Cavity Aperture Research Articles

Investigation of the Relationship Between Mandibular Morphology and Upper Airway Dimensions

In this study, the authors aimed to perform a novel and extensive analysis, based on the most applicable correlations between the mandibular and upper airway parameters, using cone beam computed tomography across all malocclusion classes. The authors also focused on gender-dependent differences in an Iranian population. Images were acquired from adult patients using cone beam computed tomography. The patients were classified into three groups of malocclusion classes (class I: 13 males and 27 females, class II: 13 males and 27 females, and class III: 25 males and 15 females). For each patient, 10 parameters for the mandible and 23 parameters for the pharynx, pyriform aperture, and nasal cavity were evaluated in the images. Pearson's correlation coefficient showed significant correlations between the mandibular morphology and upper airway dimensions in each malocclusion class. In females, the menton angle had a significant correlation with pharyngeal dimensions in all malocclusion classes. In males, the bigonial width, bicondylar width, and symphyseal height of the mandible were correlated with pharyngeal dimensions in all classes. The greatest correlation between the mandible and upper airways was observed in class III malocclusions, and the lowest correlation was observed in class I malocclusions. In addition, the mandibular parameters had relationships with the nasal cavity and pyriform aperture. It is important to consider the knowledge of the relationship between some characteristics of the mandible and airways in various clinical approaches.

Optimizing solar dish performance using analytical flux distribution in focal region

In this paper, thermal performance analysis of 4 m2 solar dish collector is presented.The focal image characteristics of the solar dish are determined to propose the suitable design of a receiver. A flat plate was used for the receiver to measure flux distribution in the focal region. The measurement had been done in the midday. Intercept factor based on this distribution had been calculated and was obtained to calculate thermal efficiency after total heat loss was described. From the experiment, total heat loss was formed by conductive and radiative in the receiver. The results showed that the increase in total heat loss followed the increase in receiver temperature and it caused a decrease in thermal efficiency. On the peak of the measurement or in midday, receiver temperature can achieve 138°C and it gave around 1200-Watt heat loss and it was dominated by radiative heat loss for around 80%. The thermal efficiency of the system due to flux distribution measurement in the focal region was above 70% and it was classified as high average but we needed to cover this flux up so it did not lose a lot of heat. Cavity aperture would keep around 20% total heat loss and it minimized radiative heat loss from the flux. The design of cavity aperture was the next discussion to insulate thermal heat reflection of the parabolic dish system from high radiative heat loss.©2020. CBIORE-IJRED. All rights reserved

Sensitivity analysis of parabolic trough concentrator using rectangular cavity receiver

The objective of this work is the investigation of a parabolic trough concentrator (PTC) with a linear cubical cavity receiver which operates with thermal oil as the working fluid. The solar collector is investigated in order to achieve maximum thermal efficiency. The PTC is investigated optically in Sol Trace software, while the thermal modeling is conducted by a code in Maple software. The developed model is validated with experimental data from the literature. Finally, a good agreement has been found between the measured thermal efficiency and the calculated thermal efficiency based on the presented model. Different geometrical dimensions of the cavity receiver were investigated based on sensitivity analysis including cavity position, cavity aperture, cavity height and cavity tube diameter. Also, the system is examined for different operating conditions. According to the results, the lower tracking and optical errors lead to higher optical performance. The best cavity depth is equal to the cavity aperture width. It was found that the higher concentrator aperture increases the absorbed energy. Moreover, it is found that the cavity has to be located in the focal line of the parabola. The highest absorbed heat and thermal efficiency of the solar system calculated was equal to 618.09 W, and 77.26% respectively for the cavity tube diameter of 5 mm.

