A study and comparison of the modes of diffusion combustion of hydrogen and methane at their outflow from the annular nozzle together with the flow of supplied air from the coaxially located circular nozzle

The article presents qualitative data on the study of the process of diffusion combustion during the outflow of a gas jet from a nozzle apparatus with a certain arrangement of nozzles. The nozzle apparatus is a round nozzle with a straight channel and a coaxially located annular slot. In the experiments, hydrogen or methane was supplied through an annular slot, and the air was supplied through a central circular micro nozzle. The main features of the diffusion combustion of hydrogen and methane during the outflow from the nozzle apparatus are revealed and a qualitative comparison of the processes is carried out. In both cases, at the initial stage, laminar combustion is observed near the nozzle exit and a breakthrough of the flame front occurs with the release of an incombustible mixture of combustible gas and air. At a high flow rate, the flame separates from the nozzle exit. The fundamental difference is that hydrogen exhibits significantly better combustion stabilization characteristics at the nozzle exit.

OPERATOR METHOD IN THE PROBLEM OF A PLANE ELECTROMAGNETIC WAVE DIFFRACTION BY AN ANNULAR SLOT IN THE PLANE OR BY A RING

Purpose: The problem of a plane electromagnetic wave diffraction by an annular slot in the perfectly conducting zero thickness plane is considered. As a dual problem, the problem of diffraction by a perfectly conducting zero thickness ring is also considered. The paper aims at developing the operator method for the axially symmetric structures placed in free space. Design/methodology/approach: The problem is considered in the spectral domain. The scattered field is expressed in terms of unknown Fourier amplitudes (spectral functions). The annular slot is given as a unity of two simple discontinuities, namely of a disk and a circular hole in the plane, which interact with each other. The Fourier amplitude of the scattered field is sought as a sum of two amplitudes, the Fourier amplitude of the field of currents on the disk and Fourier amplitude of the field of currents on the perfectly conducting plane with circular hole. The operator equations are written for these amplitudes, which take into account the electromagnetic coupling of the disk and the hole in the plane. The equations use the reflection operators of a single isolated disk and a single hole in the plane. They are supposed to be known and can be obtained for example by the method of moments.The reflection operators can have singularities. After transformations, the equations are obtained, which are equivalent to the Fredholm integral equations of second kind and they can be solved numerically. Findings: The operator equations relative to the Fourier amplitudes of the field scattered by the discussed structure are obtained. The far zone scattered field for an annular slot and a ring for different values of parameters are studied. Conclusions: The rigorous solution of the problem of the electromagnetic wave diffraction by an annular slot in the plane and by a circular ring is obtained. The problem is reduced to the Fredholm integral equations of second kind. The far field distribution for different parameters is studied. The developed approach is an effective instrument for a number of problems of antenna technique to be solved. Key words: circular hole; disk; annular slot; ring; operator method; diffraction

An Effective Pulsed-Periodic Chemical HF(DF) Laser

Abstract— A working process is proposed for an HF(DF) laser, in which evacuation of the reactor is completely excluded. The workflow consists of the following stages: (1) displacement of the reaction products, which are formed after initiation of the working mixture, by an inert gas and (2) subsequent displacement of the inert gas by the working mixture. A design solution is proposed for the system of gas puffing into the reactor. Gas is supplied through an annular slot at one of the reactor ends, which makes it possible to minimize the consumption of inert gas used for displacing the reaction products after initiation of the working mixture. The amount of residual HF(DF) gas in the reactor is incapable of affecting the generation energy in the next cycle. It has been experimentally shown that the displacement technology does not lower the lasing energy in comparison with the pumping technology, but significantly reduces the duration of the HF(DF)-laser operating cycle by approximately two orders of magnitude).

Compact Dual-Passband Three-Dimensional FSS with Good Angular Stability and Both-Side Fast Roll-Off Characteristics

A compact dual-passband three-dimensional (3D) frequency selective surface (FSS) is proposed based on multiple square coaxial waveguides (SCWs), which exhibits good angular stability and both-side fast roll-off characteristics. The unit cell of the proposed 3D FSS is composed of one parallel plate waveguide (PPW) propagation path and two SCW propagation paths. By etching a centered annular slot, each SCW path forms two identical short SCWs. Each short SCW inherently generates one square slot resonance. In each SCW path, on the account of electromagnetic coupling between two square slot resonators provided by two short SCWs, the square slot resonant mode will split into even-/odd-resonant modes. Accordingly, each SCW path can provide a flat second-order passband with two transmission poles. Due to the reflection and out of phase of electromagnetic waves, four transmission zeros located at both sides of the passbands are introduced for high frequency selectivity, realizing both-side fast roll-off performances. In order to explain the operating principle, the electric-field distributions at transmission-zero/pole frequencies are investigated. Finally, an FSS prototype is fabricated and measured, and the results exhibit good angular stability for both TE and TM polarizations under incident angles from 0° to 60°. In addition, the proposed 3D FSS has a compact unit cell.

Optimisation Analysis of Structural Parameters of an Annular Slot Ejector Based on the Coanda Effect

To investigate the effect of structural parameters on the performance of an annular slot ejector, a series of numerical simulations were conducted with single-factor analysis. Moreover, a multifactor grey relational analysis was applied to examine the correlations between the structural parameters and entrainment ratio. Subsequently, the optimised model was verified by comparing the simulated results with experimental data. Results show that the performance of the optimised ejector model was improved. The RNG k-ε turbulent transport mode can simulate the internal field characteristics of an annular slot ejector, and the corresponding simulated results, as verified by experiment, satisfy engineering requirements. In addition, a quantitative correlation between structural parameters and entrainment ratio was obtained as follows: e (nozzle clearance) > θ (diffusing chamber angle) > HL (mixing chamber length) > d (throat diameter) > KL (diffusing chamber length). This work may provide a certain guiding significance for the design and application of annular slot ejectors.

A Triband Patch Antenna with Monopole-like and Patch-like Radiation Patterns for Multifunctional Wireless Systems

A triband patch antenna with monopole-like and patch-like radiation patterns for multifunctional wireless systems is proposed. The antenna consists of a single square radiation patch with an annular slot, a ground plane, and a top-loaded metal sheet. The top-loaded metal sheet is shorted to the ground plane for producing a zeroth-order resonant (ZOR) mode, which has an omnidirectional radiation pattern at the lowest operation band, and its performance is robust to the location of the probe feed. With the annular slot and the off-center probe feed, a dual-resonant TM01 mode is excited, yielding unidirectional radiation patterns for the two upper operation bands. The ZOR and the dual-resonant TM01 modes can be independently controlled, and a triband antenna prototype with a square patch of 24 mm is fabricated and tested. The first bandwidth is 2.5–2.7 GHz with omnidirectional radiation pattern, the second and the third bandwidths with unidirectional radiation are 3.3–3.9 GHz and 4.8–6.1 GHz, and the realized gains over the three bands are about 2.6, 6.5, and 7.5 dBi, respectively.