Air Slot Research Articles

Optimum design and analysis of the application of the air slot on the building horizontal sun-shading board

ABSTRACTThe sun-shading board is an important way to improve the indoor thermal environment. And air slot is the critical component to improve ventilation effect of sun-shading board. It not only can promote heat dissipation of sun-shading board but also can improve ventilation effect of building window. The shading coefficient of shading board and vorticity influence of air slot are the main principles of designing configuration and size of air slot. The horizontal sun-shading board of residential building south window in Nanjing is the study object. The shading and ventilation effect of shading board with various configurations and size is analyzed quantitatively. And appropriate configuration and size are obtained on the basis of comprehensive consideration of various factors.

A Scalable THz Photonic Crystal Fiber With Partially-Slotted Core That Exhibits Improved Birefringence and Reduced Loss

A photonic crystal fiber (PCF) based on high resistivity silicon is reported that exhibits high birefringence, low loss, and flat dispersion characteristics across a wide bandwidth in the THz regime. Except for the center region, which remains the background dielectric, its core is occupied by a set of rectangular air slots. The material and configuration lead to high birefringence and low loss. The simulation results, which include the material losses, indicate that a birefringence value of 0.82 and a total loss of 0.011 cm−1, including the effective material loss and confinement losses, are achieved at 1.0 THz. These values are a factor of ten times higher and four times lower, respectively, than many recent designs. The numerical analyses also demonstrate that the reported PCF can be scaled to any desired portion of the THz regime, while maintaining a similar birefringence, simply by changing the lattice constant. This “scalable” characteristic is shown to be applicable to other PCF designs. It could facilitate a novel way of testing THz fibers, i.e., it suggests that one only needs to test the preform to validate the performance of the fiber at higher frequencies. This outcome would significantly reduce the design complexity and the costs of PCF testing.

Optimal pole width ratio for high force density linear switched reluctance motors

The double salient structure significantly reduces the forces in a linear switched reluctance motor (LSRM). The structure is then optimized for high force densities. The pole width is the key parameter in the double salient structure with this paper focusing on the optimal pole width ratio for a high force density LSRM using qualitative and quantitative analyses and experimental measurements. The qualitative analysis based on a linear flux linkage model shows a maximum average force for various translator and stator pole widths. Then, a finite element analysis (FEA) based parametric modeling method is used to validate the results and to calculate the optimal pole width range. Force measurements then agree well with the FEA results. They both show that the optimal stator pole width ratio is 0.4 to 0.45 and the optimal translator pole width ratio is 0.45 to 0.5 for a high force density in the LSRM. The optimal width ratio does not change with the air gap or slot depth. 摘要 双凸极作为直线开关磁阻电机 (LSRM) 的特征结构对于电机的出力性能有着较大的影响。由于极宽是双凸极结构的关键尺寸, 因此该文从理论定性分析、有限元定量分析和实验测量3个方面探究了提升LSRM力密度的最佳定动子极宽比。利用磁链线性模型定性地分析了定动子极宽如何影响电机平均输出力, 从机理上揭示了定子和动子极宽分别存在使得平均输出力最大的极值点。利用参数化建模方法建立了有限元分析模型, 定量地验证了理论分析的推断并给出了最大平均输出力所对应的最佳定动子极宽比范围。通过实验测量了不同定动子极宽的力曲线, 实验测量结果和有限元计算结果相一致, 从而验证了有限元分析的准确性。有限元分析和实验结果表明：对于提升LSRM力密度的最佳定子极宽比范围为0.4~0.45, 最佳动子极宽比范围为0.45~0.5, 且最佳定动子极宽比范围基本不受气隙、槽深的影响。

Highly Birefringent Single-Mode Suspended-Core Fiber in Terahertz Regime

In this study, we report a highly birefringent terahertz (THz) fiber that contains rectangular air slots in the suspended core. The proposed fiber can provide a high birefringence of the order of 10−2 over a wide frequency region in single-mode operation. An ultrahigh birefringence of 0.078, low effective material loss of 0.39 dB/cm, and low confinement loss of 1.25 × 10−5 dB/cm are obtained simultaneously at 0.95 THz. Moreover, numerical results indicate that a low dispersion with small variation can be achieved, and the power profile envelope has a Gaussian shape, which is important for coupling with common THz sources. The calculated coupling efficiency is as high as ∼95% for y -polarization mode. It is anticipated that the proposed suspended-core fiber would be useful in THz polarization maintaining wave guidance and bacteria detection applications.