Additively manufactured trapezoidal grooves for wideband and high gain Ku‐band antenna

Grooves around aperture antennas are known to be instrumental in obtaining directive antenna patterns. The shapes of the grooves are often restricted to rectangular or triangular due to manufacturing difficulties in traditional metal machining, and because of this reason, the effect of groove shape on antenna performance is often overlooked. The aim of this study is to analyze different groove shapes with the help of additive manufacturing. Waveguide slot fed, dual cavity aperture antenna with grooves is designed and the effect of groove shapes on antenna performance is studied at Ku band. Two antennas with and without grooves are built using 3D printing technology. Measured antenna performance reveals 5 GHz bandwidth covering 10 to 15 GHz for Ku-band satellite communications and part of the X-band applications. Proposed antenna achieves 13.25 dBi peak gain at 14 GHz and the gain is better than 11.25 dBi over the entire Ku-band uplink and downlink frequency bands.

Design of Low-Profile Multi-Band Half-Mode Substrate-Integrated Waveguide Antennas

An effective method of designing low-profile cavity-backed multi-band antennas is introduced based on half-mode substrate-integrated waveguide (HMSIW) technique. By loading U-shaped strips outside the radiating aperture of an HMSIW cavity, additional resonances can be produced, thus leading to the realization of multi-band capability. An inset $50~\Omega $ microstrip feedline is employed to energize the HMSIW cavity, whereas the loaded strips are excited through proximity coupling from the radiating aperture of the HMSIW. The proposed antenna is constructed on a single-layered substrate with a low profile of 0.024 free-space wavelength. To validate the multi-band responses, prototypes of the single-band HMSIW antenna as well as dual-band and triple-band antennas are fabricated and measured, respectively. The experimental results show that the proposed antennas possess advantages of stable radiation patterns with a gain of 5–5.9 dBi as well as acceptable front-to-back (FTB) ratio of larger than 10 dB over different frequency bands.

Three-dimensional computed tomographic examination of pelvic cavity in Van Cats and its morphometric investigation.

This study was carried out to determine the morphometric values of the pelvic cavity, the cranial and caudal pelvic aperture by three-dimensional (3D) reconstruction of the images obtained by computed tomography in adult Van Cats and to show the differences between these indicators in both genders. A total of 16 adult Van Cats, eight male and eight female, were used in the study. Animals were anesthetized with ketamine-xylazine combination and were scanned by computerized tomography. Images of the pelvic cavity were obtained. Three-dimensional reconstruction of the pelvis was performed with three-dimensional modelling program. Measurements of the diameters of the pelvic cavity, the cranial and caudal pelvic aperture were calculated from these images, and statistical analyzes were performed. Three-dimensional modelling of the pelvic cavity of Van Cats were examined between males and females. The results showed that there were significant (p<.05) differences between measurement of the pelvic inclination, the medial transverse diameter, the caudal transverse diameter and the angle between ischiatic arch. In addition, the correlations between age and weight were found statistically significant (p<.05) with the dorsal transverse diameter, the intermediate transverse diameter and the caudal transverse diameter in males. On the other hand, the correlations of age were statistically significant (p<.01) with the cranial pelvic aperture and the caudal pelvic aperture in females. In conclusion, some biometric values of pelvic cavity were observed to be statistically different in Van Cats.

Metasurface Antennas Embedded in Small Circular Cavities for Telemetry Applications

This paper introduces a metasurface-inspired antenna embedded in a circular metallic cavity with a very small diameter (from 0.25 λ0 down to 0.12 λ0, where λ0 is the wavelength in vacuum at the operating frequency). The proposed concept is introduced and explained: It consists of placing a capacitive surface at the cavity aperture. This capacitive effect is obtained using multi-layer capacitively coupled strips. Our numerical results demonstrate that the impedance bandwidth is larger than that of standard patch antennas embedded in the same cavity size. Various prototypes have been manufactured, and measurements are found to be in good agreement with numerical results in all cases. The practical applications of these small metasurface antennas are demonstrated with telemetry applications for flying vehicles.

