical modifications of the collector. Therefore, the performance of SCC includes the prime parameters such as the out-turn of aperture entrance gap and cavity structure outer cover materials. Water rate of flow and comparison of SCC and FPC are the other parameters considered for the current study. Experimental results have to be compared with any simulation tool in order to achieve better performance. Using the Artificial Neural Network (ANN) tool of the MATLAB software, the simulations have been validated. The successful creation of the progressed model in ANN has the set of variables that are fetched out. The experimental and simulated end results match with each other in an appropriate manner.

Thermal performance and design parameters investigation of a novel cavity receiver unit for parabolic trough concentrator

This paper discusses an improved concept for a cavity receiver unit for Solar Parabolic Trough Collectors (PTC) with the application of hot mirror coating (HMC) on a cavity aperture. This design aims to lessen radiant energy losses while operating at higher temperature by incorporating a variety of optically active layers. The theoretical background is presented, which was derived in previous work, and the resulting implementation in a simulation code. The layout and results of an experiment were discussed, which allowed us to make contact with the simulation with minor adjustments. It was seen that the correspondence between the experiment and simulation results was encouragingly close (Chi squared p > 0.8 and p > 0.95), which allowed investigation of simulations of different receiver designs. Simulated outcomes for the temperature of the heat transfer fluid, temperature maps and efficiencies are presented. Our proposal indicates temperature related benefits when compared to other popular designs in terms of the heat transfer fluid temperature and efficiency, which is about 7% higher at temperatures exceeding ∼600 °C.

Experimental testing of a solar air cavity-receiver with reticulated porous ceramic absorbers for thermal processing at above 1000 °C

Concentrated solar energy can be used as the source of high-temperature heat for industrial processes, but the challenge is to design a solar receiver that can effect such a thermal conversion efficiently. This study reports on the engineering design and experimental testing of a 5 kW solar cavity-receiver containing a reticulated porous ceramic (RPC) structure that can absorb high-flux radiation volumetrically and heat up, by convection, an air flow serving as the heat transfer fluid. The thermal performance, characterized by the thermal efficiency and the air outlet temperature, was determined experimentally for four parameters, namely: RPC material (silicon-infused silicon carbide or SiSiC, alumina, and ceria), mean pore size (range 0.8–2.5 mm, corresponding to 10–30 pores per inch or PPI, at 0.90 porosity), solar concentration ratio (range 1965–3900 suns over a 4 cm-diameter cavity aperture, supplied by a high-flux solar simulator), and air mass flow rate (range 2–10 kg/h). Thermal efficiencies between 0.22 and 0.69 were obtained at steady-state air outlet temperatures ranging from 1160 to 450 °C. Larger pores enhance heat transfer while variable porosity across the RPC can reduce temperature gradients and potentially contribute to the design optimization. The highest efficiency of 0.69 was achieved by the SiSiC 10 PPI cavity at an air outlet temperature of 1133 °C and air mass flow rate of 9.9 kg/h. The solar receiver design proved to deliver a high-temperature air flow (>1000 °C) with a reasonably high thermal efficiency (>0.65).

Dual-Band 2 × 2 MIMO Antenna with Compact Size and High Isolation Based on Half-Mode SIW

This paper presents a close-spaced dual-band 2 × 2 multiple-input multiple-output (MIMO) antenna with high isolation based on half-mode substrate integrated waveguide (HMSIW). The dual-band operation of the antenna element is achieved by loading a rectangular patch outside the radiating aperture of an HMSIW cavity. The HMSIW cavity is excited by a coaxial probe, whereas the rectangular patch is energized through proximity coupling by the radiating aperture of HMSIW. The antenna elements can be closely placed using the rotation and orthogonal arrangement for a 2 × 2 array. Small neutralization lines at the center of the MIMO antenna can increase the isolation among its elements by around 10 dB in the lower band and 5 dB in the higher band. A prototype of the MIMO antenna is fabricated and its performance is measured. The measured results show that the resonant frequencies are centered at 4.43 and 5.39 GHz with bandwidths of 110 and 80 MHz and peak gains of 6 and 6.4 dBi, respectively. The minimum isolation in both bands is greater than 35 dB. The envelope correlation coefficient is lower than 0.005 within two operating bands.

Modeling and simulation of transverse wakefields in PWFA

A simplified model describing the PWFA (plasma wakefield acceleration) transverse instability in the form of a wake function parameterized only with an effective cavity aperture radius a is benchmarked against PIC-simulations. This wake function implies a 1/a4 scaling of the transverse wakefields, which indicates transverse intra-beam wakefields typically several orders of magnitude higher than in conventional acceleration structures. Furthermore, the wakefield formalism is utilized to perform a parameter study for a 1.5 TeV plasma wakefield accelerator, where the constraint on drive beam to main beam efficiency imposed by transverse wakefields is taken into account. Eventually, a parameter set with promising properties in terms of energy spread, stability and luminosity per power was found.

Sensitivity analysis of a parabolic trough concentrator with linear V‐shape cavity

AbstractIn the present investigation, a solar parabolic trough concentrator (PTC) with a linear cavity was examined by using a developed numerical model. More specifically, a V‐shape cavity receiver was studied in this work as a new and alternative design. The use of a cavity in a PTC is a very promising idea because it leads to high efficiency and to low investment cost. Up today, the emphasis in the use of cavities is given in dish concentrators and so there is a need for investigation of cavities also in linear concentrators. Different dimensional and operational parameters of the PTC with a V‐shape cavity were considered. More specifically, the position, aperture area, and the tube diameter of the V‐shape cavity, solar irradiance, inlet temperature level, and mass flow rate were evaluated based on sensitivity analysis. The results revealed that the highest optical performance was attained when the cavity was placed at the PTC focal line. Moreover, it is found that there is an optimum cavity aperture area to determine the greatest thermal efficiency. For the optical errors of 5, 10, 15, 20, and 35 mrad, the optimum cavity aperture wide was calculated at 5, 5, 6, 7, and 8 cm, respectively, with the tracking error to be 0°. The highest thermal performance has found when the collector operates with low inlet temperature, high flow rate, high solar irradiation level, and small cavity tube diameter.

High-temperature hydrogen production by solar thermochemical reactors, metal interfaces, and nanofluid cooling

Solar thermochemical reactors have been considered in recent studies because of converting the solar energy to a fuel, which is called solar fuel. In such reactors, heat transfer is a dominant phenomenon in generating products. Providing the optimum thermal energy for the solar thermochemical cycle can be gained by adjusting the size of the solar concentrator. In this study, the sizing of the solar concentrator is studied and the best size of the cavity is calculated by the Monte Carlo method. In this reactor using solar energy, the intermediate metal is converted to solar fuel. ZnO/Zn is considered to be the intermediate metal for the reaction. Next, the solar reactor is modeled in three dimensions and all types of heat transfer mechanisms, i.e., conduction, convection, and radiation along with chemical reaction conditions, are also considered. Sensitivity analysis is done based on the solar concentrator size and the aperture cavity. The results show that the optimum size of the dish collector is 5.168 m and the aperture cavity diameter was gained 5 cm for 10 kWth solar reactor. Nanofluid is used as cooling fluid, with the best modeled fluid flow rate for this structure, the ratio of annual fluid flow to nanofluid being 1. By examining the hydrogen production reactor, the amount of hydrogen produced in the system is 34 mol m−3. Also, the irradiation distribution of the cavity receiver and the temperature distribution of the solar reactor were modeled and analyzed.