Computational investigation of power efficient plasma‐based reconfigurable microstrip antenna

A cold plasma-based re-configurable rectangular microstrip antenna has been computationally investigated. A power efficient frequency tunable patch antenna design is proposed wherein the substrate is replaced by a combination of air and plasma slots. The novel design consisting of plasma elements in localised regions achieves good tunability with minimal power requirements. Significant amount of frequency reconfigurability is achieved by varying the plasma density and slot configuration. A parametric study comparing the approximate power requirements and tunability of different designs has been presented. Finally the radiation properties of the proposed microplasma-based microstrip antenna has been evaluated.

Highly efficient coupler for dielectric slot waveguides and hybrid plasmonic waveguides

A compact, highly efficient optical coupler for dielectric slot waveguides and hybrid plasmonic waveguides based on transition layers (air slot grooves) was investigated. The power-coupling efficiency of 75% for the direct coupling case increased to 90% following the insertion of an intermediate section. By performing time-averaged Poynting vector analysis, we successfully separated the factors of transmission, reflection, and radiation at the coupler interface. We found that the insertion of optimal air grooves into the coupler structure contributed to the improvement of coupling performance. The proposed compact structure is characterized by a high transmission efficiency, low reflection, small length, and broad-band spectrum response.

The Design and Magnetic Measurement of a SuperBend Dipole Magnet at SSRF

In order to increase the critical photon energy, and to save space for accommodating more insertion devices, four normal bend magnets will be replaced by high field ones during the phase-II beamline project of the Shanghai Synchrotron Radiation Facility (SSRF). The design of these superbends has been finished; the first one has been manufactured and measured recently at SSRF. This water-cooled resistive magnet has a total length of 1000 mm and a steering field of 2.32 T. An air slot in the magnet pole was used to control the uniformity of the field integral distribution. The design as well as the magnetic measurement results are presented. Also presented is a newly developed field shimming method, which has been verified as effective and convenient in the field integral shimming of a magnet with straight air slots in the poles.

A Compact Multi-Beam End-Fire Circularly Polarized Septum Antenna Array for Millimeter-Wave Applications

In this paper, a novel circularly polarized end-fire septum antenna based on substrate-integrated-waveguide (SIW) is proposed in the 60-GHz band. By introducing four symmetrical tapered curved air slots in three stacked open-ended SIW layers, the antenna can obtain an operating bandwidth from 57.2 to 63.4 GHz for both AR $\vert S_{11}\vert dB. Besides, the half-power-beam-width and 3-dB axial-ratio (AR) beam-width are all wider than 79°, and a stable gain of 7.57 dBic with a variation of 0.15 dBic can be achieved in the working band. A $4 \times 4$ SIW Butler matrix based on SIW with three same substrates is then designed. The modified two-layer phase shifters realized by the different path distance are employed in the folded Butler matrix. By combining the antenna element and the Butler matrix together, a four-beam antenna array with circular polarization wave is realized. The proposed array has been fabricated and measured. The measurement results show that the antenna gain up to 11.01 dBic, −10 dB impedance and isolation bandwidth from 57.8 to 62.5 GHz (except at around 58.3 GHz), stable radiation pattern and a wide angular range of ±37° can be obtained. The measured AR values of the main lobe range of four beams are all less than 5 dB from 58 to 60 GHz.