Investigation of a novel small-sized bifacial cavity PTC and comparison with conventional configurations

In this study, a cavity and a full circular absorber small-sized parabolic trough collector (PTC) were compared regarding their optical and thermal behavior. First of all, the cavity receiver configuration was optimized regarding its optical performance by modifying the cavity aperture width and the distance between the focus of the parabola and the receiver’s center line. Moreover, the local concentration ratio and the local absorbed solar irradiation intensity at the receiver’s periphery were defined and calculated in each configuration. After that, both configurations were examined thermally under several different inlet operating temperatures (10–200 °C) considering water as the working medium. More specifically, the thermal efficiency and the overall heat losses were first calculated while the convective heat transfer coefficient was also determined and the Nusselt number as well as the friction factor were calculated and validated through theoretical models. In addition, an analytical method was developed in order to validate the simulation results and deviations lower than 1% have been found. The cavity receiver it was found to absorb 13% more solar irradiance and appeared 10.3% greater thermal efficiency on average compared to the full receiver one. Finally, the particular geometries were compared with an optimized conventional PTC configuration and it was found that the cavity PTC exceeds the last one in thermal performance by 10.35%. Also, the cavity PTC was finally optimized and compared to the already optimized conventional PTC and a mean enhancement of 12.16% was revealed. This enhancement should be taken into account in similar comparisons, since it is independent from the mass flow rate. Last but not least, a tracking error analysis was conducted and it was found that the tracking error does not affect significantly the comparison between the cavity and the conventional PTC. The design and the simulation of the examined models were conducted in Solidworks environment.

Development of two new semi-empirical formulas for estimation of solar absorptance in circular cavity receivers

In this paper two new semi-empirical formulas for calculating the equivalent absorptance of solar irradiation at the inner surface of cylindrical cavities is proposed. The multiple reflections that occur at the interior of the cavity were first analyzed considering a two-dimensional geometrical approach and thus the first analytical relationship for the equivalent solar absorptance was revealed. In addition, a three-dimensional ray tracing analysis was conducted through Solidworks Flow Simulation. Several different cavity aperture’s widths as well as solar absorptance coefficients (α = 0.5–0.9 per 0.1) were examined in both analyses and it was found that the two dimensional analytical approach exceeds the simulation by 1.50–6.83% on average going from the highest to the lowest solar absorptance value. Finally, two new correlations were developed for correcting the analytical approach according to the 3D ray tracing with the optimum between them to provide a mean error at the equivalent solar absorptance calculation of about 0.78%, 0.55%, 0.40%, 0.21% and 0.18% for the five different absorptance coefficients were examined.

Nano-array assisted metal-organic polyhedra membranes for the pervaporation of aromatic/aliphatic mixtures

Metal-organic polyhedra (MOP), as a new type of molecule-based porous nanocage, is a promising material in membrane separation. However, it is a challenge to obtain pure MOP membrane to take full advantage of its nanocage. In this study, [Cu24(5-tBu-1,3-BDC)24(S)24] (MOP-tBu) membranes were prepared on the surface of ceramic tubular substrate with the assistance of Co(OH)2 nano-array. MOP-tBu molecules were dynamic pressure-driven assembled into the confinement space of vertically arranged Co(OH)2 nanosheets, which were previously formed on the substrate through hydrothermal synthesis. With this strategy, the MOP-tBu molecules can form an ultrathin defect-free separation layer on the surface of the substrate. Due to the open Cu2+ unsaturated sites (CUSs) and rich benzene rings in its structure, the MOP-tBu membrane has permselectivity towards the aromatic compounds. In addition, the MOP-tBu membrane is endowed with high permeability because of its large cavity and small apertures. Therefore, the membranes were used to separate aromatic/aliphatic mixtures through pervaporation. When separating 50 wt% toluene/n-heptane mixtures, the permeate flux of the MOP-tBu membrane was 800 g m−2 h−1 with the separation factor of 5.4. The high permeability of the membrane exhibited great potential in the separation of aromatic/aliphatic mixtures.

