This paper describes in a very easy and intelligible way, how the diffraction efficiencies of binary dielectric transmission gratings depend on the geometrical groove parameters and how a high ...efficiency can be obtained. The phenomenological explanation is based on the modal method. The mechanism of excitation of modes by the incident wave, their propagation constants and how they couple into the diffraction orders helps to understand the diffraction process of such gratings and enables a grating design without complicated numerical calculations.
Isocyanates readily reacts with NaN
3
in the presence of ZnCl
2
in organic solvents to form the corresponding carbamoyl azides. The formation of carbamoyl azides completed in 5–10 min at room ...temperature, which prevent the risk of release of hydrogen azide. The obtained carbamoyl azides without isolation can be used for the preparation of 1-substituted tetrazol-5-ones.
Smith-Purcell effect is well known as a source of monochromatic electromagnetic radiation. In this paper we present the generalized theory of Smith-Purcell radiation from periodic beams. The ...form-factors describing both coherent and incoherent regimes of radiation are calculated. The radiation characteristics are investigated in two practically important frequency ranges, THz and X-ray, for two modulation profiles, most frequently used in practice - a train of microbunches and a Gaussian-shaped one, characterized by sinusoidal modulation with an arbitrary modulation depth. On the base of the theory developed we show that a modulated electron beam consisting of a set of bunches makes it possible to improve significantly the spectral line monochromaticity of the light emitted, reaching values better than 1% for short gratings. We demonstrate as well that Smith-Purcell radiation can be used for non-destructive diagnostics of the depth of modulation for partially modulated beams. These findings not only open up a new way to manipulate the light emission using Smith-Purcell effect but also promise a profound impact for other radiation sources based on charged particle beams, such as undulator radiation in FELs, next-generation X-ray radiation source based on inverse Compton scattering, in a wide range from THz to X-rays.
The study considers diffraction radiation, which is excited when an electron moves near a cluster of two interacting subwavelength particles. The interaction is manifested in the fact that the ...radiation field from each particle is determined not only by the external field of the electron, but also by the field of the neighboring particle. Based on the obtained expressions for the radiation field, the function of cluster polarizability is determined. It characterizes the cluster response to the field of the electron as a whole. It is interesting that the obtained response function of the cluster to an external field, even in the framework of linear theory, generally depends on the external field itself.
The numerical investigations of liquid film development in the last stages of steam turbines were performed. This data was used to suggest the position of the suction slot used to evacuate the liquid ...phase from the turbine flow path. The object of study is a periphery 2D section of vanes cascade. The movement of coarse droplets in the blade passage was simulated. Their collision with the blade surfaces results in the appearance of additional sources of mass and momentum for liquid film. The influence of theoretical Mach number on the features of liquid film formation was studied. The distributions of main characteristics, reflecting the formation of the film, have been obtained. They were used to analyse the liquid phase flow along the surfaces and to point out base recommendations about the location of the suction slot.
This paper presents the results of an experimental study of the integral characteristics of the intrachannel liquid film suction in a flat cascade of turbine stator blades. Two slots for removing the ...liquid film from the interblade channel were arranged on the pressure surface of the stator blade. The experiments were carried out with initial steam wetness y0 = 3 ÷ 9.5 % and theoretical Mach number downstream the cascade Mlt = 0.6 ÷ 0.78. The operation mode of the moisture removal system was determined by the relative pressure drop on the moisture-removing slots and varied over a wide range. The investigations were carried out for both the operation of the moisture-removing slots one at a time and the combined suction of the liquid film simultaneously through both slots. The measurement system used in the experiments allowed separately determining the mass flow rates of steam and liquid removed from the interblade channel. The obtained integral characteristics served to evaluate the influence of various factors on the efficiency of the intrachannel moisture removal system. Based on the analysis of the research results, recommendations on the design and operation of intrachannel moisture removal systems have been formulated.
The liquid film suction process through the slot is considered. The stator blade row of the last stage of the steam turbine was used as an object of study. Based on the CFD modelling of two-phase ...flow in blades cascade the boundary conditions for slots modelling have been obtained. The numerical analyses of film removal were conducted in a domain including only a flow zone near the studied slot. The multi-phase VOF model was used to calculate the interaction between liquid and steam phases and model the interface evolution during the water removal process. Four different geometries of the slots were considered. For each of them, the unsteady calculations at two different operating regimes have been performed. The numerical results provide information about film suction details in a space of the slot. The behaviour of the film flow was analysed for each slot shape. The conditions of the film separation and its further breakup have been considered. For the studied slot designs efficiency analysis was performed. The results have shown how the way the liquid film moves in the slot effects on the removed water and steam mass flow rates.
The resonance condition of a leaky mode propagating in a dielectric multilayer, which is supported by a mirror and excited by a free-space wave from the cover medium, is simply derived from the phase ...of the reflection at the mirror and cover interfaces. The leaky mode resonance is used to obtain 100% first-order diffraction efficiency in a reflection resonant grating by destructive interference in the direction of Fresnel reflection. A number of examples support the validity of this condition for high efficiency and illustrate the usefulness of this intelligible representation of the diffraction phenomena for the synthesis of novel diffractive elements.
The findings in application of laser diagnostic systems for the investigation of wet steam flows in flow paths of steam turbines, specifically, in channels of various configurations, are reviewed. ...The experimental results accumulated over more than a decade enabled the authors to generalize and formulate the essential features of the movement of coarse erosion-hazardous droplets downstream of turbine cascades and in interblade channels. The regions with liquid phase particles are found using the data of visual analysis. The results of application of the particle image velocimetry/particle tracking velocity (PIV/PTV) methods, which implement algorithms for determining vector fields of particle velocities, are presented. The features of the distribution of kinematic characteristics of the liquid phase in various regions of turbine cascades, which affect the erosion wear rate, are discussed. Data are presented on the effect of the blade profile on the formation of trajectories of droplet flows, and methods for improving the separation ability of a blade operating in a wet stem flow are proposed. Using the experimental database on liquid phase velocity fields in turbine channels of various configurations, a semiempirical model of the flow of large erosive-dangerous droplets is formulated. It describes their movement in a cocurrent steam flow and interaction with the walls of the interblade channels. A review is presented of engineering solutions that were obtained on the basis of theoretical and experimental studies of wet steam flows using laser diagnostic systems. The concept of blade surface heating, heating steam jet injection, and optimization of the in-channel separation system is examined. The principles are formulated for the development of approaches based on laser flow diagnostic systems in the field of application of neural networks, which should considerably extend the capabilities of experimental studies since they offer the potential for increasing the amount of data obtained by implementing such experimental methods.
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