Analysis of heat and mass transfer of the different moist object geometries with air slot jet impinging for forced convection drying

In the present work, the effect of the different geometric moist objects with straight and reverse semi-circular on the heat and mass transfer enhancement of the jet drying was conducted with a numerical analysis. The drying jet was a laminar 2-D jet stationed at a constant jet distance from the moist object. The diameter of the object, jet distance from the moist object and initial jet height were fixed in all cases. Temperature and mass distributions were obtained inside the object for different jet velocities. A finite volume method was used to solve the governing equations for momentum and energy by using ANSYS Fluent 17.0 software program. Calculations were performed for four different Reynolds numbers, namely, Re = 100, 200, 300, and 400. It was found good agreement with the experimental data available in the literature. The results showed that the geometry of straight semi-circular moist object had better performance of heat and mass transfer than that of the reverse moist object geometry. In addition, increasing Reynolds number showed a positive effect on heat and mass transfer. Locally, jet drying was found to be most effective near the stagnation point on the leading side of the objects.

Designing a miniaturized photonic crystal based optofluidic biolaser for lab-on-a-chip biosensing applications

Abstract Optofluidic biolasers indicate promising potential and properties that make them highly competitive in the development of state-of-the-art biophotonics technologies. One of the bright outlooks and perspectives that could have a profound impact on the current developing situation and trend of such a new found technology is the photonic crystal based optofluidic biolaser. In this article, we theoretically propose a new lab-on-a-chip design of slotted photonic crystal optofluidic biolaser. Within this scheme, the air slot and medial air holes of the miniaturized photonic crystal slab are infiltrated with organic dye solution, acting as the laser gain region. This structure provides a facility for incorporation of the biological molecules in those fluidic gain mediums. Simulations show that, in addition to the proper lasing characteristics, like the spectral linewidth of 0.27 nm and power conversion efficiency of 26%, the proposed device is highly sensitive to the subtle biological changes that may occur in its cavity and shows the sensitivity of 277 nm/RIU.

Slot air jet impingement cooling over a heated circular cylinder with and without a flow confinement

In this work, a numerical investigation has been carried on an air slot jet impingement over a circular cylinder with and without a top confinement using the v′2‾-f turbulence model. In the parametric study, the Reynolds number (ReD), defined based on the cylinder diameter, D, is varied from 4500 to 20,000. The ratio of spacing between the nozzle exit to the cylinder target, H and the width, S of the nozzle, H/S is varied from 2 to 10. The non-dimensional slot width, D/S considered in the present study are 1, 2 and 4. The local distribution and average Nusselt numbers obtained from numerical simulations are validated against the available experimental data of jet impingement over a flat and cylindrical surfaces without confinement. It is observed that the local Nusselt numbers obtained from the present numerical model compare well with the experimental data. To understand the effect of confinement, a flat plate confinement at the exit of the nozzle has been considered. The non-dimensional length of the confinement, Lconf/D was varied from 0 to10 in the parametric study. Numerical results reveal that the top confinement reduces the average Nusselt number by 25% at ReD = 4500, D/S = 4 and H/S = 2, while the influence confinement on the cooling rate is negligible for D/S = 1. Based on the numerical study, a correlation has been provided for the average Nusselt number over the heated cylinder.

Analysis of cooling performance and combustion flow in advanced vortex combustor with guide vane

Numerical simulation was performed to study the flow characteristics of advanced vortex combustor (AVC) with guide vanes and slots for aircraft engine. The results show that structural parameters of guide vane have significant effects on AVC, when a/B=0.4, b/H=0.4, c/L=0.1, it can obtain desirable dual-vortex structure, acceptable pressure loss and better combustion efficiency. AVC with guide vane has better performance than AVC without guide vane. Five slots air film cooling are brought in, the effect of flow injection angle (θ=30°, 60° and 90°) and injection ratio (R=1.2, 1.5, 2.0) on cooling performance of AVC are analyzed. The results show that there are 5 change regions for each cooling efficiency under different injection conditions. The variation law of the first region is different from the four region behind. The first slot air mainly mixes with the main flow and gets involved in the combustion while the four region behind can play a good role in cooling efficiency. Meanwhile, the effects of θ and R on flow field, temperature field, total pressure loss, combustion efficiency, outlet temperature distribution factor (OTDF) and the average cooling efficiency are presented. Finally, the film cooling conclusions are explained by field synergy theory, and results show that it can optimize the wall cooling effectiveness by field synergy theory.