Optical performance study of different shapes of solar cavity receivers used in central receiver system plant

ABSTRACT In the current study, we present the optical efficiency of six different shapes of cavity receivers that are mostly used in solar power tower systems. This study was conducted in applied research unit for renewable energies (URAER) at Ghardaïa province, Algeria. Each heliostat reflects the sunray into the centre point of the cavity aperture situated at 7.4 m on the top tower. In order to find the orientation of each heliostat, several parameters relating the position of the sun and heliostat tower system are estimated. Optical simulation was performed by means of TracePro® 2013 ray tracing software using the MCRT (Monte Carlo ray trace) method. The results show that conical and trapezoidal shapes perform better than other studied cavities. They mostly exhibit the highest optical efficiency reaching 92.65%, 91.81% at absorptivity 85% and an optical efficiency of 90.88% and 89.30% at absorptivity 75%.

Electromagnetic scattering from a cavity embedded in an impedance ground plane

This paper is concerned with time‐harmonic electromagnetic scattering from a cavity embedded in an impedance ground plane. The fillings (which may be inhomogeneous) do not protrude the cavity and the space above the ground plane is empty. This problem is obviously different from those considered in previous work where either perfectly conducting boundary conditions were used or the cavity was assumed to be empty. By employing the Green's function method, we reduce the scattering problem to a boundary‐value problem in a bounded domain (the cavity), with impedance boundary conditions on the cavity walls and an impedance‐to‐Dirichlet condition on the cavity aperture. Existence and uniqueness of the solution are proved for the weak formulation of the reduced problem. We also propose a numerical method to calculate the radar cross section (RCS), which is a parameter of physical interest. Numerical experiments show that the proposed model and numerical method are efficient for the calculation of RCS from cavities.

Experimental and numerical performance analyses of a Dish-Stirling cavity receiver: Geometry and operating temperature studies

Higher performance cavity receivers are needed to increase the competitiveness of solar power plants. However, the design process needs to be improved with more relevant experimental and numerical analyses. Thereby, the performance of four different Dish-Stirling cavities is investigated experimentally analyzing the influence of the cavity aperture diameter and shape at various operating temperatures. Temperatures inside the cavity receiver were collected together with the electrical power produced by the engine-generator. Then, a thermal system simulation was modelled and a comprehensive multi-parameter and multi-operation validation was performed. To improve this validation, the temperature distribution across the receiver tubes was analyzed in order to relate temperatures on the irradiated region with the non-irradiated one, where thermocouples can measure. The simulations were later used to obtain cavity receiver efficiencies, temperatures and loss breakdowns. The results show that the cavity receiver must be studied in optimization processes in conjunction with the other system components. Moreover, the reverse-conical cavity was found to be more efficient than a nearly cylindrical shape. Regarding the cavity receiver thermal losses, radiation and natural convection present similar contributions in the system under study. Finally, it was found that thermocouples installed on a non-irradiated region can be used to obtain peak receiver temperatures if the measurements are rectified by a correction value proportional to the DNI.

Multi-objective optimization of the aiming strategy for the solar power tower with a cavity receiver by using the non-dominated sorting genetic algorithm

The extremely non-uniform solar flux distribution in the solar power tower plant can badly cause some crucial problems for the solar receiver such as the local hot spot, the thermal stress, and the thermal deformation. Homogenization of the solar flux distribution is an effective method to avoid these problems, and has become an important research topic. The objective of the present study is to homogenize the solar flux distribution on the inner surfaces within the cavity receiver while keeping the optics loss as low as possible by replacing the conventional single-point aiming strategy with optimal multi-point aiming strategies. Multi-objective optimizations of the aiming strategy for the solar power tower with cavity receivers are performed by using the non-dominated sorting genetic algorithm. The distribution of the aiming points on the cavity aperture and the allocation of the aiming points for each heliostat are optimized simultaneously. The following conclusions can be made: (1) The uniformity of the solar flux distribution on the aperture does not always signify the uniformity of the solar flux distribution on the inner surfaces, where the later one is what we are truly concerned about. Therefore, the optimization of the aiming strategy should take charge of the solar flux distribution on the inner surfaces rather than on the aperture. (2) The multi-objective optimization can provide the trade-off between the non-uniformity of the solar flux distribution and the optics loss in the form of Pareto optimal fronts. (3) The optimal aiming strategies provided by the multi-objective optimization can significantly homogenize the solar flux distribution on the inner surfaces within the cavity at a minimum cost of optics loss. (4) For the optimal aiming strategies at all time except the noon, there exists a west-east asymmetry of the aiming point distribution on the aperture. Moreover, the asymmetry gets less obvious as the time gets closer to the noon.

Conifer tracheids resolve conflicting structural requirements: Data, hypotheses, questions

The nature of conduction involves movement of a liquid (under tension or pressure) through a solid (cell walls necessary to direct the liquid and provide mechanical strength). The numerous consequences of the liquid/solid nature of the conductive interface in plants can be viewed as a series of conflicting requirements that are resolved by various mechanisms. For example, the types of mechanical strength conferred by thicker cell walls (latewood) run counter to optimal conduction (earlywood). Conflict resolution situations are examined with light microscopy and SEM to show in detail not merely conflicting requirements but the various types of resolution in various conifers. Abies is presented as exemplary of a cool temperate conifer with numerous aspects to earlywood/latewood structure. Tropical conifers (Araucaria) present different compromises; the riparian conifer Dacrydium guillauminii has only earlywood; the parasitic conifer Parasitaxus has only latewood. Particular conifers have only some of the features by which latewood differs from earlywood. Cell dimorphism is only one aspect of resolution of conflicting requirements; others include modifications in pit size, shape, and density; the nature of the pit membrane; the nature of the pit cavity, pit border and pit aperture; and surface relief (warty layer) of the tracheid wall. The invention of coniferous bordered pits involves a circular shape, so that tension on the margo strands is equal, and thus the pit can be closed. These factors and margo pore maximization necessitate expending a large amount of space to pits in earlywood, the strength of which is thereby lessened and must be compensated by greater wall strength in latewood. The paper concludes with a series of twenty features which represent resolutions of conflicting requirements in terms of anatomical structure. Wood physiological literature is integrated with the anatomical observations.

Effects of geometric parameters on thermal performance for a cylindrical solar receiver using a 3D numerical model

The geometric parameters of a cavity receiver play critical roles in solar energy conversion and heat transfer. However, the effects of geometric parameters on thermal performance have not been studied sufficiently, especially for a cylinder cavity receiver with a 3D numerical model. In the present study, the effects of aperture diameter and cavity length are numerically simulated using the finite element method by ANSYS 17.0. The combined convection and radiation loss is taken into consideration in the simulation process. A simulation validation is also proposed with a comparison between the numerical simulation result and published data from the theoretical model. Good agreement has been achieved. The combined heat loss increases considerably with an increase in aperture diameter from 184mm to 300mm. Attending to the number of loops and the corresponding cavity length, a maximum thermal efficiency is achieved with five loops at a 480mm cavity length. This paper provides a successful example of the design of a cylinder cavity receiver.

Thermal Performance and Operation of a Solar Tubular Receiver With CO2 as the Heat Transfer Fluid

A high-temperature, high-pressure solar receiver was designed as part of the advanced thermal energy storage project carried out in collaboration with Abengoa Solar NT at CSIRO Energy Centre in Newcastle, Australia, with support through the Australian Renewable Energy Agency (ARENA). The cavity-type receiver with tubular absorbers was successfully installed and commissioned, using concentrated solar energy to raise the temperature of CO2 gas to 750 °C at 700 kPa in a pressurized, closed loop system. Stand-alone solar receiver tests were carried out to investigate the thermal characteristics of the 250 kWt solar receiver. The on-sun full-load test successfully achieved an outlet gas temperature of 750 °C while operating below the maximum allowable tube temperature limit (1050 °C) and with a maximum pressure drop of 22 kPa. The corresponding estimated receiver thermal efficiency values at full flow rate were 75% estimated based on measured receiver temperatures and heat losses calculations for both single aim-point and multiple aim-point heliostat control strategies. The use of a quartz glass window affixed to the receiver cavity aperture was tried as a means for improving the receiver efficiency by reducing convective heat losses from the receiver aperture. However, while it did appear to significantly reduce convective losses, a more effective metal support frame design is necessary to avoid damage to the window caused by stresses introduced as a result of distortion of the supports due to heating by the spillage of rays from the heliostat field.