Research on the Temperature Field of High-Voltage High Power Line Start Permanent Magnet Synchronous Machines with Different Rotor Cage Structure

For line start permanent magnet synchronous machines (LSPMSMs), the eddy current loss in the rotor, which has of significant effects on rotor working temperature, may cause thermal demagnetization to permanent magnet. Therefore, this paper addresses an investigation on the temperature distribution in LSPMSM based on a 6 kV, 315 kW prototype with solid starting cage bar. Firstly, the loss distributions, obtained from a 2-D transient electromagnetic field calculation, are determined as the distributed heat source in thermal analyses. Then, the fluid-thermal coupled analyses are performed, by which the temperature distributions in the machine are determined. Meanwhile, the calculated motor performance is verified via comparison with the measured results. The calculation results show that the temperatures in the rotor core and permanent magnets are relatively high. To find the solution for reducing the rotor working temperature, a rotor air slot structure was proposed in this analysis. The theoretical calculation indicates that the rotor working temperature reduction is obvious with the rotor air slot in the machine. Therefore, the operating situation of solid rotor LSPMSM could be improved effectively with the proposed rotor thermal solution, which also benefits the machine reliability and safety.

Broadband Tunable Add/Drop Filters Based on Dielectric Double-Disk Microcavities

Herein, we present a spectrally tunable add/drop filter based on a dielectric double-disk microcavity. Numerical simulation shows that a whispering gallery mode of this filter has a very large wavelength tuning range of 103 nm for a 20 nm change of an air slot between the double disks. Based on this mechanism, broadband wavelength tuning and on/off switching are demonstrated in this paper. Under the resonance condition, drop power and through power at gap size of 10 nm were obtained as 0.87 and 0.0036, while the on/off ratios of the signal at the through port and the drop port were 35:1 and 105:1, respectively.

Two‐dimensional analytical investigation of the parameters and the effects of magnetisation patterns on the performance of coaxial magnetic gears

In this study, a two-dimensional analytical model has been presented for coaxial magnetic gears. Based on Maxwell's equations the extracted model has been obtained via the solution of the Laplace and Poisson equations by using the separation of variable technique for each sub-region (internal and external magnets, internal and external air gaps and slots). Then the integral coefficients of the general solutions have been obtained by using the boundary conditions and continuity between sub-regions. The proposed analytical model can be used as a tool for design and optimisation of magnetic gears. The influences of the number of pole-pairs, the magnetisation patterns, the size of slot-opening and the segment ratio of the two-segment Halbach pattern on the transmitted torque and unbalanced magnetic forces have been analytically investigated. Finally, to illustrate the efficacy of the proposed model, the analytical results of the magnetic field distribution, transmitted torque and unbalanced magnetic force have been compared with those obtained from finite element analyses.

Experimental and numerical investigations of slot jet impingement with and without a semi-circular bottom confinement

In this paper, the details of experimental and numerical investigations of slot air jet impingement cooling of a circular heated cylinder have been presented. To improve heat transfer rate behind the cylinder, a semi-circular confinement is also considered. In the parametric study, the Reynolds number ReD, defined based on the cylinder diameter D, is varied from 6000 to 20,000. The ratio of the spacing between the nozzle exit and the heated cylinder H to the width S of the nozzle, H/S is varied from 2 to 12 and the non-dimensional parameter, the diameter of the target to the slot width, D/S=5.5, 8.5 and 17 are considered. To understand the effect of the bottom flow confinement, the ratio of the confinement radius Rc to the radius R, of the heated cylinder, Rc/R was varied from 1.7 to 3.7 and the ratio of the width of the bottom opening W of the confinement to the radius of the heated cylinder, W/R is varied from 0 to 1.2. Numerical simulations are carried out using the v′2‾-f model to obtain the flow pattern and temperature distribution over the cylinder and in the fluid region. In the case of jet impingement flow with a semi-circular confinement wall behind the target cylinder, after the flow separation from the cylinder, the heated fluid is diverted towards the inner wall of the confinement. The major part of the diverted hot fluid leaves through the opening provided at the bottom of the flow confinement without a direct contact with the bottom surface of the heated cylinder. In the case of smaller size semi-circular confinement walls, Rc/R=1.7 and 2.6, the strength of recirculation is higher than that of the unconfined flow and the flow with a larger size confinement. Hence, the local Nusselt number values are higher at the bottom surface of the heated cylinder when smaller size semi-circular confinement walls are used behind the cylinder.