Design of a Novel Wideband and Dual-Polarized MagnetoElectric Dipole Antenna

A wideband antenna with ±45° dual polarization is proposed. The antenna is mainly comprised of four printed trapezoidal metal walls standing on a ground plane that forms a 3-D open square aperture cavity structure with tapered cut on the four wall edges. The metal walls are fed by two orthogonally positioned (±45°) feeding networks, forming two pairs of dipole arms. Because of the excited magnetic-electric resonances, wide bandwidth can be achieved. The proposed antenna is fabricated, and the measured results show that it has an impedance bandwidth of 56% (1.62–2.87 GHz) for VSWR < 1.5. In addition, isolation of larger than 30 dB is also exhibited across the bandwidth between the two feeding ports. Because the proposed antenna has a hollow inside structure, it is a good candidate for multiband sharing aperture antenna element. Furthermore, it has a simplified fabrication process and is suitable for outdoor base station antennas that require VSWR < 1.5.

Experimental Investigation on Heat Losses From Differentially Heated Cylindrical Cavity Receiver Used in Paraboloid Concentrator

In the present study, an experimental testing facility is created to analyze the heat losses from the cylindrical solar cavity. Tests are carried out under the temperature range from 225 °C to 425 °C for a cavity inclination from θ = 0–90 deg in steps of 30 deg. It is observed that for off-flux investigation of solar cavity receiver, near isothermal wall temperature condition can be realized with the differential heating arrangement. The total loss is found to be the highest when the cavity aperture is positioned at sideways (θ = 0 deg). It decreases by 43–51% when the cavity is inclined (θ = 90 deg). The conduction loss is found to be accounted for up to 32–34% of the total heat loss, whereas the cavity radiative loss is estimated to be 13%, 16%, and 20% of the total heat loss, respectively, for cavity wall temperature 225 °C, 325 °C, and 425 °C. The investigation of convective losses showed significant change with cavity tilt angles. It is 46–54% of the total heat loss when the cavity aperture is facing sideways (θ = 0 deg), whereas its value reduces up to 4% of the total heat loss when the cavity aperture is facing downward (θ = 90 deg). A Nusselt number correlation has been developed for predicting the convective heat loss from a open cavity. The Nusselt number correlation correlates 100% of data within ± 20% deviation.

Numerical Investigation on Trapezoidal Cavity Receiver Used In LFR with Water Flow in Absorber Tubes

In the present study, numerical three dimensional model of trapezoidal cavity used in LFR was analysed. Results are presented in the form of Thermal losses occurring from the receiver operating with an absorber tube temperature from 350-550 K in step of 50 K and emissivity varied from 0.5-1.0. Effect of wind blowing below lower glass plate (cavity aperture) were also analysed considering the heat transfer coefficient from 5 to 25 W/m2K. At lower absorber temperature (350 K) convective losses is found to be 43% of the total heat loss whereas radiative losses accounted 57%. For higher absorber temperature radiative losses are dominant (77%) and convective losses are reduced to 23%. The air temperature gradient in the horizontal direction (parallel to lower glass plate) is found to be negligible whereas it is varied significantly in vertical direction (normal to lower glass plate). The average cavity air temperature is observed to be 480 K for low wind flow (h=5 W/m2K) and it reduces to 360 K for h=25 W/m2K. This has resulted in increased convective losses (27% higher).