Improved method for field analysis of surface permanent magnet machines using Schwarz–Christoffel transformation

Air gap field solution for an outer rotor permanent magnet (PM) machine is derived based on numerical Schwarz–Christoffel (SC) transformation of a single slot geometry and analytical solution of a point wire field in the rectangular canonical domain. This approach takes into account geometrical distortions of PM edges and field evaluation points located along the air gap centre, which occur due to conformal mapping of the slotted air gap into a slotless domain and impair the accuracy of the existing analytical field solutions using SC transformation and complex relative air gap permeance. The increased accuracy of the improved solution is confirmed by comparing the air gap flux density waveforms produced by the PMs and armature winding, cogging torque, and total torque with the results of time-stepping transient finite element simulation.

Terahertz Polarization Splitters Based on Total and Partial Coupling in Dual Slotted Core Polymer Fiber: Comparison and Analysis

Two terahertz (THz) polarization splitters based on dual slotted core polymer fiber are proposed and numerically investigated. The splitter structures are based on dual cores composed of subwavelength-scale air slots that are independently suspended within the fiber, which not only allows for single-mode propagation for the two orthogonal polarization modes with low absorption losses but enables them to couple with each other as well. Polarization splitters based on both symmetric and asymmetric dual slotted core structures, respectively, based on total and partial coupling are proposed and analyzed. The transmission modes, splitting lengths, and pertinent performance parameters of the two polarization splitters are investigated and numerically analyzed at a center-frequency of 1.0 THz. Comparisons of the two splitters with similar structural parameters are also carried out, which shows a comparably short splitting length of ∼1 cm and an ultra-low transmission loss of 0.4 dB with the asymmetric structure having a broader bandwidth and better extinction ratios.

An improved conformal mapping method for magnetic field analysis in surface mounted permanent magnet motors

PurposeThe purpose of this paper is to present an improved conformal mapping (ICM) method that simultaneously considers the influence of relative recoil permeability of PMs, the armature reaction, the stator slotting, and the magnetic saturation on determination of the PM operating point in its different parts.Design/methodology/approachThe ICM method is a time-effective method that considers the magnetic saturation by suitable increments in air-gap length under each tooth and also the width of slot openings. In this paper, the analytical and numerical conformal mappings such as the Schwarz-Christoffel (SC) mapping are used for magnetic field analysis due to the permanent magnets and the armature reaction in one slotted air gap. The field solution in the slotted air gap is obtained through the modulation of field solution in one slotless air-gap using the complex air-gap permeance.FindingsThe ICM method can consider the magnetic saturation in different electric loadings, and also the variation of PM operating points in its different parts.Practical implicationsThe ICM method is applied to one surface mounted permanent magnet (SMPM) motor and is verified by comparing with the corresponding results obtained through finite element method (FEM), and frozen permeability finite element method (FP-FEM).Originality/valueThis paper presents an ICM method with a new technique for saturation effect modeling, which can be used to separate and calculate the on-load components of air-gap field and torque.

Comparative analysis of various methods for modelling surface permanent magnet machines

In this study, six different modelling methods for permanent magnet electric machines are compared in terms of their computational complexity and accuracy. The methods are based primarily on conformal mapping, mode matching, and harmonic modelling. In the case of conformal mapping, slotted air gap of a complex machine geometry is transformed to a smooth slotless air gap where analytical expression for field solution is available. The solution in the canonical domain is then mapped back to the original slotted air-gap domain. Mode matching or subdomain method, as it is called in different sources, is using a solution of Laplace's equation to model the slotted air gap. In harmonic modelling, the machine cross-section is divided into homogeneous regions that are represented using Fourier series and coupled with each other using boundary conditions. The boundary value problems in both the mode matching and harmonic models are solved to obtain the field solutions. The performance of the modelling methods are evaluated by comparing the global parameters such as cogging torque, electromagnetic torque, back-emf as well as the simulation time with the results of finite-element transient analysis.